Spectroscopy, also know as spectrometry, can be confusing unless you
remember one simple definition: Spectroscopy is the study of squiggly
lines. But the technical person seems to prefer the real definition that
spectroscopy is the science and analysis of the visible and
near-infrared (VNIR) spectra of materials.
As in every subject there is more than one technique you can use to
get your desired results. Each uses some sort of detector, or
spectrometer, to make measurements. The most common technique is
called reflection spectroscopy, which measures the amount of light given
off by a given material. This technique produces a reflection curve
(peak) or spectrum. Each substance reflects a different amount of
light, which makes it easier to measure the amount of each mineral
found in a sample. This uniqueness is noticeable by looking at the
different peaks in the spectrum.
Since you can't compare VINR spectra with the naked eye, we use a
spectroscopy software. This software compares the spectra from the
U.S.G.S. (United States Geological Survey) spectral library to the unknown
source we are trying to study. It is kind of like cutting the material up
and naming the percentage of each mineral that's found in the unknown
substance, but instead you are measuring the reflected light.
Since the spectral library is made up of earthbound minerals,
sometimes the program errors out because the software only knows the
substances of the minerals found in the USGS library. In order to solve
this problem, we must break up the VINR line and then that section to
the spectra in the spectral library. Another problem is that the software
program does not automatically reduce the "noise"
(bumpiness) at the end of the spectra and the water bands (the squiggly
lines) found at the beginning of the substance. The way to solve this is to
set up the software charts between the wavelengths (the light emitted) of
2.0 to 2.4 micrometers. Then we can either go straight to comparing the
whole spectrum or pick parts of the spectrum to compare. With this data
we can understand what minerals exist in the field sample and use that
knowledge to determine how the geologic area was formed and make
plans for future rover traverses.
|View a larger image in a new browser window.
In this plot we have 3 different spectral readings. This helps the
user to compare multiple samples at one time, which saves time and
shows the likenesses and differences between the 3 readings.
Towards the left side you can see the effect of the atmosphere
absorbing all the light, leading to tall, "squiggly" lines.
Then in the middle we notice the multiple peaks in the spectra. And
to the right we see the "noise" bands--bumpy lines
caused by low signal strength.