非标称对流层误差对GBAS完好性的影响

地基增强系统(GBAS)中,非标称对流层误差引起的平均垂直保护级(VPL)增量为2.29 m,误差包络精度降低,系统完好性风险增大。针对上述问题,基于修正的Hopfield模型,综合考虑天气和卫星仰角实时变化情况,以及飞机与地面站的实时距离,提出一种实时计算非标称对流层误差的方法;鉴于该方法对甚高频频数据播发(VDB)传输带宽要求较高,提出拟合计算方法,将实时误差拟合为距离和卫星仰角的函数。仿真计算单点、进近区和终端区3种飞行场景下的VPL,分析非标称对流层误差对GBAS完好性的影响,结果表明:采用实时计算方法时,平均VPL增量为1.55 m,非标称对流层误差的包络精度提高32.52%;采用拟合计算方法时,平均VPL增量为1.27 m,包络精度提高44.54%,VDB传输数据减少,GBAS完好性风险降低。

Impact of non-nominal troposphere error on GBAS integrity

In current ground-based augmentation system (GBAS),the average vertical protection level (VPL) increase caused by non-nominal troposphere error is 2.29 m,the accuracy of bounding is reduced and the integrity risk is increased.Faced with the above problems,a real-time method was proposed based on the modified Hopfield model.With real-time method,the non-nominal troposphere error was calculated according to the real-time weather changes,satellite elevation angle and the distance between aircraft and ground station.Given the high requirement of the real-time method for very high frequency data broadcast(VDB) transmission bandwidth,a fitting method was proposed,in which error is a function of distance and elevation angle.Simulations compute the VPL under the flight scenarios of single point,approach area and terminal area with the aim of evaluating the impact of non-nominal troposphere error on GBAS integrity.The results show that,with the real-time bounding method,VPL is averagely increased by 1.55 m and the accuracy of bounding is increased by 32.52％;with fitting method,VPL is averagely increased by 1.27 m,the accuracy of bounding is increased by 44.54％,the VDB transmission data is less,and the GBAS integrity risk is decreased.