Band Residual Difference Algorithm for Retrieval of SO 2 From the Aura

Abstract—The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resolution, coupled with global coverage, for space-based UV measurements of sulfur dioxide (SO 2). This paper describes an OMI SO 2 algo-rithm (the band residual difference) that uses calibrated residuals at SO 2 absorption band centers produced by the NASA opera-tional ozone algorithm (OMTO3). By using optimum wavelengths for retrieval of SO 2, the retrieval sensitivity is improved over NASA predecessor Total Ozone Mapping Spectrometer (TOMS) by factors of 10 to 20, depending on location. The ground footprint of OMI is eight times smaller than TOMS. These factors produce two orders of magnitude improvement in the minimum detectable mass of SO 2. Thus, the diffuse boundaries of volcanic clouds can be imaged better and the clouds can be tracked longer. More significantly, the improved sensitivity now permits daily global measurement of passive volcanic degassing of SO 2 and of heav