5. Theoretical Study of Bare Soil Parameters’ Effects on GPS Multipath Observables

In the past two decades, GNSS-R has emerged as a new and attractive remote sensing technique. The geodetic/geophysical GPS receivers are out-of commercial and their recorded multipath observables have potentials for geophysical parameters detections, e.g. soil moisture, vegetation growth and snow depth. Based on the developed forward GPS multipath model, effects of bare soil parameters on GPS multipath observations are evaluated here. Wave synthesis technique is employed to get the coherent scattering coefficients at VV, HH, RR and LR polarizations, while the bare soil dielectric constant is calculated by a microwave dielectric soil-water mixing model. Effects of three-frequencies GPS modulations (L1 band, L2 band and L5 band) are evaluated: although there are apparent differences for GPS multipath observables, it is not the effects of bare soil but the direct broadcasting signals since soil scattering properties at these frequencies (L band) are the same. Soil texture and surface roughness have almost no effects on GPS observables. As the soil temperature changes from SubZero to above zero, the amplitudes of SNR, phase and code pseudorange increased. Soil moisture also affects GPS observables, as moisture content increases, the amplitudes of GPS observables increase.