LEO GPS接收机仪器偏差估计

Estimation of LEO GPS receiver instrument biases

LEO GPS观测已成为空间电离层研究重要手段之一,通过GPS双频观测值获取的TEC则是电离层探测的一个重要参量,为获取高精度TEC需估计和消除GPS接收机仪器偏差(DCB).本文旨在探索一种全新的LEOGPS接收机仪器偏差的估计方法:基于电离层球对称的假设,利用CHAMP和COSMIC原始GPS观测数据,采用几何映射函数,通过最小二乘解算出GPS接收机仪器偏差.结果表明:(1)2008年1月份期间,通过上述方法解算的仪器偏差都较稳定,相比COSMIC网上发布结果,标准偏差都在0.6 ns以内;(2)COSMIC(轨道高度大约800km)仪器偏差估计结果优于CHAMP(轨道高度大约400 km)的结果,原因为:对于不同轨道高度LEO GPS仪器偏差估计,其较高轨道高度的电离层球对称假设影响较小.

The GPS LEO measurements have become a powerful tool for special ionospheric studies, and TEC derived from GPS dual frequency measurements is an important parameter in ionospheric detection. The GPS receiver instrument biases （often called differential code biases （DCB）） must be estimated and eliminated from the data in order to obtain precise TEC. The objective of this paper is to grope for a brand-new method of estimation of LEO GPS receiver instrument biases： based on the assumption of spherical symmetry of ionosphere, utilizing raw GPS observation data from CHAMP and COSMIC, applying geometric mapping function, the instrument biases could be calculated by least-square technique. The results show that： （1） during Jan.1~31,2008, the DCB calculated by above method were stable, and compared with the web-published result of COSMIC all the standard deviations were less than 0.6 ns; （2） the estimated DCB of COSMIC （orbit altitude about 800 km） were better than that of CHAMP （orbit altitude about 400 km）, the reason is that for estimation of DCB at different LEO orbit altitudes, the effects of spherical symmetry of ionosphere at higher orbit altitude were less.