APPLICATION OF ASTER BAND-RATIO IMAGES FOR GEOLOGICAL MAPPING IN ARID REGIONS: THE NEOPROTEROZOIC ALLAQI SUTURE, EGYPT

The Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) data is a multi-spectral imaging system that was launched in 2000 on the Terra Satellite. It has14 bands in different parts of the electromagnetic spectrum; 3 in the visible and near infrared (VNIR) with 15m spatial resolution, 6 in short wave infrared (SWIR) with 30m spatial resolution, and 5 in the thermal infrared (TIR) with 90m spatial resolution. Compared to the Enhanced Thematic Mapper Plus (ETM+), ASTER has better spectral range and better spatial resolution in the VNIR. ASTER false-color and band-ratio images are compared to equivalent ETM+ images that has proven to be useful for geological mapping in arid regions specially the identification of geological materials. We used remote sensing data covering part of the Neoproterozoic Allaqi Suture in southern Egypt to evaluate the usefulness of ASTER false-color and band-ratio images for geological mapping in arid regions. The Allaqi suture is defined by ophiolites, shelf sediments, arc volcanics and granitoids that are deformed by S-verging fold and thrust belt. 7-3-1 ASTER image is equivalent to 7-4-2 ETM+ image (ARAMCO combination); this ASTER image is useful for outlining lithological units as well as structural and morphological features. 4/7-4/1-2/3*4/3 ASTER image is equivalent to 5/7-5/1-3/4*5/4 ETM+ (Sultan’s combination) and 4/7-3/4-2/1 ASTER image is equivalent to 5/7-4/5-3/1 ETM+ image (Abram’s combination). Both ASTER band-ratio images are very useful in defining lithological units specially serpentinites, granites and marbles. In addition, we qualitatively evaluated spectral curves for rock types common in the Allaqi suture to introduce new ASTER band-ratio images to be used for geological mapping in arid regions. 4/1-3/1-12/14 ASTER image is recommended because of the presence of diagnostic spectral features in these bands. This band-ratio image had the highest optimum index factor (OIF) compared to other selected ASTER band-ratio images. Moreover, the 4/1-3/1-12/14 ASTER image incorporates bands from the VNIR, SWIR and TIR regions of the electromagnetic spectrum. Visual geological interpretation of this band-ratio image is in good agreement with published regional geological maps and field data and detailed geological mapping conducted by us.