China State Bureau of Surveying and Mapping, Beijing 100039, China
The effort for the geoid determination in China has lasted for nearly half a century. A large-scale measurement of astro-gravimetric leveling network was carried out from 1950s to the 1970s. The average resolutions of the network are 1.5°´1.5° in the eastern area of China and 2.5°´ 2.5° in the west. The China (Quasi) Geoid (CQG80) derived from this network shows that the difference between the remote measured points of this network and Xi'an Geodetic Origin is estimated at ±2.7 m in average.
It is obvious that CQG80 is far from meeting the needs of China's economic development and national defense as well as the research on geo-science in this country. Now a new (quasi) geoid (CQG2000) was computed in early 2001 to meet the needs of the first part of the new century, which is with high accuracy, high resolution and covers all the territories of China. The accuracy of CQG2000 has been upgraded one magnitude, from 3-5 m of the CQG80 to the grade of centimeter. And its average resolution has been raised from 2°´2° to 15′´ 15′. Additionally the coverage of CQG2000 has extended to all the mainland and maritime areas of China. CQG2000 has passed the field test and production check and accepted by National Bureau of Surveying and Mapping, so it has been officially issued for public use in the whole country.
Three technical problems were encountered during the computation of CQG2000. The first is the research and computation of China's mainland geoid. The second is the research and computation of China's maritime geoid. And the third one is the research and computation of the match of China's mainland and maritime geoids.
I.RESEARCH AND COMPUTATION OF CHINA'S MAINLAND GEOID
The usual way internationally to solve this problem is to make a combined adjustment of a local gravity geoid with a GPS leveling network, which is improved meantime through local gravity and topographic materials. This is a feasible way to deal with such problems in China at present. The major problem in China is that the resolution of the gravimetric data is rather low and the data are unevenly distributed. In view of the situation, the following project is taken to compute China's mainland gravity geoid after research and experiment:
1. Computation Project for China Mainland Gravity Geoid