Improved remote sensing estimates of lava flow cooling: A case study of the 1991-1993 Mount Etna eruption

Infrared radiance data acquired by the Landsat thematic mapper (TM) provide information regarding the thermal state of active lavas, which can be used to estimate flow surface temperatures and thus lava cooling. Saturation of one or both of TM's short-wave infrared (SWIR) wavebands has meant, howeve r, that previous studies of lava flow cooling have approximated what is alm ost certainly an n thermal component now surface temperature distribution ( where n > 1), with a single pixel-integrated temperature (PIT). We show tha t the high sensitivity of TM's SWIR wavebands to the small amount of high-t emperature (e.g., similar to 1000 degrees C) material exposed in hot fractu res within the flows cooler (e.g., similar to 200 degrees C) surface crust results in the calculation of PITs that are higher than the temperature of this crust, which is usually the dominant radiative component. This causes heat loss from such pixels to be overestimated. We present adaptations that allow more realistic heat loss estimates to be produced using TM data by a ssuming that a second high-temperature component contributes to the radianc e measured from saturated pixels and by defining an appropriate range for t he temperature of the lava crust. By analyzing a suite of five TM images ac quired during the 1991-1993 eruption of Mount Etna we present more realisti c estimates of how this flow cooled, as well as results that show how the f low regime of the lava evolved over time. The methods we present will conti nue to be of use as, although the next generation of high spatial resolutio n sensors such as the Landsat 7 enhanced thematic mapper plus (ETM+) and th e Terra advanced space-borne thermal emission and reflection radiometer (AS TER) will be less susceptible to saturation than TM, the problem will still persist.