Using Reflectance Spectrometry to Identify Compositions Credit NASAJPLCal

Using Reflectance Spectrometry to Identify Compositions Credit: NASA/JPL-Cal. Tech/LANL Credit: NASA/JPL-Cal. Tech

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: Chem. Cam/LANL/IRAP/CNES Credit: Univ. of Toronto

Types of Spectra Credit: http: //csep 10. phys. utk. edu/astr 162/lect/light/spectra 2. 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.

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