Spaceborne monitoring of high temperature volcanic thermal features: studies using the ERS Along Track Scanning Radiometer

Wooster, Martin John (1998). Spaceborne monitoring of high temperature volcanic thermal features: studies using the ERS Along Track Scanning Radiometer. PhD thesis The Open University.



Satellite-based instruments have long been suggested as suitable for monitoring thermal phenomena occurring at the surface of active volcanoes. Past studies using data from high spatial resolution instruments indicated the effectiveness of this technique, but such data are expensive, time-consuming to obtain, and offer a poor temporal resolution. This thesis uses data from the European Remote Sensing satellites’ Along Track Scanning Radiometer (ATSR) to analyse infrared thermal emittance from a variety of volcanic thermal features at low spatial resolution (1 km2) but high temporal resolution (~ 3 days), with data from vegetation fires also being investigated. I calibrate the (previously uncalibrated) 1.6 μm channel of ATSR-1, and go onto show how nighttime data in this waveband can be used to characterise emittance from high temperature surfaces, even if these are significantly smaller than the ATSR pixel size.

Procedures are developed to detect hotspots in ATSR data, filter out cloud contaminated observations, and quantitatively analyse the measurements of infrared thermal flux. ATSR time-series datasets are then used to study thermal emittance from active lava domes at Lascar Volcano (Chile) and Unzen Volcano (Japan), with volcanological interpretations being made from the observed variations in radiance. At both volcanoes the dominant source of nighttime shortwave infrared thermal flux is found to be high temperature surfaces heated by fumarolic degassing. During the monitoring period, decreases in shortwave infrared flux indicate an increased hazard at Lascar, such a change indicating blockage of the degassing system and an increased likelihood of a major pressure-driven explosive event. The reverse is found to be true at Unzen, where increases in shortwave infrared flux are found to be generally related to increases in magma supply (both being positively correlated with the flux rate of magmatic gas) and so to an increased frequency of hazardous pyroclastic flow from the growing dome.

ATSR time-series studies of active lava flows at Fernandina Volcano (Galápagos Islands) and Mount Etna (Sicily) indicate that such data can also be used to document the thermal evolution of a developing lava flow field. Though necessitating assumptions regarding the flow-field thermal structure, ATSR-based estimates of the area of emplaced lava compare favourably with those obtained using higher spatial resolution imagery. For the 1991 - 1993 Etna flow, the estimates of flow surface temperature and area are used to investigate the importance of the various heat loss mechanisms. Results indicate that radiative losses dominate, but that basal conduction is also highly significant.

The Moderate Resolution Imaging Spectrometer (MODIS) of NASA’s Earth Observing System (EOS) will soon provide a new source of multi-waveband, high temporal resolution data, available to the general volcanological and remote sensing community via the EOSDIS data network. I recommend that consideration be given to nighttime operation of the MODIS shortwave infrared channels, since studies using ATSR suggest that these data have considerable potential for the thermal monitoring of active volcanoes.

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