User Guides - Sentinel-3 SLSTR - Level-2 Processing - Sentinel Online
The SLSTR Level-2 products are generated via three processors (processing overview at Level-2 Processing Overview):
- SST/L2P and LST products
- FRP products
- AOD products
The processor generating SST/L2P and LST products, namely the SLSTR L2 IPF, includes three core modules:
- The Sea Surface Temperature (SST) processing module that implements five single-algorithm SST algorithms. Each derives SST as weighted combinations of the brightness temperatures measured in both view (nadir and oblique) and by the thermal channels (S7 to S9).
- The L2P processing module that implements the Level-2 SST product following the Group for High Resolution Sea Surface Temperature (GHRSST) data processing specification. This SST field is a composite of the single-algorithm SST variables generated in the previous module. Each SST is atmospherically smoothed following the ATSR model. Only the "best" product for the local conditions is taken into account for outputting.
- The LST processing module that includes a split-window method, using radiances from two channels whose band centres are close in wavelength, to determine the effective radiometric temperature of the Earth's surface "skin" in the instrument field of view ("skin" referring to the top surface in bare soil conditions and to the effective emitting temperature of vegetation "canopies" as determined from a view of the top of a canopy). This method assumes that the linearity of the relationship between LST and BT results from linearization of the Planck function and linearity of the variation of atmospheric transmittance with column water vapour amount.
In addition to these main modules:
- one module is dedicated to checking the input Level-1B files and auxiliary files to verify their presence and self-consistency,
- one module gathers general functions such as deriving pixel-by-pixel estimates of radiance, BT, radiance uncertainty and BT uncertainty for channels S2, S3, S6 to S9, F1 and F2,
- one module is dedicated to product formatting, which populates and writes out the product metadata and data fields.
The processor generating the FRP products, namely the FRP IPF, shares with the SLSTR L2 IPF the module checking the input data and the module gathering general functions. Details about the FRP core processing will be provided as soon as the verification and validation process will be completed.
The AOD processing, performed via the AOD IPF, will be completely independent from the others. It will include four main modules:
- on module to check the input SLSTR L1 data and auxiliary files (this module is equal to the corresponding one of the other two processors),
- super-pixel processing module aiming to compute the combined TOA reflectance associated with each super-pixel,
- a retrieval module, which analyses the aerosol condition and retrieve the aerosol characteristics through a double optimisation process,
- the output module aiming to populate and write out the product metadata and data fields.