The principal industrial users of land-observation satellite systems are several hundred oil and gas, mining, and engineering or environmental companies worldwide. The primary system used is Landsat/MSS (Multi-spectral Scanner), the data from which are now used operationally as an improved geologic mapping tool to help direct more expensive geophysical surveying and drilling, thus assisting exploration decision making. Use is also made of SKYLAB photography, SEASAT and SIR-A (Shuttle Imaging Radar) radar, and the new Landsat/TM (Thematic Mapper) data. Industrial use will soon be made of data from France's SPOT (1985), India's IRS (1986), the European Space Agency's ERS (1987), Canada's RADARSAT (1990), and Japan's JERS (1991) remote-sensing satellites.

Data representing these systems were evaluated during the 7-yr, $10-million joint Geosat Committee-NASA/JPL Test Case Program. Begun in 1977, the objective of this program was to assess, in known geologic areas, the value of existing and potential satellite remote-sensing methods for petroleum exploration, mineral exploration, and engineering geology applications. The published study includes an evaluation of sensors, data-processing techniques, and interpretation methods.

Some conclusions include the following. The Landsat/TM combines the visible and very near Infrared (IR) spectral bands of the MSS, with the shortwave IR 1.6-2.2 µm band region, which can indicate the presence of clays, carbonates, and sulfates. This system allows greater rock and soil discrimination than the MSS alone. Similarly, the TM bands demonstrate numerous, as yet little understood, geobotanical anomalies clearly related to leaking gas over oil and gas deposits. Landsat data, as well as that

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resulting from future satellite and airborne systems, must be utilized in an interactive manner with field geology and spectrometer measurements and computer-processing techniques to obtain the optimum integrated geologic, geophysical, and geochemical information contained in these data. Successful applications of satellite remote sensing requires a realistic understanding of the earth's surface and its relationship to the exploration models being used. As originally recommended by the Geosat Committee, the addition of the shortwave IR TM spectral bands, higher spatial resolution (10-20 m), and Synthetic Aperture Radar in the present and planned systems, combined with the Landsat/MSS system, will substantially improve these systems as a whole for more efficient geologic mapping and im roved exploration success worldwide.

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