利用GRACE卫星精密微波测距确定星间平均电子密度

本文介绍如何利用GRACE两颗卫星之间K波段双频微波精密测距和轨道数据，得到星间平均电子密度.发展了一种将连续轨道电子密度极小对齐到零的方法，以消除整周模糊度；借助CHAMP卫星朗缪探针测量得到的轨道电子密度基值以及GPS掩星数据计算的等离子体垂直梯度标高，进一步修正了GRACE星间电子密度所固有的偏差；从而得到大约500 km高度上长达近十年的全球电子密度数据.为了检验消除偏差后GRACE星间电子密度数据的可靠性，对比了GRACE卫星过Millstone Hill雷达上空时，非相干散射雷达观测到的大致同时和相近位置的电子密度数据，结果显示，二者之间的线性相关系数为0.97，平均偏差为-7.26%，GRACE星间电子密度总体稍微偏低，偏差的标准差为18.6%.为进一步验证本文方法所得数据的可用价值，利用消除偏差后的电子密度数据，对GRACE卫星与CHAMP卫星在近乎相同的地方时而高度不同的近圆极轨道上飞行的情况下，两颗卫星观测到的电子密度随经度和纬度的全球分布进行了对比分析.多方面的对比检验证明，本文方法得到的几乎连续10年的GRACE高度上全球电子密度数据基本可靠，为电离层气候学与天气学研究提供了宝贵资料.

Determination of mean electron density between GRACE A and B satellites with precise microwave ranging

This paper presents how to get mean electron density, N_e, between two satellites of GRACE A and B from precise microwave ranging at K band. A new method is developed to remove the integer cycle ambiguity, in which the orbital minimum electron densities for every continue data segments are moved to zero. With the help of CHAMP orbital base N_e measured by Langmuir Probe along with the plasma vertical scale height derived from CHAMP/GPS occultation, the inherent biases in the mean electron density between two GRACE satellites are corrected. Thus a large data set of global electron density almost continuous for ten years is established. To examine the reliability of the data, a comparison is made between the satellite GRACE N_e and the Millstone Hill radar measured N_e when the two satellites passing over the radar. It shows that the linear correlation coefficient between the two groups of N_e is as high as 0.97, the mean error deviation is -7.26% and the standard deviation 18.6%. To validate further the usage value of the data, a comparative analysis is made on the global distributions versus longitude and latitude of the electron densities observed from GRACE and CHAMP when they orbit the Earth in nearly the same local time but at different altitudes. All the comparative tests direct to the point that the global electron density database established from GRACE by using the newly developed method is generally reliable, providing valuable data for space weather and space climate research.