A COMPARATIVE HYPERSPECTRAL STUDY OF HYDROCARBON SEEPAGES NEAR UVALDE, TEXAS

The purpose of this study is to use high resolution, ground-based hyperspectral imagery to map and study the distribution and alteration patterns of migrated hydrocarbons in the Anacacho Limestone. Both Visible Near Infrared (VNIR) and Shortwave Infrared (SWIR) scans were obtained from the inactive Dabney asphaltic limestone pit mine near Uvalde, Texas. This study seeks to use comparative methods of hyperspectral pixel composition classification in order to maximize the advantages of hyperspectral data acquisition while minimizing the limitations. Techniques compared in this study include the Mixture-Tuned Matched Filtering (MTMF), Spectral Angle Mapper (SAM), and Linear Spectral Unmixing methods of classification. Data were processed with band subsetting, spectral smoothing, and Minimum Noise Fraction (MNF) transformation, with endmembers derived from laboratory-obtained spectroradiometer data and training pixels identified through MNF analysis. Classification maps show moderately cohesive high-asphalt seepages in discontinuous layers throughout the limestone matrix. The outcrop is punctuated by thin, continuous bentonite ash layers reflecting volcanically active periods of deposition. Utilizing ground-based hyperspectral scans allows for fast and continuous mapping of the distribution of target deposits at high resolution, although somewhat lower precision than discrete physical sampling.