Simultaneous Measurements of Site Locations by GPS Interferometers Referred to VLBI and SLR Sites in Japan

Analysis of GPS phase observations carried out on December 6, 7, 8, 12, and 14, 1988, yielded the coordinate components of 11 observation sites in central Japan (Tsukuba, Shimosato and the others). As a fiducial point, either of Tsukuba or Shimosato was fixed, whose coordinates were determined by other previous studies using Very Long Baseline radio Interferometry (VLBI) and Satellite Laser Ranging (SLR), respectively. In order to evaluate accuracy of site coordinate determination with GPS measurement, we compared the coordinates determined by fixing Tsukuba with those by fixing Shimosato on December 8 and 14. The difference of the site positions between the VLBI and SLR referred analyses showed almost the same amount on each day, and the mean difference became about 1.33 m in length. On the other hand, the repeatability of the baseline vectors was less than about 0.87 m, which was smaller than the above differences. One of the most probable causes of such a large difference will be inconsistency between VLBI and SLR reference frames. Another one will be the error in the satellite ephemerides. Incomplete satellite constellation over Japan might be another one.