Detection of volcanic SO2 by spaceborne infrared radiometers

Current infrared narrowband instruments, such as Moderate Resolution Imaging Spectrometer (MODIS) or Spinning Enhanced Visible and InfraRed Imager (SEVIRI), can be used to locate volcanic SO2 plumes. A three-channel technique has been proposed by Prata et. al. [Prata, A.J., Rose, W.I., Self, S., OʹBrien, D.M., 2003. Global, long-term sulphur dioxide measurements from TOVS data: a new tool for studying explosive volcanism and climate. AGU Geophysical Monograph 139: Volcanism and the Earthʹs Atmosphere (pp. 75–92). Ed. by A. Robock and C. Oppenhaimer.], which considers the difference in brightness temperature (BT) in the SO2 absorption band around 7–8 µm between an observed value and an estimated value interpolated from two other channels. The technique relies on the assumption that the interpolated BT value is a good approximation of the BT that would have been observed in the absence of SO2. In this study we use a sophisticated radiative transfer model in order to test this assumption and assess the sensitivity of this three-channel technique to the vertical profiles of temperature and water vapour, the surface temperature, the vertical distribution of the SO2, the viewing geometry, the presence of ash, and the presence of low- and high-level clouds. The capabilities and limitations of such a technique are discussed. An example is also shown as a proof of concept using data from the SEVIRI instrument onboard the MSG satellite.