Publication Date:
2016-02-17
Description:
Volcanic Plume Removal (VPR) is a procedure developed to retrieve the ash optical depth, effective radius and mass, and sulphur dioxide mass contained in a tropospheric volcanic cloud from the thermal radiance at 8.7, 11, and 12 μm. It is based on an estimation of a virtual image representing what the sensor would have seen in a multispectral thermal image if the volcanic cloud were not present. Ash and sulphur dioxide were retrieved by the first version of the VPR using a very simple atmospheric model that ignored the layer above the volcanic cloud. This new version takes into account the layer of atmosphere above the cloud as well as thermal radiance scattering along the line of sight of the sensor. In addition to improved results, the new version also offers easier and faster preliminary preparation and includes other types of volcanic particles. As in the previous version, a set of parameters regarding the volcanic area, particle types, and sensor are required to run the procedure. However, in the new version, only the mean plume temperature is required as input data. It this work a set of parameters have been computed for different types of plume particles (andesite, obsidian, pumice, ice, water, and sulphuric acid droplets), for both the Mt. Etna (Italy) and Eyjafjallajökull (Iceland) volcanoes, and for the MODIS Terra and Aqua instruments. Two different synthetic images, one for Mt. Etna and one for Eyjafjallajökull, are used to compare the results from the new and old procedures. Finally, a sensitivity analysis was conducted to investigate variations in VPR ash and sulphur dioxide retrievals as a function of plume altitude and particle type.
Electronic ISSN:
1867-8610
Topics:
Geosciences
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