THE CONTRIBUTION OF SATELLITE OBSERVATIONS TO GLOBAL
CLIMATE, OCEAN AND TERRESTRIAL MONITORING
Location: Mechanical Engineering G31 LT
Location of Posters: Old Gym
Wednesday 28 July AM
Presiding Chair: G.Ohring (NOAA/NESDIS/Office of Research and Applications,
Camp Springs, MD 20746-4304, USA)
GLOBAL OBSERVING SYSTEMS
JSM41/W/26-B3 Invited 0900
TERRESTRIAL CLIMATE-RELATED OBSERVATIONS AND SATELLITE DATA
Josef Cihlar (GCOS/GTOS Terrestrial Observation Panel for Climate c/o Canada Centre for Remote Sensing Ottawa, Ontario, Canada. E-mail: josef/cihlar@ccrs.nrcan.gc.ca)
Concerns about the magnitude and rate of environmental changes at various spatial scales have led to the realization of the need for systematic, sustained observations that would help improve our understanding of these changes as well as facilitate the development and implementation of appropriate response actions. In the climate-terrestrial domain, the climate processes, climate impacts on the ecosystems and feedbacks to climate are of primary interest. To address these issues, the Global Climate Observing System (GCOS) and the Global Terrestrial Observing System (GTOS) have collaborated through a joint Terrestrial Observation Panel for Climate (TOPC). Following an analysis of scientific and modelling issues, TOPC identified a limited number of critical variables that need to be determined at various temporal frequencies and spatial resolutions, globally (GCOS-32). Given the extreme heterogeneity and the logistical as well as financial difficulties of collecting surface measurements, a combination of satellite and surface measurements is the only feasible response to these observation requirements. TOPC proposed a five-tier strategy, with Tier 1 consisting of few sites where many variables are observed using complex instruments (and possibly for a limited period) to Tier 5 consisting of a complete satellite coverage of the global landmass. The intermediate tiers consist of surface observatories focused on ecological, cryospheric, and hydrological processes and related variables. This tier-based framework takes advantage of the existing observation networks, employing their capabilities for climate studies and for an improved use of satellite data. Both surface and satellite observations to date have deficiencies with respect to climate applications because most of these were not intended to be used for this purpose. Aspects such as comprehensiveness of observations, consistency and comparability of methods, calibration, and others therefore need considerable improvements. These improvements, followed up by the establishments of long-term sustained observation programs are a major challenge for the global observing systems. They are being pursued in collaboration with surface regional networks and with the space agencies as part of an Integrated Global Observation Strategy. The numerous present and planned satellite missions will make possible major improvements in global terrestrial observations. The Kyoto Protocol and the importance of terrestrial carbon sinks therein, as well as recent emphasis the need for systematic climate observations by COP-4, have underlined the importance and urgency of these implementation activities.
JSM41/W/25-B3 Invited 0930
THE ROLE OF SATELLITE DATA IN THE ATMOSPHERIC COMPONENT OF GCOS
M.J. Manton (Bureau of Meteorology Research Centre, Melbourne, Victoria, Australia,
Email: m.manton@bom.gov.au)
The Global Climate Observing System (GCOS) is an international program aimed at ensuring that the overall global observing system accounts for the various needs of the world-wide climate community. In addition to supporting regional climate activities, GCOS provides key data for seasonal to inter-annual prediction and for activities under the UN Framework Convention on Climate Change. The atmospheric component of GCOS builds on the existing networks of the World Weather Watch (WWW) and the Global Atmosphere Watch (GAW) of the World Meteorological Organization (WMO). A significant component of the additional benefits of GCOS is the promotion of baseline measurements that allow both for the calibration of regional networks and for the monitoring of global features of the climate system. In situ baseline networks of GCOS are the GCOS Upper Air Network (GUAN) and the GCOS Surface Network (GSN). Satellite data play a vital role in complementing these in situ observations.First satellite observations are used to support the calibration and validation of in situ data, such as GUAN. Secondly they make a vital contribution to data assimilation by providing global coverage of atmospheric variables, and this contribution is especially apparent in reanalysis projects. The third contribution of satellite data is through the generation of specific products, such as cloud analyses and precipitation products. These routine data sets are recognised by GCOS as providing essential global products on the state of the climate system. Satellite data are of fundamental importance to GCOS in the monitoring of the global radiation budget. While satellite data are vital to the overall climate observing system, their value is limited unless rigorous standards of calibration and consistency are established and maintained. Long-term climate monitoring requires much more stringent quality control than that which is normally applied to satellite missions of short-term duration. One of the roles of GCOS is to work with the relevant agencies to ensure that these issues are taken into account in all relevant observation programs.
JSM41/W/33-B3 Invited 1000
THE OCEAN OBSERVING SYSTEM FOR CLIMATE
Neville SMITH (Bureau of Meteorology Research Centre, Melbourne Vic. 3001, AUSTRALIA,
E-mail: N.Smith@BoM.GOV.AU)
The concepts of a Global Ocean Observing System and a Global Climate Observing System (GOOS and GCOS, respectively) were developed nearly ten years ago. Ocean observations for climate lie at the intersection of these two systems. Through the first half of this decade, a conceptual design for the ocean observing system for climate was developed, building upon the technical and scientific advances of Programs like the Tropical Oceans-Global Atmosphere Experiment (TOGA, 1985-94) and the World Ocean Circulation Experiment (WOCE, 1990-). The design described a system that would serve operational seasonal-to-interannual prediction, climate monitoring (e.g., sea level rise) and the development of various other climate products (e.g., global sea surface temperature and surface wind analyses). Subsequently there has been a concerted effort to identify the appropriate methods and mechanisms to implement and maintain the system. The observing system for seasonal-to-interannual prediction was given high priority, as was the development of a global in situ and remote network for monitoring variations in global sea level. A large fraction of the proposed elements now have long-term support. Unlike meteorology, oceanography did not have access to an implementation mechanism dedicated to the cause of ocean and climate observations. Recent decisions have now created such a body, the Joint Technical Commission for Oceanography and Marine Meteorology, to serve GOOS and GCOS plus research needs. Several other strategies are being developed to encourage long-term investment in the ocean observing system. The Global Ocean Data Assimilation Experiment (see Smith, "Toward Operational Oceanography And Climate Prediction", U7 Symposium on Integrated Global Monitoring Networks, this Conference) is being used to develop and promote an integrated approach and to develop and implement the required ocean estimation methods. GODAE is also working hard with the satellite community to ensure the requisite remote sensing systems are available. Argo, an initiative to populate the global oceans with profiling floats, will provide a greatly enhanced capability to sample the subsurface ocean. A set of ocean "observatories", using advanced mooring technology, are being proposed to provide on-going, improved estimates of ocean-atmosphere fluxes and provide extended Eulerian ocean time-series. The recent meeting of the Conference of the Parties to the Framework Convention on Climate Change accepted that increased efforts must be made to address gaps in the Global Observing Networks. Such recommendations have...
JSM41/L/02-B3 Invited 1050
TOWARD A SATELLITE-BASED CLIMATE OBSERVING SYSTEM
Graeme L Stephens (Colorado State University, Department of Atmospheric Science, Ft. Collins, CO 80523-1371, 970-491-8550 (voice), 970-491-3430 (fax), stephens@atmos.colostate.edu, cc: linin@atmos.colostate.edu).
Tracking the course of climate change requires a commitment to global-scale observations maintained over periods extending beyond decades and longer. The need to understand the nature of climate change to the point of ultimately assigning cause and effect places stringent and as yet not well understood requirements on these global-scale observations. In a statistical sense it is a difficult enough task to identify (typical) small trends in observed variables above the (typical) observed large climatic variability. This task is made all the more difficult by changing observing practices over the course of time. The problem of observing climate is now at an acute stage given the worldwide demise of conventional meteorological observing networks.
The scientific and programmatic challenge before us is to put in place an observing system or systems that provide observations of key parameters with both sufficient precision and accuracy on time scales that exceed duration of commitment.
The ongoing demise of conventional observing networks places increasing importance on use of satellite measurements not only to fulfil the operational needs of meteorological agencies but also to serve as the basis of a global climate observing system. The regular-in-time and global-in-space nature of these satellite observations makes them particularly attractive for climate research and monitoring purposes. Current operational satellite systems, however, are not optimized for this purpose. In using these operational-based satellite observations, scientists over the past decade have struggled in an attempt to understand and take account of such factors as lack of sensor calibration, sampling problems associated with platform drifts, lack of continuity of observations among a number of other issues.
The definition and design of a climate observing system is a topic of obvious importance in the realm of global climate change. It is also a topic under study by operational satellite agencies which now consider climate either as part of their mandate or are in the process of considering climate requirements in the planning for future observing systems. An example of this consideration has occurred through during the process of the convergence of the US military and civilian meteorological satellite programs under NPOESS.
This talk attempts to discuss critical elements of a climate observing system and will draw on examples and lessons learned from experience in using current satellite data. The distinction between monitoring versus climate process observations will be addressed and some suggestion as to the basic traits of observing systems that address these two distinct aspects of climate will be discussed.
Wednesday 28 July AM
Presiding Chair: P.Schluessel (Meteorologisches Institut, Universitaet Muenchen, Germany)
ATMOSPHERIC MONITORING
JSM41/L/05-B3 Invited 1120
REANALYSIS OF THE TOVS NOAA/NASA PATHFINDER ARCHIVE: APPLICATION TO CLIMATE RESEARCH
Alain CHEDIN
Improving our understanding of the Earth’s climate natural variability as well as detecting potential anthropogenic climate change require, in particular, accurate estimates of many coherently determined surface, atmospheric, thermodynamic, and chemical variables. Among them, some vary quite slowly in time and space while others may vary by several orders of magnitude and in a very complex way, involving many factors. It is now recognized that the value of a global (time and space) description of their characteristics, both in the troposphere and in the stratosphere, is extremely high at this time.
Advances in the ongoing research are based on a multidisciplinary approach, using both modeling and observation. Only by using this approach can such advances be made in the understanding of the earth-ocean-atmosphere system and its sensitivity to anthropogenic changes and allow to make predictions about its short- and medium-term evolution. The basic tool for observing the planet on a global and continuous basis is the satellite, in either a polar or geostationary orbit. In this way, the main components of the Earth system can be observed with instruments which measure the radiances in either high of low spatial or spectral resolutions in a large variety of wavelengths (microwaves, infrared, visible and beyond). A few years ago, NOAA and NASA initiated the Pathfinder programme for the reanalysis of operational meteorological satellite observations.
We present, in this paper, the main characteristics of the TOVS Pathfinder ‘Path-B’ data set, resulting from the reanalysis of High resolution Infrared Radiation Sounder (HIRS-2) and Microwave Sounding Unit (MSU) observations with the ‘Improved Initialization Inversion’ (3I) physico-statistical retrieval algorithm. This method is ‘model-independent’ (no influence of any forecast of climate model products), and takes great care of eliminating systematic biases that might occur, during one satellite life, or from one satellite to another, between calculated and observed radiances. 3I-derived climate variables are: the temperature and the water vapor vertical structure, the surface temperature and characteristics (emissivity, presence of snow, ice, deserts, etc.), the cloud field description (top, amount, type), and more integrated products like the longwave vertical radiative fluxes. Several auxiliary data sets (RAOBs in-situ measurements, SSM/I, AVHRR or ERBE observations, ISCCP or model analyses, etc.) have been used to carry out extensive validations of 3I-derived variables. If the validation...
JSM41/E/04-B3 1150
RESULTS FROM THE NOAA AVHRR ATMOSPHERIC PATHFINDER PROJECT
GEORGE OHRING and Herbert Jacobowitz (NOAA/NESDIS Office of Research and Applications 5200 Auth Rd. Suitland, MD 20746-4304)
This paper reports on the data sets of the NOAA AVHRR Atmospheric Pathfinder Program and their applicability to climate studies. As part of the NOAA/NASA Pathfinder Program, NOAA is reprocessing the archived AVHRR observations since 1981 into research quality atmospheric data sets. The raw observations were recalibrated using a vicarious calibration technique for the visible and near-infrared channels and an improved treatment of non-linearity for the infrared channels. State-of-the-art algorithms are used to process the global observations into channel radiances, total cloud amount, the components of the Earth's radiation budget (Outgoing Longwave Radiation and Absorbed Solar Radiation), and aerosol optical thickness (ocean areas only). The radiances and Earth radiation components are determined for clear, cloudy, and all-sky conditions. The output products are generated on an equal area grid with a resolution of approximately 110 km (1o latitude by 1o longitude at the equator), twice daily, and averaged over 5 day (pentad) and monthly periods. Applications of the data sets to radiative forcing, aerosol-cloud interactions,surface temperature/absorbed solar radiation/cloud relationships, and monitoring volcanic aerosols are presented. Problems with the use of the AVHRR for some climate studies are also described.
JSM41/E/10-B3 1205
INTER-ANNUAL VARIABILITY OF ATMOSPHERIC WATER VAPOR AS SEEN FROM THE TOVS PATHFINDER PATH A DATA SET
AMITA MEHTA and Joel Susskind 910.4, NASA-Goddard Space Flight Center Greenbelt, MD USA 20771
The atmospheric water vapour is a major greenhouse gas and plays a critical role in determining energy and water cycle in the climate system. A new, global, long-term (1985-98) water vapour data set derived from the TIROS Operational Vertical Sounder (TOVS) Path A system will be introduced in the presentation. An assessment of the accuracy of the TOVS Path A water vapour data will be presented. The focus of this oral presentation will be on the inter-annual variability of the water vapour distribution in the atmosphere and how it affects clear-sky outgoing longwave radiation variability. A comparison of water vapour distribution during 1986/97 and 1997/98 ENSO will also be presented.
