The objective of this component of the PARTS project is the retrieval of aerosol optical depth during cloud free episodes over ocean (and possibly land). From the retrieved optical depth and an assumed aerosol vertical number density, it is intended to produce vertical profiles of aerosol extinction.
The retrieval is to use an optimal estimation algorithm using a forward model which describes the satellite-measured radiance as a function of the atmosphere's optical depth. The model we have developed is based on a 32 layer atmosphere and considers the effects of multiple scattering, molecular absorption and Rayleigh scattering.
We model radiative transfer through the atmosphere with the DISORT algorithm. This algorithm has the flexibility to define an atmosphere in terms of several homogeneous layers containing particles described by their phase function (or asymmetery parameter) and single scatter albedo. Look up tables (LUTs) of reflected and transmitted radiance are calculated as functions of solar and satellite viewing geometry as well as optical depth.
Surface reflectance plays a vital role in the forward model's radiance calculations. It is proposed that we may eventually retrieve aerosol over land surfaces using the
product and sea surfaces with Cox and Monk adjusted albedo values. Our first forward model will use the MODIS albedo product over land and a constant value over sea.
The parameter to be determined from the retrieval process is optical depth. From optical depth and an assumed vertical aerosol extinction distribution profile an aerosol extinction profile can be achieved.
Will be put here as they arise.
As gridded data become available they can be obtained from here .