LI Jiren and HUANG Shifeng
Institute of Water Resources and Hydropower Research, Beijing 100044,China
Since 1998, remote sensing (RS) has been used in the management of hydrology and water resources, which shows the superiority of RS in impersonality, grandiosity, dynamic and economy as one of the important space information collecting technologies. These years, there has a popular application of GIS in the management of hydrology and water resources at a high level, with characteristics as combination of RS, GIS and GPS (so-called “3S” technology). These new and higher technologies have been maturely used in the respects of flood and waterlogging disaster monitoring and evaluating, water resources and water environment investigating, soil corrosion and soil protection, river and reservoir sedimentation monitoring, river/lake and river mouth evolvement investigating as well as soil moisture and drought condition monitoring.
Since 1998, there are main developments in following aspects:
The RS Operational Running System for Flood and Waterlogging Monitoring and Evaluating, which is established in the RS Application Center under Ministry of Water Resources, started test running in 1998 and put into formal running in 2001. The RS Operational Running System for Flood and Waterlogging Monitoring and Evaluating plaid an important role when the floods occurred in the Yangtze River Basin and North China in 1998, by which the scientific information was timely provided to the State Council and the State Headquarters of Flood Control and Drought Relief. The system can finish remote sense monitoring and evaluation of flood and waterlogging according to the concerned technical and time requirement, operational flow and mode, which make a new progress for the application of RS in flood control and disaster reducing.
At present, when the plane with SAR flies over the disaster area from some kilometers away, what actually happening in the area can be real time displayed, stored and copied on hard disk in the monitoring center in Beijing, with only a few second to be lagged.
The solid monitoring network consists of spaceflight (Satellite-borne SAR), upper air (airborne SAR) and lower air (helicopter), with the macro and dynamic monitoring from meteorological satellite, will insure the monitoring the water structure condition and disaster development when flood and waterlogging occurring.
The basic background data base on GIS has been taken as the main suporting to evaluate disaster. The important levels of the data base consist of DEM, water body, water structures, earth application, social-economy, communications and etc. The evaluated results are flooded area, flooded inhabits and farmland area, including special topic maps, statistics reports and analyzing reports.
The shortage of water resources has become one of the main factors to restrict the sustainable development of society and economy in China. As water resources restricting the other factors of environment, the shortage of water resources has made water environment worsening, vegetation decreasing, desertisation and species reducing. Moreover, chemical, oil and heat pollution in water is also a severe problem that China will face at, because the influence from water environment is not less than that from the shortage of water. Therefore, RS is playing more and more important role in water resources investigating.
In 1980s, investigation of surface water body was mostly made with near-infrared RS images. These years, SAR images have been used to investigate the status and dynamic change of the surface water bodies such as rivers, reservoirs and lakes.
126.96.36.199 Research on the distributed or sub-distributed hydrological models
The distributed or sub-distributed hydrological models can fully consider the uneven distribution of underlayer conditions (vegetation, soil, earth application and landform) in space, so as to correctly reflect yield change in time and space and increase the precision of hydrological forecasting and simulating, which is the basic and necessary structural form that large scale hydrological model combine with atmosphere model. RS will provide the underlayer conditions for this kind of hydrological models, so as to determine the model parameters or directly provide input. At present, the research on yield mechanism is the main influence on the development of research of distributed and sub-distributed hydrological model. These hydrological models are not only the powerful stool of hydrological forecasting and simulating, but also the effective means to estimate local water resources (including underground and surface), especially they can reflect the distribution of yield in time and space and the distribution of part water resources in space.
188.8.131.52 RS monitoring of precipitation
The research has made a great progress on the quantitative rainfall forecasting and measuring with meteorological satellite and Doppler radar for rainfall measuring, which have almost meet the requirement of application now with the precision of the former reaching 70%—80% and the precision of latter reaching over 80%. These RS means can change the traditional point rainfall monitoring to area rainfall monitoring, which will fully reflect the unevenness of rainfall distribution in time and space so that prolong the leading time of flood forecasting with the rainfall input to the networks for the distributed hydrological models.