JSM41/W/30-B3 1220
DERIVATION OF GLOBAL WATER VAPOUR DISTRIBUTIONS FROM ATSR DATA
Ian BARTON (CSIRO Marine Research, Australia, Email: ian.barton@marine.csiro.au)
A new product to be provided by the ATSR instrument team is a global distribution of averaged infrared brightness temperatures on a spatial scale of 18 km (10 arc-minutes in latitude and longitude). Data for a one-month period are analysed to demonstrate the potential of these data to provide a vertical and horizontal distribution of water vapour amounts over the global oceans. The six ATSR infrared channels (nadir and forward views at three wavelengths) are applied in a similar manner to those on the infrared sounding channels on the operational meteorological satellites. The weighting functions of the ATSR channels are found to give better vertical resolution in the lower troposphere than the typical channels used in the latest operational instruments.
JSM41/P/01-B3 1235
SEASONAL AND INTERANNUAL VARIABRITY OF BRIGHTNESS TEMPERATURE OVER INDIAN SUBCONTINENT
Ramesh P. SINGH and Nrusingha C. Mshra (both at Department of Civil Engineering, Indian Institute of Technology, Kanpur - 208 016, India, email: ramesh@iitk.ac.in)
The seasonal and yearly variations of brightness temperature measured by SSM/I satellite over land and ocean regions of India during the years 1987 to 1995 show characteristic behaviour. The brightness temperature variations over Indian land region is attributed to the different geological divisions of India. The brightness temperature variations over Arabian ocean and Bay of Bengal show systematic pattern. The brightness temperature changes significantly with latitude which show typical pattern. These systematic and typical pattern is interpreted in relation to seasonal and interannual variability of Monsoon over India and surrounding regions. From the brightness temperature, the snow thickness in the northern part of India, liquid water path (LWP) and total precipitable water (TPW) have been deduced for different seasons and also analysed yearly during 1987 - 1995. The effect of the north-west and south-west monsoon is clearly seen on the seasonal and interannual variations of brightness temperature and meteorological parameters. The role of seasonal and interannual variations of brightness temperature will be discussed in the global change and climatic variations.
Wednesday 28 July PM
JSM41/W/13-B3 1400
GNSS OCCULATION SOUNDING FOR CLIMATE MONITORING AND ATMOSPHERIC CHANGE ANALYSIS
Gottfried Kirchengast and Andrea K. STEINER (Institut fuer Meteorologie und Geophysik, Universitaet Graz, Halbaerthgasse 1, A-8010 Graz, Austria, Email: andi.steiner@kfunigraz.ac.at), Luis Kornblueh, Elisa Manzini, and Lennart Bengtsson (Max-Planck-Institut fuer Meteorologie, Bundesstrasse55,D-20146 Hamburg, Germany)
The Global Navigation Satellite System (GPS and GLONASS, generically GNSS) based radio occultation technique is an active limb sounding technique exploiting quasi-horizontal transatmospheric sat-to-sat links. Both neutral atmospheric and ionospheric refractive properties are probed and profiles of associated fundamental atmospheric variables such as temperature, humidity, and electron density can be retrieved with high quality. The method bears great utility for climate studies in providing an unique combination of global coverage, high vertical resolution and accuracy, long-term stability, and all-weather capability. A domain of highest strength of the method is the profiling of the thermal structure in the upper troposphere and stratosphere. As indications exist that the changing thermal structure in this domain is a sensitive indicator of atmospheric change (or climate change) and anthropogenic climatic impacts, respectively, we expect that occultation sounding can furnish unique data to globally monitor this changing structure with unprecedented accuracy.
We undertook to rigorously test the climate monitoring and atmospheric change detection capability of GNSS occultations by an integrated analysis involving: (i) realistic modeling of both the neutral atmosphere (T42L39-GCM up to the mesopause) and ionosphere (empirical, solar-activity dependent 4D model) over the time span 1995 to 2020, (ii) realistic observation system simulations of observables (phases and amplitudes) of a small GNSS receiver constellation (6 satellites) over this time period, (iii) a state-of-the-art occultation data processing chain for temperature profile retrieval in the upper troposphere/stratosphere (core region 8 to 40 km) for establishing a significant set of realistic simulated measurements over the period, (iv) a multivariate statistical analysis of 1996-2020 temporal trends in latitude-height slices of both the "true" states from the atmospheric modeling and the "measured" states from the database of retrieved temperature profiles, and (v) an assessment, by methods of statistical inference, of whether and to what degree the GNSS occultation observing system was able to detect trends in the atmospheric evolution (i.e., atmospheric change) from 1996 to 2020.
This ambitious study is expected to be still in progress at the time of the meeting and the latest status will thus be reported. We will discuss in some detail how we actually implemented steps (i) to (v) noted above, with emphasis on critical scientific and technical areas. Furthermore, we plan to present preliminary results on the climate trend analysis.
JSM41/E/23-B3 1415
CLOUD-RADIATIVE FORCING TO FORM A COLD AIR-MASS WITH LOW-LEVEL CLOUDS OVER THE SUBARCTIC NORTH PACIFIC DURING SPRING AND SUMMER
HIROSHI KAWAMURA, Hiroyuki Takeda and Nobuyuki Kikuchi Center for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980, Japan
It is known by the ship observations that the subarctic North Pacific is frequently covered by low-level clouds (LLC) and fogs during spring to summer. It is also confirmed by the historical records of air temperature that the air-mass in the boundary layer over this ocean is rather uniform and colder, by about 5C, than that over lands in the same latitude band. This air mass occasionally blows toward south-west and bring cold summer to Japan, which causes serious agricultural damages and called "Yamase event".
In order to understand formation process of the cold air-mass over the subarctic ocean, the role of LLCs is investigated using the ISCCP (International Cloud Climatrogy Project) data set. It is shown that LLC amount over the ocean north of 40N exceeds 70% in summer season, and optical thickness of LLC increases with time and has a peak in July. A core of the optically thick cloud is located in the Bering Sea. To estimate the LLC radiative forcing, radiation at the top of LLC and cloud-free surface is calculated by a radiative transfer code. The ISCCP cloud parameters are used as well as atmospheric parameters of the ECMWF data. The grid and time step of calculation are 280x280km and 1 minute, respectively. The monthly statistics are derived from the estimates obtained for five years of 1988-1992. The short wave radiation is reduced to 50% because of reflection at the cloud top. In contrast, the upward long wave radiation at the cloud top does not differ so much from that at the ocean surface because the altitude of cloud is low and the top temperature is close to SST. The strong contrast in the net radiation over the lands and oceans north of 40N is evident, and this is the main reason for generation of the cold air mass over the subarctic North Pacific during spring to summer.
JSM41/W/11-B3 1430
A NEW SATELLITE-BASED CLIMATOLOGY OF CLOUDS IN THE NEW ZEALAND REGION
Howard LARSEN, Warren Gray, and Peter Norris, National Institute for Water and Atmospheric Research, PO Box 14-901, Wellington, New Zealand, email: h.larsen@niwa.cri.nz
A cloud climatology of the New Zealand - South West Pacific region has been derived from AVHRR satellite data using a new cloud classification algorithm. The high-resolution climatology covers a large area of the ocean region around New Zealand, some 3500 km square, from 22°S to 55°S and 150° E to 167° W. It is based on data from May 1997 to the present. Clouds have been classified directly into classes based on their radiative properties and their spatial variability rather than traditional 'cloud type' classes.
Results from the first year of operation show clearly differentiated patterns of cloud coverage at different cloud heights and the effects of the New Zealand landmass. Low, warm clouds, for example, were frequent in a band between 40ºS and 50ºS but their occurrence is suppressed for several hundred kilometres either side of the New Zealand landmass. Significant seasonal variations in the pattern of cloud cover over the region are also apparent. Current GCM output is not entirely consistent with the measurements represented in the climatology, suggesting refinements are needed in modelling cloud-climate interactions in this region. Some of the discrepancies in modelled low cloud estimates are consistent with ocean-atmosphere interactions.
JSM41/L/04-B3 1445
CLOUD CLIMATOLOGY FROM NOAA-9 SPLIT WINDOW AND COMPARISON BETWEEN CLOUD TYPE FROM SPLIT WINDOW AND TRMM RAIN OBSERVATIONS
Toshiro Inoue (Ph.D. Meteorological Research Institute, 1-1, Nagamine, Tsukuba, Ibaraki 305-0052, Japan TEL : +81-298-52-9046(direct) FAX : +81-298-55-2552 e-mail : tinoue@mri-jma.go.jp FAX : +81-298-55-2683)
Using split window data, we can classify optically thin ice cloud and optically thick clouds. We construct the monthly mean cloud cover map for three cloud types (cumulonimbus-, cirrus- and low-level stratocumulus/cumulus- type) over the quasi- global area (50N-50S) in 1987 and 1988 from the split window data on board NOAA-9. The meaning of the cloud type classification by split window is verified using the rainfall information observed from PR (Precipitation Radar) data on board TRMM(Tropical Rainfall Measuring Mission). The TRMM has also VIRS (Visible and Infrared Scanner) and TMI(TRMM Microwave Imager). Using the split window of VIRS, coincident and collocated cloud type information and PR rainfall information are compared. We found optically thicker and colder cloud classified by the split window corresponded well to the PR/TRMM rainfall data.
JSM41/W/10-B3 1500
VARIABILITY IN SURFACE TEMPERATURE, CLOUDS, AND SEA ICE COVER IN THE POLAR REGIONS INFERRED FROM INFRARED AND PASSIVE MICROWAVE DATA
JOSEFINO C. COMISO (Laboratory for Hydrospheric Processes, Code 971, NASA/Goddard Space Flight Center, Greenbelt, MD, USA, 20771, email: comiso@joey.gsfc.nasa.gov)
Two decades of satellite infrared and passive microwave data have been analyzed to study seasonal and decadal changes in surface temperature, cloud cover, and sea ice cover in the polar regions. The data analyzed were derived from three key sensors, namely: the Advanced Very High Resolution Radiometer (AVHRR), the Scanning Multichannel Microwave Radiometer (SMMR), and the Special Scanning Microwave Radiometer (SSM/I). To better understand what two decades of data can reveal compared to one or a fraction, we analyzed several decades of in-situ temperature measurements and our results indicates that the trend values tend to stabilize as soon as fifteen to twenty years of data are available. The results of our analysis indicate significant warming in both poles, similar to what has been observed from station data, while the sea ice cover show decreases in extent in the north and no significant change in the south. Large seasonal and interannual variability is however observed, and the presence of the Antarctic Circumpolar Wave in the south, that goes around the continent at a periodicity of eight years, may affect ability to detect changes in the extent of the ice cover. Surface temperatures inferred from infrared data are also biased because of inability to obtain data during cloudy conditions. Cloud statistics from AVHRR data and possible effects on the surface temperature and ice cover will be presented.
JSM 41/E/28-B3 1515
SIX YEARS OF COMPOSITE INFRA-RED IMAGES SOUTH OF FORTY DEGREES SOUTH AT THREE HOUR INTERVALS
Charles STEARNS, Bruce Sinkula, Rob Holmes, Matt Lazzara, and J.T. Young (all at Space Science and Engineering Center, Universsity of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin 53711, USA)
At the University of Wisconsin Antarctic Meteorological Research Center (UWAMRC) a composite infrared (IR) image of Antarctica is formed every three hours and saved to an optical disk. The image is of the 11.5 to 12.5 micrometer (surface temperature) band: the image is 1.0 megabyte in size: the resolution is 10km. Regions without data in the 100 minute sampling window white. The initial geostationary satellites used and their longitude are GOES-7 , 112 degrees West; GMS, 140 degrees East; Meteosat-3, 0 degrees; Meteosat-4, 75 degrees West,. The initial polar orbiting are NOAA 11 and NOAA 12. The time of the composite images is within 50 minutes of the indicated time on the image. The image extends from the South Pole to approximately 34 degrees South in the corners with New Zealand in the upper left hand corner and to 58 degrees South at the edges closest to the South Pole. A VHS tape of the composite IR images from 31 October 1992 to 30 November 1998 is prepared from the archive at the UWAMRC. The original image resolution is 10 km but the transfer of the images to the tape increases the resolution to about 20 km. Each image is displayed for 0.3 seconds. Images are timed and dated for reference when requesting more detailed data from the UWAMRC.
JSM41/L/02-B3 Invited 1550
A SATELLITE-DERIVED FRESHWATER FLUX CLIMATOLOGY: THE HAMBURG OCEAN ATMOSPHERE PARAMETERS AND FLUXES FROM SATELLITE DATA
Jörg Schulz , Peter Bauer, Lars Schanz (German Aerospace Center, Linder Höhe, D-51147 Köln, Germany, email joerg.schulz@dlr.de), Volker Jost (Meteorologisches Institut, Universität Hamburg, Bundesstraße 55, D-20146 Hamburg, Germany, email jost@dkrz.de), Peter Schlüssel (Meteorologisches Institut, Universität München, Theresienstraße 37, D-80333 München, Germany, email HYPERLINK mailto:schluessel@meteo.physik.uni-muenchen.de schluessel@meteo.physik.uni-muenchen.de)
Knowledge of turbulent fluxes between ocean and atmosphere is along with radiative fluxes of great importance to improve our understanding of the large scale climate system. Accurate estimates of these fields can be used as a direct forcing of ocean circulation models or for evaluating the results of coupled climate models that have obviously problems at the air-sea interface. In this talk a climatology of freshwater flux at the sea surface will be presented together with a review of the used retrieval schemes, a comprehensive error assessment, and some examples for the application of such a climatology. The climatology extends over 10.5 years of data and consists of global fields of latent heat flux, freshwater flux, net longwave flux, rainfall, and all associated atmospheric and oceanic parameters. The error assessment is based on validation of the retrieval algorithms and on comparisons to other climatologies constructed from different type of data. As an example comparisons to buoy data gained during the subduction experiment 1991 to 1993 in the eastern subtropical North Atlantic will be shown. This data set is one of the few data sets which are useful to compare not only instantaneous measurements but also long time averages.
