The range of salinity and temperature measurements used to develop models for the dielectric constant of sea water have in the past been limited to values appropriate for the open ocean. But there are important water bodies such as the Great Salt Lake in Utah with salinities much larger than those encountered in the open ocean. Extrapolating existing models to values of salinity beyond the limits of the data used to create the model can result in unrealistic predictions in remote sensing applications. This can be prevented by using a model for conductivity based on the definition of salinity and ensuring that polynomials used to model the other unknown parameters result in bounded behavior at high salinity. New laboratory measurements with high salinity (up to 150 pss) are reported and used to test a model with these adjustments.

A decomposition and reconstruction theorem (DRT) is introduced to advance computation and provide physical understanding for the scattering from fractal surfaces (FPs). The profile of FP is decomposed into test profiles (TPs), and the scattering of FP is reconstructed using the scattering of TPs to enhance the computational efficiency. A new method that applies DRT on the extended boundary condition method combined with the truncated singular value decomposition technique (TEBCM) is presented and referred to as TEBCM-DRT. The method of TEBCM-DRT is employed to solve the scattering from realistic soil surfaces, and the results are validated against other scattering models. Moreover, the efficiency of TEBCM-DRT and its validity range are investigated. The result shows that TEBCM-DRT improves computational efficiency to 1.95 x 10⁵ and 7.35 x 10² times, respectively, compared to TEBCM and the conventional method of moments for a wide range of roughness. In addition, TEBCM-DRT indicates that the amplitude and direction of propagation of scattering modes are dependent on deterministic TPs. This relationship benefits for obtaining the accurate height of an arbitrary point on the profile from bistatic scattering coefficients.

This article proposes a closed-form asymptotic solution for the bistatic coherent scattering of a multilayered rough surface structure based upon its effective dielectric constant (EDC) in specular direction. The EDC is modeled by establishing an equivalence of the coherent scattering between the multilayered rough surface structure and a half-space homogeneous medium. The scattering solution is then solved using the scalar Kirchhoff approximation (SKA) method. This new method is referred to as the SKA-EDC method, and it is applied to analyze the sensitivity of the EDC and coherent reflectivity to bare soils with realistic parameters at P- and L-bands. The result indicates that EDC can give different responses to the soil moisture variations with respect to the coherent reflectivity, enabling the potentials of root-zone soil moisture retrieval. At incidence angle smaller than 35°, EDC gives the same value for both polarizations, and the coherent reflectivity can show a significant response to soil at depths <15–50 cm at 0.80 GHz and <5–15 cm at 1.57 GHz, depending on soil moisture. The simulation also demonstrates that subsurface roughness has a trivial effect on the EDC and coherent reflectivity for three rough surfaces separated by continuously dielectric profiles. Subsurface can, thus, be assumed to be flat for reducing uncertainty in soil moisture inversion algorithms when the subsurface roughness is unknown.

Fractal geometry function provides a practical way to simulate natural rough surface for electromagnetic scattering calculation of microwave remote sensing. In our study, we generate three-dimensional random rough surface based on band-limited Weierstrass-Mandelbrot model and carry out a series of quantitative analyses of the relation between fractal parameters and rough surface parameters. In order to eliminate the artifical reflection from the truncated boundary of rough surface model, a tapered incident wave model is built to illuminate the surface profile model with the use of sampling strategy. The tapered incident wave is introduced into the classical Two-Scale Model to calculate backscattering coefficient. The proposed model is applied to simulate the scattering of sea clutter based on the fractal sea surface model. Its simulation results are compared with real sea surface scatterometer measurement experiments in Beihai, Guangxi province and the overall deviation is less than 10%. The results validate the efficiency of the proposed model in obtaining the scattering simulation data on sea surface for parameter inversion of active microwave remote sensing.

This study explores the potential of P-band and L-band radiometry for estimating soil moisture and temperature profiles. A total of 3977 hourly in-situ soil data were collected at depths ( d ) of 5-60 cm in Beltsville, MD, USA. Using the data, a coherent model was utilized to generate synthetic brightness temperatures at an incidence angle of 40 degrees for frequencies of 0.8, 0.9, 1.1, and 1.4 GHz. These synthetic brightness temperatures facilitated the estimation of soil moisture ( m_v ) and temperature ( T ) profiles, which were modeled as quadratic functions with three coefficients. The inversion problem was formulated as a least squares problem and optimized by the Adaptive Simulated Annealing (ASA) algorithm. Regression analysis highlighted the sensitivity of the soil moisture and temperature function coefficients on the brightness temperature at 1.4 GHz and the differential between 1.4 GHz and 0.8 GHz (R ² = 0.62 − 0.97), yielding the best-fit models to describe the relationships. The application of the ASA algorithm incorporating the best-fit models to constrain the search spaces, showed the RMSE of soil moisture m_v ≤ 0.04 cm ³ / cm ³ and soil temperature T ≤ 1.35 for depths d ≤ 20 cm , and m_v ≤ 0.10 cm ³ / cm ³ , T ≤ 1.60 for d ≤ 60 cm . A streamlined inversion method was also investigated which used the best-fit models as the retrieval formula and solely relied on the V-pol data. The streamlined inversion method achieved comparable retrieval accuracy but reducing the runtime from 770s to 0.54s for one inversion. This approach simplifies the data collection process by eliminating the need for H-pol data, potentially broadening its flexibility and applicability.

A macroscopic dielectric constant (MDC) model is proposed to describe the impact of a dielectric layered medium with two-layer rough surfaces (TLRSs) on 2-D electromagnetic scattering. The MDC model is based on the Kirchhoff approximation (KA) method to find an equivalence between the total fields on a TLRS and on a single-layer rough surface (SLRS). With this model, evaluating the scattering over a TLRS can be reduced to a simple SLRS scattering problem. The KA method is used in conjunction with the MDC model to calculate the bistatic scattering coefficients at different surface roughness conditions. The results are in good consistency with the values obtained using the method of moments. Extensive numerical results confirm that the MDC varies along the profile of the top surface as the surface roughness increases, and the variations in the surface roughness and medium depth can significantly affect the fluctuation and mean value of MDC.