Adaptive Tropospheric Delay Modelling in GPS/INS/Pseudolite Integration for Airborne Surveying

Integrated GPS/INS systems have been used for geo-referencing airborne surveying and mapping platforms. However, due to the limited constellation of GPS satellites and their geometric distribution, the accuracy of such integrated systems cannot meet the requirements of precise airborne surveying. This problem can be addressed by including additional GPS-like ranging signals transmitted from the ground-based pseudolites (PLs). As GPS measurement geometry could be strengthened dramatically by the PL augmentation, the accuracy and reliability of an integrated system can be improved, especially in the vertical component. Nevertheless, some modelling challenges exist in PLs augmentation. As PLs are relatively close to receivers, the unit vectors from a PL to he reference and rover receivers can be significantly different. PL tropospheric delay modelling errors cannot be effectively mitigated in a differencing procedure. Furthermore, PL signals propagate through the lower troposphere, where it is very difficult to accurately model the signal delay due to temporal and spatial variations of meteorological parameters. In this paper, an adaptive PL tropospheric delay modelling method is developed to reduce such modelling errors by estimating meteorological parameters in a model. The performance of this adaptive method is evaluated with field test data. The testing results have shown that the PL tropospheric delay modelling error can be effectively mitigated by the proposed method.