Phase Error Analysis and Compensation of GEO-Satellite-Based GNSS-R Deformation Retrieval

Beidou geostationary Earth orbit (GEO) satellite-based global navigation satellite system reflectometry (GNSS-R) technique has been developed for measuring surface deformation in a carrier-phase-based, cost-effective, and continuous manner. However, several improper assumptions in the original system and method, such as neglecting the slight GEO satellite movement during angle determination and deeming interchannel phase difference as time-invariant, can introduce certain errors in estimating the surface deformation. In this work, these issues were analyzed and improved for more accurate estimations. Utilizing a Wilkinson power divider, the interchannel phase error is estimated and calibrated with direct signal in the master channel. The GEO-motion phase error is theoretically modeled and compensated for based on precise ephemeris. A compensating algorithm of GNSS-R deformation retrieval technique utilizing Beidou GEO satellites is presented, by which encouraging results are yielded from field experiments emulating long-term monitoring. On artificial targets, the retrieval root mean square (RMSE) is better than 8 mm.