GASP: GOME Aerosol Spectral Processor

GASP is the GOME Aerosol Spectral Processor developed in order to generate the aerosol optical thickness (AOT) product starting from the spectra measured by GOME instrument. The GOME instrument, on board the ERS-2 satellite, has been designed in order to collect radiation over the entire wavelength region from 240 to 790 nm, in which several atmospheric species and also aerosols and clouds can be observed. In this paper the scheme and the functionalities of GASP are described. GASP provides the aerosol optical thickness at the reference wavelength of 550 nm and the aerosol class for cloud free pixels. The retrieval scheme, based on the maximum likelihood principle, uses as forward model GOMESIM, suitably tuned in order to simulate a MODTRAN like behavior. The aerosol classification is made choosing the minimum among the least squares residuals computed for different aerosol classes that can be distinguished in the troposphere. In order to show the results obtained by GASP a first set of real data has been processed and analyzed.