Time sampling errors mostly concerning precipitation measurements in the tropics have been assessed by comparisons to radar data gained during TOGA COARE. The sampling error for a grid resolution of 2° by 3° and a sampling time of 3 weeks can be as high as 30% if only one satellite overpass per day was available. If data of two SSM/Is were combined this error can be diminished to less than 4% in the case of 4 overpasses a day.
Improvements of the climatology can be expected if knowledge gained from the Tropical Rainfall Measuring Mission (TRMM) is used to improve SSM/I rainfall algorithms. This shall reflect in both reduction of random error through higher accuracy of TRMM retrievals and reduction of systematic time sampling errors by knowing more about the mean diurnal cycle of precipitation over the ocean.
JSM41/E/01-B3 1620
GLOBAL MONITORING OF PRECIPITATION ON MONTHLY AND SHORTER TIME SCALES UTILIZING LOW-ORBIT AND GEOSYNCHRONOUS SATELLITE OBSERVATIONS
ROBERT ADLER, NASA/Goddard Space Flight Center, Code 912, Greenbelt, MD, 20771 ; Scott Curtis, NASA/GSFC, JCET/UMBC, Code 912, Greenbelt, MD, 20771 George Huffman, NASA/GSFC, SSAI, Code 912, Greenbelt, MD, 20771 David Bolvin, NASA/GSFC, SSAI, Code 912, Greenbelt, MD, 20771 Eric Nelkin, NASA/GSFC, SSAI, Code 912, Greenbelt, MD, 20771
A satellite-based system to monitor global precipitation on monthly and shorter time scales is described. The monitoring system is based primarily on the Global Precipitation Climatology Project (GPCP) global, monthly, 2.5ƒx 2.5ƒ latitude-longitude product which utilizes precipitation estimates from low-orbit microwave sensors (SSM/I) and geosynchronous IR sensors and raingauge information over land. The low-orbit microwave estimates are used to adjust or correct the geosynchronous IR estimates, thereby maximizing the utility of the more physically based microwave estimates and the finer time sampling of the geosynchronous observations. Information from raingauges is blended into the analyses over land. This globally complete, monthly product is available from January 1986 to the present, with an extension back to January 1979 underway using non-SSM/I data.
The monthly GPCP merged data product is augmented in real-time by low-orbit microwave (SSM/I) estimates. Anomalies from climatological means are produced from both the GPCP and microwave fields to monitor the evolution of global precipitation, including the calculation of ENSO precipitation indices for real-time (five-day running means) climate monitoring and comparison with previous ENSO anomalies.
On an even shorter time scale, a new daily, 1ƒx 1ƒ latitude-longitude global analysis has been developed starting in January 1997 utilizing low-orbit microwave and geosynchronous IR information using a similar method as is used to produce the monthly GPCP product.
JSM 41/E/260-B3 Invited 1635
SATELLITE REMOTE SENSING OF PRECIPITATION
ERIC BARRETT (School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK, Email: e.c.barrett@bris.ac.uk)
As recently as 30 years ago, knowledge of global precipitation amounts, distributions, and temporal variabilities relied almost entirely on measurements made by raingauges. Rainfall climatologies even from that era were almost all limited to the continental land masses, excluding Antarctica as well as the North Polar ice cap. More recently, much additional information has been gathered by remote sensing systems, notably by ground-based weather radar, but most of all from meteorological satellites operating passively in the visible, infrared, and microwave regions of the electromagnetic spectrum, and newly (since 1997) actively too, in the microwave region. Thus, although raingauge networks have generally declined in recent decades, as this paper illustrates our knowledge of global rainfall climatologies today has become much more advanced. This fact is important not only for its own sake, but also on account of the significance of precipitation for global modelling, especially of the atmosphere, hydrosphere, cryosphere and biosphere. This review paper first recalls some of the more significant findings of satellite remote sensing in respect of precipitation since 1969. Next, it identifies some of the greatest problems and challenges facing the satellite precipitation science community today. Finally, it suggests where related resources might be focused most usefully in the near-term future, not least to ensure that appropriate information on global precipitation on time-scales ranging from seasonal-interannual to decadal be secured for a wide range of potential end-users.
JSM41/W/01-B3 1705
A COMBINED INFRARED AND MICROWAVE TECHNIQUE FOR STUDYING THE DIURNAL VARIATION OF RAINFALL OVER AMAZONIA
ANDREW J. NEGRI (1), Emmanouil Anagnostou (2) and Robert F. Adler (1)
(1) NASA/GSFC, Laboratory for Atmospheres, Greenbelt, MD 20771, e-mail: negri@erin.gsfc.nasa.gov (2) Dept. of Civil and Environmental Engineering, U. Conn., Storrs, CT 06269
Over 10 years of continuous data from the Special Sensor Microwave Imager (SSM/I) aboard a series of Defense Department satellites has made it possible to construct regional rainfall climatologies at high spatial resolution. Using the Goddard Profiling Algorithm (GPROF), monthly estimates of precipitation were made over the region of northern Brazil, including the Amazon Basin, for 1987 to 1998. GPROF is a physical approach to passive microwave precipitation retrieval, which uses the Goddard Cumulus Ensemble (cloud) model to establish prior probability densities of precipitation structures. Precipitation fields from GPROF were stratified into morning and evening satellite overpasses, and accumulated at monthly intervals at 0.5 degree spatial resolution. Important diurnal effects were noted in the analysis, the most pronounced being a land/sea breeze circulation along the northern coast of Brazil and a mountain/valley circulation along the Andes. There were also indications of morning rainfall maxima along the major rivers, and evening maxima between the rivers. The addition of simultaneous geosynchronous infrared (IR) data leads to the current technique, which takes advantage of the 30 minute sampling and 4 km spatial resolution of the infrared channel and the better physics of the microwave retrieval. The resultant IR method is subsequently used to derive the diurnal variability of rainfall over the Amazon basin, and further, to investigate the relative contribution from its convective and stratiform components.
JSM41/E/06-B3 1720
GLOBAL PRECIPITATION FIELDS FROM ACTIVE MICROWAVE SENSORS
G.D. Quartly, T.H. GUYMER and M.A. Srokosz Southampton Oceanography Centre, Empress Dock, Southampton, Hants, SO17 3SH
For over a decade precipitation information has been available from infrared satellites such as METEOSAT and passive microwave sensors such as SSM/I. Recently developments have been made in the processing of active microwave data from the TOPEX altimeter so that it too can provide information on rain. This talk will summarise the technique and examine the fields produced from 6 years of consistent data from one satellite. The processing yields not only the familiar geographical patterns of rainfall but reasonable estimates of the rain rates involved. The small footprint of the instrument allows studies of the short-scale variations in rainfall, which reveal the organization of rain events typically to have a larger size to the west of ocean basins than to the east. As the altimeter also provides estimates of the wave height and wind speed, we can observe which weather conditions the precipitation is preferentially associated with. We will compare our results with studies using infrared and passive microwave sensors, indicating both the advantages and disadvantages of a TOPEX- derived climatology, and discuss the prospects for further active microwave sensors, such as TRMM (launched in November 1997) and TRMM II.
JSM41/E/29-B3 1735
SSMI WIND SPEED CLIMATOLOGY OF THE TIME OF MONSOON WIND ONSET IN THE WESTERN ARABIAN SEA
DAVID HALPERN (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, U.S.A., email halpern@pacific.jpl.nasa.gov)
Forecasting the time of onset of monsoon wind in the western Arabian Sea is an important unsolved problem. Prior to measurements of the surface wind field by satellite, there was an absence of suitable surface wind observations over the Arabian Sea. The NASA scatterometer (NSCAT) surface wind vectors revealed that the time of the 1997 onset of 12 m/s south-west monsoon wind speeds in the western Arabian Sea preceded the onset of monsoon rainfall in Goa, India, by 3 - 4 days. Wind speed and direction data were necessary to establish a dynamical mechanism between times of onset of 12 m/s wind speed off Somalia and rainfall in Goa. Except for NSCAT, no satellite scatterometer wind product recorded adequately sampled 2-day 1° x 1° averaged wind vectors, which are the required space and time scales, to examine the onset of the Somali Jet. However, the greater-than-95% steadiness of summer monsoon winds allows the use of satellite measurements of surface wind speed. The Special Sensor Microwave Imager (SSMI) recorded surface wind speed with adequate sampling to produce a 1-day, 1° x 1° data product during 1988 - 1998. SSMI data had been uniformly processed throughout the period. Times of onset of SSMI 12 m/s wind speed off Somalia were 21 May 1988, 24 May 1989, 17 May 1990, 28 May 1991, 8 June 1992, 28 May 1993, 30 May 1994, 7 June 1995, 29 May 1996, 12 June 1997, and 15 May 1998. Uncertainty of the 1992 and 1996 times of onset were increased because of the absence of SSMI data on 6 and 7 June 1992 and on 30 May 1996. Correlations of the timing of monsoon wind onset with El Niño will be described. The difference between times of onset of 12 m/s wind speed and Goa rainfall will be discussed. At the time of abstract submission, Goa rainfall data have not arrived from the India Meteorological Department.
JSM41/E/17-B3 1750
SIMULTANEOUS REMOTE SENSING OF AEROSOL FEATURES AND SURFACE REFLECTANCE WITH SPACE-BORNE SPECTROMETRY
Daren LU, Mingzhen Duan,(Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,CHINA, e-mail: ludr@sun.ihep.ac.cn)
In quantitative remote sensing of atmospheric and earth surface parameters with space-borne optically spectral sensors, atmospheric correction and surface (background) influence deduction are key steps for both surface and atmospheric remote sensing, respectively. In principle, these two steps are with same task, i.e., decoupling or separation of respective contributions to spectral radiance (or normalized reflectance) observed by space-borne sensors. A lot of efforts have been paid to solve this problem. Most of them are using supplementary information obtained by ground-based observation or climatological means for the atmosphere or surfaces. Owing to the limitations of simultaneous surface measurements and temporal and spatial variation of the atmosphere and earth surfaces, above-mentioned efforts are always faced significant error or very limited usefulness. It is commonly recognized that the best or ideal way is simultaneous remote sensing of the atmosphere and surface with space-borne sensors alone (with least assumptions). In general there are three approaches towards simultaneous remote sensing, i.e., multi-angle measurements, multi-spectral measurements, and multi-polarization measurements, and their combinations. In different assumptions, each of them may apply to simultaneous remote sensing. After general discussion, this paper will mainly focus on the approach with multi-spectral observation in Visible-NIR waveband. The present approach includes two steps, the first step is to establish approximate formulae which may explicitly give quantitative contribution of the atmosphere and surface to satellite-borne sensors measurements. The second step is to establish retrieval scheme by using the above mentioned formulae and the spectral dependence of both the atmospheric optical depth and surface reflectance. Details about principle and preliminary results are given in this paper.
Thursday 29 July AM
Presiding Chair: P.Schluessel (Meteorologisches Institut,
Universitaet Muenchen, Germany)
ATMOSPHERIC MODELLING by monitorring
JSM41/W/28-B4 0930
POTENTIAL OF METEOSAT SECOND GENERATION TO CLIMATE MONITORING
Yves M. Govaerts, Arlindo Arriaga and Johannes Schmetz (EUMETSAT, Am Kavalleriesand 31, D-64295 Darmstadt, Germany, email govaerts@eumetsat.de, arriaga@eumetsat.de, schmetz@eumetsat.de)
In 2000, EUMETSAT will launch the first Meteosat Second Generation (MSG-1) satellite centred on zero degree longitude. In comparison with the current Meteosat satellites, the MSG system will feature enhanced observation capabilities. Its Spinning Enhanced Visible and Infrared Imager (SEVIRI) provides data in 12 spectral channels instead of 3, distributed throughout the short and long wave parts of the electromagnetic spectrum. The imaging frequency is 15 minutes and the sampling resolution at the sub-satellite point is 3´ 3 km for all channels except the VIS high-resolution band which has a 1´ 1 km nadir resolution. The above enhancements have been driven by the increasingly stringent requirements of the meteorological user community in the areas of nowcasting and numerical weather prediction. The combined improvements in spectral coverage, imaging frequency and ground resolution were needed to better characterise clouds and the vertical structure of the atmosphere, to improve the sampling of dangerous weather patterns, and to derive more accurate atmospheric motion vectors. Calibration of the IR channels is carried out using on-board blackbody operated at two temperatures and vicarious calibration methods. The visible and near infrared channels calibration relies on vicarious method using bright desert targets. Calibration is a critical requirement for climate applications and the expected accuracy will be discussed first. The SEVIRI characteristics, in conjunction with the MSG mission duration (at least 12 years of continuous observations), provide the basis for improved and new products to be used for climate monitoring. The climate observations of SEVIRI are wide spread with enhanced capabilities for observing cloud micro-physical properties, water vapour and land surfaces. In particular, the increased spectral coverage and time-space sampling of MSG imagery are expected to open new avenues for the study of land surface properties, their diurnal variation, and the associated land surface and land-atmosphere interaction processes. Various examples of climate product derived form MSG observations will be given. MSG also carries a radiation budget scanner (GERB), the first instrument of this type in geostationary orbit. Simultaneous observations of spectral radiances from SEVIRI and broadband radiances from GERB will enable novel studies of regional radiation budget parameters.
