Digital Image Processing of Landsat7 data and GIS Application for Geological Investigation in Jebel Erba Area, Red Sea Hills, NE Sudan A

Abstract

ABSTRACT Digital image processing and Geographic Information System techniques, together with a limited reconnaissance ground truthing, have been used to investigate the geology of the area around J. Erba and J. Oda of the Sudanese Red Sea Hills (RSH). The methodology fulfilled and the procedures followed during this study enabled the establishment of geodatabase named GeoRSH and the production of two geological maps of scale 1:2§0,000. The area of study occupies the central part of RSH of Sudan that belongs to the Nubian Sector of the Arabian-Nubian Shield (ANS). It forms part of the Gebeit terrain that is known to be created among the other four terrains of NE Sudan (Tokar, Heya, Gabgaba and Gert) during the Pan-African event (950-500Ma) due to subduction-related processes and collisional tectonics and sutured together by dismembered-ophiolite belts and major shear zones. The geology of the area comprises high-grade gneisses, volcanosedimentaiy sequences metamorphosed in the greenschist facies, all intruded by syn and syn-to-late orogenic calc-alkaline intrusives and post-orogenic alkaline bimodal gabbro-granite complexes. The coastal plain is geologically characterized by Cenozoic siliciclastic and shallow marine rift- related sedimentary sequences. Pliocene-Pleistocene is ‘represented by the thick older gravel unit a11d the emergent linear reef terraces. Several digital image processing techniques have been implemented to enhance the Landsat7 ETM+ digital satellite data. A Digital mosaic that covers almost all the Sudanese Red Sea Hills has been created using nine Landsat7 scenes. A 3x3 high-pass filtered color composite image with a central coefficient of 16 proves to create the most optimized images that appear relatively brighter and more saturated. Four color composite triplets of band ratio images; B3/B5, B3/Bl, B5/B7; B5/B7, B5/B4, B3/B1; B5/B7, B5/Bl, (B3/B4)(B5/B4) and B5/B7, B3/Bl, B4/B3, have been composed to assist geological mapping. Directed band ratioing of the ratio color composite (B5/B7, B5/B4, B3/Bl) resulted in a well enhanced image that is characterized by satisfying saturated colors, strong retention of topographic expression and well pronounced lithological discrimination. Unstandardized and standardized principal component analyses have been done using the six reflected bands as well as a four selected bands. II