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March 18 3 om U115 M&M
A Multisensor Approach to the Remote Sensing of Volcanic Emissions
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NASA’s series of Earth Observing System satellites present remote
sensing volcanologists with a potent suite of instruments for the study
of volcanic emissions. In this presentation we focus on applications of
data acquired with the Advanced Spaceborne Thermal Emission and Reflection
Radiometer (ASTER), Atmospheric Infrared Sounder (AIRS), Moderate-Resolution
Imaging Spectrometer (MODIS), and Multiangle Imaging SpectroRadiometer
(MISR). The volcanic emission products of interest are sulfur dioxide,
silicate ash, and sulfate aerosols. The ASTER, MODIS, AIRS, and MISR data
are applied to studies of the sulfur dioxide, ash, and aerosol emissions
associated with recent eruptions of Mount Etna.
The measurements provided by these instruments are complimentary. ASTER
collects visible and near-infrared (VNIR), short-wave infrared (SWIR),
and thermal infrared (TIR) radiance measurements at (nadir) spatial resolutions
of 15 m, 30 m, and 90 m, respectively. MODIS collects radiance measurements
in 32 spectral channels between the VNIR and TIR. The majority of these
measurements are acquired at a (nadir) spatial resolution of 1 km. There
are MODIS intruments on two EOS platforms, providing daily coverage of
the Earth at non-Tropical latitudes. AIRS collects radiance measurements
in over 2300 spectal channels between the SWIR and TIR, with a (nadir)
spatial resolution of approximately 17 km. MISR acquires multispectral
VNIR radiance measurements at nine distinct viewing angles through the
simultaneous use of nine nadir-, fore-, and aft-viewing cameras. The spatial
resolution of the nadir scene and the red channels of the off-nadir scenes
is 275 m. The remaining off-nadir scenes have a spatial resolution of
1100 m.
The high spatial resolution of ASTER data allows us to detect volcanic
emissions at low concentrations, making ASTER the primary instrument for
monitoring passive emissions of sulfur dioxide. The comprehensive spectral,
spatial, and temporal coverage provided by MODIS make these data the most
vesatile for the study of volcanic sulfur dioxide, ash, and aerosol emissions.
The high spectral resolution of AIRS data permits unambiguous identification
of sulfur dioxide, ash, and aerosol and facilitates the estimation of
the quantities of these materials. In addition, AIRS data are used to
map the 3D distributions of atmospheric temperature and water vapor.
MISR data are used to derive estimates of aerosol optical depth, cloud-top
altitude, wind direction, and wind speed. Volcanic plumes and clouds exhibit
apparent displacement, known as parallax or disparity, in the off-nadir
views relative to the nadir view. These disparities are a function of
the altitude of these features as well as wind-induced motion during the
seven minute period required to obtain a suite of fore- and aft-viewing
scenes over a given point on the Earth’s surface.