JSM41/E/22-B4 0945
THE ANTARCTIC METEOROLOGY RESEARCH CENTER: AN INTEGRATED
METEOROLOGICAL DATABASE FOR RESEARCH IN THE SOUTHERN HIGH LATITUDES
Matthew Lazzara, George WEIDNER, J.T. Young and Charles Stearns (all at the Space Sceince and Engineering Center Universsity of Wisconsin, 1225 West Dayton Street, Madison, Wisconsin 53706, USA)
The Antarctic Meteorological Research Center (AMRC) was created in 1992 with funding from the National Science Foundation's United States Antarctic Program (USAP) Office of Polar Programs (OPP) to provide improved access to meteorological data available in Antarctica to the wider scientific community, provide a single source for data from both ground based and satellite derived meteorological data and to provide real-time date to those tasked with providing weather forecasts in support of operations funded by USAP during the Austral Summer field season. Since, meteorological data from Antarctica is only some 40 years old, satellite derived data sets for the Antarctic represent a larger fraction of the recorded data than in other areas. For the Antarctic, the integration of satellite derived data with other data sets provides an important contribution to the study of climate change in the high latitudes and the connections at various time scales between the lower and higher latitudes. Since that time the AMRC has collected, archived and made available to users a significant amount of meteorological data in support of atmospheric research, research in other fields requiring meteorological data, operational forecasting and educational support. A review of the present set of data collected and archived by the AMRC will be given. These data sets include satellite data from the geostationary and polar-orbiting satellites, synoptic observations, radiosonde observations, automatic weather (AWS) observations and National Meteorological Center's (NMC) Medium Range Forecast Model (MRF) analyses and forecast for use over Antarctica. Recent product additions are a low-mid level infrared wind product and satellite derived winds from the water vapour channel of the GMS-5 satellite in an online archive. Future data from anticipated new satellite platforms will be presented. Examples of the current uses of the AMRC database will be given.
JSM41/W/08-B4 Poster 1000-01
THE STRATOSPHERIC AEROSOL AND GAS EXPERIMENT III
Larry W. Thomason (Atmospheric Sciences Division, NASA Langley Research Center, Hampton, VA 23681 USA, Email: l.w.thomason@larc.nasa.gov). Michael C. PITTS (Science Applications International Corporation, One Enterprise Parkway, Suite 250, Hampton, VA 23666, USA, email: m.c.pitts@larc.nasa.gov)
The Stratospheric Aerosol and Gas Experimen (SAGE) III is the latest in a series of satellite-based instruments to use the polar occultation technique to measure stratospheric and upper tropospheric aerosols and trace gas species. The first instrument will be launched aboard a Russian Meteor 3M platform in Fall 1999. Later flights are scheduled for the International Space Station in 2002 and a Flight-of-Opportunity between 2000 and 2005. SAGE III preserves the robust characteristics of the SAGE series, including self-calibration and high vertical resolution, and adds new capabilities designed to contribute to understanding global climate change. Among these enhancements is a lunar occultation mode in which night time species such as nitrogen trioxide and chlorine dioxide are measured (in addition to ozone and nitrogen dioxide). During solar occultation, measurements of the oxygen A band will be used to infer temperature and pressure profiles from 0 to 85 km. In addition, finer spectral resolution measurements of nitrogen dioxide features near 440 nm and ozone around 600 nm will improve the quality of inferences of those species relative to SAGE II measurements. The spectral coverage of aerosol extinction measurements has been extended to 8 measurements between 385 and 1550 nm compared to SAGE II measurements at 385, 453, 525, and 1020 nm. SAGE III should make significant contributions to understanding the long-term ozone trend and the processes that underlie it. In this presentation, we will discuss the SAGE III instrument design, retrieval algorithm, data products, and plans for validation.
JSM41/W/31-B4 Poster 1005-02
AN EMPIRICAL MODEL FOR GLOBAL ATMOSPHERIC TEMPERATURE ANOMALIES
Olavi KARNER (Tartu Observatory, 61602 Toravere, Estonia, email: olavi@aai.ee)
Global record of temperature fluctuations in the lower troposphere (the lowest 5 miles of the atmosphere) and the lower stratosphere (covering an altitude range of about 9-12 miles) have been monitored by satellite since 1979. The monthly-averaged temperature anomalies for the entire length of record, available online http://www.ghcc.msfc.nasa.gov/temperature/), have been analysed by means of fitted autoregressive and integrated moving average (ARIMA) models. A nonstationary first order IMA model appears to be appropriate to represent the temporal variability of global temperature anomalies during the period. The model explains about 95 per cent of variance in the stratospheric case. This enables one to use it for short-term predictions of the anomalies. An example will be presented.
JSM41/E/32-B4 Poster 1010-03
RADIOMETRIC CALIBRATION OF THE EARTH'S SCAN IMAGES TRANSMITTED BY GEOSTATIONARY SATELLITE GOMS IN THE VISUAL AND IR SPECTRAL RANGES
S.G.PUGACHEVA, V.V.Shevchenko (both at Sternberg State Astronomical Institute, Moscow University, Universitetskii pr.13, Moscow, 119899, Russia, email: pugach@sai.msu.su)
The technique of calibrating scan images using the Moon's image can be successfully used for the radiometric calibration of the onboard apparatus of the first Russian geostationary artificial meteorological satellite (GOMS) launched on October 31, 1994, in accordance with the program Meteorological Service for the Population. For realization of meteorologic observations satellite GOMS has television complex, which gives in actual time scale of the digital images of a cloudy, snow and ice cover and measures of radiation temperature of a surface of an ocean, land and high bound of a clouds. The calibration procedure is based on the comparison of the output data of the onboard apparatus of the geostationary satellite GOMS with a photometric database that includes measured values of brightness and temperature for a large number of lunar-surface areas. To this end, an automated database was created, which contains brightness and temperature values for 1954 areas of the lunar surface, measured by the global scanning of the illuminated lunar disk in the visual (0.445 micron) and infrared (10-12 micron) spectral ranges during a complete lunation. It is known that the emission of the lunar surface in the visual and infrared spectral ranges is stable and constant in space and time and can easily be described analytically. A generalized digital analytical model of the lunar brightness and thermal fields makes it possible to calculate the necessary photometric parameters, surface brightness and temperature for any geometry of the angular parameters of photography and illumination with an accuracy achieved by ground-based photometry. The root-mean-square errors in the determination of the rightness and of the radiation temperature are + 1.5 relative units and + 1.5 K, respectively. The IR channel records thermal fluxes objects with radiation temperatures between 213 and 313 K. The noise level does not exceed 1 K.
JSM41/W/04-B4 Poster 1015-04
HIGH RESOLUTION SYNOPTIC TOTAL OZONE IMAGING FROM A GEOSTATIONARY SATELLITE : A CASE STUDY USING GOES-8 INFRARED RETRIEVALS, GOME OBSERVATIONS AND A NUMERICAL ADVECTION MODEL
Yvan J. ORSOLINI (Norwegian Institute for Air Research; email : orsolini@nilu.no) Fernand Karcher (METEO-FRANCE, Centre National de Recherches Meteorologiques, Toulouse)
The second generation European weather satellite to be launched near the year 2000 is designed to routinely and synoptically monitor total ozone using infrared remote sensing, with a full coverage of the Earth disk. These total ozone observations are likely to convey a wealth of information about dynamical processes in the lower stratosphere. Hence, there is a need for validation and characterization of total ozone structures observed from geostationary satellites before ozone IR remote sensing from such a platform could be routinely used for meteorological applications. A set of high spatial resolution (pixel size near .1 degree) total ozone synoptic images have been produced hourly for the period February 23 to 24 using the GOES-8 IR radiance in 13 channels. The GOES-derived total ozone in the imaging window, covering the eastern US and contiguous maritime areas, is validated against the total ozone measured by GOME. These images show with great detail fine-scale total ozone filaments. The reality of such features is corroborated by a 5-day numerical simulation of the ozone distribution using analysed ECMWF winds, and an initial 3D ozone field from Microwave Limb Sounder data from the Upper Atmosphere Research Satellite.
Presiding Chair: H.Kawamura (Center for Atmospheric and Oceanic Studies,
Tohoku University, Japan)
OCEAN MONITORING
JSM41/L/03-B4 Invited 1040
GLOBAL SEA SURFACE TEMPERATURE MONITORING FROM SPACE; CURRENT ISSUES OF DEFINITION, ACCURACY AND VALIDATION.
Ian S. Robinson (School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, UK)
Sea surface temperature (SST) is a variable, readily measured from space, which has importance as a driver of air-sea interaction processes, for assimilation into coupled ocean-atmosphere models, and as an indicator of climate change. This talk reviews the differing requirements for accuracy and resolution of global SST data, which are driven by diverse applications of the data. These are compared with the current best achievements of satellite infrared systems in applying corrections for atmospheric effects on the measured radiation. Now that atmospheric correction accuracies using dual-view systems are approaching 0.1 C, it is becoming clear that both the application and the validation of space-derived SST are subject to the thermal structure of the upper ocean. Several reasons are presented to support the proposal that the skin temperature of the upper few microns of the sea surface is the most appropriate measure of SST. This is what is viewed directly by satellite sensors, it is what controls air-sea fluxes, and it is the only definition of SST which is not arbitrarily dependent on the depth of sampling. However, this raises issues of diurnal variability of the skin temperature which need to be handled in a consistent and systematic way in the compilation of SST databases, if SST is to be useful and unambiguous as an indicator of climate change. The potential synergy of geostationary and polar orbiting sensors for generating composite SST fields is considered in this context. Finally the question of validation is addressed, identifying the need for a more comprehensive availability of in situ radiometric measurements of the skin temperature.
JSM41/W/36-B4 1110
THE USE OF RADIATIVE TRANSFER MODELLING IN IMPROVING SATELLITE SEA SURFACE TEMPERATURE RETRIEVAL
BK MCATEE, M Boterhoven, A Rodger, and MJ Lynch (Remote Sensing and Satellite Research Group, School of Physical Sciences, Curtin University of Technology, GPO Box U1987, Perth WA 6845, Australia, email: pmcateebk@cc.curtin.edu.au) AF Pearce (CSIRO Marine Laboratories, PO Box 20, North Beach WA 6020, Australia, email: alan.pearce@marine.csiro.au)
Satellite-derived sea surface temperature (SST) may be improved by the incorporation of regional atmospheric information into the SST retrieval algorithm. Our discussion of satellite SST retrieval will include computer modelling of radiative transfer as well as the development, performance and sensitivity analysis of SST algorithms.
The algorithms currently under development are designed to improve the accuracy of SST retrieval by accounting for seasonal and latitudinal variation in climatic conditions through the incorporation of the computer simulation of the radiative transfer process into the scheme using an atmospheric transmittance model. Data input to the model may be derived from sources such as radiosonde and TOVS measurement of atmospheric properties.
Progress in algorithm development will be discussed along with the effectiveness of particular algorithms in various scenarios and a description of field measurements of SST and validation of the algorithms.
JSM41/W/15-B4 1125
SATELLITE OBSERVATIONS OF SEASONAL TO DECADAL VARIABILITY IN THE LARGE-SCALE OCEANIC FRONTAL ZONES
Alexander KAZMIN (Frontier Research System for Global Change/Institute for Global Change Research, SEAVANS N 7F,1-2-1 Shibaura, Minato-ku, Tokyo 105, Japan, email:kazmin@frontier.esto.or.jp)
Sea surface temperature (SST) from weekly global satellite data at 18 km resolution for the period of 1982-97 and estimates of the surface forcing due to wind stress and net heat flux were used to investigate global monthly climatology of the large-scale oceanic frontal zones (OFZ), seasonal and interannual variability of SST gradient in several frontal zones, response of OFZ to decadal climate changes, and the meridional frontogenesis in the North Pacific. A computer animation of the full-resolution monthly climatologies of SST gradient provided detailed dynamic global picture of OFZ seasonal variability. Spectrum analysis of time series of SST gradient revealed a seasonal signal as well as interannual variations that, in the equatorial zone, are related to ENSO events. While 16-year time series is insufficient to detect decadal cycle, it still was useful for documenting the changes in OFZ associated with specific climatic shift of late 1980s from cool to warm conditions in the mid-latitude North Pacific. Both subtropical and subpolar OFZ revealed response to this shift, evident in spatial structure and SST gradient anomalies pattern. Estimates of meridional frontogenesis in the North Pacific due to wind and heat forcing on seasonal and decadal timescales have been compared with observed rates of frontogenesis.
JSM41/E/20-B4 1140
A REVIEW ON STUDIES OF THE WARM-CORE RING IN THE KUROSHIO-OYASHIO TRANSITION ZONE USING SATELLITE-DERIVED SSTs AND PREDICTION OF ITS SHORT-TERM VARIATIONS
HIROSHI KAWAMURA Center for Atmospheric and Oceanic Studies, Faculty of Science, Tohoku University, Sendai 980, Japan
The Kuroshio and the Oyashio meet in the Pacific ocean east of Japan and a complex oceanic feature associated with warm and clod eddies appears in this region. Therefore, the Kuroshio-Oyashio transition zone is sometime called "the confluence zone" or "the perturbed region". This region is also well known as one of the good commercial fish grounds in the world ocean. Since the large temperature difference between the Kuroshio and Oyashio waters, there appear many temperature fronts. SSTs derived by AVHRR on board the NOAA series satellite have contributed to understand mechanisms of the oceanic variations and to monitor the front locations, which are associated with the promising commercial fish grounds. In the presentation, the oceanographic studies performed in this region using AVHRR-SSTs are reviewed, focusing on the evolution of understanding toward prediction of the short-term variations relating to the warm-core eddies. The contour dynamics was successfully introduced to simulate a drastic variation of two warm-core rings, whose boundaries are visualized by the SST images. Predictability of the contour dynamics is examined for four spring seasons by using daily SST images with high-spatial resolution, and almost of the drastic events are well simulated for about three weeks. This means that combination of SST images and the contour dynamics model can be used to predict the short-term variation of warm-core rings. Social needs and practical methodology of the short-term prediction will be presented.
JSM41/W/24-B4 1155
SPACEBORNE SCATTEROMETERS AND MICROWAVE RADIOMETERS IN THE STUDIES OF OCEAN-ATMOSPHERE INTERACTION
W. Timothy LIU and Wenqing Tang (both at Jet Propulsion Laboratory, Caltech,
email: liu@pacific.jpl.nasa.gov)
Spaceborne scatterometers are designed to measure ocean surface wind vectors and, therefore, ocean-atmosphere momentum flux, under both clear and cloudy conditions. The scatterometers on a series of European Remote Sensing Satellites (ERS) have provided surface wind measurements since 1991. The National Aeronautics and Space Administration (NASA) launched scatterometers NSCAT in 1996 and Quikscat in 1999, with continuous improvements in spatial resolution and coverage. The operational Special Sensor Microwave / Imagers (SSM/I) have monitored ocean surface wind speed, integrated water vapor (IWV), and rain since 1987. The Tropical Rain Measuring Mission (TRMM) Microwave Imager (TMI), which was launched in 1997 measures additional frequencies from which all weather sea surface temperature (SST) can be retrieved. Ocean surface evaporation or latent heat flux can be derived from the spacebased measurements of wind speed, IWV, and SST, or it can be retrieved directly from the radiances observed by TMI.
