Observing Aerosol Extinction in the Nadir and Limb Using Hyperspectral Instruments
Smith, Andrew; Dudhia, Anu; Grainger, Roy Gordon
University of Oxford, UNITED KINGDOM
Hyper-spectral IR instruments contain huge amounts of underexploited information describing continuum scatterers and absorbers. Analysis of the MIPAS data set has concentrated on retrievals of molecular species. However, there is a significant amount of information to be obtained from the continuum, avoiding discrete molecular lines. MIPAS is an instrument well adapted to detection of aerosols. The limb view gives good vertical resolution and a deep space background that does not interfere with continuum signals. The IR spectra contains information about aerosol "type" that is not available from measurements in the visible and so is good for the classification of aerosol signals. A spectral aerosol extinction product based on the MORSE retrieval is presented which takes advantage of these properties. Classification by several methods, including simple radiance ratios and singular vector decomposition are compared. The data is also compared to the ORAC aerosol retrieval which uses visible channels and so provides independent confirmation of results. In the nadir, IASI measurement are used to demonstrate aerosol detection and classification using measurement covariance methods that seek to minimise the significance of natural spectral variability relative to irregular events.