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Sample Images
Radiative transfer simulations (16K image)
Uppermost curve shows the simulation of a down-looking satellite observation of a background atmosphere. Next (partly overlapping) curve shows the same background, perturbed by the presence of a sulfur dioxide plume at 12 km altitude (SO2 concentration = 0.3 atm cm). SO2 absorption features are apparent at wavelengths of 7.3 and 8.7 micrometers. Lowermost curve shows the effect of water droplets (optical depth 1.5, cirrus-type size distribution) within the SO2 plume. Symbols indicate the brightness temperatures that would be measured by the HIRS/2 infrared channels. An SO2 detection algorithm has been developed for HIRS/2, after analysis of many radiative transfer simulations like these shown here. This SO2 alarm is based upon the sensitivity of the 7.3 micrometer channel to SO2 and thresholds set on the differences in brightness temperature between various HIRS/2 channels. This alarm has been tested with HIRS/2 observations of the 1980 Mount St. Helens and 1979 Sierra Negra eruptions. We will use a similar alarm algorithm for MODIS to detect large SO2 anomalies.

H2S transmission spectrum (5K image)
This plot shows the transmission of a 1.5 atm cm column of H2S gas. The absorption line data used to generate this plot is from the HITRAN database over the 6.3 to 10 micrometer wavelength range, and new estimates (Bykov et al. reference given below) covering 1.3 to 4.2 micrometers. This data is being used to simulate measurements of volcanic H2S by AIRS and TES at different viewing angles. H2S is roughly 50 times less absorbing than SO2 in the mid-infrared. Only extremely large quantities will be detected by EOS instruments (At 40 degrees off nadir, the detection limit is about 0.2 atm cm H2S for TES, and about 0.8 atm cm H2S for AIRS) [1 atm cm H2S = 30 tons H2S per km2].

Pre-launch EOS activities
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