Three examples will be presented to show oceanic responses (as exhibited through spacebased SST and sea level changes) to surface wind and thermal forcing at different temporal and spatial scales - during the transition of a storm, the seasonal changes of monsoons, and an El Nino episode.
JSM41/E/08-B4 1210
SEA SURFACE TEMPERATURE OBSERVATION FROM TRMM MICROWAVE IMAGER
Misako KACHI, Akira Shibata, Hiroshi Murakami and Keiji Imaoka (Earth Observation Research Center (EORC), National Space Development Agency of Japan (NASDA), 1-9-9 Roppongi, Minato-ku, Tokyo 106-0032, JAPAN, email: kachi@eorc.nasda.go.jp)
The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) has an added 10 GHz channel compared to the Special Sensor Microwave Imager (SSM/I) which has been operating since 1987. The 10 GHz channel is more sensitive to sea surface temperature (SST) than higher frequency channels. The SST retrieved from TMI is compared to the monthly mean SST produced by Reynolds and Smith (1994), and accuracy of the monthly TMI SST is within 0.5 C, and it satisfies requirement for SST measurement.
In 1998, the El Nino warm episode was diminished from early to mid May, and sudden cooling of SST over the central and eastern equatorial Pacific was clearly observed from TMI. TMI can measure SST under clouds by using microwave signal from the sea surface, while the infrared sensors cannot. Since TRMM carries the visible infrared sensor, we could compare SST coincidentally observed by both microwave and infrared sensors. NASDA will launch ADEOS-II satellite that also carries both microwave sensor, the Advanced Microwave Scanning Radiometer (AMSR) and visible infrared sensor, the Global Imager (GLI) in 2000. In the same year, NASA will also launch the EOS-PM1 satellite, which carries AMSR-E modified from AMSR. We expect that coincidentally observations of SSTs from microwave and infrared sensors will continue after TRMM.
Thursday 29 July PM
Presiding Chair: H.Kawamura (Center for Atmospheric and Oceanic Studies,
Tohoku University, Japan)
OCEAN MONITORING (cont)
JSM41/E/13-B4 Invited 1400
OCEAN COLOR REMOTE SENSING AND JAPANESE OCEAN COLOR SATELLITE ACTIVITIES
JOJI ISHIZAKA (Faculty of Fisheries, Nagasaki Univ., 1-14 Bunkyo, Nagasaki,852-8521 Japan, E-mail: ishizaka@net.nagasaki-u.ac.jp)
Ocean color is the only remote sensing technology to monitor biology in the ocean. The Coastal Zone Color Scanner (CZCS) launched by NASA is the first ocean color sensor specifically designed to detect phytoplankton pigments. The sensor collected data during 1978 to 1986, although the sensor was not continuously operated. The spatial and temporal variability of the CZCS phytoplankton pigments was far larger than the biological oceanographers had been expected. After ten years of blank, Ocean Color and Temperature Sensor (OCTS), developed by National Space Development Agency of Japan (NASDA), was onboard of Advanced Earth Observing Satellite (ADEOS) launched on August 1996. Although the satellite stopped operation on June 1997, OCTS collected 8-months (November to June) of fully global 1-km resolution ocean color data. Global composite data and Intensive Local Area Coverage (LAC) data around Japan of sea surface chlorophyll-a were available through internet with near real time. Those data were verified with sea truth data from the global ocean. The ocean color data time series is now continued by NASA SeaWifs. Ocean color remote sensing is now facing the new era. Global Imager (GLI) will be onboard of ADEOS-II launched on the fall of 2000 by NASDA. NASA is planing MODIS, and ESA is planing MERIS. Those sensors have larger numbers of channels than previous sensors and should be useful for the monitoring of coastal waters as well as open ocean. Multi-sensor operation should cover global ocean more frequently than by single-sensor operation. Future challenges of the ocean color remote sensing will be discussed.
JSM41/E/27-B4 Invited 1430
CONTRIBUTIONS OF SATELLITE ALTIMETRY TO GLOBAL OCEAN MONITORING
ROBERT CHENEY (NOAA/NESDIS National Oceanographic Data Center, 1315 East-West Highway, Silver Spring, MD 20910 USA, email rcheney@nodc.noaa.gov)
An uninterrupted flow of satellite altimeter data has been available since the launch of ERS-1 in 1991 and Topex/Poseidon in 1992. With the Jason-1 and Envisat altimeters due to be launched in 2000, it is likely that we will continue to enjoy this observational wealth for years to come. Satellite altimetry has enabled a variety of phenomena to be monitored in near-real time. Operational applications include tracking of the Loop Current and its eddies in the Gulf of Mexico and assimilation of altimeter sea heights in ocean models used to forecast El Nino. With nearly 7 years of the highly-accurate Topex/Poseidon data already collected, low-frequency phenomena such as the North Atlantic Oscillation are being studied, and stable values for the rise of global sea level are being obtained. This presentation will review progress in these areas and discuss plans for future altimeter missions.
JSM41/W/14-B4 1500
MONITORING A WESTERN BOUNDARY CURRENT USING SATELLITE AND IN-SITU DATA
Richard COLEMAN, Ken Ridgway, Rick Bailey (CSIRO Marine Research, Hobart, Tasmania, Australia, email r.coleman@marine.csiro.au), Dave Mickler (University of Colorado, Boulder, Colorado, USA)
We compare the circulation through two sections crossing a western boundary current (East Australian Current, EAC) in the Tasman Sea from in-situ XBT casts and T/P altimeter data. The sections cross the current in the north at 26S (Brisbane-Fiji), where the current intensifies and in the south at 34S, just beyond the main separation point of the EAC mean flow.
Surface steric height relative to 800 db (the depth of the casts) is inferred from the XBTs using a high-resolution T-S climatology with the along section mean (from 20 transects observed between 1992-1999) removed to obtain surface anomalies. We also project the steric height onto a deeper reference level (2000 db) using a regression method derived from historical data. Raw along-track T/P data are first mapped onto the location and date of each XBT cast using optimal interpolation. Both in-situ and satellite data are then 'projected' onto 'standard' sections at a uniform along-track spacing. Over 20 realisations of each data type are available over the common period (Oct 1992 - 1999).
The surface height anomalies from each data type are in good agreement (~3-5 cm rms) down to spatial scales of 300 km. Below this length scale, the in-situ data resolves small changes which are beyond the capability of the interpolated altimeter fields. We also investigate the relative proportions of baroclinic to barotropic variability in the altimeter fields. The deeper reference level is needed to resolve the baroclinic flow associated with the EAC and its eddies within the coastal region. Away from this highly energetic region, the 800 db level is generally sufficient to capture the main baroclinic variability. In the north Tasman Sea we observe a region where the T/P variability is significantly less than that of the in-situ data. This would appear to be related to unresolved barotropic flow. The ability of each data type to resolve both spatial and temporal signals of interest is studied using regression methods, spectral analysis and wavelet techniques. The results provide a basis for designing future monitoring programs which utilise these data techniques in an efficient manner.
Finally, we present results documenting the mean flow and variability of the EAC from
the combined dataset. We observe interannual fluctuations in the EAC transport of up to
10 Sverdrups.
JSM41/W/09-B4 1515
VARIATIONS OF GLOBAL MEAN SEA LEVEL OBSERVED DURING THE TOPEX / POSEIDON MISSION
R. S. NEREM, D. P. Chambers, E. W. Leuliette, (all at the Center for Space Research, The University of Texas at Austin, Austin, TX, 78712, nerem@csr.utexas.edu) G. T. Mitchum (Dept. of Marine Sciences, University of South Florida, 140 Seventh Ave. South, St. Petersburg, FL, 33701, USA, email: mitchum@seas.marine.usf.edu) B. S. Giese (Dept of Oceanography, Texas A&M University, College Station, Texas, 77843, USA, email: giese@sweeney.tamu.edu)
The TOPEX/POSEIDON (T/P) satellite altimeter mission has been mapping global sea level every 10 days since its launch in August 1992. One of the objectives of climate change research is to establish the rate at which global mean sea level is increasing, so that it can be compared to similar predictions from global climate models. For this application, interannual variations can be quite troublesome, as they tend to mask the longer-term variations due to climate change. Using the T/P altimeter data, we observed a sharp rise in global mean sea level (~2 cm) during the 1997-1998 ENSO event, followed by a fall in sea level. We find these variations can be reproduced with GFDL’s MOM2 ocean model, allowing us to determine the signal is confined to the upper 300 m of the water column. The sea level observations appear to match similar variations observed in satellite measurements of sea surface temperature over the same time period. In addition, they can be represented by the "ENSO modes" of an EOF analysis of the T/P sea level observations. Finally, comparison of the T/P measurements with tide gauge measurements appears to rule out the observed change being caused by an instrumental effect. These ENSO variations have important implications for using altimeter data to detect climate change, the most notable of which is that a time series of several decades in length may be required unless a technique can be found to remove the ENSO variations from the T/P observations. We are experimenting with several statistical/modelling techniques to accomplish this, and will discuss the progress of these efforts. In addition, we will discuss a physical explanation for why ENSO is changing global mean sea level.
JSM41/W/34-B4 1530
ALTIMETRIC SEA SURFACE HEIGHT (SSH), RELATIVE TO THE ELLIPSOID
Dr John Blaha (Institution: Naval Oceanographic Office Email: lahaj@navo.navy.mil)
Altimetric sea surface height (SSH), relative to the ellipsoid, is produced routinely with sub-5 cm accuracy. Global ocean circulation monitoring that would exploit this precision, will require, in addition, determination of the difference of satellite SSH from the geoid. We show comparisons of two methods to remove the effect of the geoid on SSH over the western North Atlantic. The first method fits the time mean of the SSH record on individual satellite groundtracks to a climatological mean of dynamic height. The second method specifies dynamic height by taking in situ observations along selected groundtracks at the times of altimeter overflights. We show the comparisons on 19 TOPEX/POSEIDON groundtracks sampled by aircraft-deployed bathythermographs in the region 25N-40N, 75W-50W. Temperature profiles, from the surface to 800 m, were taken 15-20 km apart (in the along-track sense) within 24 hr of the altimeter measurements. Steric sea level estimates relative to 2000 dbar were computed from these observations. For comparison purposes, differences were computed between the aircraft dynamic heights and the mean-adjusted altimeter heights. This distribution (along tracks crossing the features of the subtropical gyre) shows the competing effects of measurement error in the bathythermograph data and sampling error in the climatological means.
JSM41/W/06-B4 1545
MONITORING ANTARCTIC ICE SHEET WITH SATELLITE RADAR ALTIMETER DATA
V. Nuth (Dept. of Geological Sciences and the Center for Space Research, The University of Texas at Austin, Austin, TX 78712, email: van@csr.utexas.edu), C. R. Wilson (NASA HQ, Geodynamics and Geopotential Fields Code YS, Washington, DC 20546, email: cwilson@hq.nasa.gov) M. K. Cheng (Center for Space Research, email: cheng@csr.utexas.edu) C. K. Shum (Dept.of Civil and Evironmental Eng. and Geodetic Science, Ohio State University, email: ckshum@osu.edu)
Since the launch of Seasat, radar altimeter data have contributed enormously to the study of glaciology. Until the launch of ICESAT, spaceborn radar altimeter data remain the only means to monitor ice mass balance on a global scale. However, the rugged ice surface topography has meant that this data set cannot be used readily without significant on-ground reprocessing. We use retracked pairs of altimeter measurements at the satellite cross-over points along with a waveform cross-correlation method to compute the estimate of ice sheet elevation changes over time. We report here results obtained from analysis of ERS-1 data over the Antarctic Ice Sheet. Our elevation time series show that while Antarctica as a whole exhibits a reasonable seasonal signal both in amplitude and phase, selected regions in West Antarctica appear to have undergone large elevation changes which are speculated to be associated with seasonal snowfall and other effects.
JSM41/W/07-B4 Poster 1620-05
ESTIMATION OF GLOBAL AIR-SEA TRANSFER OF CO2 USING TOPEX/POSEIDON DUAL-FREQUENCY BACKSCATTER
Nelson FREW, David Glover, Erik Bock, Catherine Goyet, Scott McCue and Richard Healy (Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543 USA, e-mail:nfrew@whoi.edu)
Global and regional estimates of ocean-atmosphere gas fluxes are limited by the uncertainties in current gas transfer velocity parameterizations. These model functions use wind as the sole controlling parameter. However, many other factors, including boundary layer stability, wave age, and surface films strongly affect gas exchange rates.
We outline a new method for estimation of transfer velocity using altimeter backscatter as a more direct measure of sea surface roughness and, therefore, transfer velocity. The algorithm assumes a linear relationship between mean square wave slope and gas transfer velocity for wavenumbers >50 rad/m. Estimates of mean square wave slope from the nadir-looking C- and Ku-band microwave altimeters aboard TOPEX/Poseidon are used to derive monthly global maps of transfer velocity. The monthly maps show a strong correlation with NCEP and FNMOC global winds for the same periods. The transfer velocity fields, combined with in situ observations and ocean colour estimates of biological productivity, are applied in a 3-D ocean GCM to estimate global seasonal and annual CO2 fluxes. The theoretical background and empirical observations underlying the new algorithm will be presented.
