利用衛星雷射測距之觀測數據和Bernese計算衛星軌道

Abstract

儘管GPS衛星定軌技術發展至今已經相當地成熟，但是GPS定軌自身的精度，仍然要仰賴單點精度較高的衛星雷射測距系統(Satellite Laser Ranging, SLR)來驗證比對，故此衛星雷射測距之存在價值是必要且必須的。本研究欲使用瑞士Bern大學開發之軟體Bernese 5.0，通過ILRS(International Laser Ranging Service)的官方網站，下載衛星雷射測距的觀測數據來計算衛星軌道。本研究選擇了重力衛星GRACE(Gravity Recovery and Climate Experiment)做為定軌之對象，而在利用SLR觀測數據計算軌道之前，首先必須取得GRACE衛星之先驗軌道，本研究則利用GPS對GRACE的電碼觀測數據來計算GRACE的概略坐標做為先驗軌道，並以簡動力法計算GRACE的軌道。該軌道將與JPL所提供的GNV軌道進行比較以求得軌道差異量，結果所示在一日軌道弧長的情況下，GRACE軌道差異量之標準差為徑向：±12.2cm、沿軌道向：±54.7cm、橫向：±31.6cm；多日軌道弧長下，GRACE軌道差異量之標準差為徑向：±9.9cm、沿軌道向：±36.2cm、橫向：±13.8cm。

Satellite Laser Ranging (SLR) is able to verify the accuracy of GPS-determined orbits, because SLR has precisions at cm or sub-cm levels. This objective of this research is introducing satellite orbit determination using the SLR data from ILRS with the Bernese 5.0 GPS software from University of Bern. The GPS data are from GRACE, a mission to monitor the global gravity field. Before SLR orbit determination for GRACE, a priori orbit of GRACE is computed using GPS code observation. A comparison of the orbits from JPL and from our SLR solution is discussed in this study. According our SLR orbit using 1 day of observations, the standard deviations of the orbit differences in the radial, along-track and cross-track directions are 12.2, 54.7 and 31.6 cm respectively. With three days of SLR data, the standard deviations are 9.9, 36.2 and 13.8 cm. The orbit differences at GRACE arcs with SLR data achieve few cm.