Plume Imaging Using an IR Camera to Estimate Sulphur Dioxide Flux on Volcanoes of Northern Chile

Abstract:

Remote sensing is a fast and safe method to obtain gas abundances in volcanic plumes, in particular when the access to the vent is difficult or during volcanic crisis. In recent years, a ground-based infrared camera (NicAir) has been developed by Nicarnica Aviation, which quantifies SO₂ and ash on volcanic plumes, based on the infrared radiance at specific wavelengths through the application of filters.

NicAir cameras have been acquired by the Geological Survey of Chile in order to study degassing of active volcanoes. This contribution focuses on series of measurements done in December 2013 in volcanoes of northern Chile, in particular Láscar, Irruputuncu and Ollagüe, which are characterized by persistent quiescent degassing. During fieldwork, plumes from all three volcanoes showed regular behavior and the atmospheric conditions were very favorable (cloud-free and dry air).

Four, two and one sets of measurements, up to 100 images each, were taken for Láscar, Irruputuncu and Ollagüe volcano, respectively. Matlab software was used for image visualizing and processing of the raw data. For instance, data visualization is performed through Matlab IPT functions imshow() and imcontrast(), and one algorithm was created for extracting necessary metadata. Image processing considers radiation at 8.6 and 10 µm wavelengths, due to differential SO₂ and water vapor absorption. Calibration was performed in the laboratory through a detector correlation between digital numbers (raw data in image pixel values) and spectral radiance, and also in the field considering the camera self-emissions of infrared radiation.

A gradient between the plume core and plume rim is expected, due to quick reaction of sulphur dioxide with water vapor, therefore a flux underestimate is also expected. Results will be compared with other SO₂ remote sensing instruments such as DOAS and UV-camera.

The implementation of this novel technique in Chilean volcanoes will be a major advance in our understanding of volcanic emissions and is also a strong complement for gas monitoring in active volcanoes such as Láscar, Villarrica, Lastarria, Cordón Caulle, among others and in rough volcanic terrains, due to its portability, easy operation, fast data acquisition and data processing.