中文摘要：

目前长三角地区GNSS网已应用于该地区上空水汽的日常监测和水汽层析的研究。由于该GNSS网站间距较大、分布不均匀,斜路径观测值不能完全满足高精度水汽三维层析的需要,因此,本文对该地区进行了多模GNSS（GPS、Galileo、GLONASS、BDS）的观测仿真和水汽层析试验。结果表明,多模GNSS观测值角度变化范围大,在空间分布更均匀,相同观测条件下,多模GNSS观测值明显降低了空间格网的空格率,特别是改善了大气中上层格网的观测值覆盖情况。多模GNSS观测值弥补了单系统观测分布不均的状况,为空间格网提供了更为丰富的大气观测信息。通过仿真层析试验可以看出多模GNSS能够明显改善层析效果,尤其能够提高地面5km以上的层析精度。

英文摘要：

Currently,the GNSS network of Yangtze River delta has being applied to monitor the water vapor above this region and research water vapor tomography.Studies have shown that the dictances between stations are large and inhomogeneous,that will make it difficult to get the high tomography precision.Therefore,a simulation test of multi GNSS observations on tomography is introduced.The multi GNSS observations are more homogeneous in spatial distribution than a single positioning system,which can reduce the space rate of the grid,especially increase the number of the grid with information at middle and high layers.The multi GNSS observation can provide more and better water vapor information which can patch up deficiency of a single positioning system.A simulated water vapor tomography is carried out,and the result shows that the multi GNSS observations could improve the accuracy of tomography,especially above the 5km height layer of the atmosphere.