Presiding Chairs: A.Rango (U.S. Department of Agriculture, Beltsville, MD 20705-2350, USA) T.Engman (NASA/GSFC, Greenbelt MD 20771 USA)
TERRESTRIAL MONITORING
JSM41/LL/01-B4 Poster 1625-06
A STUDY OF THE ARCTIC SNOWPACK BY USE OF SYNTHETIC APERTURE RADAR (SAR) IMAGERY
M Johansson and I A BROWN Climate Impacts Research Centre, Björkplan 6A, S-981 42 Kiruna, Sweden maria.johansson@natgeo.su.se, iabrown@natgeo.su.se
The extent and properties of the snow cover in polar regions is of great importance to the earth’s radiation balance which is influencing the global climate. Therefore snow in the polar regions is an important study object when discussing climate change. A technique using satellite imagery in order to survey and describe the Arctic snowpack would be an important tool in the future, especially as input to global climate models (GCM) and for runoff forecasts made by hydropower companies. The synthetic aperture radar (SAR) is very suitable for operating in polar regions since it is independent of polar nights and cloudy skies. An additional advantage of the SAR-sensor is it’s use of microwaves and the microwaves capability to penetrate the surface, i.e. the snowpack and it’s substrata, which theoretically gives access to a three dimensional view of the snowpack.
The objective of this work is to investigate the use of SAR-imagery to study snow and snow melt in polar regions. The study focuses on the change in snow distribution and snow composition displayed through backscatter in SAR imagery during one spring season. Field data are collected at two filed sites in northern Sweden and Norway at 3-4 occasions at each field site during spring coincident with the acquired satellite imagery. The vertical variation in the snowpack is described by snow depth, dielectric constant, density and temperature measurements at selected profiles distributed over the field sites. The grain size and the stratigraphy of these profiles are ocularly described as well as the surface roughness of the snow cover. Analyses of ERS-1 and Radarsat-1 imagery are compared with the field observations. The field measurements will give a three-dimensional view of the snow cover which will be the background for a discussion highlighting the possibilities to calculate the snow pack status, i.e. liquid water content, density etc. to predict penetration depths, scattering and absorption of the microwaves at the time of satellite overpass. We will also discuss the need of multi-polarisation SAR-data, here HH and VV, within short time spans and the possibilities to follow the change in the snowpack through SAR-backscatter during spring.
JSM41/W/23-B4 Poster 1630-07
VOLCANIC SO2 EMISSIONS - A 20-YEAR SATELLITE RECORD
Gregg Bluth (Department of Geological Engineeringand Sciences, Michigan Technological University,Houghton, MI 49931, USA, email HYPERLINK mailto:gbluth@mtu.edu); gbluth@mtu.edu); Arlin Krueger (Atmospheric Chemistry and Dynamics,NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA, email krueger@chapman.gsfc.nasa.gov)
Data from the Total Ozone Mapping Spectrometer (TOMS) instruments have enabled us to develop a near-continuous record of worldwide explosive volcanism since 1978. While the original volcanogenic data product was sulphur dioxide, more recent advances have enabled the detection of ash clouds. In addition to the study of individual eruptions, these data have been used to place constraints on global volcanic SO2 emissions by explosive-type eruptions, both by infrequent, large eruptions and lower level, but more frequent events.
The current TOMS database includes well over 100 eruptions, including multiple eruptions during a continuous episode of activity. The magnitude of SO2 clouds range from >10 million tonnes (Mt) to as little as a few kilotonnes (kt). The longevity, and thereby long-term hazards, of the clouds likewise cover a wide range with Pinatubo removal occurring at a rate of 35 days (e-folding time), most mid-sized (200-5000 kt) eruptions from 2 - 10 days, and most small eruptions decaying within 1-2 days. Previous work estimates that explosive volcanic activity emits on the order of 4 Mt SO2/yr. However, new work suggests this estimate of annual flux may increase due to more intensive examination of the database focusing on smaller events, such as the prolific Nyamuragira volcano, Zaire. We report on some of the longer term (e.g., multiyear to decadal) trends in global volcanic activity observed through satellite observation, and how these trends may affect hazard planning and mitigation efforts. We also update the progress on a new NASA mission in hazard mitigation, VOLCAM, featuring a TOMS instrument upon a geostationary platform.
JSM41/E/09-B4 Invited 1635
SATELLITE REMOTE SENSING OF GLOBAL SNOW COVER – A BRIEF HISTORY
R.L. Armstrong, (National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA,
email rlax@kryos.colorado.edu)
Snow cover is an important variable for climate and hydrologic processes due to its effect on energy and moisture budgets. In terms of spatial extent, snow cover is the largest single component of the cryosphere with a mean maximum areal extent of 47 million km2, about 98% of which is located in the Northern Hemisphere. During the past three decades much important information on Northern Hemisphere snow extent has been provided by the NOAA weekly snow extent charts derived from visible-band satellite imagery (e.g. NOAA/AVHRR, GOES, METEOSAT, GMS). This product represents the longest single time series of any geophysical product obtained from satellite. Beginning in 1997 the spatial and temporal resolution of the original analysis ( approx. 190 km and 7 days respectively) was improved to become a daily product with a spatial resolution of 25 km. Limitations associated with visible wavelength data include the inability to acquire information below clouds or during darkness and the fact that data are limited to snow extent only. Because of the ability to penetrate clouds, provide data during darkness and the potential to provide an index of snow depth or water equivalent, passive microwave satellite remote sensing can greatly enhance snow measurements based on visible data alone. It is now possible to monitor the global fluctuation of snow cover over a 20 year period using passive microwave data (Scanning Multichannel Microwave Radiometer (SMMR) 1978-1987 and Special Sensor Microwave/Imager (SSM/I), 1987-present). A comparison of the visible and passive microwave time-series shows the visible data to have higher variability but trends are similar showing a decrease of approximately 0.4 % per year. The passive microwave data indicate less snow-covered area than the visible data throughout the year with the greatest differences in the fall and early winter when the snow cover is shallow. Results from new algorithms designed to reduce this error are presented.
JSM41/E/07-B4 1705
TOWARDS AUTOMATED MULTISPECTRAL SNOW MAPPING
PETER ROMANOV, Ivan Csiszar, and Garik Gutman NOAA/NESDIS, Office of Research and Applications, Camp Springs, MD
Current daily and weekly snow products at NOAA are generated by analysts, who use visible imagery from geostationary and polar orbiting satellites. There is no automated satellite-derived product based on the visible and/or infrared data, however. The automated satellite-derived snow product based on SSMI and/or AMSU microwave observations is used by the analysts only for verification because of the coarse resolution and remaining ambiguities. The present study is based on GOES Imager, NOAA AVHRR and DMSP SSM/I data over North America during the 1998-1999 snow season. The data from all channels on two GOES imagers (East and West) were intercalibrated with NOAA-14 corresponding channels and updated on a bi-monthly basis. The synergy between SSM/I, GOES Imager, and NOAA AVHRR observations has been utilized by taking advantage of the ability to observe ground surface through clouds by SSM/I, frequent views from GOES throughout the day, and the high resolution full coverage of northern latitudes by AVHRR. The SSM/I daily 30-km spatial resolution automated snow maps are produced routinely at NESDIS. They have been used as the primary source for a daily snow map. The shortcomings of the SSM/I-derived maps, such as spatial resolution and snow detection over forests, have been alleviated by a combined use of visible, mid-IR and IR from GOES and AVHRR. Daily composites based on the maximum brightness temperature have been constructed from GOES and AVHRR. All pixels in a daily composite are then classified into snow, snow-free and cloudy. The visible (0.6 5m) reflectances are corrected for angular effects with a semi-empirical kernel driven model. The mid-infrared reflectances were derived from GOES (3.9 5m) and NOAA (3.7 5m) data by subtracting the thermal component from observed radiances. The mid-IR reflectances did not exhibit any significant angular variability. They are then combined with the visible reflectances to form a snow index that is resistant to data contamination by most cloud types. Daily composites of this index are produced over North America from the combined data of the two GOES Imagers and NOAA-14 AVHRR. To produce weekly snow maps, 7-day composites have been formed based on the maximum snow index, reducing cloud contamination even further and filling the data gaps in the daily composites. We conducted validation and comparison of the derived snow maps with reports from ground stations and the current operational snow analysis at NOAA.
JSM41/W/12-B4 1720
CRYSYS: COLLABORATIVE APPROACH TO MONITORING AND MODELLING THE CRYOSPHERE IN CANADA
BARRY E. GOODISON, Climate Research Branch, Atmospheric Environment Service, 4905 Dufferin Street, Downsview, Ontario, M3H 5T4 Ross D. Brown, Atmospheric Environment Service, 2121 Trans-Canada Highway, Dorval, Québec, H9P 1J3. Claude R. Duguay, Centre d’études nordiques, Université Laval, Sainte-Foy, Québec, G1K 7P4 Gregory M. Flato, Canadian Centre for Climate Modelling and Analysis, Atmospheric Environment Service, P.O. Box 1700, Victoria, British Columbia, V8W 2Y2 Roy M. Koerner, Glaciology, Terrain Sciences Division, Geological Survey of Canada, 601 Booth St., Ottawa, Ontario K1A 0E8 Ellsworth F. LeDrew, Department of Geography, University of Waterloo, Waterloo, Ontario, N2L 3G1 Anne E. Walker, Climate Research Branch, Atmospheric Environment Service, 4905 Dufferin Street, Downsview, Ontario, M3H 5T4
CRYSYS (Use of the Cryospheric System to Monitor Global Change in Canada) is a Canadian collaborative research effort involving 14 universities, four federal institutions, and one non-profit organization, established originally as an Interdisciplinary Science Investigation (IDS) in NASA’s Earth Observing System (EOS) Program. Recognizing the importance of the cryosphere in both the global and regional climate system, CRYSYS has evolved to bring together a wide range of Canadian cryospheric expertise in remote sensing, modelling, field investigations, data integration and data management to provide improved capabilities for monitoring the state of the cryosphere, and a greater understanding of cryospheric processes and variability. The main scientific goals of CRYSYS are: (1) to develop capabilities for monitoring and understanding regional and larger-scale variations in cryospheric variables; (2) to contribute to the development and validation of local, regional and global models of climate/cryospheric processes and dynamics, and to improve understanding of the role of the cryosphere in the climate system; and (3) to assemble, maintain and analyze key historical, operational and research cryospheric data sets to support climate monitoring and model validation. These goals are addressed through the cryospheric components especially important within Canada (sea ice, snow, lake ice, glaciers and ice caps, and permafrost/frozen ground), but recognizing their application in a global context. The team’s field expertise and on-going intensive field investigations throughout Canada are key elements in the development and validation of new remote sensing algorithms and techniques (e.g. snow water equivalent, lake ice freeze-up/break-up, sea ice motion, freeze/thaw of frozen ground, growth of glaciers and ice caps), the use of these data for improved model development (e.g. Canadian GCM, CLASS), and the creation of reliable time series for climatological and hydrological analyses.
CRYSYS, through its focus on climate/global change in Canada, will continue to contribute to international programs, including EOS, WMO/GCOS through the Canadian cryospheric GCOS activities, and to WMO/WCRP through GEWEX, ACSYS and the new CLIC initiative. This presentation will provide a summary of significant CRYSYS-supported research on monitoring and modelling the cryosphere with remotely sensed and in situ data, will highlight CRYSYS contributions to GCOS objectives, and will provide an assessment of the current state of the cryosphere in Canada.
JSM41/W/21-B4 1735
COMPLEMENTARY USE OF SATELLITE AND IN SITU DATA FOR MONITORING SPATIAL AND TEMPORAL CHARACTERISTICS OF SNOW COVER IN CANADA
BARRY GOODISON, Ross Brown and Anne Walker: (Climate Processes and Earth Observation Division, Atmospheric Environment Service, Downsview, Ontario, CANADA, M3H 5T4.
E-mail:ross.brown@ec.gc.ca)
Satellite observations are an indispensable component for mapping and monitoring of the
cryosphere over large, high latitude land masses, such as Canada, where in-situ data are limited. Satellite sensing of snow cover has been found to be especially important for hydrological and climatological analyses and the assessment of variability and change over a range of spatial and temporal scales including monthly-seasonal and annual-decadal time scales. The CRYSYS project (Use of the Cryospheric System for Monitoring Global Change), a Canadian-led interdisciplinary science project in the NASA/EOS program, supports two important areas of research related to snow that are contributing to an enhanced ability to document spatial and temporal variations in snow cover: (1) the development, validation and refinement of empirical and theoretical algorithms for snow cover properties (extent, water equivalent, wet/dry state) in varying landscapes using passive and active microwave data, and (2) the merging of satellite and in-situ data to extend the satellite record and provide compatible and consistent information for climate variability studies, change detection, and validation of GCM transient climate simulations. This paper will present the results of new research on developing passive microwave SWE algorithms for forested areas, and the development of a satellite-derived SWE time-series (1988/89-1997/98) and climatology for the Prairie region of Canada taking account of the effects of wet snow. The paper will also present results from the merging of in-situ and satellite information that yielded monthly time series of snow cover extent information over North America and Eurasia from 1915. The reconstructed snow cover series show evidence of a significant 20th Century decrease in spring snow cover extent over Eurasia that corresponds with enhanced 20th Century spring warming over this continent. The problem will conclude with recommendations on requirements for monitoring snow cover for the Canadian GCOS program.
