Volcanic gas emission studies using optical remote sensing techniques

The total flux of sulphur dioxide from the Italian volcanoes Etna, Stromboli and Vulcano was determined using the differential absorption lidar (DIAL) technique. The measurements were performed from an oceanographic research ship making traverses under the volcanic plumes with the lidar system sounding vertically. Total fluxes of about 25, 180 and 1,300 tonnes/day for Vulcano, Stromboli and Mt. Etna, respectively were found. These data, collected with an active remote sensing technique, were compared with simultaneous recording with passive differential optical absorption spectroscopy (DOAS) using the sky radiation as the light source. Since the geometry of the light paths crossing the volcanic plume is not well defined in the passive measurements, a correction to the DOAS data is required. Lidar measurements on atomic mercury were also made for the plumes from Stromboli and Vulcano, but the system sensitivity and range only allowed estimates of upper limits for the Hg fluxes.