Indirect approach to invariant point determination for SLR and VLBI systems: an assessment

We assess the accuracy of some indirect approaches to invariant point (IVP), or system reference point, determination of satellite laser ranging (SLR) and very long baseline interferometry (VLBI) systems using both observed and simulated survey data sets. Indirect IVP determination involves the observation of targets located on these systems during specific rotational sequences and by application of geometrical models that describe the target motion during these sequences. Of concern is that most SLR and VLBI systems have limited rotational freedom thereby placing constraint on the reliability of parameter estimation, including the IVP position. We assess two current approaches to IVP analysis using survey data observed at the Yarragadee (Australia) SLR and the Medicina (Italy) VLBI sites and also simulated data of a large rotationally constrained (azimuth-elevation) VLBI system. To improve reliability we introduce and assess some new geometric conditions, including inter-axis, inter-circle and inter-target conditions, to existing IVP analysis strategies. The error component of a local tie specifically associated with the indirect determination of SLR and VLBI IVP is less than 0.5 mm. For systems with significant rotational limits we find that the inter-axis and inter-circle conditions are critical to the computation of unbiased IVP coordinates at the sub-millimetre level. When the inter-axis and inter-circle geometric conditions are not imposed, we retrieve biased vertical coordinates of the IVP (in our simulated VLBI system) in the range of 1.2–3.4 mm. Using the new geometric conditions we also find that the axis-offset estimates can be recovered at the sub- millimetre accuracy (0.5 mm).     

Slr Contributions To Fundamental Physics

The gravitomagnetic interaction of general relativity must be incorporated into the Earth gravity model in order to obtain an unbiased measure of Earth's multipoles, and the strength of this relativistic interaction can also measured from SLR data by being introduced as a fit-for parameter in the total model. SLR measurements of the perigee precession rates of LAGEOS (and similar type) satellites are also a precise way to search for Yukawa-like interactions of range comparable to orbit sizes; and preferred frame effects in gravitational theory can also be sought. SLR's correlated measurements of particular parameters which appear in the models used to fit both SLR and LLR data can be brought into the LLR fits, achieving something like a grand fit of those data sets; this should contribute toward substantial improvement in the precision with which scientifically interesting parameters are determined in LLR and other interplanetary ranging missions.     

Current Status And Future Plans For The Chinese Satellite Laser Ranging Network

The Chinese SLR Network consists of 5 fixedstations located in Shanghai, Changchun, Beijing, Wuhan and Kunming respectively and 2 mobilesystems. The single shot precision for Lageos for these stations is in therange of 12–30 mm. Improvements of system performance for all stations are under way.The Chinese SLR Network participates in the national project CrustalMovement Observation Network of China, and is actively supporting the global and regionalprojects, such as ILRS, IERS, WPLTN (Western Pacific Laser Tracking Network) andAPSG (Asia-Pacific Space Geodynamics). The operation center and the datacenter for the Chinese SLR Network is located at Shanghai Observatory. The Lageos dataanalysis report for the global stations has been published every two weeks at the web siteof Shanghai Observatory since September 1999.     

北京人卫激光观测站kHz激光测距系统升级实现

本文介绍了北京人卫激光观测站的kHz激光测距系统的改造与实现情况,并对kHz卫星激光测距系统的实测结果进行了简析,比较了不同激光发生器的测距激光。研究结果表明,该站的kHz卫星激光测距系统已经初步实现,且观测数据量和观测精度较以往低重复频率激光发生器都有所改善。