Cracking the GPS-SLR orbit anomaly
Cracking the GPS-SLR orbit anomaly
复制标题
破解GPS-SLR轨道异常
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
B. Haines
中科院分区：
文献类型：
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作者：
M. Ziebart;A. Sibthorpe;P. Cross;Y. Bar;B. Haines
全球科学界已严重依赖全球定位系统作为观测、监测和模拟地球系统过程的工具，如海平面上升、冰后反弹、板块构造和水文循环。这些过程的信号每年以毫米级变化。此外，全球定位系统数据被用作实现全球国际地面参考框架的基石之一。GPS卫星轨道估计中的任何系统误差或偏差都将混叠到这些分析中。GPS轨道精度的主要独立测试是对SVN 35和SVN 39的激光跟踪。从卫星激光测距数据和从GPS轨道（使用相位和伪距数据估计）得出的高度比较表明，一致和棘手的偏差为4-5厘米。激光测距精度为5-6毫米，因此怀疑问题出在GPS轨道估计过程的某些方面。虽然偏差似乎很小，但就我们预测卫星轨道的能力而言，它具有一些强烈的连锁效应-高度上5厘米的误差导致2.1 E-09 m/s2量级的重力场错误建模，以及大约2米的沿着轨道预测误差。此外，由于轨道周期的平方与半长轴的立方成正比（开普勒第三定律），很明显，一个小的高度误差可以映射成一个显著的轨道周期误差。在这项研究中，来自伦敦大学学院和美国宇航局喷气推进实验室的一组科学家试图解决GPS轨道异常。在定轨过程中采用了新一代高精度非保守力模型。这些力模型包括两种效应：行星辐射压力（PRP）和天线推力（AT）。PRP在这里是由地球发射的辐射（长波- LW）和反射的辐射（短波- SW）的组合效应。AT是由于L波段载波中传输的能量而对卫星产生的反作用力。在本文中，我们描述的数据源和建模技术。轨道确定测试使用JPL的GIPSY OASIS II软件进行。我们提出了五天的精确轨道的初步结果。在这些测试中，当使用新的力模型时，SLR偏差减少了2.1 cm。此外，我们还注意到，GPS SV质心与激光后向反射器阵列之间的公认偏移数字可能存在误差，其中一颗卫星误差为11毫米，另一颗卫星误差为13毫米。结合我们的力建模结果，我们可以预测SLR偏差减少了32 - 34 mm，这是一个显着的减少。
The global scientific community has come to rely heavily upon GPS as a tool to observe, monitor and model Earth system processes such as sea level rise, post-glacial rebound, plate tectonics and the hydrological cycle. These processes have signals varying at the level of millimetres per year. In addition GPS data is used as one of the corner stones for the realisation of the global international terrestrial reference frame. Any systematic errors or biases in the estimates of the GPS satellite orbits will alias into these analyses. The principal independent test of GPS orbit accuracy has been laser tracking of SVN35 and SVN39. A comparison of altitudes derived from both satellite laser ranging data and from GPS orbits (estimated using phase and pseudorange data) shows a consistent and intractable bias of 4-5 cm. Laser ranging accuracy is at the level of 5-6 mm and hence it is suspected that the problem lies in some aspect of the GPS orbit estimation process. Whilst the bias may seem small it has some strong knock-on effects in terms of our ability to predict the satellite orbits – an error of 5cm in height results in a mis-modelling of the gravity field of the order of 2.1E-09 m/s2 and an along track prediction error of circa 2m. In addition, as the square of the orbital period is proportional to the cube of the semi-major axis (Kepler’s third law) it is clear that a small height error can map into a significant orbital period error. In this study a team of scientists from University College London and the NASA Jet Propulsion Laboratory have sought to resolve the GPS orbit anomaly. We have applied a new generation of high precision nonconservative force models in the orbit determination process. These force models cover two effects: Planetary Radiation Pressure (PRP) and Antenna Thrust (AT). PRP here is the combined effect of radiation both emitted (Long Wave – LW) and reflected (Short Wave – SW) by the Earth. AT is the reaction force on the satellite due to the energy transmitted in the L-band carrier waves. In the paper we describe the data sources and modelling techniques applied. Orbit determination tests were carried out using JPL’s GIPSY OASIS II software. We present initial results for five days of precise orbits. In these tests the SLR bias is reduced by 2.1 cm when using the new force models. In addition it has come to our notice that the accepted figure for the offset between the GPS SV centre of mass and the laser retro-reflector array may be in error by 11 mm for one satellite and 13 mm for the other. Combined with our force modelling result we can posit a reduction in the SLR bias of 32 – 34 mm, which is a significant reduction.