Analysis of Airborne Visible/Infrared Imaging Spectrometer (AVTRIS) data of volcanic hot spots

In July 1991, the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) was flown over Mount Etna and Stromboli, Italy. At the time, magma-filled vents, of subpixel dimensions, occupied the summit craters of both volcanoes. For pixels located over these hot spots, thermal radiation dominates the sensor response between about 1-4 and 2-4 μm, the latter figure being the upper limit of spectral coverage. One thermal source within the Northeast Crater of Mount Etna is evident at wavelengths as short as I 0 μm despite this intensity, therc is no saturation of the AVIRIS sensors because of their wide dynamic range. A curve-fitting algorithm is used to match the thermal spectra with Planck radiation models, in order to derive information on temperature distributions at the subpixel scale. Difficulties arise because the sequential readout of detector elements during scanning leads to interband spatial misregistration. Although the standard preprocessing of AVIRIS data includes a linear interpolation of adjacent pairs of cross-track pixels to compensate for the readout delay, this procedure only complicates further the extraction of subpixel resolution thermal information. Only by reconfiguring AVIRIS, such that all spectral channels arc recorded simultaneously, could this problem be completely overcome. Nevertheless, by examining geometrically unprocessed spectra, and selecting from thcm thermal measurements in a few adjacent channels, meaningful radiometric calculations are possible in some cases. In this manner, we estimate that one of the hot spots on Stromboli was at ≈600°C and occupied ≈ 15 m 2 of ground. The methodologies proposed here are applicable to any hyperspectral record of thermal emission of volcanic or other origin