Abstract
Abstract. A new optimal estimation algorithm for the retrieval of sulphur dioxide (SO2) has been developed for the Infrared Atmospheric Sounding Interferometer (IASI) using the channels between 1000–1200 and 1300–1410 cm−1. These regions include the two SO2 absorption bands centred at about 8.7 and 7.3 μm (the ν1 and ν3 bands respectively). The retrieval assumes a Gaussian SO2 profile and returns the SO2 column amount in Dobson units and the altitude of the plume in millibars (mb). Forward modelled spectra (against which the measurements are compared) are based on the Radiative Transfer for TOVS (RTTOV) code. In our implementation RTTOV uses atmospheric profiles from European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological data. The retrieval includes a comprehensive error budget for every pixel derived from an error covariance matrix that is based on the SO2-free climatology of the differences between the IASI and forward modelled spectra. The IASI forward model includes the ability to simulate a cloud or ash layer in the atmosphere. This feature is used to illustrate that: (1) the SO2 retrieval is not affected by underlying cloud but is affected if the SO2 is within or below a cloud layer; (2) it is possible to discern if ash (or other atmospheric constituents not considered in the error covariance matrix) affects the retrieval using quality control based on the fit of the measured spectrum by the forward modelled spectrum. In this work, the algorithm is applied to follow the behaviour of SO2 plumes from the Eyjafjallajökull eruption during April and May 2010. From 14 April to 4 May (during Phase I and II of the eruption) the total amount of SO2 present in the atmosphere, estimated by IASI measurements, is generally below 0.02 Tg. During the last part of the eruption (Phase III) the values are an order of magnitude higher, with a maximum of 0.18 Tg measured on the afternoon of 7 May.
Highlights
The magmatic processes of an active volcano can be monitored, and potentially explained, by observations of volcanic emission into the atmosphere
The volcanic SO2 plume can be used as a proxy for volcanic ash within the first few hours of its release, when the effect of wind shear and gravitation have not separated the ash plume from the SO2
A new optimal estimation (OE) scheme has been developed for Infrared Atmospheric Sounding Interferometer (IASI) measurements to estimate the height and column amount of a volcanic SO2 plume together with the associated pixel-by-pixel error estimates
Summary
The magmatic processes of an active volcano (during both quiescent and eruptive phases) can be monitored, and potentially explained, by observations of volcanic emission into the atmosphere. In recent years more advanced, high resolution spectrometers, such as the Ozone Monitoring Instrument (OMI) on-board AURA from 2004, the Infrared Atmospheric Sounding Interferometer (IASI) and the Global Ozone Monitoring Experiment-2 (GOME-2) on-board the Meteorological Operational satellite (MetOp-A from 2006), have made possible the study of quiescent volcanic activity (Carn et al, 2008). Near-real time estimates of SO2 are available globally for hazard warning purposes (e.g. from OMI, GOME-2, Atmospheric Infrared Sounder, AIRS and IASI) The accuracy of these data is restricted by the assumptions that need to be made (e.g. the altitude of the volcanic plume) in order to provide a fast (near-real time) system. This region is an atmospheric window (relatively high transmittance) and, at IASI spectral resolution, does not contain significant spectral information about the plume altitude/profile It is probably the most useful region for monitoring those volcanoes characterized by continuous quiescent degassing Carboni et al.: IASI SO2 retrieval both the British Atmospheric Data Centre (BADC) archive and EUMETSAT Unified Meteorological Archive Facility (UMARF) archive
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call