Photometric Properties of Phobos Derived from CRISM and OMEGA Observations
Abstract
The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instruments have recently acquired disk-resolved, hyperspectral image cubes of Mars’ satellite Phobos. These observations cover a wavelength range from 0.4 - 5µm and have spatial resolutions ranging from 200m/pixel to 2300m/pixel. The six OMEGA observations and the one CRISM observation were acquired at a variety of viewing and lighting geometries, and they provide coverage of Phobos over phase angles ranging from 30° to 100°. We have used published shape models of Phobos along with knowledge of instrument positions at the time of the observations to determine the incidence, emergence, and phase angle for each pixel in the CRISM and OMEGA observations. The effects of lighting and viewing geometries on the measured I/F values may be understood by approximating the photometric properties of the surface using a Hapke model. We have used the six OMEGA observations to solve for the wavelength-dependent Hapke parameters that create the best-fit global-average model for the surface of Phobos. The data are best modeled by a phase function that is backscattering and fairly constant across all observed wavelengths, which is typical of a dark surface. The average single scattering albedo increases monotonically with wavelength until ~2.5µm, at which point thermally emitted contributions become increasingly relevant. We model thermal contributions to total measured radiance at wavelengths >2.5 µm and use this to estimate maximum daytime surface temperatures between 300-350K. There are some deviations from global average behavior across the surface of Phobos, and we will discuss the locations and potential causes of these variations. We have also applied our knowledge of the global average photometric behavior of Phobos to compare overlapping locations in the CRISM and OMEGA images that were acquired under different lighting and viewing conditions. Phobos observations are ideal for a direct comparison between the two instruments due to the absence of spatially and temporally variable atmosphere in the data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.P52B..01F
- Keywords:
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- 5460 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Physical properties of materials;
- 5464 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Remote sensing;
- 6055 PLANETARY SCIENCES: COMETS AND SMALL BODIES / Surfaces;
- 6230 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS / Martian satellites