Minimize Level-2

SLSTR Level-2 processing is divided into three main sub-chains, each activated by a specific switch included in the configuration parameters:

  • SST / L2P processing (divided respectively into two independent processes)
  • LST processing
  • FRP processing.

In addition to these main processes:

  • a section is dedicated to checking Level-1B files and auxiliary files to verify their presence and self-consistency
  • a common section 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
  • a product formatting section populates and writes out the product metadata and data fields.

SST/L2P processing includes two independent processes:

  • The Sea Surface Temperature (SST) processing module which 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 which 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.

LST processing 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 linearisation of the Planck function and linearity of the variation of atmospheric transmittance with column water vapour amount.

FRP processing is a six-stage process:

  1. Cloud-free land pixels which pass both spatial and spectral filter tests are considered as potential fire pixels.
  2. Scenes surrounding potential fire pixels are characterised. 
  3. Pixels which pass either absolute or contextual tests are confirmed as fire pixels.
  4. Confirmed fire pixels are screened for false alarms (caused by sun glint or desert signals).
  5. Fire radiative power is computed.
  6. FRP uncertainty and detection confidence are computed for each fire pixel.

However, coming evolutions are planned. The updated algorithm is not specified but will be mainly based on the one implemented in the SLSTR Level 2 prototype, so mainly based on this six-stage process.

Note also that modules of cloud detection will be added over ocean and Land pixels (respectively Bayesian and simplified Bayesian technics).