ALBERT

Description: An optimization approach has been developed for simultaneous retrieval of aerosol properties and normalized water-leaving radiance (nLw) from multi-spectral, multi-angular, and polarimetric observations over ocean. The main features of the method are (1) use of a simplified bio-optical model to estimate nLw followed by an empirical refinement within a specified range to improve its accuracy; (2) improved algorithm convergence and stability by applying constraints on the spatial smoothness of aerosol loading and Chlorophyll-a (Chl-a) concentration across neighboring image patches and spectral constraints on aerosol optical properties and on nLw across relevant bands; and (3) enhanced Jacobian calculation by modeling and storing the radiative transfer (RT) in aerosol/Rayleigh mixed layer, pure Rayleigh scattering layers, and ocean medium separately and then coupling them to calculate the field at the sensor. This approach avoids unnecessary and time-consuming recalculations of RT in unperturbed layers in Jacobian evaluations. The Markov chain method is used to model RT in the aerosol/Rayleigh mixed layer and the doubling method is used for the uniform layers of the atmosphere-ocean system. Our optimization approach has been tested using radiance and polarization measurements acquired by the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) over the AERONET USC_SeaPRISM ocean site (6 February 2013) and near the AERONET La Jolla site (14 January 2013), which respectively reported relatively high and low aerosol loadings. Validation of the results is achieved through comparisons to AERONET aerosol and ocean color products and retrievals performed using the Generalized Retrieval of Aerosol and Surface Properties algorithm (Dubovik et al., 2011) on AirMSPI data. Uncertainties of aerosol and nLw retrievals due to random and systematic instrument errors are analyzed by truth-in/truth-out tests with three Chl-a concentrations, five aerosol loadings, three different types of aerosols, and nine combinations of solar incidence and viewing geometries.