Articles | Volume 9, issue 7
Atmos. Meas. Tech., 9, 2877–2907, 2016
Atmos. Meas. Tech., 9, 2877–2907, 2016

Research article 08 Jul 2016

Research article | 08 Jul 2016

Joint retrieval of aerosol and water-leaving radiance from multispectral, multiangular and polarimetric measurements over ocean

Feng Xu1, Oleg Dubovik2, Peng-Wang Zhai3, David J. Diner1, Olga V. Kalashnikova1, Felix C. Seidel1, Pavel Litvinov2, Andrii Bovchaliuk2, Michael J. Garay1, Gerard van Harten1, and Anthony B. Davis1 Feng Xu et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 2Laboratoire d'Optique Atmosphérique, UMR8518, CNRS/Universite Lille-1, Villeneuve d'Ascq, France
  • 3Department of Physics, University of Maryland, Baltimore County, Baltimore, Maryland, USA

Abstract. An optimization approach has been developed for simultaneous retrieval of aerosol properties and normalized water-leaving radiance (nLw) from multispectral, multiangular, 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 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, 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. For comparison, the USC_SeaPRISM retrieval is also performed by use of the Generalized Retrieval of Aerosol and Surface Properties algorithm (Dubovik et al., 2011). 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.

Short summary
We developed an algorithm for aerosol and water-leaving radiance retrieval in a simultaneous way.