A new method of drainage network extraction using SAR radar images: a case study of Djanet (Algeria)

Abstract

An oriented, connected, acyclic graph can be used to represent a hydraulic network. We can consider the network as a set of arcs and nodes. Our research work entails extracting a drainage network from satellite images by preprocessing the data to have features that will compute the minimum cost function. In this paper, we propose an approach to obtain a drainage network based on information theory and mathematical morphology. Our idea is to consider a drainage network as a set of segments crossed two by two in a node. The best network segments minimize the variance calculated in the directions of propagation, maximize the covered geodesic distance, and are most rectilinear. To get results, we have applied these treatments: filtering, segmentation, minimization of a cost function and mathematical morphology operators. Our proposed approach gives excellent results of high quality and quantity. However, there are still some problems in this study, especially the choice of an adaptive index of linearity that differentiates the drainage network from the surrounding environment. Existing methods use a DEM to extract drainage networks, because they indicate networks where water circulates (3D topography). By contrast, in this study, we use images from ERS-1/2 satellites in order to exploit radar waves, thanks to their penetrating capacity and sensitivity to the dielectric and geometric properties of the land. The temporal and spatial resolutions of the SAR images also allow a historical monitoring of hydraulic networks because of the continual availability of SAR data.