Soil Permittivity Estimation Over Croplands Using Full and Compact Polarimetric SAR Data

Soil permittivity estimation using polarimetric synthetic aperture radar (PolSAR) data has been an extensively researched area. Nonetheless, it provides ample scope for further improvements. The vegetation cover over the soil surface leads to a complex interaction of the incident polarized wave with the canopy and subsequently with the underlying soil surface. This article introduces a novel methodology to estimate soil permittivity over croplands with vegetation cover using the full polarimetric (FP) and compact polarimetric (CP) modes. The proposed method utilizes the FP and CP scattering-type parameters,
$\theta _{\text {FP}}$
and
$\theta _{\text {CP}}$
, respectively. These scattering type parameters are a function of the soil permittivity and the Barakat degree of polarization. The method considers the extended Bragg (X-Bragg) scattering model for the soil surface. In particular, these scattering-type parameters explicitly account for the depolarizing structure of the scattered wave while characterizing targets. Thus, the depolarization information in terms of surface roughness in the X-Bragg model gets inherent importance while using
$\theta _{\text {FP}}$
and
$\theta _{\text {CP}}$
, unlike existing scattering-type parameters. Therefore, the proposed technique enhances the expected value of the inversion accuracies. This study validated the major phenology stages of four crops using the UAVSAR full-pol and simulated compact pol SAR data and the ground-truth data collected during the SMAPVEX12 campaign over Manitoba, Canada. The proposed method estimated permittivity with a root mean square error (RMSE) of 2.2–4.69 for FP and 3.28–5.45 for CP SAR data along with a Pearson coefficient,
$r\ge 0.62$
.