CRISM Web Site

This web site contains links to CRISM browse products, pre-PDS release data products, reference information, and resources related to CRISM data acquisition and analysis in support of MSL landing site selection.

(1) MRO Support of MSL Landing Site Selection:

The MRO project and the CRISM, HiRISE, and CTX science and operations teams support the MSL landing site selection process through the acquisition of high resolution panchromatic, multispectral, and hyperspectral orbital remote sensing data. The first MSL landing site selection workshop was held in May, 2006. At that workshop 30+ candidate landing sites were proposed by the Mars science community. Following the second MSL landing site selection workshop held in October 2007, the number of sites considered has been reduced to 10 sites. Here, we present CRISM observations of these 10 candidate sites in preparation for the 3rd MSL landing site selection workshop, to be held September 15-17, 2008.

(2) An Overview of CRISM Observations of the Candidate MSL Landing Sites:

The characteristics of the standard CRISM data acquisition modes and resulting data products are listed in the table below. The MSL candidate landing site survey campaign has resulted in the acquisition of at least one high quality Full Resolution Targeted (FRT) observation for each of the initial candidate sites. Many of the candidate sites are of great scientific interest irrespective of the MSL landing site selection process. As a result additional CRISM hyperspectral coverage is clustered around those sites with previously known mineralogical diversity.

CRISM also acquires multispectral survey data of the candidate landing sites as a natural consequence of the ongoing global mapping (multispectral survey) campaign, which have subsequently been made into a mosaic to generate an excellent overview of the mineral diversity at each one of these sites.

Type	Observation Mode	Spatial Resolution	Footprint Dimensions
FRT	Hyperspectral/Gimbaled (545 channels)	~20 m/pix	~10x10 km
HRL	Hyperspectral/Gimbaled (545 channels)	~40 m/pix	~10x20 km
HRS	Hyperspectral/Gimbaled (545 channels)	~40 m/pix	~10x10 km
MSW	Multispectral/Push-Broom (73 channels)	~100 m/pix	~10x45, 180, or 540 km
MSP	Multispectral/Push-Broom (73 channels)	~200 m/pix	~10x45, 180, or 540 km

(3) An Overview of CRISM Browse Images of Candidate MSL Landing Sites:

This early release of special products that will be archived to the Planetary Data System consists of map-projected versions of CRISM images. The many spectral channels in CRISM data have been condensed to 7 thematic color images that show spectral variations related to the types of minerals present. The seven versions of the data show:

The browse products are organized by candidate landing site. For each site there is the multispectral context map and one or more targeted observations designated by a product ID. For example, one of the targeted observations for the Nilli Fossae Trough site is FRT00008530. "FRT" specifies the type of observations from the table above, and "00008530" is the unique hexidecimal identifier or target ID associated with a target.

The targeted and multispectral map browse products for each site can be accessed by clicking on the site name or the site location in the table below. The targeted observation browse products are arranged in a matrix where each column is a different CRISM observation and each row is a different browse version of the image.

(3.1) Map Projection Standards for the Browse Products

Multispectral Mapping Browse Products: The multispectral browse product context maps span 3x3 degrees in planetary central angle. Each map is in an equirectangular projection at 256 pixels per degree, referenced to the nearest equator-ward 5 degree increment in latitude. For example, the center latitude of projection for a site at 2 degrees north is 0 degrees; the center latitude of projection for a site at 7 degrees north is 5 degrees north. At the center latitude of projection, 1 pixel corresponds to 231.53 meters.

Targeted Observation Browse Products: All of the images are in simple cylindrical projection at 3072 pixels per degree, referenced to the nearest equator-ward 5 degree increment in latitude. For example, the center latitude of projection for a site at 2 degrees north is 0 degrees; the center latitude of projection for a site at 7 degrees north is 5 degrees north. 3072 pixels per degree was chosen because it approximates the native resolution of CRISM data, and is at the same time a whole multiple of 256 pixels per degrees (the scale of most Mars global data products). At the equator, 1 pixel in a map-projected targeted browse product is 19.294 meters.

In addition, the locations of the CRISM images are provided in *.lbl text files. These indicate the location of the corners of the no-grid CRISM images (*.png) in E longitude and latitude, the resolution of the pixel at the center of the image, and the projection (cylindrical) used to generate these products.

