The New Technology for Soil Moisture Measurement Based on GNSS-S Radar

Soil moisture is a key variable governing land–atmosphere water and energy exchanges. This letter proposes a novel soil moisture retrieval technique based on GNSS-S (Global Navigation Satellite System–Scattering) radar. Unlike conventional GNSS-R systems that are restricted to specular reflection points, the proposed GNSS-S radar exploits distributed GNSS backscattering to enable continuous bistatic imaging of surface soil moisture. The system is mounted on an airborne or spaceborne platform and uses navigation satellites as illuminators of opportunity. GNSS-S imaging is achieved through signal-level preprocessing, backprojection-based image formation, geometric correction, and relative radiometric calibration. Airborne experiments demonstrate that continuous surface imaging with a spatial resolution of approximately 100 m × 100 m can be achieved using L-band GNSS signals. Comparative analysis with in-situ soil moisture measurements shows consistent spatial distribution trends, and quantitative evaluation reveals moderate to strong correlations depending on bistatic geometry. These results validate the feasibility of GNSS-S radar for area-wide soil moisture monitoring and highlight its potential as a complementary technique to conventional active SAR systems.