Information on Atmospheric Aerosol in OMI Measurements

Atmospheric aerosol is monitored using OMI (Ozone Monitoring Instrument) measurements of reflected sunlight in a series of narrow wavelength bands between 331 nm to 500 nm. A Principle Component Analysis (PCA) is performed to quantify the information content of OMI measurements on aerosols. This analysis is based on synthetic measurements for a large number of scenarios. Synthetic measurements are generated for an atmosphere containing desert dust, biomass burning or weakly absorbing aerosol with a variety of aerosol optical depths, aerosol layer altitudes, refractive indices and size distributions. The range of aerosol parameters considered is assumed to cover the natural variability of atmospheric aerosols. The principal component analysis is performed for various observation geometries and surface types including ocean, soil and vegetation. When the surface albedo is accurately known and clouds are absent, OMI measurements have 2 to 4 degrees of freedom that can be attributed to aerosol parameters. An additional wavelength band is evaluated, that comprises the O2-O2 absorption band at a wavelength of 477 nm. It is found that this wavelength band adds significantly more information than any other individual band. The PCA is applied to assess the capability of the aerosol retrieval to discern various aerosol types as well as clouds.