Development and application of new techniques for sulfur dioxide monitoring at active volcanoes.

摘要

This dissertation presents the results from two research projects that address issues in ground-based remote sensing of volcanic SO 2 emissions. In the first project we compare high-temporal resolution SO2 data measured with Differential Optical Absorption Spectroscopy (DOAS) with long period (LP) seismicity. Prevailing east-to-west winds on the volcanic island of Montserrat in the West Indies facilitate the placement of two automated DOAS instruments in permanent locations resulting in daily SO2 fluxes every 1--5 minutes for ∼7 hours each day. An attempt to make one-to-one comparisons between individual LP events and SO2 fluxes proved difficult due to large flux-to-flux variability, random "spikes", and apparent dependencies on time of day. Instead, daily averages of SO 2 emissions were computed and compared to LP seismicity. Larger amplitude LPs were associated with increasing SO2 (depressurization), and periods when LP events were more numerous occurred when SO2 emissions were relatively the lowest on average (pressurization).; The second part of this dissertation describes an effort to design and test a digital camera capable of imaging and spatially mapping SO2 concentrations in a large portion of a volcanic plume. For this project, we used a digital camera with a 1024x1024 CCD array, a uv bandpass filter centered at 307 nm, and a 105 mm lens to create an image of light intensities covering a narrow range of uv wavelengths sensitive to SO2 absorption. The camera was calibrated and tested by imaging calibration cells, power plant emissions, and plumes from four active volcanoes. Power plant and volcanic plume images show exceptional detail in plume discrimination up to 16 km distant. However, more research is required for proper calibration as calculated absorbances for known power plant concentrations are ∼60--70% lower than those computed for the calibration cells. Also, average plume absorbances decrease with distance due to scattered light from the intervening atmosphere. An exponential correction applied to correct for this "air light" has been moderately successful.