SU_(A)ATSR v4.21
This version provides:
        - reprocessing of global 17 year processing for ATSR-2 and AATSR 
          based on V2.1 L1b input data including minor changes :
	- Per retrieval uncertainty estimate over land has been 
	  downscaled to better represent the actual uncertainty
	- single scattering albedo (SSA), absorbing aod (AAOD), 
	  dust aod (D_AOD) are provided as diagnostic variables to enable
	  consistent treatment of the data for the interested user / modeller.
	- files are provided in netcdf-4 format to be 
	  compliant with CCI requirements
	- angström exponent is now provided between 550nm and 870nm


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More detailed explanation of sub-directories L2 and L3.

Level 2:

Directory L2:
Resolution - 10x10 km2 sinusoidal
Format NetCDF version 4

All retrieved variables are stored as vectors depending only on the unlimited dimension "pixel_number".
For each reported successful retrieval the following variables are available in the level 2 NetCDF files:

 - Latitude, Longitude 
 - AOD - at 550, 670, 870 and 1600 nm  
 - Ångström exponent (550nm - 870nm);
 - Per-pixel uncertainty estimates in AOD at 550, 670, 870, 1600nm; 
 - fine mode AOD (FM_AOD550)
 - dust aod (D_AOD550) and absorbing aod (AAOD550) derived from retrieved total AOD and fine mode AOD
   The actual composition (dust / absorption) of the fine and coarse mode is based on 
   climatological values which are used in the retrieval.
 - single scattering albedo (SSA550) (climatoglogy)
 - atmospherically corrected surface reflectance 550, 670, 870, 1600nm (nadir only) 
 - cloud fraction in the 10x10km superpixel
 - land / ocean flag (a 10x10km pixel can only have one surface type)
 - time of measurement
 - viewing geometry (solar zenith, view zenith and relative azimuth angle) for forward and nadir



Level 3: 

Level 3, directory L3_DAILY:
daily files
Resolution - 1 degree x 1 degree global grids
Format NetCDF version 4

Level 3 data is stored as global 2 dimensional grids depending on lat / lon.                     
Latitude, Longitude (Vectors specifying the grid box centre locations)
Mean and standard deviation of the following variables:
 - AOD (550, 670, 870, 1600nm)
 - AOD per pixel uncertainty (550, 670, 870, 1600nm)
 - Ångström (550nm - 870nm)
 - surface reflectance (550, 670, 870, 1600nm)
 - fine mode AOD (AOD550 * fine_mode_fraction)
 - dust AOD (AOD550 * (1 - fine_mode_fraction) * dust_fraction)
 - absorbing AOD (AOD550 * (1 - SSA))
 - SSA
 - cloud_fraction
 - view geometry
 - surface type (for mixed land/sea grid boxes, the mean surface type gives the fraction of land retrievals 
   within that grid box for that day or month)

Level 3, directory L3_MONTHLY:
same as L3_DAILY, but monthly averages and s.d.

Furthermore provided in the L3 products are minimum and maximum values of AOD L2 uncertainties.
Additionally propagated uncertainties for AOD550, AOD670, AOD870, AOD1600 are provided 
which take estimates of daily and monthly sampling uncertainties into account.