LITHOLOGIC MAPPING USING ADVANCED SPACEBORNE THERMAL EMISSION AND REFLECTION RADIOMETER (ASTER) DATA IN THE WHITE SANDS, NEW MEXICO REGION

Granite, marble, limestone, sandstone, rhyolite, and basalt were mapped using 19 ASTER scenes in the Rio Grande rift near White Sands, New Mexico. ASTER data consist of three 15-m, six 30-m, and five 90-m resolution bands in the 0.52 to 0.86-mm, 1.65 to 2.43-mm, and 8.13 to 11.65-mm wavelength regions, respectively. Each ASTER scene consists of nine reflectance bands in the 0.52 to 2.43-mm wavelength region, which were converted from radiance (Level_1B data) to reflectance data using atmospheric correction software, and five ASTER emissivity bands (AST_05 data) spanning the 8.13 to 11.65-mm wavelength region that were downloaded from the Eros Data Center. All mapped units were visually compared to a 1:500,000 geologic map for accuracy assessment.

Limestone, and intermediate- and mafic-volcanic rocks exhibit a 2.33-mm absorption feature because of CO₃ and Fe,Mg-OH, respectively. This absorption feature was mapped using a relative band depth absorption ratio (RBD) consisting of band 7 (2.26 mm) added to band 9 (2.395 mm) and divided by band 8 (2.33 mm; RBD8; (7+9)/8). Al-OH and H-OH absorption features indicative of muscovite, clay and gypsum-rich rocks were mapped using the relative band depth ratio band 4 (1.65 mm) added to band 7 (2.26 mm) and divided by band 6 (2.21 mm; RBD6; (4+7)/6). Quartz-rich rocks exhibit a 9.2-mm absorption feature, which was mapped using a band ratio of band 14 (11.3 mm) divided by band 12 (9.1 mm) (BR14/12). RBD8 images deliniate Tertiary basalts and intermediate volcanic rocks and Pennsylvanian limestones. The RBD6 image highlights Pennsylvanian evaporite beds and Precambrian, muscovite-rich granites and some possibly altered or muscovite-rich Tertiary rhyolitic rocks. Precambrian quartzites, Cambrian and Pennsylvanian sandstones are highlighted in the BR14/12 image.

A band ratio composite image in which red = BR14/12, green = RBD6 and blue = RBD8 was used to identify rock types. The band ratio composite image illustrates quartz-rich sandstones as red, muscovite-rich granites, and evaporite-rich rocks as green, and limestones, basalts and intermediate volcanic rocks as blue. The composite image was particularly useful for mapping rock-types that contained mixed mineralogy such as muscovite-rich quartzites and clay-rich sandstones, which appear yellow in the image.