Mt. Etna aerosol optical thickness from MIVIS images

This work focuses on the evaluation of Aerosol Optical Thickness (AOT) in Mt. Etna volcano area starting from the analysis of MIVIS VIS images. MIVIS images and ancillary data (atmospheric profiles, photometric measurements, atmospheric infrared radiances, surface temperatures, ground reflectances, SO2 abundances) were collected during the Sicily '97 campaign. Data elaboration was performed with extensive use of 6S radiative transfer model, determining optical thickness with an inversion algorithm that uses atmospheric vertical profile, ground reflectance data and radiance measured by the first MIVIS spectrometer (channels 1-20; range 0.44-0.82 mu). Ground reflectance is the most problematic parameter for the algorithm. In order to have a low and 'uniform' surface reflectance, only pixels located at an altitude between 2000-3000 in a.s.l. were analysed. At this altitude, AOT is very low during non-eruptive periods: at Torre del Filosofo (2920 in a.s.l.) on June 16th 1997, during one MIVIS flight, AOT at 0.55 mu was 0.19. The uncertainty about ground reflectance produces significant errors on volcanic background AOT, and in some cases the error is up to 100%. The developed algorithm worked well on volcanic plume, allowing us to determine the plume related pixels' AOT. High plume AOT values minimize the problems deriving from reflectance uncertainty. Plume optical thickness shows values included in a range from 0.5 to 1.0. The plume AOT map of Mt. Etna volcano, derived from a MIVIS image of June 16th 1997, is presented

Mt. Etna aerosol optical thickness from MIVIS images

This work focuses on the evaluation of Aerosol Optical Thickness (AOT) in Mt. Etna volcano area starting from the analysis of MIVIS VIS images. MIVIS images and ancillary data (atmospheric profiles, photometric measurements, atmospheric infrared radiances, surface temperatures, ground reflectances, SO2 abundances) were collected during the «Sicily '97» campaign. Data elaboration was performed with extensive use of 6S radiative transfer model, determining optical thickness with an inversion algorithm that uses atmospheric vertical profile, ground reflectance data and radiance measured by the first MIVIS spectrometer (channels 1-20; range 0.44-0.82 n). Ground reflectance is the most problematic parameter for the algorithm. In order to have a low and 'uniform' surface reflectance, only pixels located at an altitude between 2000-3000 m a.s.l. were analysed. At this altitude,AOT is very low during non-eruptive periods: at Torre del Filosofo (2920 m a.s.l.) on June 16th 1997, during one MIVIS flight, AOT at 0.55 n was 0.19. The uncertainty about ground reflectance produces significant errors on volcanic background AOT, and in some cases the error is up to 100%. The developed algorithm worked well on volcanic plume, allowing us to determine the plume related pixels'AOT. High plume AOT values minimize the problems deriving from reflectance uncertainty. Plume optical thickness shows values included in a range from 0.5 to 1.0. The plume AOT map of Mt. Etna volcano, derived from a MIVIS image of June 16th 1997, is presented

RETRIEVAL OF TROPOSPHERIC ASH CLOUDS OF MT. ETNA FROM AVHRR DATA

This paper focuses on three eruptiveevents of the Mt. Etna volcano: July 22nd 1998,April 26th 2000 and the recent eruption of July-August 2001. Such eruptions may be a severethreat to aircraft safety, as in the April 2000event. From the AVHRR visible images theheight of the top of the clouds is estimated,using geometrical methods, knowing bothNOAA satellite and Sun positions. The resultsare then compared with information derivedfrom radio-sounding data etc.. The volcanic ashparticles with diameters of 1-10 mm are notdetectable by aircraft radar but they may beremotely sensed using thermal infrared data.The well-known algorithm, based on theAVHRR channel 4 and channel 5 brightnesstemperatures difference [Prata, 1989; Schneideret al. 1994], is here applied to highlight the ashclouds of Mt. Etna volcano. Even though it wastypically used to detect and follow the volcanicclouds of stratospheric eruptions, here it is succesfullytested for tropospheric plume too.Some good results of this technique are presentedtogether with some basic problems. Thiswork points out that it could be useful to preparea procedure to monitor Mt. Etna eruption cloudsanalysing TIR data. Such a procedure shouldautomatically alert (in real time, using the newMeteosat Second Generation satellite) and indicatethe cloud direction on the basis of atmosphericradio-sounded and/or predicted data