SCoBi Multilayer: A Signals of Opportunity Reflectometry Model for Multilayer Dielectric Reflections

Abstract

A multilayer module is incorporated into the Signals of Opportunity (SoOp) Coherent Bistatic Scattering model (SCoBi) for determining the reflections and propagation of electric fields within a series of multilayer dielectric slabs. This module can be used in conjunction with other SCoBi components to simulate complex, bistatic simulation schemes that include features such as surface roughness, vegetation, antenna effects, and multilayer soil moisture interactions on reflected signals. This paper introduces the physics underlying the multilayer module and utilizes it to perform a simulation study of the response of SoOp-R measurements with respect to subsurface soil moisture parameters. For a frequency range of 100–2400 MHz, it is seen that the SoOp-R response to a single dielectric slab is mostly frequency insensitive; however, the SoOp-R response to multilayer dielectric slabs will vary between frequencies. The relationship between SoOp-R reflectivity and the contributing depth is visualized, and the results show that SoOp-R measurements can display sensitivity to soil moisture below the penetration depth. By simulation of simple soil moisture profiles with different wetting and drying gradients, the dielectric contrast between layers is shown to be the greatest contributing factor to subsurface soil moisture sensitivity. Overall, it is observed that different frequencies can sense different areas of a soil moisture profile, and this behavior can enable subsurface soil moisture data products from SoOp-R observations.

Retrieval of Subsurface Soil Moisture and Vegetation Water Content from Multi-frequency SoOp-Reflectometry: Sensitivity Analysis

“…Based on previous research findings [9], [44], it is reasonable to assume, for the purpose of this study, a dominantly coherent reflection. SCoBi-Veg models the specular reflectivity (coherent component), Γ s , as the matrix equation [18], [43],…”

“…Recent experiments and simulation studies have shown the potential of multi-frequency SoOp-R to measure RZSM [10], [16]- [19]. A single frequency SoOp-R observation will be sensitive to the entire SM profile within the sensing depth [18]. It is therefore necessary to combine observations at multiple frequencies and solve an inverse problem to estimate this full profile and obtain SM retrievals at different depths.…”

Retrieval of Subsurface Soil Moisture and Vegetation Water Content from Multi-frequency SoOp-Reflectometry: Sensitivity Analysis

“…Based on previous research findings [9], [44], it is reasonable to assume, for the purpose of this study, a dominantly coherent reflection. SCoBi-Veg models the specular reflectivity (coherent component), Γ s , as the matrix equation [18], [43],…”

“…Recent experiments and simulation studies have shown the potential of multi-frequency SoOp-R to measure RZSM [10], [16]- [19]. A single frequency SoOp-R observation will be sensitive to the entire SM profile within the sensing depth [18]. It is therefore necessary to combine observations at multiple frequencies and solve an inverse problem to estimate this full profile and obtain SM retrievals at different depths.…”