Characterization of a UV camera system for SO2 measurements from Popocatépetl Volcano

Abstract

Since 2016, a UV camera records images of the Popocatépetl Volcano for continuous monitoring of the SO2 plume. Five band-pass filters (300a, 300b, 307, 310, 330) with the different bandwidth (BW) of 10 and 25nm with transmissions centered at 300nm (BW=10) nm), 300nm (BW=25 nm), 307nm (BW=25 nm), 310nm (BW=10 nm)and 330nm (BW=10 nm) are used for the analysis. In order to fully characterize the filters and improve our knowledge of the errors affecting the results, the UV camera was used together with a UV spectrometer for experiments and measurements. Gas cells with different concentrations were prepared to simulate field conditions and to calibrate the SO2 column images when measuring from a fixed site. Our study is focused on a) applying the required corrections due to vignetting by the instrumentation as well as flattening the light intensity gradients in the field of view, b) determining the effect on the results when using different interference filters, c) applying a simplified light dilution correction and d) performing an a posteriori calibration correction using four interference filters. Our results show that a permanently installed and well-characterized camera, even with the rather long distance from the crater (11.3 km), can provide valuable and reliable information of the SO2 emissions from the Popocatépetl Volcano.