Space Shuttle

The first detection of clay and carbonite-bearing minerals from Earth orbit has been confirmed by JPL and U.S. Geological Survey scientists who flew an infrared radar exper iment on NASA's second space shuttle flight in November 1981.

The new results, from the Shuttle Multispectral Infrared Radiometer (SMIRR), are reported in the Dec. 3, 1982, edition of Science magazine.

Identification of the minerals, detected by their spectral reflectances in the infrared portion of the spectrum, represents the first time minerals other than limoite (a common suite of iron-bearing minerals) have been identified by spacecraft sensor.

Previously, identification of these minerals was possible only by using laboratory sampling techniques.

SMIRR identified limestone (a carbonate-bearing rock), kaolinite (a hydrous, aluminum silicate clay mineral), and possibly montmorillonite (a hydrous silicate of aluminum) from orbit. Certain types of clay minerals are commonly associated with certain types of mineral deposits, and are commonly used as guides in ore exploration.

SMIRR results showed that the sensor's spectral resolution is superior to all previous multispectral sensors flown in space.

Experimenters used SMIRR data taken between Kharga and Aswan, Egypt, to determine the instrument's success in identifying different minerals from orbit. The sparsely vege tated region with varied, exposed geological units, was well mapped and was therefore used as ground-truth segment.

The SMIRR system used 17.8-centimeter (7-inch) diameter telescope with 10 channels ranging in wavelength from the visual red through the shortwave infrared.

Channels used on SMIRR were chosen after JPL and USGS scientists tested different rocks and soils with field spectrometers to determine which bands could best differen tiate between different classes of rocks.

SMIRR's extremely narrow spectral resolution enabled it to distinguish subtle reflectance variations in different clays.

For example, the difference between montmorillonite and kaolinte lies chiefly in the extreme slope of the reflectance curve for kaolinte in the wavelength region from 2.1 to 2.2 microns. NASA's Skylab and Landsat observations and all of the aircraft sensors currently in use have broad sensor spectral bandwidths that cannot detect such subtle reflectance difference.

SMIRR's results will aid in designing future orbital systems for mapping geologic units from space.

Principal investigators of the experiment are Dr. Alexander F.H. Goetz of JPL and Dr. Lawrence Rowan of the USGS, Reston, Va.

SMIRR was developed for NASA's Office of Space and Terrestrial Applications.

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