Statistical Description of Seedbed Surface by Structuring Objects and Surface Generation Algorithm
Résumé
Knowledge and description of the micro topographic surface have a large impact on remote sensing and soil science. Several studies have focused on the characterization of roughness and description of the surfaces. The understanding and the accounting for the interaction of electromagnetic waves, the flow and the infiltration of the surface with roughness interfaces requires a good description of the latter. An agricultural soil has clods and holes. Such structuring objects contribute to defining the soil random roughness. The present study focuses on the characterization of these objects and presents an algorithm of surface generation with structuring objects. This study relies on a gradient-based method introduced recently in order to identify automatically the individual clods, holes or large aggregates on a three-dimensional digital elevation model (DEM) of the soil surface [1-2]. The DEM under consideration represent seedbed surfaces recorded just after tillage operation. The studied soil presents moderate roughness and unmarked tillage patterns and for a first approach, it can be modelled as isotropic Gaussian process [3]. In this paper, we propose a new approach of surface modelling and we show that the seedbed surface under consideration can be modeled by an initial surface on which clods and holes are laid down. One seedbed surface is studied here. We show that the contours of detected objects are well approximated by half-ellipsoid. From the large set of detected objects, we derive the statistical distributions characterizing orientation of ellipsoid, the major axis, the minor axis and the maximum altitude. The surface density of clods and holes is also evaluated and the interdependence of these parameters is analyzed. We propose a surface generation algorithm according to the statistical distributions. After removal of the structuring objects, a residue remains on the surface[4]. We show that the residu is not independent of the objet on the surface). We establish from this algorithm that the isotropy property depends on the probability law of the ellipse orientation. The influence of ellipse horizontal flattening factor is also investigated. [1] O. Taconet, E. Vannier, and S. Le Hégarat-Mascle, "A contour-based approach for clods identification and characterization on a soil surface," Soil and Tillage Research, v, pp. 123-132, 2010. [2] O. Chimi-Chiadjeu, E. Vannier, R. Dusséaux, and O. Taconet, "Influence of gradient estimation on clod identification on a seebed digital elevation model," Environmental & Engineering Geoscience, vol. 17, pp. 337-352, 2011. [3] R. Dusséaux, E. Vannier, O. Taconet and G. Granet, "Study of backscatter signature for seedbed surface evolution under rainfall - Influence of radar precision," Progress in Electromagnetics Research, in press. [4] M. Zribi, A. Le Morvan-Quemener, M. Dechambre, N. Baghdadi, "Numerical backscattering analysis for rough surfaces including a cloddy structure," vol. 48, no. 5, pp. 2367-2374, May 2010