一种降低电离层梯度影响的Hatch滤波算法

目前，地基增强系统（Ground-Based Augment System，GBAS）中的主要问题是：尽管使用载波平滑降低了伪距噪，利用差分技术消除了用户和基准站间的大部分共同误差，从而减少了差分改正值中的误差。但是电离层时间梯度和空间梯度于这两个过程中产生了额外的误差，阻碍了差分改正值质量的进一步提高。基于对电离层时间和空间梯度引起的额外误差的分析，并考虑平滑伪距噪声，文章提出了一种新的Hatch滤波方法，该滤波器的时间常数是随卫星仰角、电离层时间和空间梯度以及用户与参考站之间的距离而实时变化的。该方法降低了差分改正值误差，提高了定位精度。并且通过差分定位仿真并对比传统的单频Hatch滤波方法，发现使用该方法后，减小了差分校正值的误差。

A New Hatch Filter to Mitigate the Effect of Ionosphere Gradient for GBAS

The main problem in GBAS(Ground-Based Augment System) is that,though carrier smoothing filter and LDGPS(Local differential GPS) improve the accuracy of the pseudorange by reducing the noise in the pseudorange and eliminating most common error between the user and the reference station respectively,they also bring in some extra error due to the effect of ionosphere temporal and spatial gradient.Based on the analysis of this error,considering the smoothing noise,this paper suggests a new algorithm on the new Hatch filter whose smoothing window width varies flexibly with the satellite elevation,ionosphere variation and distance from the user to the reference station.Through the positioning process in GBAS emulation platform for several hours and the comparison to the performance of traditional Hatch filter,we found that the error in the differential correction can be smaller after applying this new method.