HR: 14:25h
AN: V12E-04    [PDF]
TI: Forward modeling of volcanic aerosols transmissions at different latitudes; quantifying the effects of varying tropospheric water vapor on ash detection.
AU: * Watson, I M
EM: watson@mtu.edu
AF: Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI 49931 United States
AU: Rose, W I
EM: raman@mtu.edu
AF: Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI 49931 United States
AU: Realmuto, V J
EM: Vincent.J.Realmuto@jpl.nasa.gov
AF: Visualization and Scientific Animation Group, MS 168-414 Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Bluth, G J
EM: gbluth@mtu.edu
AF: Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI 49931 United States
AB: Current algorithms for volcanic ash cloud detection by satellite, based upon a difference in transmissivity of silicate ash at 11 and 12 microns, are subject to significant and yet poorly quantified modulation by atmospheric water vapor. In order to investigate these effects we have written an aerosol forward model, based upon Mie-scattering code, and embedded it in a MODTRAN-based atmospheric radiative transfer model. This facilitates investigation of errors associated with inverse solutions derived from satellite data, and more importantly for this study, can be used to vary the atmosphere within which a hypothetical volcanic ash cloud is contained. We have taken images of the most well parameterized ash clouds of the satellite age, the sequence of eruptions of Mt. Spurr in mid to late 1992, and applied the forward model to predict transmission spectra of the ash clouds. Calculations were performed for the ash clouds both within the cloud's original atmosphere and within that of a sequence of eruptions of Soufriere Hills Volcano, Montserrat, in the British West Indies in the late 1990s. Preliminary results indicate a +1-3.5 K brightness temperature difference (BTD) effect associated with increasing the temperature and water vapor content of the atmosphere. This translates to a significant loss of detectability in terms of cloud area; up to half the area of the clouds no longer have a negative brightness temperature difference, and an effect on reducing the optical depth and mass of the cloud. In most cases there was very good agreement between the 'clear ocean' BTD and the modeled effect, suggesting a potential source of in-image calibration for detection algorithms. In terms of mass and optical depth retrievals however, it is obvious that both 11 and 12 micron channel radiances are affected by the presence of water vapor, clearly indicating the need for atmospheric correction before quantifying the size or concentration of ash in clouds from satellite data.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0365 Troposphere--composition and chemistry
DE: 8409 Atmospheric effects (0370)
DE: 8414 Eruption mechanisms
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting