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D.R. Klassen (Rowan University), J.F. Bell III (Cornell University)
We gathered images using the 256\times256 InSb array NSFCAM at the NASA Infrared Telescope Facility during and around the 1999 opposition. These images cover a spectral range from 1.5 to 4.0 \micron\ at a spectral resolution of about 100. The images presented here cover the early Martian northern summer season (LS = 91 - 129\arcdeg\ ).
The images we calibrated to radiance factor using star images of the G2IV star BS5409, which was at similar airmass to Mars. Data were taken close in time so as to minimize errors due to any changes in local relative humidity. In general the bright regions have peak radiance factors of 0.5 to 0.6 at 2.25\micron\ and 0.3 to 0.4 at 3.5\micron; dark regions have radiance factors of 0.15 to 0.2 at 2.25\micron\ and 0.1 to 0.15 at 3.5\micron. These are consistent with our previous work with images from the 1995 opposition.
Using band ratio techniques previously developed, we can locate and discriminate the composition of Martian volatiles. In general we find that these maps show the northern summer cloud belt and indicate that it is composed only of H2O ice. There is also some indication that clouds in the southern hemisphere may be composed of CO2 ice. We also see indication of the residual, water ice, north polar cap but, as expected, no sign of the polar hood clouds seen in the northen spring season.
We will also present preliminary results from our previously developed principal components analysis and linear mixture modeling. This technique is more robust at tracking volatile spectral signatures as it is less affected by local mineralogic spectral signatures.
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