An Improved Four-Parameter Soil Complex Dielectric Mixing Model in Microwave Remote Sensing

The soil complex dielectric permittivity (CDP) is a fundamental physical quantity utilized in microwave remote sensing to estimate soil moisture. Although several four-parameter (soil temperature, moisture, clay content, and frequency) semiempirical complex dielectric mixing models (SEMs) have been developed, they do not consider the changes in soil CDP caused by the conversion of bound water to free water due to temperature variations. This study proposes an improved SEM (also known as the Dobson-Jin model) based on the Dobson SEM. The improvements include: 1) rectifying the distortion phenomenon in the imaginary part of the Dobson model and minimizing the error in calculating sand using the Dobson model; 2) reducing the number of input parameters from seven to four; and 3) dividing soil water into strongly bound water and soil-effective water (the sum of weakly bound water and free water) and successfully simulating the “competitive mechanism” of soil CDP variation with temperature by establishing the weakly bound water to free water conversion functions and the weakly bound water proportion functions. Experimental validation using measured data from 31 types of soils has demonstrated that the Dobson-Jin model is capable of accurately calculating the CDP of sand, loam, and clay within the range of 1.4–18 GHz and water content volume of 0–0.5 (cm
$^{3}\cdot \text { cm}^{-3}$
). In summary, the Dobson-Jin model is expected to improve the accuracy of microwave remote sensing inversion of soil moisture.