Characterization of Oligocene Sands and Gravels, Wad Ghoweiba, Northwest Gulf of Suez, Egypt, Using Spectral Signature and Principal Component Analysis of Terra Aster Images

The Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) is an advanced multi-spectral imager that was launched on board NASA's TERRA Spacecraft in December 1999. ASTER covers a wide spectral region with 14 bands from the visible to thermal infrared with high spatial, spectral and radiometric resolutions. An additional backward looking near-infrared band provides stereo coverage. The spatial resolution varies with wavelength; 15 m in the visible and near infrared (VNIR, 3 bands), 30 m in the short wave infrared (SWIR, 6 bands), and 90 m in the thermal infrared (TIR, 5 bands). Each ASTER scene covers an area of 60 X60 km. In the present study the 3 VNIR and the 6 SWIR bands have been used to discriminate the Oligocene sands and gravels from the surrounding rock units that are exposed near the mouth of Wadi Ghoweiba, at the northwestern side of the Gulf of Suez. Spectral reflectance curves of 9 rock units were extracted from ASTER data and were subsequently examined. The spectral reflectance curve for the Oligocene sands and gravels shows a spectacular unique behavior compared to the spectral reflectance curves of the other 8 rock units. Based on the spectral reflectance behavior, ASTER bands 1, 2 and 5 are found to be the most suitable bands for discriminating the Oligocene sands and gravels from the surrounding 8 rock units. Therefore, the highest percentages of information of these bands were quantitatively extracted from the principal component (PC) analysis using Eigen matrix. The highest percentages of information contributed by bands 1,2 and 5 were found to be in PC2, PC6 and PC9, respectively. A principal component color image (PC2, PC6 and PC9 in B, G, R) showed the Oligocene sands and gravels in a characteristic orange color. This result was verified using the available geological maps followed by field check. The method used here is effective for exploring new sites of the Oligocene sands and gravels that are being extensively used as raw materials for concrete and other building purposes