Using Reflectance Spectrometry to Identify Compositions

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Using Reflectance Spectrometry to Identify
Compositions
Credit NASA/JPL-CalTech/LANL
Credit NASA/JPL-CalTech
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How Do We See Mars?
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How Do We See Mars?

• Our eyes, cameras, and mission instruments use
  the sunlight reflected off its surface.
• Spectra primer

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Spectra Are Fingerprints

• Spectra are unique to elements and minerals
• Used to identify minerals rocks

Credit ChemCam/LANL/IRAP/CNES
Credit Univ. of Toronto
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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
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Types of Spectra
Credit http//csep10.phys.utk.edu/astr162/lect/li
ght/spectra2.gif
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Using the ALTA to take a Spectrum

• These rocks are Mars rocks that youlike a
  rover on a missionare analyzing. Your task it
  to determine their possible compositions, by
  comparing the Mars rocks spectra to known Earth
  rocks spectra.

Credit Wards Scientific
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Using the ALTA to take a Spectrum

• These rocks are Mars rocks that youlike a
  rover on a missionare 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

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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

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Taking the Dark Voltage

• What happens if you place the ALTA down flat and
  dont turn on any of the lights?
• You still have a number - ALTAs photodetector
  and electronics dont go to zero. This is your
  Dark Voltage

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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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Terrestrial Spectrum 1
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Terrestrial Spectrum 2
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Terrestrial Spectrum 3
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Terrestrial Spectrum 4
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Terrestrial Spectrum 5
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Terrestrial Spectrum 6