Lithological mapping in the Central Eastern Desert of Egypt using ASTER data

This study presents new methods for using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for lithological mapping in arid environments. Visible, near-infrared and short wave infrared reflectance data have been processed and interpreted for mapping ophiolitic and granitic rocks at Fawakhir, Central Eastern Desert of Egypt. Image spectra show that the ophiolitic lithological members (serpentinites, metagabbros, and metabasalts), grey granite, and pink granite have absorption features around spectral bands 3, 6, and 8. ASTER band ratios ((2+4)/3, (5+7)/6, (7+9)/8) in RGB are constructed by summing the bands representing the shoulders of absorption features as a numerator, and the band located nearest the absorption feature as a denominator to discriminate between different ophiolitic and granitic rocks. The results show that ASTER band ratios ((2+4)/3, (5+7)/6, (7+9)/8) in a Red–Green–Blue (RGB) color combination identifies the ophiolitic rocks (serpentinites, metagabbros, and metabasalts) much better than previously published ASTER band ratios analysis. A Principal Component Analysis (PCA) was also implemented to reduce redundant information in highly correlated bands. PCA (5,4,2) in RGB enabled the discrimination between ophiolitic rocks and between the grey granite and pink granite. Thus, this technique is also recommended for mapping different types of granitic rocks. A new up-to-date lithologic map of the Fawakhir area is proposed based on the interpretation of ASTER image results and field verification work. It is concluded that the proposed methods have great potential for lithological mapping in arid and semi arid regions with similar climate and rock units as the Central Eastern Desert of Egypt.