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Using Reflectance Spectrometry to Identify Compositions. Credit: NASA/JPL- CalTech /LANL. Credit: NASA/JPL- CalTech. How Do We See Mars?. Our eyes, cameras, and mission instruments use the sunlight reflected off its surface. Spectra Are “Fingerprints”.
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Using Reflectance Spectrometry to Identify Compositions Credit: NASA/JPL-CalTech/LANL Credit: NASA/JPL-CalTech
How Do We See Mars? • Our eyes, cameras, and mission instruments use the sunlight reflected off its surface.
Spectra Are “Fingerprints” • Fingerprints can be used to identify individual people Credit: http://www.moillusions.com Credit: http://math-blog.com Credit: http://www.vetmed.vt.edu
Spectra Are “Fingerprints” • Spectra are unique to elements and minerals • Used to identify minerals; rocks Credit: ChemCam/LANL/IRAP/CNES Credit: Univ. of Toronto
Types of Spectra Credit: http://csep10.phys.utk.edu/astr162/lect/light/spectra2.gif
Using the ALTA to take a Spectrum • These rocks are “Mars” rocks that you—like a rover on a mission—are analyzing. Your task it to determine their possible compositions, by comparing the Mars rocks’ spectra to known Earth rocks’ spectra. Credit: Ward’s Scientific
Using the ALTA to take a Spectrum • These rocks are “Mars” rocks that you—like a rover on a mission—are analyzing. Your task it to determine its possible composition, by comparing the Mars rocks’ spectra to known Earth rocks’ spectra. • Buttons on front, LEDs & detector on the back • Push each button on the front and see what happens on the back
Using the ALTA to take a Spectrum • What is the ALTA doing? • Light from diode strikes the surface of the sample • Light reflected off the sample enters the detector • Read-out on the front indicates how much of the light has been reflected (voltage) • Because each ALTA has its own sensitivities, the read-out should be compared to the reflectance of white paper
Taking the Dark Voltage • What happens if you place the ALTA down flat and don’t turn on any of the lights? • You still have a number - ALTA’s photodetector and electronics don’t go to zero. This is your “Dark Voltage”
Using the ALTA to take a Spectrum • Need a large flat surface if possible. • Try not to let outside light into the detector. • Work in groups of 4; one can hold the sample and ALTA, one can press the buttons, one to record the data, etc. • Begin with taking the data for two stacked pieces of white paper.
