Monitoring Renewed Volcanic Activity at Mount St. Helens with High-Resolution Thermal Infrared Data: ASTER, MASTER and FLIR

Since the beginning of renewed eruptive activity at Mount St. Helens numerous thermal infrared (TIR) remote sensing data sets have been acquired to monitor changes in temperature and thermal flux from the new dome. High-resolution (5 m) TIR data from the MODIS-ASTER airborne simulator (MASTER) were acquired during the first 20 days of activity along with several Forward-Looking Infrared (FLIR) camera surveys from both helicopter and ground-based stations. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument has acquired a total of 10 cloud-free data sets from October 2004 to August 2005 with 90-m spatial resolution in the TIR. The pre-eruption data show no measurable increase in surface temperature before the first eruption on October 1. MASTER TIR data acquired during the first 3 weeks of activity show maximum temperatures of ~330 C (on October 14) and concurrent FLIR camera data show maximum temperatures of ~675 C, in narrow (~1-m) fractures of molten rock on the new dome. Thermal flux calculations from both MASTER and FLIR data at that time indicate a radiative cooling rate of ~700 J/m2/s over the new dome, corresponding to a radiant power of ~24 MW. Preliminary results from ASTER data analysis show a general increase in the number of "warm pixels" in the crater throughout the year and temperature information extracted from these areas will be presented as a chronology of temperature and thermal flux changes. Higher-resolution FLIR surveys that were approximately concurrent with some of the ASTER images compared to the ASTER-derived temperatures have been used to validate ASTER measurements and model sub-pixel temperature components. The results so far demonstrate that TIR data provide important information on the thermal evolution of the surface during eruptive episodes.