VARIATION OF THE 3-MU-M ABSORPTION FEATURE ON MARS - OBSERVATIONS OVER EASTERN VALLES-MARINERIS BY THE MARINER-6 INFRARED SPECTROMETER

A new approach for calibration of the shortest wavelength channel (1.8 to 6.0 mu m) of the Mariner 6 infrared spectrometer was derived. This calibration provides a new description of the instrument response fun ction from 1.8 to 3.7 mu m and accounts for the thermal contribution t o the signal at longer wavelengths. This allows the two segments from 1.8 to 6 mu m to be merged into a single spectrum. The broad water of hydration absorption spans these two segments and is examined in these merged spectra using a method of band integration. Unlike previous an alyses which rely on ratios at two wavelengths, the integration method can assess the band strength independently from the albedo in the nea r infrared. Spectra taken over the eastern end of the Vadles Marineris are examined for variations of the band-integrated value, and three d istinct clusters are found. Within the estimated uncertainty, two clus ters (both low and high albedo) have approximately the same integrated band depth. The third cluster (medium albedo) has an integrated band depth about 10% higher. This difference cannot be systematically attri buted to either surface or atmospheric parameters and suggests variati on in the amount of water either chemically or physically bound in sur face materials. Approximately one-half of the high integrated band dep th cluster is associated with chaotic terrain at the source of outflow channels, the other half occurs over lower inertia plains adjacent to chasmata. This suggests both surface physical properties and mineralo gy as well as water in exchange with the atmosphere contribute to the 3-mu m bound water absorption.