Identification and Characterization of Lowlands in the Ouaddai Region using Landsat and SRTM images

Abstract

Abstract: In arid and semi-arid zones, the use of lowlands has considerably increased in number and surface area, dueto the fertility of their soils and their hydromorphic character. The aim of this article is to identify and characterize lowlands in the Ouaddaï region using satellite imagery. The methodological approach is based, on the one hand, on the semi-automatic method that took into account vegetation indices (NDVI) and parameters (slope and water accumulation) generated from Landsat OLI TIRS and SRTM images. On the other hand, field surveys confirmed theresults of the spatial analyses. Analysis of the NDWI for 2022 clearly shows that high values in the range -0.18 to 0.59 areobserved almost everywhere in the mapped area. The NDVI calculation enabled us to estimate the water content of thefoliage of the vegetation cover, which is between -0.15 and 0 for the lowlands in the dry season. A reclassification of slopes enabled us to categorize slopes (1% to 3%). The reclassification of slopes enabled us to distinguish a broad plain in almost the entire area of the region, rich in lowlands. The field method enabled us to categorize the lowlands: primary lowlands with intense rural activities (Ouadi Biteha, Ouadi Hamra, Ouadi Chok etc.) and secondary lowlands where activities are limited. Keywords: Identification, Landsat, SRTM, Remote sensing, Biogeography, Ouaddaï, Chad.