In imaging spectroscopy, a photograph is taken in a way that measures the intensity of light at a number of different wavelengths. This process generates a separate light spectrum for every pixel in the photograph.
Imaging spectroscopy can be used by telescopes and spacecraft to study Mars.
Reflectance spectroscopy and thermal emission spectroscopy are two types of imaging spectroscopy.
Reflectance spectroscopy measures the visible and infrared light spectrum of the sunlight reflected from an object. After the spectrum of the light emitted by the sun is taken into account, a spectrum that is specific to the reflecting material is calculated. This spectrum can be compared to a library of known spectra. The Compact Reconnaissance Imaging Spectrometer for Mars, an instrument on the Mars Reconnaissance Orbiter, uses reflectance spectroscopy to identify minerals on the surface of Mars.
Thermal Emission Spectroscopy
Thermal emission spectroscopy, also known as infrared imaging, measures the infrared light that is released by any object as a result of normal molecular vibrations. The spectrum of this light provides information on the composition of the object that emitted it, and that object's temperature. The Thermal Emission Spectrometer on Mars Global Surveyor used thermal emission spectroscopy to learn about dust in the Martian atmosphere and the surface temperature on Mars. The Thermal Infrared Imaging Spectrometer on the Mars Orbiter Mission spacecraft also uses this technique.
It is also possible for a single instrument to combine both of the above methods to perform multispectral imaging. The Thermal Emission Imaging System on Mars Odyssey is capable of multispectral imaging.
Library of thermal infrared spectra maintained by Arizona State University's Mars Space Flight Facility: https://speclib.asu.edu/
- Shaw GA & Burke HK. 2003. Spectral Imaging for Remote Sensing. Lincoln Laboratory Journal, 14(1), 3-28. https://courses.cs.washington.edu/courses/cse591n/07sp/papers/Shaw2003.pdf
- Johns Hopkins Applied Physics Laboratory. Compact Reconnaissance Imaging Spectrometer for Mars. http://crism.jhuapl.edu/index.php
- Arizona State University. Mars Global Surveyor Thermal Emission Spectrometer. http://tes.asu.edu/index.html
- Indian Space Research Organization. Payloads. In PSLV-C25/Mars Orbiter Mission. https://www.isro.gov.in/pslv-c25-mars-orbiter-mission/payloads
- Arizona State University School of Earth & Space Exploration. Frequently Asked Questions. In Mars Odyssey THEMIS. http://themis.asu.edu/faq