Passive infrared spectroscopic remote sensing of volcanic gases: Ground-based studies at White Island and Ruapehu, New Zealand, and Popocatépetl, Mexico

Abstract

Gaseous volcanic emissions provide important insights on volcanic processes and may aid in predicting eruptive activity, but traditional in situ measurements are prohibitively dangerous at many volcanoes. Here we describe techniques for remotely measuring volcanic gas composition, at ranges up to tens of kilometers, using ground-based passive infrared spectroscopy. The principles of passive in frared spectroscopic remote sensing are discussed, and the effects of thermal contrast on the detectability of gases in various viewing geometries are quantita tively examined. This examination reveals that, for ground-based measurements, a sky background usually provides the best results. Our initial remote sensing campaign (April-May, 1996) at the White Island and Ruapehu volcanoes in New Zealand, combining passive Fourier transform infrared (FTIR) spectroscopy with traditional COSPEC and direct sampling measurements, confirmed this and demonstrated spectroscopic detection of S0 2 , H 2 0 and HC1 at ranges of up to 6 km, with good agreement between FTIR-derived and direct sampling based gas ratios. In measurement campaigns at Mexico's Popocatepetl volcano (February 1997 and February 1998), we monitored variations of S0 2 , SiF 4 , HC1, and HF, and extended the range of sky-background passive infrared techniques to over 17 km. In the highest temporal resolution study to date of short-term compositional variations associated with an explosive eruption (25-26 February 1997), we ob served a steady increase in SiF 4 /S0 2 over several days preceding the eruption, followed by a tenfold decrease in this ratio over a few hours immediately after wards, a signature suggesting an adiabatic expansion prior to and during a gasdriven explosion. We examine the ultimate range limits of ground-based passive FTIR spectroscopy and possible future extensions to imaging and airborne in struments.

Volcanic SO<sub>2</sub> and SiF<sub>4</sub> visualization using 2-D thermal emission spectroscopy – Part 1: Slant-columns and their ratios

“…For the analysis of spectra at 4 cm −1 taken on 16/17 November 2008 the value 275 K was used and for those taken on 28 May 2009 a temperature of 280 K was chosen. Although an exact value of the plume temperature is not known, the visualization and determination of molecular ratios between SiF 4 and SO 2 are quite insensitive to the plume temperature as described by Love et al (2000) and shown in Sect. 5.1.…”

“…According to our knowledge thermal emission spectroscopy to characterize volcanic emissions was applied for the first time in 1996 by Love et al (1998Love et al ( , 2000 and Goff et al (2001). From thermal emission spectroscopy, SO 2 , SiF 4 , H 2 O, CO 2 (Goff et al, 2001) and even HCl (Love et al, 2000) have been determined in volcanic gas plumes.…”

“…From thermal emission spectroscopy, SO 2 , SiF 4 , H 2 O, CO 2 (Goff et al, 2001) and even HCl (Love et al, 2000) have been determined in volcanic gas plumes. However, good H 2 O and CO 2 results have proven to be difficult to obtain because of their high atmospheric background.…”

First Simultaneous Visualization of SO2and NO2Plume Dispersions using Imaging Differential Optical Absorption Spectroscopy

“…3-6 Several types of remote sensing techniques are available for observing the temporal and spatial characteristics of these gases in plume emitted from various point sources such as power plants and volcanoes, such as Correlation SPECtrometer (COSPEC) method, 7 the SO 2 camera technique, 8 Fourier-Transform spectroscopy in the IR (FT-IR), [9][10][11] and passive differential optical absorption spectroscopy (DOAS). However, these methods do not support simultaneous measurements of multiple trace gases.…”

Non-Luminous Flame Temperature Determination Method Based on CO2Radiation Intensity

“…This method is usually used to yield the atmospheric constituents and temperature. It is the simplest possible remote measurement of * e-mail: s.cieszczyk@pollub.pl volcanic gases [1]. Additionally, in the case of combustion processes signicant information about the processes can be obtained from their radiative emissions.…”