Dominant backscattering mechanisms at L-band during dynamic soil moisture conditions for sandy soils

- Obtain high temporal resolution radar observations using a ground-based UF-LARS
- Investigate dominant backscattering mechanisms under dynamic soil moisture conditions
- Provide insights into the volume scattering for dry soils by a physically-based model
- Evaluate sensitivity of the observed and modeled radar backscattering coefficient

In this study, we investigate dominant backscattering mechanisms under different soil moisture (SM) and roughness conditions for bare sandy soils, and discuss potential impacts on active microwave algorithms for soil moisture estimation. This study used ground-based observations of backscattering coefficient (σ0) over three drydown periods. Under rough soil conditions, surface scattering was the dominant mechanism during both dry and wet periods, and the σ0 followed a power-law relationship with SM, with R2 values > 0.86. However, under smooth soil conditions, the relationship was negative for SM < 0.07 m3/m3. A simple volume scattering model was used to provide plausible explanation for such a behavior due to volume scattering. Sensitivities of σ0 to SM using both observed and modeled σ0 were analyzed. The observed sensitivity was higher for smooth soil than that for rough soil, when surface scattering was the dominant mechanism, while the sensitivity estimated by the AIEM model was largely unaffected by surface roughness. Observations at VV-pol were more sensitive to SM than at other polarizations by up to 1 dB/0.01m3/m3 for rough soil, while the AIEM model estimated similar sensitivities at both VV and HH-pol, with the maximum difference between the modeled and observed sensitivities of 3 dB/0.01m3/m3. This study demonstrates that volume scattering under dry, smooth conditions and a non-linear relationship between σ0 and SM under rough conditions in sandy soils may have significant impacts on estimate of SM using active algorithms.