Impact of Soil Moisture and Vegetation Water Content on Backscatter Simulated by WCM at Different Radar Parameters in Maize Field

Abstract

This paper analysis the effects of soil moisture and vegetation water content (VWC) on total backscattering (σ_tot^0) simulated by water cloud model (WCM) throughout a growth cycle of maize at different frequencies, polarization modes, and incidence angles. Firstly, the bare soil backscatter (σ_soil^0) was simulated by Integral Equation Method (IEM) surface scattering model [1] or Dubois empirical backscattering approach [2]. Then, to analysis the effect of vegetation cover, a standard and a double layer WCM based on parameter sets of three published studies [3]-[5] are applied in this study area to simulate the two components of σ_tot^0, direct backscatter from vegetated surface (σ_veg^0) and attenuated soil backscatter (〖γ^2 σ〗_soil^0). The input parameters of IEM, Dubois and WCM are supported by a series of ground measurements performed in Florida during the entire growth season, which includes soil moisture, surface roughness and vegetation biomass measurement. According to the analysis at different frequency and incident angle, the increase of bulk VWC can lead to either an increase or decrease in σ_(tot ). The different impact is determined by either σ_veg^0 or 〖γ^2 σ〗_soil^0 is the main contributor to σ_tot^0. At higher frequencies and larger incident angles, where the dominant part is from σ_veg^0, σ_tot^0 will increase with increasing bulk VWC. While, when 〖γ^2 σ〗_soil^0 becomes the main contributor to σ_tot^0, increasing bulk VWC leads to a denser canopy and thus more incoming microwave is attenuated. Therefore, increasing bulk VWC results in a decrease in σ_tot^0. Besides, according to the results obtained at C-band, different incident angle, HH-polarized microwaves are more sensitive to changes in bulk VWC, especially at larger incident angle. VV-polarization is less affected by vegetation cover, σ_tot^0is sensitive to soil moisture even at peak biomass and large incidence angles, which is attributed to scattering along the soil-vegetation pathway.