Abstract
A method for simulating delay-Doppler maps (DDMs) of global navigation satellite system signals reflected from land surfaces with heterogeneous terrain is developed from first principles. The method follows previous work for ocean DDMs in the geometric optics limit of the Kirchhoff approximation. Unlike the ocean method, however, where surface heights are assumed to be random with homogeneous statistics, this method decomposes the surface heights into a deterministic part obtained from a digital elevation map (DEM) and a random part representing the residual between the surface and the DEM. The method accounts for the displacement of reflected power into bins of lower delay due to raised surface terrain. The method also provides for the modulation of the normalized bistatic radar cross section by DEM-derived surface slopes over the glistening zone of the DDM. A technique to register Cyclone Global Navigation Satellite System (CYGNSS) DDM bins in delay-Doppler space for land applications is also proposed. The DEM-based method is applied to a CYGNSS track over the Soil Moisture Sensing Controller And oPtimal Estimator (SoilSCAPE) site at Tonzi Ranch, CA, USA. The DEM-based method has potential application for spaceborne monitoring of a variety of environmental parameters.
Highlights
R EFLECTIONS of global navigation satellite system (GNSS) signals and other signal of opportunity from earth’s land surfaces are sensitive to a variety of geophysical parameters, including soil moisture, freeze/thaw state, snow water equivalent, snow depth, aboveground biomass, vegetation water content, and permafrost
We develop a digital elevation model (DEM)-based model for global navigation satellite system-reflectometry (GNSS-R) measurements of a bare surface in the geometric optics limit of the Kirchhoff approximation
We found that Cyclone Global Navigation Satellite System (CYGNSS) delay-Doppler maps (DDMs) over Tonzi Ranch have large incidence angles due to the site’s location near the northern edge of the CYGNSS coverage zone
Summary
R EFLECTIONS of global navigation satellite system (GNSS) signals and other signal of opportunity from earth’s land surfaces are sensitive to a variety of geophysical parameters, including soil moisture, freeze/thaw state, snow water equivalent, snow depth, aboveground biomass, vegetation water content, and permafrost. A DEM-based method using level rough patches has been proposed to account for received power levels that are less than predicted by a strictly planar rough surface but greater than predicted by purely noncoherent scattering [13], [14]. We develop a DEM-based model for GNSS-R measurements of a bare surface in the geometric optics limit of the Kirchhoff approximation.
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