ASTER SATELLITE REMOTE SENSING: A SIGNIFICANT LEAP IN FACTUAL GEOLOGIC MAPPING

The ASTER multispectral satellite offers unprecedented opportunities for factual geological mapping from space. Most geologic maps are not factual, they usually represent formations which are a combination of lithologies. Formation maps serve few people accept for geologists. Formations change according to new data and concepts, but lithology does not. The ability to map spatially continuous lithologies, even with some vegetation is a major geologic tool. With the increased spectral bands of ASTER the concept of resolution is a different paradigm. The smallest sample or square seen on an enlarged image is a pixel. However, components smaller than a pixel can be identified if the signal to noise is sufficient and the component has a unique spectra. Of course no tool is perfect and the images should be considered as probability maps. With field checking and confidence of the terrane, spectral signatures can be extrapolated and interpolated to make coherent geological maps.

Many rock types can be distinguished visually on airphotos once the tone, texture and color have been established. However, many rocks change in the visible part of the spectrum due to a variety of geological reasons. Limestone, as an example, may be light or dark. Contact metamorphism may change the color, or tone even though the composition remains essentially calcium carbonate. Increased spectral bands can provide improved identification on the composition of materials and provide increased efficiency for producing factual geologic maps.

Wavelengths longer than the visible part of the spectrum can map important spectral characteristics of geologic materials. The Short Wave Infra Red (SWIR) can distinguish clay, carbonate and sulfate species. The Thermal Infra Red can distinguish between silicates.

This paper will provide examples of mapping geologic materials from the ASTER satellite in conjunction with ground observations and field spectra.