For a given acquisition, retrieve the aerosol optical thickness estimate for input into the radiative transfer evaluation.
The supplied aerosol optical thickness data is a geospatially sparse point cloud and only exists for the years 2002 to 2008, supplemented by monthly composites.
Essentially the spatial extent of the acquisition in longitude and latitude for the WGS84 datum is intersected with the geospatial extent of the aerosol data, and a mean value extracted.
If the year of acquisition falls within 2002-2008, then select the points that have a timestamp of within 0.5 days of the acquisition, and fall within the geospatial intersection area of interest. If no data are found, fallback to a monthly aggregate for that year. If this also fails, then fall back to an all-time monthly aggregate. If this also fails then return a nominal value of 0.06.