Vol.41-1 ABSTRACT
AbstractSuccessful development of space techniques highlighted the necessity of an accurate geoid model. Especially the demand for the geoid to have a 10 centimeter precision has been increasing in order to obtain orthometric heights with space techniques. A precision geoid datermination in the vicinity of Japan was carried out to match the above-mentioned requirements. With careful editing of surface gravity data, a spherical FFT method was employed to process the whole area simultaneously in high resolution. The uncertainty of the geoid in short wavelengths was estimated at about 6 centimeters. The geoid was compared with five nets of GPS/leveling to evaluate the errors in both long and short wavelengths. The discrepancies showed that the tilted plane errors of 1-4ppm in long wavelengths exist consistently in the maximum declination of the east-west direction. The tilt was also found in the comparison with VLBI data. Although the sources of the errors were not clearly datermined, the stability of the tilted errors shows the advantage of the geoid datermination method employed. After removing the best estimated tilt errors, the uncertainty of the geoid in short wavelengths is 8.6 centimters for the area of up to about 400 * 600km2. A significant improvement of the geoid was confirmed over the pre-existing geoid models for Japan. To consider the geoid features in relation to the geologic/tectonic structures, several approaches were done with the geoid, Among them the important characteristics of the geoid became vivid in the areas where the effects of the plate collisions are significant, by looking into the geoid slopes. In addition, it was pointed out that the different characters of the geoid undulations show the difference of the plate collisions between those at the Kuril Trench-Japan Trench boundary and those at the Ryukyu Trench-Nankai Trough boundary. It suggests the importance of precision geoid study on tectonics. Recommendations were also given to extend the present study to further improve the geoid determination. It will help develop wide applications of space techniques to the fields of geodetic/geophysical study and of local surveys. |