LAUSR

Global navigation satellite system reflectometry (GNSS-R) is a passive technique for remote sensing of soil moisture, which has continuous all-day and all-weather applicability on different platforms. New GNSS signals with advanced modulation and higher power are expected to improve the performance of GNSS-R. In this study, we performed a ground-based dual-antenna GNSS-R experiment on farmland and collected 15-min raw intermediate frequency (IF) data with a central frequency of 1175.42 MHz hourly over two different 24-h periods. The power ratio between the direct and reflected signals from quasi-zenith satellite system (QZSS) satellites was computed using a self-developed software-defined receiver with 1-ms coherent integration and 200-ms incoherent adds. Then, soil moisture was resolved using a semiempirical model based on power ratios. Solutions were evaluated using measurements obtained using a time-domain reflectometry (TDR) probe. Results demonstrated that signal power-ratio-based QZSS signals can be used to retrieve soil moisture under bare soil conditions. Moreover, for signal power-ratio-based case, results from geostationary orbit (GEO) satellite signals (STD: 0.013 and 0.007 $\text{m}^{3}/\text{m}^{3})$ performed better than those from inclined geosynchronous orbit (IGSO) satellite signals (STD: 0.033–0.071 $\text{m}^{3}/\text{m}^{3})$ .