A Novel Approach to Estimating Time-Averaged Volcanic SO₂ Fluxes from Infrared Satellite Measurements

Long-term continuous time series of ${\mathrm{SO}}_2$ emissions are considered critical elements of both volcano monitoring and basic research into processes within magmatic systems. One highly successful framework for computing these fluxes involves reconstructing a representative time-averaged ${\mathrm{SO}}_2$ plume from which to estimate the ${\mathrm{SO}}_2$ source flux. Previous methods within this framework have used ancillary wind datasets from reanalysis or numerical weather prediction (NWP) to construct the mean plume and then again as a constrained parameter in the fitting. Additionally, traditional ${\mathrm{SO}}_2$ datasets from ultraviolet (UV) sensors lack altitude information, which must be assumed, to correctly calibrate the ${\mathrm{SO}}_2$ data and to capture the appropriate NWP wind level which can be a significant source of error. We have made novel modifications to this framework which do not rely on prior knowledge of the winds and therefore do not inherit errors associated with NWP winds. To perform the plume rotation, we modify a rudimentary computer vision algorithm designed for object detection in medical imaging to detect plume-like objects in gridded ${\mathrm{SO}}_2$ data. We then fit a solution to the general time-averaged dispersion of ${\mathrm{SO}}_2$ from a point source. We demonstrate these techniques using ${\mathrm{SO}}_2$ data generated by a newly developed probabilistic layer height and column loading algorithm designed for the Cross-track Infrared Sounder (CrIS), a hyperspectral infrared sensor aboard the Joint Polar Satellite System’s Suomi-NPP and NOAA-20 satellites. This ${\mathrm{SO}}_2$ data source is best suited to flux estimates at high-latitude volcanoes and at low-latitude, but high-altitude volcanoes. Of particular importance, IR ${\mathrm{SO}}_2$ data can fill an important data gap in the UV-based record: estimating ${\mathrm{SO}}_2$ emissions from high-latitude volcanoes through the polar winters when there is insufficient solar backscatter for UV sensors to be used. View Full-Text