Modeling L-Band Synthetic Aperture Radar Observations through Dielectric Changes in Soil Moisture and Vegetation Over Shrublands

L-band airborne synthetic aperture radar observations were made over California shrublands to better understand the effects of soil and vegetation parameters on backscattering coefficient (σ⁰) for the period of 2011 to 2015. HH was always greater than VV, suggesting the importance of double-bounce scattering by the woody parts. However, the geometric and dielectric properties of the woody parts did not vary significantly over time. Instead the changes in vegetation water content (VWC) were observed to occur primarily in thin leaves that may not meaningfully influence absorption and scattering. Accordingly, unlike in the past literature, the VWC input of the plant to the model was formulated as a function of plant's dielectric property (water fraction) while the plant geometry remains static in time. A physically-based model for single scattering by discrete elements of plants successfully simulated the magnitude of the temporal variations in HH, VV, and HH/VV with a difference of less than 0.9 dB. The modeling results offer an explanation of why soil moisture correlated highly with σ⁰, which is that the dominant mechanisms for HH and VV are double-bounce scattering by trunk, and soil surface scattering, respectively.