Optical monitoring of volcanic sulphur dioxide emissions—comparison between four different remote-sensing spectroscopic techniques

• Published in: Optics and lasers in engineering Vol. 37; no. 2; pp. 267 - 284
• Main Authors: Weibring, P., Swartling, J., Edner, H., Svanberg, S., Caltabiano, T., Condarelli, D., Cecchi, G., Pantani, L.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.02.2002; Elsevier
• Subjects: Atom and Molecular Physics and Optics; Atom- och molekylfysik och optik; Correlation spectroscopy; Crystalline rocks; DOAS; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Fysik; Geochemistry; Geochemistry: general, methodology, regional studies; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Lidar; Natural hazards: prediction, damages, etc; Natural Sciences; Naturvetenskap; Physical Sciences; Southern Europe; Aeolian Islands; Tyrrhenian Sea; Sicily Italy; Italy; Mount Etna; West Mediterranean; Stromboli; Lidar; DOAS; Correlation spectroscopy; wavelength; sulfur dioxide; diffusion; atmospheric emission; plumes; Europe; remote sensing; concentration; monitoring; volcanism; optical spectroscopy; Mediterranean Sea; gases; absorption spectra
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/S0143-8166(01)00084-7

The emissions of sulphur dioxide from the Italian volcanoes Mt. Etna and Stromboli were studied in ship-borne underpasses of their plumes. Four different optical spectroscopy techniques were used and inter-compared. All techniques utilise the absorption signature of the gas in the wavelength region of around 300 nm. A differential absorption lidar was employed in active gas concentration assessment. In parallel, a differential optical absorption spectroscopy system (DOAS) provided spectrally resolved absorption spectra. In one configuration the DOAS used a vertically looking telescope and the absorption of the sky-light was studied, while a different DOAS implementation utilised the sun disc as the light source in slant-angle, long-path absorption measurements. Parallel measurements with the customary correlation spectroscopy method were also performed. Path length Monte Carlo simulations of the down-welling radiation through the volcanic plume at different sun altitude and azimuth angles have been performed taking into account also the effects of other geometric parameters as the plume height and extension. The results are discussed with special emphasis on systematic effects due to scattering.