The CRISM Analysis Toolkit (CAT): Overview and Recent Updates

Introduction: The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) Analysis Toolkit (CAT) is an IDL/ENVI-based software system for analyzing and displaying data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). We will describe CAT’s capabilities and discuss recent updates to CAT’s map projection and summary product generation functions. CRISM: CRISM [1] is a hyperspectral imaging spectrometer onboard the Mars Reconnaissance Orbiter. It covers the visible-near IR spectral range 0.4-3.9 μm at ~10 nm spectral resolution. The spectrograph consists of two channels, the VNIR channel covering 0.4-1 μm, and IR covering 1-3.9 μm. Both spectrographs are fed by a common telescope, with a dichroic beansplitter dividing incoming light between the short and long wavelength channels. Each channel employs a two dimensional array detector, imaging the entrance slit along one dimension and dispersing spectra along the other. Both channels acquire imagery with 640 pixels in the spatial dimension. The visible channel returns up to 107 spectral bands, while the IR channel returns up to 438 bands. Spectral sampling is 6.55 nm, and the effective bandpass including optical effects varies from ~9 nm in the visible to 17 nm at the longest IR wavelengths. CRISM data are acquired in either a pushbroom configuration, with the entrance slit oriented perpendicular to the ground track, or in targeted mode, where the instrument is gimbaled in the along-track direction to reduce the apparent ground speed of the slit image. In both cases, multiple frames are acquired to build an “image cube” with 1 spectral and 2 spatial dimensions. Pushbroon (mapping) mode data are acquired by staring at nadir, acquiring image frames at 15 or 30 Hz, and coadding pixels along-slit to achieve spatial sampling of 100 or 200 m square pixels over long swaths. Mapping modes include MSP, HSP, HSV, MSW, and MSV, which return different combinations of spectral bands. Full resolution targeted observations (FRT, FRS) attain spatial sampling up to 18 m from MRO’s ~370 km orbital altitude, over a butterfly-shaped ground footprint roughly 10 km wide. Reduced resolution targeted modes (HRL, HRS) provided lower data volume by coadding pixels. Two additional targeted modes result in non-square pixels (ATO, ATU). The observing parameters for different types of observations pointed at Mars' surface are summarized in Table. 1. Table 1. Summary of CRISM Mars surface observation types. Class Type Spatial Sampling (m/pxl) Mapping/ Targeted VNIR Bands IR Bands