Abstract
Abstract. The composition and emission rates of volcanic gas plumes provide insight of the geologic internal activity, atmospheric chemistry, aerosol formation and radiative processes around it. Observations are necessary for public security and the aviation industry. Ground-based thermal emission infrared spectroscopy, which uses the radiation of the volcanic gas itself, allows for continuously monitoring during day and night from a safe distance. We present measurements on Popocatépetl volcano based on thermal emission spectroscopy during different campaigns between 2006–2009 using a Scanning Infrared Gas Imaging System (SIGIS). The experimental set-up, measurement geometries and analytical algorithms are described. The equipment was operated from a safe distance of 12 km from the volcano at two different spectral resolutions: 0.5 and 4 cm−1. The 2-dimensional scanning capability of the instrument allows for an on-line visualization of the volcanic SO2 plume and its animation. SiF4 was also identified in the infrared spectra recorded at both resolutions. The SiF4/SO2 molecular ratio can be calculated from each image and used as a highly useful parameter to follow changes in volcanic activity. A small Vulcanian eruption was monitored during the night of 16 to 17 November 2008 and strong ash emission together with a pronounced SO2 cloud was registered around 01:00 a.m. LST (Local Standard Time). Enhanced SiF4/SO2 ratios were observed before and after the eruption. A validation of the results from thermal emission measurements with those from absorption spectra of the moon taken at the same time, as well as an error analysis, are presented. The inferred propagation speed from sequential images is used in a subsequent paper (Part 2) to calculate the emission rates at different distances from the crater.
Highlights
Volcanoes are known to emit large amounts of gases into the atmosphere and contribute with 10–15 % of the global anthropogenic sulphur emissions (Halmer, 2002)
Global monitoring by thermal emission measurements is possible by sounders with enough spectral resolution such as the TES (Tropospheric Emission Spectrometer) and IASI (Infrared Atmospheric Sounding Interferometer) instruments (Clarisse et al, 2008)
The Scanning Infrared Gas Imaging System (SIGIS) used is comprised of an interferometer (OPAG 22, Bruker Daltonics, Leipzig, Germany), an azimuth-elevation-scanning mirror actuated by stepper motors, a telescope, a data and video processing and control system with a digital signal processor (DSP), a camera and a personal computer (Fig. 2)
Summary
Volcanoes are known to emit large amounts of gases into the atmosphere and contribute with 10–15 % of the global anthropogenic sulphur emissions (Halmer, 2002). From the ground, infrared studies of the volcanic plume composition have mostly used the solar absorption technique and open-path and thermal emission FTIR spectroscopy. Without controlling the radiation source and can be further distinguished in (A) absorption spectroscopy, which uses the sun, moon or hot rocks as ligh2t0source and (B) thermal emission spectroscopy, using the radiation emitted by the target gas itself, which acts as the light source SO2, SiF4, H2O, CO2 (Goff et al, 2001) and even HCl (Love et al, 2000) have been determined in volcanic gas plumes. Good H2O and CO2 results have proven to be
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