The SYN AOD algorithm is performed after the SYN L1 processing and takes into account the internal SYN L1c dataset (i.e. the whole OLCI and SLSTR L1 dataset projected on the OLCI instrument grid). It is divided into 3 main modules:
- The creation of the super-pixel grid and dataset
- The aerosol retrieval module
- The post-processing module
The main processing steps are:
| Number | Processing Step | Description |
| 1 | AOD_init | Check configuration and auxiliary files are present and self-consistent |
| 2 | AOD_prep | Derive super pixel related quantities |
| 3 | AOD_retr | Aerosol retrieval |
| 4 | AOD_post | Post-processings |
| 5 | AOD_out | Populate and write out product headers and data fields. |
The SYN AOD algorithm is based on the same philosophy than the SYN SDR one. Several evolutions have been however specified:
- Inversion procedure to retrieve continuous aerosol component mixture.
- Inclusion of prior climatology of aerosol properties to constrain retrieval, especially Single Scattering Albedo.
- Uncertainty estimate per retrieval.
- Generation of new LUT set to include 4 aerosol components (dust, sea salt, fine mode strong absorbing, fine mode weak absorbing), and all combinations of 25% mixtures of these, at wavebands/geometries for both SLSTR and OLCI.
- Adaptation of CCI aerosol retrieval method both for SLSTR channels and solar/view geometry, and for SLSTR/OLCI synergy. Over glint-free ocean an adaption of spectral estimation has been performed to allow retrieval with SLSTR nadir view only.
- Inclusion of ocean model giving surface reflectance and uncertainty, dependent on wind speed, ocean colour, for SLSTR & OLCI wavebands and view geometry.