JSM41/E/19-B4 1750
PASSIVE MICROWAVE REMOTE SENSING OF FROZEN SOILS
T. Zhang, R. ARMSTRONG, and J. Smith, (all at the National Snow and Ice Data Center and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309-0449, USA, email: tzhang@kryos.colorado.edu and rlax@kryos.colorado.edu)
The timing, duration, areal extent, and depth of near-surface soil freezing and thawing are important parameters for regional climatic and hydrologic studies, and changes in these parameters are important climatic indicators and integrators. Conventional point measurements of surface soil freezing and thawing provide information for process studies in local areas. It is impractical to conduct large- or regional-scale investigations of surface soil freezing and thawing by using the point measurement method. In this study, onset, duration and areal extent of near-surface soil freezing and thawing were investigated using passive microwave remote sensing data in North America (30N and 130W to 60N and 50W) during the winter of 1997-1998. The criteria used to detect onset, duration, and areal extent of surface soil freezing include (i) a negative spectral gradient between Tb(37V) and Tb(19V), (ii) a cutoff Tb(37V). The algorithm was partly validated against field measurements in northern Plains of the United States. The primary results obtained indicate that frozen soil extent was generally in good agreement with zero degree Celius isotherm of air temperature. The boundary of frozen soil extent moved southward as the cold air was invading from north in northern Plains during the early winter. The onset of surface soil freezing ranged from September in northern and mountainous regions to December/January in southern regions. The duration of surface soil freezing varied from a few days in the south to about six months in the north and mountains. Surface soils were generally frozen before snow cover developed. Snow cover extent was also included for comparison. We will discuss the progress and problems concerning the application of pasive microwave remote sensing data to study of frozen soils.
Friday 30 July AM
Presiding Chairs: A.Rango (U.S. Department of Agriculture, Beltsville, MD 20705-2350, USA)
T.Engman (NASA/GSFC, Greenbelt MD 20771 USA)
TERRESTRIAL MONITORING
JSM41/W/19-B5 Invited 0900
SATELLITE REMOTE SENSING OF SOIL MOISTURE-THE MAXIMUM POTENTIAL OF PAST, CURRENT AND FUTURE SYSTEMS
Thomas J. Jackson, U.S. Department of Agriculture, Agricultural Research Service, Hydrology Lab, 104 Bldg. 007 BARC-West, Beltsville, MD 20705, USA email:jackson@hydrolab.arsusda.gov
The role of surface soil moisture in hydrology and climate has been defined over the past decade. A lack of a physically based soil moisture element and an observational data base for validating such models are recognized as critical sources of uncertainty in simulations and forecasts. Long term spatial soil moisture data have never been available. Although many technologies have been utilized and evaluated, none have been able to provide reliable in-situ measurements in a cost-effective manner. Satellite based microwave remote sensing is an ideal source of surface soil moisture information. Microwave sensors are sensitive to the water content of the soil and satellite sensors can provide updated image (map) products. The geographic domain for soil moisture retrieval is limited by vegetation. Vegetation reduces the sensitivity of the measurement to soil moisture changes. The reduction in sensitivity increases as frequency increases. Satellite agencies have not placed a high priority on providing instruments that are optimized for soil moisture measurement. SSM/I frequencies can only provide information for a few regions with minimal vegetation. There is a better outlook for soil moisture when the AMSR instruments are launched in the year 2000 by the U.S. and Japan. It is possible that by conducting the right kind of calibration activities with these instruments, that the data collected during the nearly ten years of SMMR observations can be more effectively utilized for long term studies. However, the greatest potential for soil moisture remote sensing is at lower frequencies, in particular L band. With current technologies it is possible to implement a spaceborne L band system with a spatial resolution that is compatible with large-scale hydrology and climate. With this system it would be possible to provide soil moisture information for 70% of the Earth's land surfaces.
JSM41/W/27-B5 0930
THE SOIL MOISTURE AND OCEAN SALINITY (SMOS) MISSION: AN OVERVIEW
Y.H. Kerr (CESBIO, 18 av E. Belin, 31401 Toulouse cedex, France, email Yann.Kerr@cesbio.cnes.fr), P. Waldteufel (IPSL , 10-12 av de l'Europe, 78140 Vélizy, France) ; G.S.E. LAGERLOEF (Earth and Space Research, 1910 Fairview Ave E, Suite 102 Seattle WA 98102-3620, USA, email lagerloef@esr.org) ; J.-P. Wigneron (INRA Bioclimatologie , Agroparc 84914 Avignon Cedex 9, France) J. Font (Dept. of Marine Geology and Physical Oceanography, Institut de Ciències del Mar - CSIC, P. Joan de Borbó s/n, 08039 Barcelona, Spain); J.-M. Martinuzzi (CNES, 18 Avenue Edouard Belin 31401 Toulouse cedex 4, France)
The goal of this paper is to present a space mission aimed at the retrieval of soil moisture and ocean salinity from space. It is now being proposed to the Earth Explorer Opportunity Programme, under the name of SMOS. The sensor is an L-band interferometer based on an innovative concept of bi- dimensional aperture synthesis method. The instrument is a Y shaped structure consisting of 3 co- planar arms consisting of an elongated array of elements operating in H and V polarization and incidence angles ranging from about 0 to 55 . The sensor has new and very significant capabilities especially in terms of multi-angular view configuration. The main goals of this mission are: (i) to provide fields of surface soil moisture and potentially of root zone soil moisture, all over the globe and every 2 to 3 days, (ii) to measure seasonal to interannual variations of sea surface salinity, (iii) to be used over ice and ice caps for research purposes. The ultimate goal is to provide global information on such key parameters (moisture and salinity) for models in the fields of oceanography, meteorology, hydrology and climate. This paper will give an overview of the SMOS Mission objectives and the main mission characteristics together with some of the technical features.
JSM41/W/02-B5 0945
DEVELOPMENT OF A SATELLITE SYSTEMS FOR MEASURING SOIL MOISTURE AND SEA SURFACE SALINITY
Edwin T. ENGMAN (Code 974, Hydrological Sciences Branch, Laboratory for Hydrospheric ProcessesNASA, Goddard Space Flight Center, Greenbelt, MD 20771, USA,
Email: tengman@neptune.gsfc.nasa.gov)
The science need for remotely sensed soil moisture and sea surface salinity has been well established in the hydrologic, oceanographic, climate change and weather forecasting communities. In spite of this well documented science need there are currently no satellite missions flying or funded to make these very important geophysical measurements. There have been a number of experimental programs that have demonstrated the feasibility of using long wave microwave sensors for estimating soil moisture and also a few that have shown the promise for measuring salinity. The principal sensor to accomplish both the soil moisture and salinity measurements is an L-band passive microwave radiometer. Unfortunately, each science driver, soil moisture sand salinity, impose quite different technical requirements on the sensor system. Soil moisture is driven by a spatial resolution on the order of 20 to 30 km and achieving this requires a very large antenna. Spatial resolution is not a driver for salinity except for possibly in the littoral zone, however the salinity measurement requires an extremely sensitive radiometer. This paper describes the several alternatives to solve the very large antenna challenge and still meet the radiometer sensitivity requirement for salinity. The paper also discusses the alternatives considered to obtain the necessary ancillary data for characterizing the surface roughness, the surface (land and ocean) temperature and the attenuation affects of vegetation needed to derive the geophysical parameters. Finally, the paper discusses proposed missions and how well they will meet the science requirements.
JSM41/W/16-B5 1000
SATELLITE MICROWAVE REMOTE SENSING OF LAND SURFACE HYDROLOGY
Toshio Koike (Nagaoka University of Technology, Nagaoka, 940-2188, Japan, email:tkoike@nagaokaut.ac.jp)
Microwave remote sensing has high potential of measurement of land surface hydrological parameters quantitatively. Their diurnal cycles and heterogeneity also can be measured by non-sunsynchronous satellites and the combination of passive and active sensors, respectively. New algorithms for snow, soil moisture, surface temperature and rain by using passive microwave sensors are developed based on microwave radiative transfer theory. They are applied to the satellite data form the TRMM Microwave Imager (TMI) and the Special Sensor of Microwave Imager (SSM/I) and evaluated by using the ground-based data through the GTS and/or obtained during the GAME-Tibet Intensive Observing Period (IOP) in 1998. The estimated hydrological parameters, snow temperature, surface soil moisture, soil surface temperature and rainfall, show good correspondence to the observed data. An algorithm for soil moisture mapping in permafrost regions is introduced by using two images of L-band Synthetic Aperture Radar (SAR), one in winter and the other in summer. The algorithm is based on a relationship between two surface roughness parameters, r.m.s. height and correlation length, and the scattering model composed by the Integral Equation Method (IEM) and formulation of volume scattering from inhomogeneous medium. This algorithm is applied to the JERS-1 SAR data in the Tibetan Plateau in 1993. The estimated soil moisture shows in good agreement with the observed one obtained during the GAME-Tibet IOP in 1998. Provide fields of surface soil moisture and potentially of root zone soil moisture, all over the globe and every 2 to 3 days, (ii) to provide decadal values of sea surface salinity, (iii) to be used over ice and ice caps for research purposes. The goal is to provide information globally on key parameters (moisture and salinity) for models in the fields of oceanography, meteorology, hydrology to name the main ones. This paper will give an overview of the SMOS Mission objectives and the main mission characteristics together with some of the technical features.
JSM41/W/22-B5 1015
ENVIRONMENTAL SIGNALS IN LAND ALTIMETER DATA: POTENTIAL FOR SOIL MOISTURE MEASUREMENT
BERRY, P.A.M., Pinnock, R.A. & Hoogerboord, J.E. Geomatics Unit, De Montfort University, Leicester LE1 9BH, UK, e-mail:pamb@dmu.ac.uk
The development of an expert system for recovery of orthometric heights from land radar altimeter waveforms has now enabled the detection of environmental signals in the altimeter dataset from ERS-1 and ERS-2.
This paper presents initial results from an ongoing research project evaluating the potential for recovery of surface soil moisture from altimeter echoes. With measurements from ERS-1/2 missions now covering almost ten years, and the planned continuation of this datastream with Envisat, radar altimetry presents a unique time series with near global sampling when in ice mode. One focus of the work presented here is on semi-arid areas such as desert margins, where results using the expert system already confirm the presence of quantifiable environmental signals in the individual waveforms
JSM41/E/24–B5 1030
A STUDY ON SOIL EROSION IN SOUTH CHINA USING REMOTE SENSING AND
GIS TECHNIQUE
ZHANG, Jiahua (Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing,100029, P.R.China email zhangjh@ast590.tea.ac.cn)
Soil erosion seriously impact on global nature resources and ecological environment, in China the total soil erosion area covers 38.26% of total China's area, of which water erosion is 48.77%, and wind erosion accounts 51.22%, the total soil erosion amount annual year is five billion ton, accounting for 10% of the whole world. In the paper hilly land soil erosion condition in Southern China is severe, surface soil has been eroded away, soil fertility drop down, particularly in red earth and granite area, the resistance of erosion is low. Soil erosion and disasters caused by floods, windstorm, landform, slope, soil erodible character and landuse type, among this the human activities including cut down tree and excavate land is main factor. Using study methods of remote sensing and geo-information system can investigate and monitor the degree and of soil erosion, in the meantime dynamic of soil erosion can been analysis by different period investigate data. The result of investigation based on remote sensing and GIS to Xingguo country show the soil erosion area and annual soil erosion amount decreased 19.09% and 43.05% respectively from 1958's to 1988's. The gray forecast state that without soil erosion area increasing from 818.04 km2 in 1988 to 1276.69 km2 in 1995, in the meantime total soil erosion amount decreased from 607.21!A104 t/a in 1988 yr. to 472.12 !A104 t/a in 1995. By comparison to different landuse types, the sediment modulus of woodland is lowest with 177.16~187.75t / km2 !$a, on the contrary the bare land is highest with 10626.76~11265.48 t /km2 a, so high vegetation coverage planting can decrease the soil and water loss. In the end some methods including conservation farming and engineer measures control soil erosion are suggested, by these can control soil erosion, and ecological cycle may take a turn for the better.
JSM41/E/03-B5 Invited 1105
LAND SURFACE RESPONSE TO HYDROLOGICAL FORCING USING TIME SERIES OF AVHRR AND SMMR 37 GHz OBSERVATIONS
Massimo MENENTI1, S. Azzali, G. Roerink, W. Verhoef2 and S. Leguizamon3 The Winand Staring Centre (SC-DLO), P.O.B.125, 6700 AC Wageningen, The Netherlands (1) Universite Louis Pasteur- LSIIT, 5 Blvd. S. Brant, 67400, Illkirch, France; e-mail menenti@sepia.u-strasbg.fr (2)National Aerospace Laboratory (NLR), P.O.B. 153, 8300 AD Emmeloord, The Netherlands (3)Universidad de Mendoza/ CIS, Aristide Villanueva 776,5500 Mendoza, Argentina
In the last few years global satellite data sets have become available to provide observations of changes of land surface conditions over significant periods of time. Although instrument- and orbit-related artefacts still affect the precision of the observations, analyses of time series of satellite observations provide new insights on the response of heterogeneous land surfaces to hydrological forcing. The paper presents highlights of studies on land surface changes in arid (Africa), semi-arid (Mediterranean) and humid (South America) climates. To extract effectively information from such large data sets three algorithms have been developed and applied: Fast Fourier Transform (FFT), Harmonic Analysis of NDVI Time Series (HANTS) and wavelets transform. The analysis (FFT) of 10 years monthly NDVI time series of Africa and South America led to a continental map of vegetation-soil-climate complexes and to document their phenology. The HANTS algorithm was also used to improve the quality of the data sets by removing cloud- contaminated observations still present in the monthly composites. Vegetation type was strongly related to the Budyko aridity index. A detailed change analysis of 10 days 1 km data of the Mediterranean basin led to identify areas most sensitive to drought. Anomalous events in the time series were best detected using the wavelets transform. Notwithstanding the low spatial resolution, the SMMR 37 GHz observations were used to monitor flooding and recession in the Pantanal, a large natural reservoir in Brazil and Paraguay.
JSM41/E/18-B5 1135
INTERANNUAL CHANGES IN GLOBAL VEGETATION ACTIVITY: COMPARING SATELLITE OBSERVATIONS AND VEGETATION MODELLING
WOLFGANG KNORR (Max-Planck-Institut fuer Meteorologie, Bundesstrasse 55, D-20146 Hamburg, Germany; Tel. : +49-40-41173-282, Fax : +49-40-41173-298, Email: knorr@dkrz.de) and Garik Gutman (NOAA/NESDIS/ERA12, WWB 712, 5200 Auth Road, Camp Springs, Maryland 20746-4304, U.S.A.)
