GNSS Imaging: a Case Study of Tree Detection Based on BeiDou GEO Satellites

Curved trajectories of traditional navigation satellites limit their performance in bistatic radar imaging system. Instead of using common Inclined Geosynchronous Orbit (IGSO)/Medium Earth Orbit (MEO) satellites in motion, a new global navigation satellite system (GNSS) imaging system based on Beidou geosynchronous orbit (GEO) satellites is presented to deal with this problem. The most prominent feature of GEO satellites is that they are stillrelative to the earth. This work includes three parts. First, a reasonable parallel assumption is provided to simplify the geometric topology of the imaging system, and the relevant path delay formula is deduced. Second, the principle of imaging based on multiple GEO satellites is proposed, and the simulation result is presented. Third, the entire signal processing, which uses a multi-correlator, is designed to improve the range resolution. Two imaging experiments targeting at the trees are described and conducted in Wuhan University to verify the imaging system. The first experiment is targeted at isolated trees, and the second experiment is focused on groves along the road. Conclusion can be obtained: the imaging result is highly consistent with the imaging area, which validates the feasibility of the method and confirms the potential use of GNSS imaging system in forest monitoring.