National Aeronautics and Space Administration

Abstract. The sulfur dioxide gas in volcanic eruption plumes is detectable from space through the near ultraviolet absorption bands of this constituent. The Nimbus 7 Total Ozone Mapping Spectrometer (TOMS), which produces daily global images of the atmospheric ozone distribution through measurement of the absorption of sunlight by ozone in the ultraviolet spectral region, is also capable of observing and resolving the size of the volcanic clouds. The sulfur dioxide clouds are discriminated from ozone and water clouds in the data processing by their spectral signature. Volcanic eruptions constitute the primary source for stratospheric aerosols which are long lived and can be very prominent following large eruptions, such as that of El Chichon in April 1982. Smaller eruptions, however, are much more frequent and constitute a more direct threat to aircraft due to ingestion of ash which accompanies the sulfur dioxide during the first hours of the eruption. The TOMS instrument is able to detect these eruptions, such as those of Galunggung, Java in 1982, Colo on Una Una, Indonesia in 1983, and Mauna Loa, Hawaii in 1984. Other eruptions which are difficult to detect in the visible and infrared, have been found with TOMS. An example of this is the eruption of Fernandina in the Galapagos Islands on April 1, 1984 which was only detected by its sulfur dioxide content. The detection limit with TOMS is close to the theoretical limit due to telemetry signal quantization of 1000 metric tones (5-sigma threshold) within the instrument field of view (50 x 50 km near the nadir).