REMOTE SENSING OF THE TRES VIRGENES AND PUERTECITOS VOLCANIC REGIONS, BAJA CALIFORNIA, MEXICO, USING THE MASTER AIRBORNE MULTI-SPECTRAL SENSOR

Multispectral airborne data from the NASA MODIS/ASTER simulator (MASTER) have been collected for two volcanic areas in Baja California, Mexico: the Tres Virgenes Volcanic Field, and the Puertecitos Volcanic Province. The Tres Virgenes Volcanic region, on the east coast of Baja California (27° 30'N) includes four volcanic systems--La Reforma Caldera to the east, Sierra Santa Ana Caldera to the north, Volcan El Azufre, and Volcan La Virgen to the south. The Puertecitos ignimbrite province (within the latitude zone 30° 30'N to 29° 55'N) spans central Baja California, and includes Isla San Luis. It exhibits rhyolitic/dacitic welded tuffs, rhyolite dome fields, intermediate composition volcanoes, and small-volume local mafic lavas. The MASTER data have a spatial resolution of ~5 meters/pixel and a swath width of ~2 km, with 11 visible-near infrared (VNIR) bands, 14 shortwave infrared (SWIR) bands, 15 mid-infrared bands, and 10 thermal infrared (TIR) bands. The spectral breadth of MASTER provides ample capability for detailed mapping of lithologies and mineral deposits. The TIR data have been atmospherically corrected using a radiative transfer algorithm (MODTRAN 3.5) within the WINVICAR software, driven with National Center for Environmental Prediction (NCEP) atmospheric profile data. TIR data were subsequently converted to emissivity (using the "alpha residuals" algorithm within WINVICAR) and compared to lab spectral data of field samples. The resulting MASTER emissivity images show regional variations in wt. % SiO₂, an important factor in distinguishing among the mafic-to-silicic members of this highly variable igneous suite. The VNIR-SWIR data have been processed with ENVI/IDL software to identify endmember spectra, utilizing the Minimum Noise Transformation, the Pixel Purity Index, and various classification techniques within ENVI. Endmembers determined by this process are then compared to field spectral data from regional validation sites for petrological identification and radiometric accuracy. Such mineralogical and petrological classifications and wt. % SiO₂ maps, in concert with field investigations, greatly increase our understanding of the relative ages, sequence, character, and distribution of recent volcanic activity in these two areas.