CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) on MRO (Mars Reconnaissance Orbiter)

Abstract

CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) is a hyperspectral imager that will be launched on the MRO (Mars Reconnaissance Orbiter) spacecraft in August 2005. MRO's objectives are to recover climate science originally to have been conducted on the Mars Climate Orbiter (MCO), to identify and characterize sites of possible aqueous activity to which future landed missions may be sent, and to characterize the composition, geology, and stratigraphy of Martian surface deposits. MRO will operate from a sun-synchronous, near-circular (255x320 km altitude), near-polar orbit with a mean local solar time of 3 PM.CRISM's spectral range spans the ultraviolet (UV) to the mid-wave infrared (MWIR), 383 nm to 3960 nm. The instrument utilizes a Ritchey-Chretien telescope with a 2.12° field-of-view (FOV) to focus light on the entrance slit of a dual spectrometer. Within the spectrometer, light is split by a dichroic into VNIR (visible-near-infrared, 383-1071 nm) and IR (infrared, 988-3960 nm) beams. Each beam is directed into a separate modified Offner spectrometer that focuses a spectrally dispersed image of the slit onto a two dimensional focal plane (FP). The IR FP is a 640 x 480 HgCdTe area array; the VNIR FP is a 640 x 480 silicon photodiode area array. The spectral image is contiguously sampled with a 6.6 nm spectral spacing and an instantaneous field of view of 61.5 µradians. The Optical Sensor Unit (OSU) can be gimbaled to take out along-track smear, allowing long integration times that afford high signal-to-noise ratio (SNR) at high spectral and spatial resolution. The scan motor and encoder are controlled by a separately housed Gimbal Motor Electronics (GME) unit. A Data Processing Unit (DPU) provides power, command and control, and data editing and compression.CRISM acquires three major types of observations of the Martian surface and atmosphere. In Multispectral Mapping Mode, with the gimbal pointed a planet nadir, data are collected at frame rates of 15 or 30 Hz. A commandable subset of wavelengths is saved by the DPU and binned 5:1 or 10:1 cross-track. The combination of frame rates and binning yields pixel footprints of 100 or 200 m. In this mode, nearly the entire planet can be mapped at wavelengths of key mineralogic absorption bands to select regions of interest. In Targeted Mode, the gimbal is scanned over ±60°f rom nadir to remove most along-track motion, and a region of interest is mapped at full spatial and spectral resolution. Ten additional abbreviated, pixel-binned observations are taken before and after the main hyperspectral image at longer atmospheric path lengths, providing an emission phase function (EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects. In Atmospheric Mode, the central observation is eliminated and only the EPF is acquired. Global grids of the resulting lower data volume observation are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties.

Color imaging of Mars by the High Resolution Imaging Science Experiment (HiRISE)

“…For example, mafic minerals (e.g., olivine, pyroxene, or calcic plagioclase feldspar) or a diversity of hydrated minerals (e.g., phyllosilicates) stand out in the 3-color data. The best way to understand what the HiRISE colors indicate about composition is to compare them directly to products derived from the $18 m/ pixel CRISM data (Murchie et al, 2007, see http://crism.jhuapl.edu/).…”

Rare jarosite detection in crism imagery by non-parametric Bayesian clustering

“…Each pixel is projected onto the top ten principal components of the image I/F data. I/F data is derived from the radiance data by computing the ratio of the radiance to the solar irradiance at Mars [13]. Data points in the following presentation refers to pixels represented as points in this 10-dimensional vector space.…”

Retrieval of Mineral Abundances of the Delta Region in Eberswalde, Mars

“…In this paper, we used one targeted mode observation, which has a full spatial resolution (FRT) of 18 m/pixel, and a spectral sampling of 6.5 nm/channel (Murchie et al, 2007).…”