Volcanic plume removal (VPR) is a procedure developed to retrieve the ashoptical depth, effective radius and mass, and sulfur dioxide mass containedin a volcanic cloud from the thermal radiance at 8.7, 11, and 12 µm. Itis based on an estimation of a virtual image representing what the sensorwould have seen in a multispectral thermal image if the volcanic cloud werenot present. Ash and sulfur dioxide were retrieved by the first version ofthe VPR using a very simple atmospheric model that ignored the layer abovethe volcanic cloud. This new version takes into account the layer ofatmosphere above the cloud as well as thermal radiance scattering along theline of sight of the sensor. In addition to improved results, the newversion also offers an easier and faster preliminary preparation andincludes other types of volcanic particles (andesite, obsidian, pumice, icecrystals, and water droplets). As in the previous version, a set ofparameters regarding the volcanic area, particle types, and sensor isrequired to run the procedure. However, in the new version, only the meanplume temperature is required as input data. In this work, a set ofparameters to compute the volcanic cloud transmittance in the three quotedbands, for all the aforementioned particles, for both Mt. Etna (Italy) andEyjafjallajökull (Iceland) volcanoes, and for the Terra and Aqua MODISinstruments is presented. Three types of tests are carried out to verify theresults of the improved VPR. The first uses all the radiative transfersimulations performed to estimate the above mentioned parameters. The secondone makes use of two synthetic images, one for Mt. Etna and one forEyjafjallajökull volcanoes. The third one compares VPR and Look-Up Table(LUT) retrievals analyzing the true image of Eyjafjallajökull volcano acquiredby MODIS aboard the Aqua satellite on 11 May 2010 at 14:05 GMT.
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