An effective method for the detection of trace species demonstrated using the MetOp Infrared Atmospheric Sounding Interferometer

Abstract

Abstract. A detection method is demonstrated for volcanic sulphur dioxide and ammonia from agriculture using data from the MetOp Infrared Atmospheric Sounding Interferometer (IASI). The method is an extension of the Brightness Temperature Difference (BTD) technique which uses the difference in brightness temperature between a small number of channels sensitive to the target species and spectral background to determine the presence of the target species. The method described here allows instead for the use of large numbers of channels with an optimal set of linear weights which effectively suppress the spectral background allowing low-noise filters to be produced which are capable of distinguishing the target species from other parameters such as interfering species, surface and atmospheric temperature, and cloudiness without retrieving these parameters explicitly. Once generated, the filters can be applied quickly and easily to identify events of interest over a large global dataset, in near-real-time if required, and in some circumstances a degree of quantitative information can be extracted about the abundance of the target species. The theory behind the generation of the filters is first described. The filters are then used in the detection of volcanic sulphur dioxide from the eruption of the Kasatochi volcano in Alaska, beginning in August 2008, and in the detection of ammonia emissions related to agriculture over Southern Asia in May 2008. The performance of new the filters is compared against that obtained using existing filters.