Contribution of Remote Sensing to Groundwater Prospecting in Fractured Environments: The Case of Pointe-Noire (Southern Republic of Congo)

Abstract

This study focuses on the city of Pointe-Noire, in the south-west of the Republic of Congo, where invoicing is more or less developed. Its main objective is to map fractured environments in order to improve groundwater prospecting by combining Landsat 8 OLI & TIRS images with SRTM data. To achieve this objective, we collected a Landsat 8 OLI & TIRS scene dating from February to August 2020 from the USGS database and ten (10) SRTM tiles from the JAXA database. All techniques applied to Landsat 8 OLI and TIRS images (PCA, textural analysis, band ratio, normalised indices, Sobel, Prewitt and Yesou directional gradient filters) using ENVI 5.3 resulted in the enhancement of linear structures contained in the raw images, extracted using GEOMATICA, enabling better mapping of geological hazards in QGIS 3.16. The linear map obtained after automatic extraction is very dense and contains linear features of varying sizes and orientations. After submitting the lineaments obtained from automatic extraction to Pareto’s statistical test, followed by their merging with the lineaments obtained from manual extraction, the various linear structures were validated by adapting their orientations to the tectonic context of the area and superimposing them of the existing geological map and topographical map (from Google Earth pro), this led to the creation of the final lineament map of the study area, comprising 750 lineaments. Analysis of the lineament spacing and texture revealed the homogeneity of the geological formations in the study area, a comparison of fracturing densities between the 2015 data (more specifically the 1980 data used) and those from our study shows, on the one hand, the dominance of NW-SE and E-W orientations in the area, thus influencing the surface hydrographic network and groundwater recharge and, on the other hand, allows us to assess the evolution of tectonic activity. The results of this work contribute to a better understanding of fractured environments in the city of Pointe-Noire.