184.108.40.206 Investigation of snow mantle, snow limit and ice stream
RS system can effectively monitor the range of snow mantle, snow state, melting condition of snow mantle，uprising of mountain snow limit and ice stream melting. These years, the new development have been made in measuring thickness of snow mantle with SAR, which makes it more precise in estimating the water equivalent of snow mantle. The successful forecasting flood occurred in Yangtze River in 1998 partly depend on monitoring snow in Qinghai-Xizang Plateau by means of RS in the winter of 1997 and spring of 1998. Melted snow is an important part of the water resources in the Northwest China. At present, RS is the most effective means of investigating water resources of ice stream and melted snow.
The quality of water resources should be paid much more attention to as the same as its quantity. With the fast development of the economy in China, it has been a very important task to harness environment pollution including water pollution. The state government has paid important attention to the water environment problems, for example, the success has been achieved in harness of water pollution in the Huaihe River Basin, harness of water pollution in Suzhou River by Shanghai and harness of water pollution in the urban rivers in Beijing. However, it has a long way to go in harnessing water pollution, and it is a long-term task to monitor water environment.
RS is very important in monitoring water environment. For example, the images of navigation infrared scanning can be used to determine the temperature increase and distribution in space caused by heat pollution of water body outside of drainage outlet of the thermoelectric stations; SAR images or infrared scanner can be used to determine the range of oil pollution and oil film thickness in the sea; and TM images can be used to determine the range of aquatic organisms (alga) and equatorial tide. In recent 10 years, a progress has been made in research on quantitative monitoring of the factors that form the quality of the water, which include turbidity, total suspended sediment, PH value and total nitrogen content. The research has been made in Guanting Reservoir and Taihu Lake on the RS quantitative measuring the chemical factors in water body with high spectrum. It is believed that the results will be applied in the actual production a few years later, which will provide an advanced, synchronous, fast and low-cost means to monitor water environment in large scale, so as to replace the traditional methods of water sampling and testing.
Drought is one of the natural disasters to make severe economic losses, which is also another factor that influences agricultural production and people life. In the influence degree and range, it is more severe than flood and waterlogging disaster. It is a difficult task to monitor drought condition with RS system. As with the various views from different departments, there are various physical standards including meteorological drought, agricultural drought, hydrological drought and etc. with various drought indexes. Although there are a few methods having developed on the base of RS data, such as the methods of thermal flux, normalization vegetation index anomaly, crop water supplying coefficient, crop shortage water coefficient and etc., which are far from the actual requirements from agricultural production. However, the development is obvious in these years, firstly, a national data base of farmland space has been developed, which can estimate the drought condition of the farmland; Secondly, some methods have paid their attention to calculate moisture in the soil section from the moisture in the soil surface layer such as water and heat coupling equation, and microwave remote sense is good at this respect. Moreover, some methods further consider the influence of vegetation, such as double layer model of farmland evaporation.
The methods only have their own reasons and localities. Because of the limit of soil moisture capacity data that are needed for parameters calibrating, some models can not be spread all over China. Some methods are difficult to be put into actual application because they can not get the synchronous meteorological factors from satellite monitoring. Because the various methods adopt different drought indexes, the various seasons can not be connected with the models. As for the above-mentioned problems, the methods based on RS data still can not be put into application of drought monitoring.
However, it has a wide foreground of use microwave RS in measuring soil moisture capacity. There is close relation between meson constants of the soil and soil moisture capacity, while the meson constants have a good relation with the dispersion coefficients of microwave back-direction.
