MAPPING OF SPECTRAL VARIATIONS ON THE SURFACE OF MARS FROM HIGH-SPECTRAL-RESOLUTION TELESCOPIC IMAGES

We analyze a high spectral resolution (R similar or equal to 200) visi ble and near infrared (0.44-1.02 mu m) telescopic spectral image of Ma rs to explore surface material variations across the observed face of the planet, which is centered on Sinus Meridiani. Two independent anal ysis methods are employed, linear mixture modeling and supervised spec tral pattern classification with an artificial neural network. Four en dmember type regions are identified with linear mixing. Further refine ment is achieved with the nonlinear neural network classification algo rithm, separating eight units of geological significance. Differences in spectral features among the mapped units are characterized. Among t he medium- to high-albedo units northern lowlands typified by Chryse P lanitia show far less evidence of bulk crystalline hematite than weste rn Arabia dr any other highland regions. The relationship of these bri ght units to the globally distributed aeolian dust is not yet clear. W ithin our image, low-albedo regions with the most pronounced crystalli ne hematite signature primarily correlate with the classic ''dark regi ons,'' with the exception of Acidalia Planitia. Spectral evidence for pyroxenes also correlates well with most of the classic low albedo reg ions, but again, Acidalia Planitia is the major exception. Significant spectral anomaly is also found in an equatorial region, Deucalionis R egio. A companion paper in this issue discusses the soil properties of Deucalionis. Our data and analysis support a compositional trend that is consistent with the global geologic crustal dichotomy of Mars, nam ely that the younger northern lowlands contain less bulk crystalline h ematite than southern highlands. (C) 1996 Academic Press, Inc.