Ground-Based Soil Moisture Retrieval Using the Correlation Between Dual-Polarization GNSS-R Interference Patterns
Marcel M. El Hajj (King Abdullah University of Science and Technology)
Susan C. Steele-Dunne (TU Delft - Mathematical Geodesy and Positioning)
Samer K. Almashharawi (King Abdullah University of Science and Technology)
Xuemeng Tian (Wageningen University & Research, TU Delft - Geoscience and Remote Sensing)
Kasper Johansen (King Abdullah University of Science and Technology)
Omar A.Lopez Camargo (King Abdullah University of Science and Technology)
Adria Amezaga-Sarries (Microwave Sensors and Electronics Sl)
Andreu Mas-Vinolas (Microwave Sensors and Electronics Sl)
Matthew F. McCabe (King Abdullah University of Science and Technology)
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Abstract
Soil moisture (SM) is an important state variable in land surface models. Here, we investigate the potential of a ground-based global navigation satellite system receiver with two linearly polarized antennas that measure the interference power (IP) of direct and reflected signals in horizontal polarization (H-pol) and vertical polarization (V-pol) to estimate SM. The coefficient of determination between the IP waveforms at H-pol and V-pol ( $\boldsymbol {R}_{ \boldsymbol {v}\mathbf {/} \boldsymbol {h}}^{\mathbf {2}}$ ) was used as a predictor of SM. A coherent specular reflection model was employed to first explore the relationship between $\boldsymbol {R}_{ \boldsymbol {v}\mathbf {/} \boldsymbol {h}}^{\mathbf {2}}$ and SM for different values of soil roughness. That relationship was subsequently applied to estimate SM from $\boldsymbol {R}_{ \boldsymbol {v}\mathbf {/} \boldsymbol {h}}^{\mathbf {2}}$ determined from global positioning system (GPS) signals acquired continuously by a ground-based receiver between May and December 2022 for an area with very smooth bare soil. The results show that the proposed method can estimate the SM of the upper 10-cm layer with high accuracy (with a root-mean-square error (RMSE) of approximately 1.5 vol.%) and demonstrate the potential of the ground-based IP technique as a practical system solution for proximal remote sensing of SM over bare soils .