非标称对流层误差对地基增强系统完好性的影响

地基增强系统(ground-based augmentation system,GBAS)中,由于不同路径方向区域范围内气象条件(温度、压强、相对湿度等)存在差异,导致系统差分修正误差中包含非标称对流层误差;即非零均值标准正态分布误差。在非标称对流层误差的影响下,机载端垂直保护级(vertical protection level,VPL)增加,系统完好性风险增大以及地面播发信号可用性降低。详细分析了非标称对流层误差对VPL的影响,发现非标称对流层误差与卫星仰角有关;并且跟踪可见卫星数目增多时,系统受非标称对流层误差的影响,VPL值进而增加。为了提高GBAS完好性,提出了一种新的选星算法,降低非标称对流层对VPL的影响,提高系统完好性信号(system in tegrity signal,SIS)可用性。仿真计算GBAS进近服务类型C(GAST C)和GBAS进近服务类型D(GAST D)场景下的VPL,分析改进的选星算法对系统完好性的影响。结果表明,改进的选星算法有效地降低了非标称对流层对GBAS完好性的影响,减小了机载端VPL值,降低了完好性风险,提高了在气象异常条件下GBAS信号的可用性。

The Impact of Non-nominal Troposphere Error on GBAS Integrity

In ground-based augmentation systems (GBAS), due to differences in meteorological conditions (temperature, pressure, relative humidity, etc.) in different path direction regions, the system differential correction errors include non-nominal tropospheric errors, called non-zero mean standard normal distribution errors. Under the influence of non-nominal tropospheric error, the vertical protection level (VPL) of the airborne increases, the risk of system integrity increases, and the availability of ground broadcast signals decreases. This paper analyzes in detail the impact of non-nominal tropospheric error on VPL and finds that the non-nominal tropospheric error is affected by the satellite elevation angle. When the number of satellites visible in the tracking increases, the system is affected by the non-nominal tropospheric error and the VPL value increases. In order to improve the integrity of GBAS, this paper proposes a new selection satellite algorithm to reduce the impact of non-nominal troposphere on VPL and improve system integrity signal (SIS). The simulation calculates the VPL under GBAS approach service type C (GAST C) and GBAS approach service type D (GAST D) scenarios, and analyzes and compares the effect on the system integrity after applying the new algorithm. The results show that the new selection satellite algorithm effectively reduces the impact of the non-nominal troposphere on the integrity of GBAS, reduces the VPL value on the airborne side, and improves the availability of GBAS signals under meteorological anomalies.