Remote sensing from satellites offers unique opportunities to monitor the state and evolution of global land vegetation. This is important, because land plants are considered to be of major importance for interannual changes in the global carbon cycle. It is particularly interesting to use remotely sensed imagery to test global models of vegetation activity. In this contribution, we compare interannual changes in vegetation cover inferred from NOAA-AVHRR data over the 1990s with the same changes simulated by the global Biosphere Energy-Transfer and Hydrology model (BETHY). We discuss the implications of differences and agreement between the two fields for the simulated carbon fluxes with BETHY. We find a pronounced impact of the El-Nino/Southern Oscillation phenomenon in both. Comparison with atmospheric CO2 data also suggests such a link, as it stresses the dominant impact of land vegetation on this time scale. The results suggest that satellite monitoring of vegetation activity could significantly enhance our understanding of the present global carbon cycle.
JSM41/E/14-B5 1150
THE RESPONSE OF SATELLITE-DERIVED NDVI TO LOCAL CLIMATE VARIATION IN SIBERIA
Rikie SUZUKI (Frontier Research System for Global Change, c/o NIED, Tsukuba, Ibaraki 305-0006, Japan, email: suzuki@frontier.bosai.go.jp)
The response of the satellite-derived Normalized Difference Vegetation Index (NDVI) to the climate (precipitation and temperature) regionality was investigated in Siberia. The NDVI was obtained from Gallo's monthly Global Vegetation Index (GVI) which is a coarse NDVI data set covering the globe. Since the vegetation in Siberia shows meridional (south-north) transitions corresponding to the climate, two meridional transects were established from arid to taiga (along 75E) and from taiga to tundra (along 110E) vegetation transitions. Using surface station temperature and precipitation data in the CD-ROM `Global Daily Summary', the profiles of NDVI, temperature, and precipitation in the two transects were compared in conjunction with the elevation of each station through 1987 to 1990. As for the temperature, WI(0) which is an annually accumulated monthly mean temperature above 0C was used. In the arid-taiga transect, it was revealed that the NDVI tends to be large at high precipitation stations (the correlation coefficient (r) between the NDVI and precipitation deviations is 0.66). This result shows that the NDVI sensitively fluctuates due to the station-to-station precipitation variation. It was illustrated that the crucial factor in the arid-taiga vegetation transect is precipitation.In taiga-tundra transect, the NDVI tends to be large at high WI(0) stations (r = 0.43 between NDVI and WI(0)), at the same time, a negative correlation between WI(0) and station elevation was found (r = -0.46). This fact means that the NDVI tends to be larger/smaller corresponding to the higher/lower WI(0) due to several hundreds meters lower/higher elevation of the station. These relationships may be an indication that the temperature factor is critical for the vegetation in taiga-tundra transect.
JSM41/W/18-B5 1205
MONITORING PHYSICAL AND BIOLOGICAL STATES OF DESERT GRASSLANDS USING REMOTE SENSING
Jerry C. RITCHIE, Albert Rango, Thomas J. Schmugge, and William P. Kustas (all at USDA ARS Hydrology Laboratory, Beltsville, MD 20705, USA, Email: jritchie@hydrolab.arsusda.gov) Frank R. Schiebe (SST Development Group Inc., 824 North Country Club Road, Stillwater, OK 74075, USA, Email: franksch@isc-durant.com)
In 1995 the USDA Agriculture Research Service Hydrology Laboratory began collecting remotely sensed data from ground, aircraft and satellite platforms to provide spatial and temporal data on physical and biological states of desert grasslands in the southwestern United States. Thesemeasurements are being used to quantify hydrologic budgets and plant responses to changes in components in the water and energy balance at the Jornada Experimental Range and the Sevilleta Long-Term Ecological Research (LTER) in New Mexico. A range of ground, aircraft, and satellite data have been collected on the physical, vegetative, thermal, and radiometric properties of two ecosystems (grass and shrub) typical of desert grassland in this area. Remote sensing campaigns have been made in dry (May/June) and wet (September/October) periods each year. Data from different platforms will allow the evaluation of landscape properties at a range of scales from meters to kilometers. Radiances measured at ground and aircraft platforms were found to be 3 to 5 % higher for a 30-m2 area at shrub sites when compared with the grass site. Landscape surface temperatures which were similar in the morning (9 am local time) showed 3 to 5 C higher temperatures at shrub sites when compared with grass sites by 1 pm local time. These differences in albedo and temperature could have significant effects on the energy and water balances of desert grasslands as shrubs continue to expand at the expense of the grass. Landsat and EOS satellite data will be used to extend these data to larger scales. These sites have been selected for EOS validation because of their long history of ground-based studies and ongoing repetitive remote sensing missions.
JSM41/W/20-B5 1220
COMPARISON OF REMOTE SENSING, MODEL AND FIELD ESTIMATES OF ACTUAL EVAPOTRANSPIRATION
GEOFF KITE and Peter Droogers, International; Water Management Institute, 35660 Menemen Izmir, Turkey. E-mail:g.kite@cgiar.org
Traditionally, actual evapotranspiration has been computed as a residual in water balance equations, from estimates of potential evapotranspiration or from field measurements by meteorological equipment. Recently, however, researchers have begun using remotely sensed data to estimate regional actual evapotranspiration. A field experiment was carried out in western Turkey over the summer of 1998 to compare the latest methods of estimating areal evapotranspiration using remotely sensed data from NOAA AVHRR and Landsat TM sensors, hydrological models at basin and point scales and field measurements, including scintillometers and net radiometer. This paper introduces the experiment, describes the data set and summarises the different estimation techniques. The results of the different methods are reviewed and compared and recommendations are made as to the suitability of the different methods for different circumstances.
Friday 30 July PM
Presiding Chairs: A.Rango (U.S. Department of Agriculture, Beltsville, MD 20705-2350, USA) T.Engman (NASA/GSFC, Greenbelt MD 20771 USA)
TERRESTRIAL MONITORING
JSM41/E/30-B5 1400
USING NOAA AVHRR PRODUCTS FOR THE GLOBAL MONITORING OF EL NIQO IMPACTS
Garik Gutman, Ivan Csiszar, PETER ROMANOV and Larry Stowe NOAA/NESDIS, Office of Research and Applications, Washington, D.C. 20233, USA
The development of the El Niqo Southern Oscillation (ENSO) in 1997-1998, the most intense in this century, has been monitored by space- and ground-based observations. This study discusses the potential of the current products, routinely derived at NOAA from measurements by the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA polar orbiting satellites, to monitor diverse ENSO impacts over the globe. Generally, ENSO impacts are manifested by droughts, excessive rain, or lack of snow cover, all affecting the agricultural production and often producing natural hazards, such as floods. We analyzed the month-to-month changes in surface-atmosphere conditions in several regions of the world, strongly affected by the 1997-1998 ENSO, using NOAA AVHRR products generated in near-real time, comprising surface and atmospheric variables, such as reflectances, temperatures, vegetation and fire indices, aerosol optical depths over ocean, fractional cloud amount, precipitation, and top-of-the-atmosphere outgoing longwave and absorbed shortwave radiation fluxes. The synergy of many variables allows us to better understand the big picture characterizing the state of the surface-atmosphere system and the relationship between different components of that system. This study demonstrates how the suite of the current NOAA satellite products derived from a single instrument in space can be used to detect ENSO-induced anomalies and to monitor the onset, extent, intensity and duration of ENSO impact on the surface-atmosphere system for diverse regions of the globe. We will discuss also some NOAA AVHRR products that are planned to be included into the suite of products for monitoring ENSO in the near future.
JSM 41/E/31-B5 1415
MONITORING LAKE LEVEL CHANGES USING TOPEX/POSEIDON AND ERS-1 ALTIMETRIC DATA. COMPARISON WITH REGIONAL HYDROLOGY
Franck MERCIER and Anny Cazenave (both at Laboratoire d'Etudes en Geophysique et Oceanographie Spatiales, 18 avenue Edouard Belin, 31401 TOULOUSE CEDEX 4, France, email mercier@boreal-ci.cst.cnes.fr)
Topex/Poseidon and ERS-1 altimeters were primarily designed to measure height of the sea surface. Nevertheless, we can also use satellite altimetry to investigate level changes of continental lakes. We use 6 years of Topex/Poseidon altimetry data to study level changes of African Lakes (lake Malawi, lake Tanganyka, lake Victoria, lake Turkana, lake Tchad and additional smaller lakes). We also analyse the ERS-1 Waveform Altimeter Product raw data set to produce lake level time series. Due to its shorter intertrack spacing, ERS-1 provides a much denser coverage of lakes than Topex/Poseidon. When available, in situ lake level measurements are compared with altimetric time series. In this analysis, we focus on the seasonal and interannual fluctuations of lake levels. Using available regional hydrometeorological data, we further study the water balance over each lake catchment basin. On the annual time-scale, we show a clear correlation between lake level and precipitation fluctuations while on the interannual time-scale, regional as well as global climatic changes are invoked.
JSM41/W/17–B5 1430
MODELING SUSPENDED SEDIMENT TRANSPORT BY INTERNAL TIDES
LI, Jiren (Remote Sensing Technology Application Center, Ministry of Water Resources, 20 West Chegongzhuang Road, Bejiing, China 100044, e-mail:ljr@mx.cei.gov.cn)
A sediment transport model was incorporated into an internal tide model to investigate the ability of internal waves to resuspend and advect sediment over continental shelfs and slope regions. Internal tides may play a dominant role in controlling the distribution of sediment where the water depth is large enough to attenuate any direct impact upon sediment distributions by wind generated surface waves and currents. A number of numerical experiments were carried out for various idealized slopes and the model was applied to an observed section of the Australian North West Shelf. In all experiments, simulated bottom layer shear stresses were large enough to resuspend sediment. During this talk, the consequences of the non-linearity and asymmetry associated with the internal wave velocity field upon resuspension, deposition, and net sediment fluxes will be discussed.
JSM41/E/11-B5 1445
IMPACT OF CO2 MULTIPLICATION ON CROP YIELD OF NORTH CHINA PLAIN BASED ON REMOTE SENSING DATA AND PLANT PHOTOSYHTHESIS MODEL
ZHANG Jiahua (Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing,100029, P.R.China email zhangjh@ast590.tea.ac.cn)
In the paper, first considering remote sensing information and crop ecophysiological characteristics, the crop yield estimation model was set up based on NOAA-AVHRR derived variables and plant photosynthesis. Among them, photosynthetic active radiation (PAR) , CPAP (Crop Photosynthetic Assimilation Potential, reflects crop photosynthetic time and area), and photosynthetic rate were calculated by remote sensing information and meteorological data. The developed model has been applied to winter wheat yield distributions in North China plain area, shows the model has better precision. Second, taking into account the impact of CO2 doubling to agro-ecosystem and its influence on winter wheat, the model further developed and the regional crop yield was estimated owe to CO2 doubled. The further changes of agricultural NPP distributions in North China plain were given using the developed model.
JSM41/L/01-B5 1500
LANDUSE/LAND COVER CHANGE AND ITS IMPLICATIONS FOR DEFORESTATION IN THE HUMID TROPICAL RAINFOREST OF WEST AFRICA: THE EXPERIENCE OF THE LAGOS REGION (NIGERIA)
Simon. O. OJO (Department of Geography, University of Lagos, NIGERIA ,
e-mail:niomr@linkserve.com.ng)
Using Remote sensing technique, a land use/land cover change study of parts of the tropical rainforest region of West Africa, with emphasis on the Ikorodu area of the Lagos region (Nigeria) is discussed. The main categories of the land uses identified include the built-up areas, agricultural lands, wetlands (vegetated and unvegetated) and the water bodies in addition to barren lands. In addition to these main categories, 5, 2, 3 and 2 sub categories were also identified for the built-up areas, agricultural lands, wetlands and the water bodies respectively. In addition, the barren lands were also identified. Data generated using the 1962 and 1983 photographs were used for the study.
The study showed that between 1962 and 1983, the built-up areas increased by more than 600% from about 82 ha. to about 573 ha. Farmlands also increased by about 13% from about 1419 ha to about 1597 ha while wetlands decreased by about 13% from 2882 ha to about 2514 ha. Water bodies also decreased by about 19% from about 27 ha to about 22 ha. Barren lands also decreased by more than 90% from about 19 ha to about 2 ha. The implications of the results for deforestation in the area in particular, and the tropical rainforest region of West Africa is discussed.
JSM41/W/05-B5 1515
COMPARATIVE ANALYSIS OF GROUND-BASED AND SATELLITE-DERIVED SHORTWAVE SURFACE IRRADIANCE MEASUREMENTS OVER RUSSIA
POKROVSKY O.M.., Dalyuk I.V.( both at Main Geophysical Observatory,Karbyshev str.7, St.Petersburg, 194021, Russia, e-mail: pokrov@main.mgo.rssi.ru)
The subject of the study is incoming shortwave surface irradiance, main goal - to increase accuracy of satellite-derived surface radiative budget (SRB) estimates. The study concerns comparison of two types of data: results of retrieval from satellite data performed in the frame of ISCCP/SRB and ground-based measurements for the period 1985-1988 over Russia. In contrast to previous studies the biases between two types of data sets were studied at high temporal resolution - 3-hourly time step. Radiative transfer model exploiting delta-Eddington approximation was used to adopt ground-based data to solar zenith angles corresponding to satellite-derived data. Systematic and random errors for 27 most representative stations from all climatic zones of Russia were analyzed. It was shown that systematic error of monthly mean deviations is 7-10 times lower than standard deviations characterizing variations of instantaneous values of incoming shortwave irradiance. The most attention was paid to the statistical analysis of 2 months having extremal variations, July and March. In July mean deviations of monthly mean values were about 25 wt/m-2, in March they were about 34 wt/m-2. The coherence of both types of data is described by mean values of correlation coefficients: 0.74 in July and 0.66 in March