A new empirical model to retrieve soil moisture and roughness from C-band radar data

A new empirical model for the retrieval, at a field scale, of the bare soil moisture content and the surface roughness characteristics from radar measurements is proposed. The derivation of the algorithm is based on the results of three experimental radar campaigns conducted under natural conditions over agricultural areas. Radar data were acquired by means of several C-band space borne (SIR-C, RADARSAT) or helicopter borne (ERASME) sensors, operating in different configurations of polarization (HH or VV) and incidence angle. Simultaneously to radar acquisitions, a complete ground truth data base was built up with different surface condition measurements of the mean standard deviation (rms) height s, the correlation length l, and the volumetric surface moisture Mv. This algorithm is more specifically developed using the radar cross-section σ0 (HH polarization and 39° incidence angle off nadir), namely, σ0HH,39, and the differential (HH polarization) radar cross-section Δσ0=σ0,23°−σ0,39° in terms of an original roughness parameter, Zs, namely Zs=s2/l, and Mv. A good agreement is observed between model outputs and backscattering measurements over different test fields. Eventually, an inversion technique is proposed to retrieve Zs and Mv from radar measurements.