For all the browse products, we present three sets of images. The thumbnail and first image on the details page is stretched uniformly across all the sites. This is to illustrate what the diversity of minerals looks like in comparitive way between all the MSL landing sites considered. But some sites possess far more subtle spectral signatures. To emphasize these, we also provide two additional browse product images: (1) stretched in a uniform manner across all the images of a given site (with '*_site_* in name), and (2) stretched to emphasize the details in an individual observation (with '*_obs_*' in name).

(4) Interpreting Browse Products

CRISM browse products are intended to provide a high-level overview of the contents of calibrated image data, and are not meant for quantitative analysis or to be interpreted with an awareness of possible false detections due to illumination or instrumental effects. However, every effort was made in the construction of the browse products to preserve useful information and the dynamic range of the original calibrated data. In addition, the mapping information specified with the map/stretch information for each product is sufficient to register the browse images with other data sets. Typically registration errors are about 200 m or less.

Four of the browse products provide an overview of surface brightness: VNIR_RGB is enhanced false color in the visible wavelength range; VNIR_VNA is the brightness at 770 nm; IR_RGB is enhanced false color in the infrared; IR_IRA is the brightness at 1330 nm. All of these products are rendered with a 3-sigma data stretch on each band.

Compositional information on the surface is concentrated in four of the browse products (VNIR_FEM, IR_MAF, IR_PHY, and IR_HYD). Not all of the sites exhibit spectral evidence for mineralogical diversity. If a location is covered in dust, it appears red in VNIR_FEM and bland in the other products. Sites with diversity in igneous mineralogy will appear interesting in IR_MAF. Sites with minerals formed by interaction of crustal rocks with liquid water will appear interesting in IR_PHY and IR_HYD.

Sites that have water ice on the surface or as clouds will appear pink, yellow or green in ir_ice, whereas those with carbon dioxide frost on the surface will appear bluish.

In addition to those caveats, many of the parameters in the latter four browse products have dependencies on solar incidence angle, surface slopes, atmospheric conditions, detector artifacts, and response to phases other than what the products were intended to show. For example, IR_PHY and IR_HYD can have bluish colors due to spectral effects of water ice, either as surface frosts or atmospheric hazes. Illumination geometry or atmospheric dust and ice hazes can create artifacts in VNIR_FEM, IR_MAF, IR_PHY, and IR_HYD. IR_PHY is particularly susceptible to detector artifacts.

An excellent reference describing the parameters used in constructing VNIR_FEM, IR_MAF, IR_PHY, IR_HYD, and ir_ice is:

(4.1) Visible and Near-infrared (VNIR) Browse Products

Information in CRISM's 107 VNIR wavelengths (at 0.36-1.05 microns) is represented as two browse products.

The first is a false color red-green-blue (VNIR_RGB) image constructed from 590, 530, and 440 nm wavelengths, that has been stretched to optimize the dynamic range at the site shown. Thus, the stretch varies from image to image. These data received an approximate correction for photometric effects, that is, differences in local solar time and the angle of sunlight to the surface. This correction was performed by dividing the brightness of Mars' surface at each wavelength ("I/F") by the cosine of the solar incidence angle (angle of sunlight to local vertical).

The second false color image (VNIR_FEM) provides information related to iron minerals. It is derived from spectral data that have been corrected for photometric effects. The parameter data have also been filtered to reduce the effect of detector noise.

Channel	Parameter	Significance	Cautions
Red	Depth of 530-nm band; relative to a continuum between 440 and 709 nm (BD530*)	Higher values indicate greater content or larger particle size of some fine-grained oxidized iron minerals	Higher values also occur where the atmosphere is dusty, or where dusty atmosphere overlies shadowed slopes
Green	Height of inflection at 600 nm; relative to a continuum between 440 and 709 nm (SH600*)	Higher values correlated with coatings or rinds present on rocks, and with some crystalline ferric oxides	Higher values also occur in hazy atmosphere, over shaded slopes, where there is a high solar incidence angle, and over ice
Blue	Integrated area in 1-micron band; from 830-1023 nm, relative to a flat continuum tangent to the reflectance peak near 750 nm (BDI1000VIS*)	Higher values indicate greater content or larger particle size of iron minerals, especially olivine and pyroxene	Weakly sensitive to crystalline ferric oxides

*See Data Product SIS for detailed formulas.

