Comprehensive analysis of spaceborne GNSS reflectometry for precision altimetry

Global Navigation Satellite System-Reflectometry (GNSS-R) has emerged as a versatile and cost-effective technique that complements traditional remote sensing methods. By using reflected GNSS signals, GNSS-R enables all-weather operation, supports the monitoring of diverse surface types. Its applications span soil moisture estimation, ocean altimetry, and ice dynamics monitoring. This study explores the potential of Grazing-Angle GNSS-R (GG-R) carrier-phase measurements for precision altimetry, focusing on retrieving sea-level anomalies (SLA) and monitoring polar regions. Data from Spire Global Inc.’s Radio Occultation (RO) constellation are compared with conventional radar altimetry missions, including Sentinel-3A/3B, Saral, and CryoSat-2. Over a period of more than two years, SLA data analyzed with 1-day intervals and 10 km spatial resolution using dual-frequency GPS measurements yielded an average RMSE of approximately 47 cm. The analysis highlights complementary strengths between the two methods, with GG-R providing valid measurements in scenarios where radar altimetry is unavailable, and vice versa. A focused evaluation of GG-R-specific collocated events confirmed the consistency of Spire’s retrievals, achieving an RMSE of 25 cm. These findings demonstrate GG-R’s ability to enhance spatio-temporal resolution and address coverage limitations in conventional systems, establishing it as a valuable tool for advancing altimetry in challenging environments.