Using Reflectance Spectrometry to Identify Compositions Credit: NASA/JPL-CalTech Credit: NASA/JPL-CalTech/LANL

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: Credit: Credit:

Spectra Are “Fingerprints”  Spectra are unique to elements and minerals  Used to identify minerals; rocks Credit: Univ. of Toronto Credit: ChemCam/LANL/IRAP/CNES

Types of Spectra Credit:

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.

Terrestrial Spectrum #1

Terrestrial Spectrum #2

Terrestrial Spectrum #3

Terrestrial Spectrum #4

Terrestrial Spectrum #5

Terrestrial Spectrum #6