THEORETICAL STUDY ON VOLCANIC PLUME SO2 AND ASH RETRIEVAL USING GROUND TIR CAMERA: SENSITIVITY ANALYSIS AND RETRIEVAL PROCEDURE DEVELOPMENTS

In this paper, a sensitivity analysis and proceduredevelopment for volcanic-plume sulfur dioxide and ash retrievalsusing ground thermal infrared camera have been carried out.The semiconductor device camera, considered as a reference, hasa spectral range of 8–14 μm with noise equivalent temperaturedifference that is better than 100 mK at 300 K. The camera willbe used to monitor and assess the hazards of Mt. Etna volcanoto mitigate the risk and impact of volcanic eruptions on the civilsociety and transports. A minimum number of filters have beenselected for sulfur dioxide (SO2) and volcanic ash retrievals.The sensitivity study has been carried out to determine the SO2and volcanic ash minimum concentration detectable by the systemvarying the camera geometry and the atmospheric profiles.Results show a meaningful sensitivity increase considering highinstrument altitudes and low camera-elevation angles. For allgeometry configurations and monthly profiles, the sensitivity limitvaries between 0.5 and 2 g · m−2 for SO2 columnar abundanceand between 0.02 and 1 for ash optical depth. Two procedures todetect SO2 and ash, based on the least square fit method and on thebrightness temperature difference (BTD) algorithm, respectively,have also been proposed. Results show that high concentration ofatmospheric water vapor columnar content significantly reducesthe ash-plume effect on the BTD. A water vapor-correction procedureintroduced improves the ash retrievals and the cloud discriminationin every season, considering all the camera geometries.