A two-step non-nominal troposphere monitor for GBAS

The non-nominal troposphere caused by hazardous horizontal tropospheric gradients poses a threat to the integrity of the safety-critical civil aviation precision approach supported by ground-based augmentation system (GBAS). The carrier phase-based monitors are widely applied for evaluating and detecting the non-nominal troposphere. However, the detection sensitivity of carrier phase-based monitor is limited by the reliability of ambiguity resolution. To isolate the impact of ambiguity resolution failure on the non-nominal troposphere monitoring, a two-step non-nominal troposphere monitor is proposed based on the multiple short-baseline reference receivers. The ambiguity resolution correctness and the non-nominal troposphere are sequentially monitored, respectively. The probabilities of false alarm and missed detection are dynamically allocated between the two-step monitoring to satisfy the integrity risk requirement. The real BDS dual-frequency data are utilized to test the proposed two-step monitoring method. The result shows that the detection sensitivity of the proposed method is improved by 40.5% when compared with the traditional single-step monitoring method. It has been demonstrated that the proposed method can effectively reduce the integrity risk of high-precision navigation service caused by the non-nominal troposphere.