Operational real-time monitoring of volcanic SO2 emission rates using an innovative SO2 camera system and sophisticated retrieval techniques (Invited)
Abstract
With the advent of SO2 camera systems some years ago, it became possible to image volcanic SO2 plumes at high temporal and spatial resolutions. Systems operating in the ultra-violet region measure the absorption of scattered solar radiation by SO2 in a narrow wavelength channel centered around 310 nm. A first-order correction for the effect of aerosol scattering is obtained by recording coincident images in at least one additional, off-band channel, typically centered around 330 nm. The promise of measuring SO2 emission rates at time resolutions comparable to geophysical techniques has led to increasingly widespread application of such systems. Until recently, however, a number of issues made SO2 camera systems difficult to use quantitatively for continuous monitoring. For one, UV-sensitive CCD camera technology lacked the durability required for continuous use. Also, because these camera systems collect very limited spectral information the potentially complex radiative transfer of a given scene, which can significantly impact SO2 retrievals, was not quantifiable. System calibrations were typically performed using gas cell measurements, but this approach is not valid for distant or optically thick plumes, or for plumes containing ash. Finally, the use of simple correlation techniques to derive plume velocity usually required manual input and did not take into account that the velocity typically varies throughout the plume. Together, these effects could easily lead to absolute errors of 100% or more in retrieved SO2 emission rates. Here we present solutions to these major challenges. First, we describe an SO2 camera system that uses two modern UV-sensitive CCD cameras with electronic shutters that are integrated with a moderate resolution UV spectrometer. The system software retrieves plume velocity fields in two dimensions, thus improving the accuracy of the derived SO2 emission rates while at the same time providing purposeful data for the study of plume dynamics and entrainment of ambient air. In addition, the spectrometer data are used to retrieve and correct for complex radiative transfer effects in the camera images. These techniques to improve the accuracy of retrieved SO2 emission rates were integrated into a continuous, real-time monitoring system for measuring SO2 output from Kilauea's summit vent starting in August 2013. Several examples from this exciting new dataset will be given, and the new opportunities for studying volcanic processes that such instruments provide will be illustrated.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.V54C..04K
- Keywords:
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- 8494 VOLCANOLOGY Instruments and techniques;
- 8485 VOLCANOLOGY Remote sensing of volcanoes;
- 8430 VOLCANOLOGY Volcanic gases