An Analysis of Proximal Volcanic Ash Emissions

Volcanic ash is a product of explosive volcanic eruptions and refers to those particles < 2 mm in size that are ejected from a volcano. Once erupted into the atmosphere, ash can be transported vast distances. Satellite remote sensing has provided us with the tools to map and monitor these plumes. These methods are restricted in viewing only that portion that is optically transparent, due to the requirement to observe the interaction of ground upwelling radiation with the plume. For this study, methods have been developed to map not only the opaque portion of the plume, but in higher spatial resolution than has been attempted previously. This has been done by using the unique emissivity spectra that are produced by materials in the thermal infrared portion of the electromagnetic spectrum. By using an end-member linear unmixing model with a spectral emissivity library of different volcanic ash types, opaque plume bearing pixels of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data have been processed. These end-member results have shown the applicability of this technique, with sampled volcanoes mapped with very low root mean square (RMS) errors. Volcanoes with unknown composition were also mapped with the library with varying degrees of success. Further expansion of the laboratory spectral library will allow more accurate assessment of these volcanoes. The collection of per pixel emissivity spectra of opaque plumes was also attempted using an experimental multispectral FLIR thermal camera apparatus, in order to collect data on the rising volcanic ash column. These data showed that the camera can produce emissivity spectra, however further calibration and correction is required in order to make a volcanological assessment of the eruptive products. Finally, a method of better tracking disconnected ash plumes is assessed. In cases where a plume is detected disconnected from or distally from the source volcano, the application of geostatistical methods to backward trajectory model data can yield the source location. This could then be used to helped point the ASTER sensor off-axis towards erupting targets, thus providing a greater quantity of data to be analyzed