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. In many scenes relatively unaltered or pyroxene-containing mafic rocks appear dark gray; olivine-containing materials appear maroon; Fe/Mg-containing phyllosilicates appear buff; and silica or Al-containing phyllisilicates appear blue-green.

The second IR browse product (IR_IRA) shows I/F at 1330 nm, which is outside the strongest atmospheric gas and mineralogic absorptions. The image has been stretched to optimize the dynamic range at the site shown, so 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.

Channel

Parameter Description and Name

Input/output Range for Uniform Stretch

Significance

Cautions

Red

Modified olivine index; measures brightness at 1080-1470 nm relative to a continuum fit to wavelengths 1700-2500 nm (OLINDEX2*)

0.0002-0.04215 to 0-254; 255 indicates no data

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.

Green

Low-calcium pyroxene index; measures brightness contrast at 1080 and 2067 nm relative to 1330 nm (LCPINDEX*)

0.0002-0.0747 to 0-254; 255 indicates no data

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*)

0.0002-0.2611 to 0-254; 255 indicates no data

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.

Channel

Parameter Description and Name

Input/output Range for Uniform Stretch

Significance

Cautions

Red

Index for presence of Fe-OH and Mg-OH containing minerals; measures brightness around 2320 nm relative to 2170 nm (D2300*)

0.0002-0.03715 to 0-254; 255 indicates no data

Higher values indicate greater content or larger particle size of iron/magnesium phyllosilicates

Weakly sensitive to shaded slopes and strong brightness boundaries.

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*)

0.0047-0.0382 to 0-254; 255 indicates no data

Higher values indicate greater content or larger particle size of aluminum phyllosilicates or hydrated silica

Weakly sensitive to shaded slopes and strong brightness boundaries.

Blue

Depth of 1900-nm band due to bound water; relative to a continuum between 1874 and 2006 nm (BD1900*)

0.0002-0.0607 to 0-254; 255 indicates no data

Higher values indicate greater content or larger particle size of hydrated minerals including polyhydrated sulfates, phyllosilicates, hydrous carbonates, and zeolites

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.

Channel

Parameter Description and Name

Input/output Range for Uniform Stretch

Significance

Cautions

Red

"Sulfate" index, a measure of bound water or ice; measures the drop in reflectance from near 2300 nm to near 2400 nm (SINDEX*)

0.0187-0.0697 to 0-254; 255 indicates no data

Higher values indicate greater content or larger particle size of minerals or glasses with bound, dissolved, or adsorbed molecular water, especially sulfates

This parameter is sensitive to water ice and to dust and atmospheric ice hazes that are accentuated at low solar incidence angles

Green

Depth of 2100-nm band in monohydrated sulfates; relative to a continuum between 1930 and 2250 nm (BD2100*)

0.0137-0.0452 to 0-254; 255 indicates no data

Higher values indicate greater content or larger particle size of monohydrated sulfates

Also sensitive to pyroxenes, and to water ice surface frost or atmospheric hazes that are accentuated at low solar incidence angles

Blue

Depth of 1900-nm band due to bound water; relative to a continuum between 1874 and 2006 nm (BD1900*)

0.0002-0.0607 to 0-254; 255 indicates no data

Higher values indicate greater content or larger particle size of hydrated minerals including polyhydrated sulfates, phyllosilicates, hydrous carbonates, and zeolites

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