Editing Thermal Emission Imaging System (section)

==Infrared camera==
[[Image:Tesvsthemis-med.jpg|right|250px|alt=Two false-color maps of the same area of Mars. The left one is very pixelated, while fine details are visible in the right one.|thumb|Spatial resolution comparison between MGS's TES instrument and Odyssey's THEMIS instrument. (The spectral resolutions are inversely related.)]]
[[Image:Asterminerals-med.jpg|200px|alt=Two maps of the same area on Earth. The left one is grayscale, while the right one is false-color and shows the distributions of quartz (red), carbonate minerals (green), and iron-rich minerals (purple).|thumb|Sample map from Terra's ASTER instrument: [[Saline Valley]], California]]
[[File:Hematite region Sinus Meridiani sur Mars.jpg|alt=A grayscale map of an area on Mars (from 5° N to 6° S and from 10° W to 358° W (or 2° E), crossing 0° in both axes), with a false-color overlay (cyan, green, yellow, red) showing hematite abundance on the surface.|right|thumb|Map showing distribution of [[hematite]] in [[Sinus Meridiani]]. This data was used to target the landing of the [[Opportunity (rover)|Opportunity rover]]. Hematite is usually formed in the presence of water. Opportunity landed in this area and did find much evidence for water.]]
THEMIS detects thermal infrared energy emitted by the Martian surface at nine different [[wavelength]]s.  Eight of these have wavelengths between 6 and 13 micrometers, an ideal region of the [[infrared spectrum]] to determine [[thermal infrared spectroscopy|thermal energy patterns]] characteristic  of [[silicate minerals]]. The ninth band is at 14.9 micrometers and is used to monitor the [[atmosphere of Mars|Martian atmosphere]].  The shortest infrared wavelength, at 6.78 micrometers, is measured twice in two bands to improve the [[signal-to-noise ratio]].  THEMIS is therefore a 10-band instrument that detects nine different wavelengths [https://doi.org/10.1023%2FB%3ASPAC.0000021008.16305.94].

The [[absorption spectrum]] measured by THEMIS contains two kinds of information: [[temperature]] and [[emissivity]].  The temperature contribution to the measurement dominates the spectrum unless the data is corrected.  In effect, a THEMIS infrared image taken during the day will look much like a [[shaded relief]] map, with slopes facing the sun being bright (hot) and shaded areas being dark (cold).  In a THEMIS image taken at night, however, thermophysical properties of the surface can be inferred, such as temperature differences due to the materials' [[grain size]] ([[thermal inertia]]).

The effect of temperature can be removed from THEMIS infrared data by dividing the image by a [[black body]] curve.  The resulting energy pattern is an [[emissivity spectrum]] characteristic of the specific minerals (or other things) found on the surface.  The presence of minerals such as [[carbonate]]s, [[silicate]]s, [[hydroxide]]s, [[sulfate]]s, amorphous [[silica]], [[oxide]]s, and [[phosphate]]s can be determined from THEMIS measurements.

In particular, this multi-spectral method allows researchers to detect the presence of minerals that form in water and to understand those minerals in their geological context.

The THEMIS infrared camera was designed to be used in conjunction with data from the [[Thermal Emission Spectrometer]] (TES), a similar instrument on [[Mars Global Surveyor]].  While THEMIS has a very high [[spatial resolution]] (100 m) with a low [[spectral resolution]] of only 10 bands between 6 and 15 micrometers, TES has a low spatial resolution (3×6&nbsp;km) with very high spectral resolution of 143 bands between 5 and 50 micrometers.

The instrument's approach provides data on localized deposits associated with volcanoes, hydrothermal processes, and the alteration of minerals by surface and/or subsurface water.

The [[Advanced Spaceborne Thermal Emission and Reflection Radiometer]] (ASTER), an Earth orbiting instrument on the Terra spacecraft, has used a similar approach to map the distribution of minerals on Earth.  Variations in the thermal infrared [[false-color]] image are due to differences in the minerals that make up rocks and soil.