A multi-sensor comparison of sulphur dioxide emissions from the 2005 eruption of Sierra Negra volcano, Galapagos Islands

Sulphur dioxide retrievals of three satellite-based sensors (the Total Ozone Mapping Spectrometer, the Ozone Monitoring Instrument and the Moderate Resolution Imaging Spectroradiometer) were performed on the volcanic cloud from the Sierra Negra, Galapagos Islands eruption of October 22 to October 30, 2005. Near-coincidental plume acquisitions on 23 October from each of the sensors were compared spatially on a pixel-by-pixel basis in order to assess the level of agreement between the retrievals. The variation in pixel size and shape between sensors was accounted for by resampling MODIS data to the geometry of the UV sensors. It was found that correlations between retrievals were wide ranging with estimates of total tonnage ranging from 60 kt up to 1800 kt. Spatial comparisons show variation according to plume altitude and overpass time and are compounded by interference from other volcanic species as well as individual instrument error. The comparison of these sensors provides an insight into the relative merits of each method and illustrates the usefulness of a holistic approach to satellite remote sensing of sulphur dioxide. This will permit the development of more robust retrieval schemes and therefore increasingly reliable estimations of volcanic SO2 emissions. (C) 2009 Elsevier Inc All rights reserved.