受电离层模型误差、站星设备时延误差等测距系统误差的影响，转发测轨系统的GEO卫星定轨精度受到严重制约。为了提高GEO卫星定轨精度，需要对测距系统误差进行定期标校。基于对SLR、VLBI系统误差标校方法的调研分析及前期工作经验，发现系统误差标校存在某些问题：某些GEO卫星并未安装激光后向反射器，不具备SLR标校系统误差的条件；同时，当前SLR和VLBI测轨网观测任务重，无法满足系统误差定期标校的需求。针对上述问题，此课题将寻求新的系统误差标校方法。2015年3月，BDS首次发射了装载了C波段透明转发器的IGSO卫星，为GEO卫星转发测距系统差确定方法提供了新思路。课题拟将该IGSO卫星和GEO卫星共用相同的地面测站天线，借助IGSO卫星开展GEO卫星测距系统误差标校方法策略和转发测轨观测方案研究，并基于转发测轨网对系统误差标校方法策略开展试验验证，分析系统误差标校对GEO卫星定轨精度的影响。

In C-Band transfer measuring system, the Precise Orbit Determination (POD) precision of Geostationary Earth Orbit (GEO) satellitesis limited by signal biases such as the station delay biases, transponder delay biases, the ionosphere delay model bias, etc. In order to improve the POD precision, the signal biases of the C-Band transfer measuring system for GEO satellites should be calibrated. However, there are many problems in signal biases calibration from investigation and the former work experience. Satellite Laser Ranging (SLR) has high precision. However, some GEO satellites have not been equipped with SLR reflectors, which make the signal biases calibration using SLR impossible. Meanwhile, the observations loading on the SLR and VLBI sites are heavy, so it is difficult for the signal biases calibration at regular intervals. To solve these problems, new signal biases calibration methods needs to be researched. The first Inclined Geosynchronous Orbit (IGSO) satellite in BDS with C-Band transponder has been launched in March, 2015, which offers new idea for signal biases calibration. IGSO satellite has high relative speed for the ground. When the IGSO and GEO satellites share the same C-Band ground station antenna, the signal biases and the satellite orbit can be seperated with the help of IGSO satellite. The signal biases can be obtained and then be applied in POD of GEO satellites. The project will study on the method/strategy of the signal biases calibration using IGSO satellite and carry out signal biases calibration experiments, with the effects of each bias being analysed.