The third vnir image (VNIR_VNA) shows I/F at 770nm, after an aproximate correction for photometric effects, that is, differences in local solar time and the angle of sunlight to the surface. The correction was performed by dividing the brightness of Mars' surface to optimizie the dynamic range at the site shown. Thus, the stretch varies from image to image.

(4.2) Infrared (IR) Browse Products

Information in CRISM's 438 IR wavelengths (at 1.00-3.92 microns) is represented as five browse products.

The first is a false color red-green-blue (IR_RGB) image constructed from 2503, 1500, and 1080 nm wavelengths, that has been stretched to optimize the dynamic range at the site shown. Thus, the stretch varies from image to image. These data received an approximate correction for photometric effects, that is, differences in local solar time and the angle of sunlight to the surface. This correction was performed by dividing the brightness of Mars' surface at each wavelength ("I/F") by the cosine of the solar incidence angle (angle of sunlight to local vertical).

The second IR browse product (IR_IRA) shows I/F at 1330 nm, after an approximate correction for photometric effects, that is, differences in local solar time and the angle of sunlight to the surface. This correction was performed by dividing the brightness of Mars' surface ("I/F") by the cosine of the solar incidence angle (angle of sunlight to local vertical). The resulting image has been stretched to optimize the dynamic range at the site shown. Thus, the stretch varies from image to image.

The third IR browse product (IR_MAF) shows information related to mineralogy of iron-containing minerals, including unaltered igneous minerals such as olivine and pyroxene as well as altered minerals including iron-rich phyllosilicates. It is derived from data corrected for photometric effects, and for effects of atmospheric gases. The atmospheric gas correction was done by dividing the spectrum of each pixel by a scaled transmission spectrum of the atmosphere, derived from comparing the summit and base of Olympus Mons. The parameter data have also been filtered to reduce the effect of detector noise.

Channel	Parameter Description and Name	Significance	Cautions
Red	Olivine index; measures brightness at 1695 nm relative to a weighted average at 1080-1470 nm (OLINDEX*)	Higher values indicate greater content or larger particle size of olivine or iron-containing phyllosilicates	Dusty regions or atmospheric dust (both of which can be recognized in VNIR_FEM) may cause elevated values. Higher values can also result from illumination effects on sunward slopes
Green	Low-calcium pyroxene index; measures brightness contrast at 1080 and 2067 nm relative to 1330 nm (LCPINDEX*)	Higher values indicate greater content or larger particle size of pyroxene; favors low-Ca pyroxene	Higher values can also result from illumination effects on shaded slopes
Blue	High-calcium pyroxene index; measures brightness contrast at 1080 and 2067 nm relative to 1470 nm (HCPINDEX*)	Higher values indicate greater content or larger particle size of pyroxene; favors high-Ca pyroxene	Weakly sensitive to ice

*See Data Product SIS for detailed formulas

The fourth IR browse product (IR_PHY) shows information related to hydroxylated minerals including phyllosilicates. It is also derived from the data corrected for atmospheric and photometric effects, and has been filtered.

Channel	Parameter Description and Name	Significance	Cautions
Red	Index for presence of Fe-OH and Mg-OH containing minerals; measures brightness around 2320 nm relative to 2170 nm (D2300*)	Higher values indicate greater content or larger particle size of iron/magnesium phyllosilicates	Weakly sensitive to shaded slopes and strong brightness boundaries. Intermittent detector artifacts at edges of images
Green	Depth of 2210-nm band due to Al-OH or Si-OH in minerals; relative to a continuum between 2140 and 2250 nm (BD2210*)	Higher values indicate greater content or larger particle size of aluminum phyllosilicates or hydrated silica	Weakly sensitive to shaded slopes and strong brightness boundaries. Intermittent detector artifacts at edges of images
Blue	Depth of 1900-nm band due to bound water; relative to a continuum between 1874 and 2006 nm (BD1900*)	Higher values indicate greater content or larger particle size of hydrated minerals	Also sensitive to water ice surface frost or atmospheric hazes that are accentuated at low solar incidence angles

*See Data Product SIS for detailed formulas

The fifth IR browse product (IR_HYD) shows information related to bound water in minerals, usually sulfates but in some cases phyllosilicates, hydrated glass, or other minerals. It is also derived from spectral data corrected for atmospheric and photometric effects, and has been filtered.

(5) Links to CRISM Browse Images of Candidate MSL Landing Sites

Click on the name of a site below to see CRISM images covering it or located nearby to view the high resolution browse images.