中文摘要：

针对全球卫星导航系统对低轨卫星定位的动态观测几何问题，对于不同低轨卫星轨道高度、不同截止高度角和不同卫星导航系统的情形，进行了导航卫星可见性分析，并在此基础上分析了几何精度因子（GDOP）。低轨卫星高度在几百km内变化时对可见性与几何精度因子的影响很小，而不同截止高度角则影响较大；另外与采用单个GPS系统相比，采用GPS—Galileo组合卫星导航系统对低轨卫星定位时，可见导航卫星数目明显增加，GDOP数值减小，且即使在截止高度角较大时也能得到较好的GDOP。

英文摘要：

The dynamic observation geometry exists in LEO satellite orbit determination while utilizing the global navigation satellite systems. The visibility and geometric dilution of precision （GDOP） analysis was carried out under different GNSS with the parameters variations of the satellite orbit altitude and the masking elevation angle. The visibility and the GDOP change slightly with the satellite altitude when it varies in the range of several hundred kilometers, while the influences of different masking elevation angles on the visibility and the GDOP are rather great. The integrated GPS-Galileo system has advantages over the single GPS navigation system for the orbit determination of LEO satellite. The former possesses more visible navigation satellites and a smaller GDOP value. High quality GDOP can also be acquired even with a rather large masking elevation angle.