Imagers versus Spectrometers

• to clarify your understanding of the difference between two common approaches to remote sensing used at Mars: imaging sensors and spectrometers
• to give you practice in conceptualizing and writing

The Mars class has given a lot of coverage to the various missions sent to Mars, their sensor packages, and the spatial, vertical, spectral, and temporal resolution characteristics. Two particularly prominent approaches and instruments have been imaging sensors and spectrometers. Among the imaging sensors have been the Mars Orbital Camera carried on NASA's Mars Global Surveyor, the THEMIS imager on NASA's Mars Odyssey, and HRSC on the ESA's Mars Express. Spectrometers have included PFS, SPICAM, and OMEGA on Mars Express and GRS on Mars Odyssey.

Your "data"

Head over to https://home.csulb.edu/~rodrigue/mars/lectures.html and scroll down to the section entitled "Sources of data on Mars available today." Visit the web sites for the spectrometers and imagers on the post 1995 missions (you don't need to read about the other types of sensors, such as thin-wire thermocouples, altimeters, gravity-field systems, and magnetometers). You may need to augment this by using Google or other Internet search engine on "spectroscopy" or "imaging system sensor" or "CCD" or similar terms. You may also find Dr. Nicholas Short's Remote Sensing Tutorial at NASA's Goddard Space Flight Center of use, particularly the introduction subsection, "Sensor Technologies." It can be accessed at http://rst.gsfc.nasa.gov/.

Both types of systems can generate spectra (intensity by wavelength readings and graphs) that can then be used to infer such information as temperatures and chemical composition. They go about it differently, however. That is, the sensor's "innards" handle incoming energy differently, one like a CCD camera and the other more indirectly.

Lab report

Write a brief report summarizing the key differences between a camera imaging system and a spectrometer. How does a camera system get intensity readings for a given wavelength band? How does a spectrometer generate a spectrum?

Diagramming the difference

It would be helpful if you came up with a drawing showing the difference in energy capture in an idealized camera imaging system and in an idealized spectrometer.