Analysis of multi-frequency polarimetric data for assessment of bare soil roughness

The aim of this study is to assess the bare soil surface roughness parameter, i.e. the root mean square height (h_rms) when the moisture is constant, using anechoic chamber measurements based on fully polarimetric scatterometer data. An incidence angle based algorithm has been proposed to assess the bare soil height h_rms. For this purpose, sets of experimental backscattering data have been evaluated on different types of rough surfaces (Rough Gaussian, h_rms = 2.5 cm, Smooth Gaussian, h_rms = 0.4 cm and Medium Mixed surface, h_rms = 0.9 cm) with known geometrical and dielectric properties. The scattering matrix of those three surfaces under test was measured in monostatic mode vs. frequency ( 1 - 19 GHz) and incidence angles ( θ = 10° to 50° in steps of 10° for h_rms = 2.5 cm and 0.9 cm and 5° for h_rms = 0.4 cm) data. An empirical relationship has been developed between backscattering, h_rms and incidence angle independently for L-, C-, X- and Ka-band for all polarizations (i.e. HH, VV and HV). This relationship provides the calculated backscattering values, which is helpful in the inversion process. A good agreement has been obtained between the observed and calculated h_rms. The analyses show the strong dependence of h_rms on incidence angle, polarization and frequency. This type of work is also helpful in the near future to predict the optimum sensor parameters (i.e. incidence angle, polarization and frequency) for measuring the bare soil roughness.