Generalized Terrain Topography in Radar Scattering Models

Abstract

Modeling of terrain topography is crucial for vegetated areas given that even small slopes impact and alter the radar wave interactions between the ground and the overlying vegetation. Current missions either exclude pixels with large topographic slopes or disregard the terrain topography entirely, potentially accumulating substantial modeling errors and therefore impacting the retrieval performance over such sloped pixels. The underlying terrain topography needs to be considered and modeled to obtain a truly general and accurate radar scattering model. In this paper, a flexible and modular model is developed: the vegetation is considered by a multilayered multispecies vegetation model capable of representing a wide range of vegetation cover types ranging from bare soil to dense forests. The ground is incorporated with the stabilized extended boundary condition method, allowing the representation of an N -layered soil structure with rough interfaces. Terrain topography is characterized by a 2-D slope with two tilt angles (α, β). Simulation results for an evergreen forest show the impact of a 2-D slope for a range of tilt angles: a 10 • tilt in the plane of incidence translates to a change of up to 15 dB in HH, 10 dB in VV, and 1.5 dB in HV for the total radar backscatter. Terrain topography is shown to be crucial for accurate forward modeling, especially over forested areas.

Space-Borne GNSS-R Signal Over a Complex Topography: Modeling and Validation

“…Therefore, we assumed that the scattering from the top canopy layer in the presence of topography remains the same as for a flat terrain. When a slope is present, the crown thickness along the propagation path is different [34]; this effect needs to be included in the modeling of crown attenuation. In this version of SAVERS, it is possible to compute the correct path through the vegetation as the local incidence and scattering angles are computed for each facet of the simulation grid.…”

GNSS-R Soil Moisture Retrieval for Flat Vegetated Surfaces Using a Physics-Based Bistatic Scattering Model and Hybrid Global/Local Optimization

“…The groundbranch/trunk double-bounce bistatic scattering contribution is equivalent to branch/trunkground double-bounce bistatic scattering contribution. According to [33], the scattering pattern of a vertically oriented finite cylinder resembles a cone. In particular, the scattering pattern of a finite cylinder presents a strong response in the specular direction.…”

“…where incident and scattering paths are denoted as i and s, respectively, and ground, branch, and trunk are expressed as G, B, and T, respectively. Moreover, the T matrixes present the transmission Stokes matrixes related to the transmission of the wave through vegetation layers (branches and trunks) [33]. Ultimately, for incoherent scattering components, the total bistatic Stokes matrix M total presented in Equation ( 2) is converted to co-pol and crosspol linearly polarized total NBRCS σ 0 total by the method in [32].…”