Evaporation is not only determined by the meteorological conditions (including temperature, wind power, solar radiation and humidity), but also determined by soil moisture capacity (water supply capacity). In hydrology, there is a mature 3-level model to simulate the process, which can relate evaporation with soil moisture capacity. Otherwise, RS has got progress in monitoring watershed evaporation, which can not be directly measured. Therefore, the combination of multiple knowledge will break it through to use RS in monitoring soil moisture capacity and watershed evaporation, so that it will get into application and make a solid base for drought monitoring and evaluating.
Soil corrosion is affected by natural factors and human being activities, which is not only involved with rainfall and runoff, but also has close relation with the factors of soil, lithology, geology, physiognomy, vegetation, landform, earth application and water system distribution. And the RS technology is the best method of getting these macro informations.
According to the dynamical factors, soil corrosion can be divided into 3 kinds of water corroding, wind corroding and melted ice corroding; According to corrosion intensity, it can be divided into levels of acuity, extremely strong, strong, medium, light and tiny; According to the corrosion risk, it can be divided into 5 levels of destroy, extremely risk, risk, less risk and without risk.
The second and third wide investigations of soil corrosion over China were respectively made with RS technology in 1998 and 2001, by which we not only get to know the soil corroding conditions in the end of 1990s and at present, but also understand the benefits from various soil conservation measures in these years, compare the results of structure harnessing and biology measures.
The underlayer information received with RS technology is also the base for developing watershed sediment yields and sink sediment model. With the development of RS technology, this kind of models have greatly considered underlying factor in these 10 years. Combination of RS technology and math models can provide the dependable means for forecasting soil corrosion and soil conservation benefits.
Since 1998, RS technologies have been widely used to investigate the dynamical change of river mouth, river channel and lake and sedimentation in reservoir.
RS images can provide the information of suspended sediment content. The comparison of the images of low water period can reflect the change of sandbanks and shallows in the water bodies of river mouth, river channel, lake and reservoir as well as the change of water depth.
The Yellow River is the famous sandy river in the world. The frequent changes of the sedimentation in the river bed cause the frequent changes of channel situation, which make a great threat to the protection of the dykes. Therefore, it is an important task to use RS images to determine the channel situation of the middle and lower reaches of the Yellow River before flood period, especially in low water period.
The change of sedimentation in river channel and river mouth is important to channel structures and port construction. The prominent work has been made with RS technology in the Nantong Reach of the Yangtze River, mouth of the Yangtze River and mouth of the Pearl River, which have plaid an important role in preventing sedimentation in river mouth and channel. RS images can not only record history, but also provide condition to analyze sedimentation change in time and space, which is one the RS advantages and it is necessary to mutually complement with hydrological data.
Sedimentation will make it change in reservoir storage year by year. It is basic necessary in reservoir regulation to understand these changes in timely and correct way, which is important for flood control, power generating and irrigation. Reservoir storage and storage curve can be determined with RS images of multi time phase and DEM before reservoir construction. By comparing with the method of global orientation system combining echo sounder measuring, the above-mentioned method has the advantages of fast and low cost. In the view that the reservoir storage measurement has not been made for the most large- and middle-sized reservoir in China and the sedimentation condition is severe, although the method is not good in precision, it is convenient and effective. For example, it is successful to measure the reservoir storage curves of Xinanjiang Reservoir and Fengman Reservoir with RS images of multi time phase. As for the lakes, the results of the landform measuring under water can used as DEM to measure lake storage change and relationship between storage capacity and water level. All these show a development of application of RS technology in water conservancy in recent 10 years.
To sum up, RS technology as a substitution of traditional means has been widely and deeply applied in hydrology and water resources management in recent years. As an advanced and effective means, RS technologies have been understood by more and more hydrologists. In order to let more hydrologists use RS technology and put into development of RS application in Water Conservancy, the problems should be settled on how to put RS technology into further application. There are 80% of the information that human being have touched involves with time and space, all which can be received by the means of observing earth. It can be affirmed that RS technology will be necessary means to solve the most problems from hydrology and water resources in this century.
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