Tracking and quantifying volcanic SO<sub>2</sub> with IASI, the September 2007 eruption at Jebel at Tair

Abstract

Abstract.In this paper we demonstrate the potential of the infrared Fourier transform spectrometer IASI in analysing volcanic eruptions, using the September 2007 eruption at Jebel at Tair as an illustrative example. Detailed radiative transfer calculations are presented, simulating IASI-like transmittance spectra for a variety of volcanic plumes. We analyse the sensitivity of IASI to SO 2 at different altitudes and demonstrate that IASI is in principle capable of sensing SO 2 down to the surface. Using the brightness temperature difference of well chosen SO 2 channels as a filter, we are able to track the plume of the Jebel at Tair eruption for 12 days, on a par with state of the art UV sounders. A method is presented for quickly estimating the altitude of a volcanic plume based on the relative intensities of the SO 2 absorption lines. Despite recent advances, it is still very challenging to retrieve vertical profiles of SO 2 from nadir viewing satellites. Currently the most accurate profiles in nadir are retrieved using backtracking of the plume with atmospheric transport models. Via full inverse retrievals using the optimal estimation method, we show the possibility of extracting medium coarse vertical profiles from IASI data. The retrieval allows us to present an evolution of the total mass of SO 2 in the plume for the Jebel at Tair eruption. An analytical relation is derived between brightness temperature differences and concentrations, which fits the experimental data very well. The spectral range of IASI also allows retrieval of volcanic aerosols. In the initial plume of the Jebel at Tair eruption, volcanic aerosols were found in the form of ice particles, for which we derived particle sizes.

Global distributions of methanol and formic acid retrieved for the first time from the IASI/MetOp thermal infrared sounder

“…In order to take advantage of the very good spatial coverage of IASI we have chosen a simple, fast and robust approach based on brightness temperature differences ( T b ), similar to the method already used for the retrieval of sulfur dioxide (Clarisse et al, 2008) and ammonia . It consists in two steps: (i) the determination of T b globally and (ii) the conversion of T b to total column amounts using one (global) or two (continental and oceanic) conversion factors.…”

“…For this purpose, we have retrieved CH 3 OH total columns at various locations of the world with an inversion model based on the Optimal Estimation Method (OEM) (Rodgers, 2000) that includes a line-by-line radiative transfer model. This is implemented in the Atmosphit software developed at the Université Libre de Bruxelles (for more information see Clarisse et al, 2008 andCoheur et al, 2005). The method is only applied in selected regions due to computational limitations.…”

Antarctic ozone hole as observed by IASI/MetOp for 2008–2010

“…Due to its large spatial coverage, combined with its low radiometric noise IASI provides twice daily global measurements of key atmospheric species enabling the analysis of species concentrations, global distribution and transport such as O 3 HNO 3 (Wespes et al, 2009). Other reactive species which are retrieved include carbon monoxide (CO) Pommier et al, 2010), methane (CH 4 ) , sulphur dioxide (SO 2 ) (Clarisse et al, 2008), ammonia (NH 3 ) , methanol (CH 3 OH) and formic acid (HCOOH) Razavi et al, 2011). For a full detailed overview of the IASI instrument, its specifications and trace gas species that can be retrieved see Clerbaux et al (2009).…”

Potential for the use of reconstructed IASI radiances in the detection of atmospheric trace gases

“…The characteristics of SO 2 spectra are described in detail by Clarisse et al (2008a). There are two bands that can be detected by IASI, the ν 1 band centred on 1150 cm −1 and the ν 3 band centred on 1360 cm −1 .…”

“…A strong feature but only found in rare events such as volcanic eruptions (Clarisse et al, 2008a) -Methane (CH 4 ) in the ν 3 band at 2550-2760 cm −1 . This band can be used to complement the ν 4 band at 1220-1380 cm −1 which is usually used to retrieve CH 4 (Crevoisier et al, 2009b), as the ν 3 band can, under certain conditions, improve the information in the boundary layer ).…”