Bi-dimensional soil roughness measurement by photogrammetry for SAR modelling of agricultural surfaces

In the description of soil roughness for SAR monitoring, the hypothesis of surface isotropy was currently admitted and in-situ roughness measurements were recorded along linear profiles. However, this paper showed for agricultural soil surfaces this hypothesis is not valid and anisotropic surface must be assumed. Stereoscopic pairs of vertical photographs were acquired to produce digital elevation models (DEM) for the soil roughness description. This paper presents a measurements method to describe the bi-dimensional soil roughness and discuss 3 advantages of the photogrammetric method compared to the linear measurements, (i) a high variability of the roughness parameters estimated by linear profiles was observed. Using the DEM, a high number of profiles were drawn for a given direction. A more accurate estimation of rms and correlation length was obtained averaging several profiles, (ii) the anisotropy were measured and represented by a directional variograms. (iii) The anisotropic roughness were decomposed in 2 models: the isotropic random roughness and the anisotropy induced by the sowing rows.