A correlation spectrometer (COSPEC) is used to measure the flux of sulfur dioxide gas emanating from volcanoes in Alaska. The device is mounted on an aircraft which flies under the volcanic plume and measures the absorption of ultraviolet light by sulfur dioxide molecules. Using the windspeed and geometry of the plume, a daily flux can be calculated.
Image courtesy of AVO / U.S. Geological Survey.Please cite the photographer and the Alaska Volcano Observatory/U.S. Geological Survey when using this image.
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