William Atkins
Friday, 20 February 2009 20:31
Science -
Space
Page 2 of 3
By partitioning (dividing) light into different wavelengths (grates within the spectrometers perform this task), scientists will be able to see which colors of light reacts to carbon dioxide (that is, some colors of light make the carbon dioxide molecules vibrate at specific frequencies—the reaction).
In this way, they can determine how much carbon dioxide is present in specific volumes of the atmosphere—and how much it is changing in these volumes, which tells them where sources and sinks (accumulations) of carbon dioxide exist.
NASA-JPL scientist Donald Crisp, the principle investigator for the mission, states,
“You can see a good example of how a grating spectrometer works by looking at the back of a compact disc illuminated by a bright light. The narrow circular tracks that record the information on the disk are very effective at splitting light into different colors." [NASA: “
NASA Mission Meets the Carbon Dioxide Measurement Challenge”]
One spectrometer actually reacts not to CO
2, but to molecular oxygen—doing the same thing, though, seeing what type (color, or wavelength) of light reacts to oxygen molecules.
Dr. Crisp explains its function:
"Oxygen makes up about 21 percent of the atmosphere. Because we know the concentration, we know how much sunlight it should absorb over any particular surface elevation. If the sunlight penetrates all the way to sea level before it is reflected back to the spacecraft, it will produce more absorption than if it penetrates only to the top of a mountain or to the top of a cloud before it is reflected to space.”
And,
“We can even use measurements of the oxygen absorption to infer the surface pressure differences associated with elevation changes as small as 100 feet. We can also detect scattering by very thin clouds or hazes that reflect less than one percent of light back to space.”
In other words, he states,
“These precise measurements of the atmospheric optical path are essential for accurate carbon dioxide measurements."
Page three concludes.
