卫星圆轨道假设对GPS无线电掩星反演地球大气参数的影响

给出GPS无线电掩星反演地球大气参数过程中计算大气折射角的解析表达式，以圆轨道假设下的大气折射角计算值为先验约束，采用迭代法对不引入圆轨道假设情况的大气折射角进行归算，在此基础，利用反演方法得到了引入和不引入圆轨道假定两种情况下大气参数（气压和温度）的差分序列，结果表明：卫星圆轨道假设对GPS无线电掩星反演大气参数的影响，在气压方面为1mbar左右，而在气温方面为1K左右，这一结果支持了目前无线电掩星定性误差估计研究中通常引入卫星圆轨道假设这个近似处理方法的合理性，同时也表明：若在高精度反演地球大气参数时，摒弃圆轨道是必要的。

THE EFFECT OF CIRCULAR SATELLITE ORBIT ASSUMPTION ON INVERTING EARTH'S ATMOSPHERIC PARAMETERS BY GPS RADIO OCCULTATION

The analytic expressions for refracting angle in GPS radio occultation are presented. Taking the refracting angle under circular orbit assumptions as a priori value, iterative processing is employed to derive refracting angle series devoid of circular orbit assumptions. Further, differenced atmospheric parameters are calculated based on an inverse method, taking into account the two different cases (inclusive of and exclusive of circular orbit assumptions).It has demonstrated that effect of circular orbit assumptions will bring about up to one milli bar bias in pressure and up to one Kelvin bias in temperature. On one hand, this result supports those researchers who are engaged in qualitative error sources analyses are liable to employ circular orbit assumptions; on the other hand, it warns it necessary to keep in mind forsaking the circular orbit assumptions when demanding accuracy is required of the atmospheric parameters.