Preliminary Performance Evaluation and Verification of GNSS-R Data Products From 22 Satellites Tianmu-1 Constellation: Comparison of BeiDou, GPS, GLONASS, and Galileo Signals Retrieval Results With Multisource Data

The Tianmu-1 occultation meteorological detection constellation is China's first commercially built low-orbit meteorological satellite system, equipped with Global Navigation Satellite System-radio occultation (GNSS-RO) and GNSS reflectometry (GNSS-R) detection payloads, supporting multi-system signal reception and processing. This article focuses on the L2 GNSS-R sea surface wind speed and soil moisture products of four systems from 22 satellites in the Tianmu-1 constellation, and systematically compares and verifies them with multi-source reference data to comprehensively evaluate their retrieval accuracy. These preliminary works have achieved encouraging results, indicating that the Tianmu-1 GNSS-R sea surface wind speed product not only has good consistency within the conventional wind speed range, but also maintains RMSE below 1.5m/s compared to the ERA5 reference wind speed. Under extreme wind speed conditions, it also has the ability to monitor typhoons. The Tianmu-1 GNSS-R cyclone wind speed product can still maintain good correlation with reference data, with a maximum CC of 0.9. The soil moisture product retrieved by Tianmu-1 shows stability in the low latitude region and has a high correlation with the ground observation network (ISMN) data, with CC values above 0.7, enabling high spatiotemporal accuracy perception of shallow soil moisture. In addition, this article also explores the performance differences and complementary advantages between the Tianmu-1 constellation and platforms such as Cyclone GNSS (CYGNSS), Fengyun-3 (FY-3), L-band radiometer, scatterometer, and Synthetic Aperture Radar (SAR), laying the foundation for future multi-source fusion remote sensing.