Volcanic SO2 and SiF4 visualization using 2-D thermal emission spectroscopy – Part 1: Slant-columns and their ratios

[摘要] The composition and emission rates of volcanic gas plumes provide insight ofthe geologic internal activity, atmospheric chemistry, aerosol formation andradiative processes around it. Observations are necessary for public securityand the aviation industry. Ground-based thermal emission infraredspectroscopy, which uses the radiation of the volcanic gas itself, allows forcontinuously monitoring during day and night from a safe distance. We presentmeasurements on Popocatépetl volcano based on thermal emissionspectroscopy during different campaigns between 2006–2009 using a ScanningInfrared Gas Imaging System (SIGIS). The experimental set-up, measurementgeometries and analytical algorithms are described. The equipment wasoperated from a safe distance of 12 km from the volcano at two differentspectral resolutions: 0.5 and 4 cm⁻¹. The 2-dimensional scanningcapability of the instrument allows for an on-line visualization of thevolcanic SO₂ plume and its animation.SiF₄ was also identified in the infrared spectra recorded at bothresolutions. The SiF₄/SO₂ molecular ratio can be calculated fromeach image and used as a highly useful parameter to follow changes involcanic activity. A small Vulcanian eruption was monitored during the nightof 16 to 17 November 2008 and strong ash emissiontogether with a pronouncedSO₂ cloud was registered around 01:00 a.m. LST (Local Standard Time). Enhanced SiF₄/SO₂ ratios were observedbefore and after the eruption. A validation of the results from thermalemission measurements with those from absorption spectra of the moon taken atthe same time, as well as an error analysis, are presented. The inferredpropagation speed from sequential images is used in a subsequent paper (Part 2)to calculate the emission rates at different distances from the crater.

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