Atmospheric Science using CRISM EPF Sequences

Near the end of September 2006, the MRO/CRISM (Compact Reconnaissance Imaging Spectrometer for Mars; Murchie et al., 2006, JGR, in press.) will acquire its first observations of Mars. MRO's Primary Science Phase beginning in early November. One of CRISM's investigations is characterization of seasonal variations in dust and ice aerosols and trace gases using a systematic, global grid of hyperspectral measurements of emission phase functions (EPFs) acquired repetitively throughout the Martian year. EPFs will also be obtained as part of each of approximately 5000 "targeted" observations of surface geologic features. EPF measurements allow accurate determination of column abundances of water vapor, CO, dust and ice aerosols, and their seasonal variations (e.g., Clancy et al., 2003, 108(E9), 5098). EPFs are measured using eleven superimposed images within which the slit field-of-view is swept across a target point on the Martian surface. When EPFs are taken as part of a global grid, 10x spatial pixel binning will be used in all of the images, providing data at 150-200 m/pixel. In the targeted observations, the central image will be obtained at either full resolution or with 2x binning (15-38 m/pixel). In all cases, hyperspectral data (545 wavelengths) will be taken during each of the 11 superimposed scans. There are two types of global EPF grids, one with better temporal sampling and one with better spatial sampling of the atmosphere. The "atmospheric monitoring campaign" consists one Martian day of pole-to-pole EPF's every ~9°\ of solar longitude (Ls). There is sufficient time for 8 EPFs in an orbit, one approximately every 22°\ of latitude. Alternate orbits (projected onto the planet) are offset in latitude by about 11°\ north or south to increase latitudinal resolution. Longitude spacing between the orbits is about 27°. The "seasonal change campaign" occurs approximately every ~36°\ of Ls. A grid similar to that executed during the atmospheric monitoring campaign is taken on 3 non-contiguous days over about 2 weeks, to provide a higher spatial density grid (longitude spacing about 10°) to monitor seasonal changes in surface material spectral properties, especially absorption and desorption of H2O. Every 3 orbits projected on the planet, the EPFs are offset by 0°, +8°, and -8°\ north or south to increase latitudinal resolution. Our presentation will discuss several aspects of the atmospheric analyses (optical depths, radiative properties, radiative transfer methodology) to be performed using the early-mission EPFs, with the primary focus being those EPFs planned for the end of September.