Multispectral Thermal Infrared Remote Sensing of Volcanic SO2 Plumes with NASA’s Earth Observing System

The instruments aboard NASA’s series of Earth Observing System satellites provide a rich suite of measurements for the mapping of volcanic plumes and clouds. This presentation will focus on applications of thermal multispectral infrared (TIR) data acquired with the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Moderate-Resolution Imaging Spectrometer (MODIS), and Atmospheric Infrared Sounder (AIRS) to the recent eruptions of Augustine and Sarychev volcanoes in Alaska and the Russian Kuril Islands, respectively. ASTER, MODIS, and AIRS provide complimentary information on the quantity and distribution of sulfur dioxide (SO2), silicate ash, and sulfate (SO4) aerosols within plumes. In addition, data from the Multi-angle Imaging SpectroRadiometer (MISR) are used to derive estimates of aerosol loading, cloud-top altitude, wind direction, and wind speed. MODIS is our workhorse for plume mapping projects. There are MODIS instruments on the Terra and Aqua platforms, ensuring at least two MODIS passes per day over most volcanoes and four passes per day over many volcanoes. The spatial resolution of MODIS TIR radiance measurements is 1 km (at nadir) over a ground swath of 2330 km. MODIS can detect both the 7.3 and 8.5 μm bands of SO2, although the 7.3 μm band is often obscured by water vapor absorption when plumes are altitudes below ~ 4 km. ASTER has five channels in the TIR, and can detect the 8.5 μm SO2 band. The high spatial resolution (90 m) of ASTER TIR radiance measurements results in high sensitivity to SO2 within a narrow ground swath (60 km). AIRS has over 2700 spectral channels between 3.7 and 15.4 μm, allowing us to make unambiguous identifications of SO2, SO4 aerosols, and ash over a ground swath of ~2330 km. AIRS can detect the 7.3 μm SO2 band, and the strength of this band partially offsets the coarse spatial resolution of this instrument (~17 km at nadir). The key to multi-sensor mapping is the availability of a standard set of tools for the processing of data from different instruments. MAP_SO2 is a graphic user interface to the MODTRAN radiative transfer model that provides tools for the estimation of emissivity spectra, water vapor and ozone correction factors, surface temperature, and concentrations of SO2. To date we have used the MAP_SO2 toolkit to analyze data from MODIS, ASTER, AIRS, and a variety of airborne instruments. Our plans for future refinements of MAP_SO2 include the incorporation of AIRS-based profiles of atmospheric temperature, water vapor and ozone, and MISR-based maps of plume-top altitude into the plume mapping procedures.