Comparison among the natural radioactivity levels, the radiogenic heat production, and the land surface temperature in arid environments: A case study of the El Gilf El Kiber area, Egypt

The El Gilf El Kiber area is one of the most promising areas for urban growth and reclamation projects in the southwest of Egypt. In the study area, the lithological units vary in age from Precambrian (mainly granite) to Quaternary (mainly sand sediments). The analysis of airborne magnetic and gamma-ray spectrometry data was incorporated into that of the remote sensing data (Landsat-8). The integrated analysis was used to detect the lithological distributions and to delineate the subsurface basement rocks that control the radioactivity in the study area. It was also used to determine the relationship between radiogenic heat production (RHP) and land surface temperature (LST) that was retrieved from the Landsat-8 thermal infrared sensor (TIRS) data. The output of the principal component analysis (PCA) of Landsat-8 Operational Land Imager (OLI) data is a false-color map (PC1, PC2, and PC3 as red, green, and blue, respectively) displaying the various lithological units in the study area. The LST map, calculated from Landsat-8 TIRS data, shows that the surface temperatures range from approximately 41 to 53 °C. The highest concentrations of eU, eTh, and K in the area were 25 ppm, 121 ppm, and 7.8%, respectively. The RHP values ranged from 1.1 μW/m³ to 15.1 μW/m³. These relatively high anomalies are associated with basement outcrops and the sedimentary rocks overlying shallow basement rocks. The total horizontal derivative (THD) of the magnetic data delineates the horizontal extension of the basement rocks. The Curie point depth (CPD), estimated from magnetic data, ranges from 35.5 km to 41.0 km. The results also exhibited geothermal gradients ranging from 16.10 °C/km to 14.14 °C/km, and heat flow ranges from 35.4 mW/m² to 40.8 mW/m². It was evident after comparing that the RHP and LST maps exhibited the same features as the gamma-ray spectrometric maps. Moreover, the areas around the basement rocks exhibited higher radioactivity, RHP, and temperature than the basement rocks themselves.