福爾摩沙衛星三號與GRACE精密定軌：姿態、相位中心及質心影響的探討

Abstract

本論文針對福爾摩沙衛星三號及GRACE衛星姿態、相位及質心影響精密定軌問題分別進行探討，採用GPS相位觀測資料以Bernese 5.0軟體進行零次差減動力法及動態法計算軌道。使用觀測姿態角資料與模式姿態角對於精密軌道成果影響差異量至少為公分量級，若姿態觀測品質不佳可能使軌道差異量達到10公分量級左右。使用模式姿態角探討質心變異對軌道的影響時，減動力軌道之三維方向差異量會較加入的質心變異量略小，因為部分之質心變異量被虛擬隨機參數吸收；而動態定軌，加入的質心變異量幾乎是原始軌道與變異軌道的差異量。在有無使用相位中心變異資料的五小時重疊動態軌道於RTN方向提高了約2~4公厘，在徑向方向改善最大，相對而言，減動力軌道改善比較小，大概為1公厘左右，而加入及不加入相位中心變異資料對於減動力與動態軌道三維差異量成果均方根值分別為0.82cm與1.89cm。福衛三號正確與變異減動力及動態軌道差異量成果中，減動力軌道的三維差異量均方根值較動態軌道為大，造成減動力軌道與動態軌道差異量最大的影響量為姿態角，相較之下其他兩影響量皆較小。當衛星上升至較高軌道高度時，福衛三號衛星的控制品質與姿態角資料都有顯著的改善。

The Bernese 5.0 software is used to compute the precise orbits of the FORMOSAT-3 and GRACE satellites using the kinematic and reduced-dynamic methods based on zero-differenced GPS phases from these two satellites missions. This study concentrates on the effects of satellite attitude, GPS antenna phase center variation (PCV) and center of mass (COM). The RMS differences between the orbits computed with observed and with nominal attitudes are about one cm; such orbit differences may reach 10 cm in the case of low-quality attitude observations. In the case of reduced dynamic orbit determination, the 3D RMS differences between the orbits computed with the original COM values and the biased COM values are less than the given COM biases, and this is attributed to the pseudo-stochastic pulse parameters that partly absorb such biases, whereas in the case of kinematic orbit determination, such orbit differences are almost equal to the given COM biases. Based on 5-hour orbit overlaps in the radial, along-track and cross-track directions, the improvement due to use of PCV is at the sub-cm level for both kinematic and reduced dynamic orbit determinations. The most significant improvement with PCV is in the radial direction. For both the kinematic and reduced dynamic approaches, the 3D overlapping differences between the orbits with and without PCV are 0.82 and 1.89 cm, respectively. The reduced dynamic orbit is more sensitive to changes in attitude, COM and PCV than the kinematic orbit. In general, the effect of attitude on orbit is larger than the effects of COM and PCV. The attitude data and control of the FORMOSAT-3 satellites are improved as the orbits are raised to higher altitudes.