Sentinel-3 Synergy processing
The Synergy processing of Sentinel-3 aims at making use of the combined information from the OLCI and SLSTR instruments to provide improved data for land surface vegetation analysis.
The L2 processing makes use of the enhanced spectral and angular capabilities of a combined instrument (the SYN instrument) to produce a product with atmosphere-corrected surface reflectance and corresponding information on aerosol properties, whereas the VGT processing uses data from OLCI and SLSTR to provide products comparable to SPOT VGT-P and VGT-S.
The L2 processing uses 18 OLCI spectral bands and 6 solar reflective bands in each SLSTR view (nadir and oblique). Thermal and atmospheric absorption bands are not considered. The images acquired for the synergy bands are co-located at OLCI spatial resolution. Aerosol retrieval is carried out at a coarser resolution (configurable). The retrieved Aerosol properties minimise an error metric based on pure spectral and dual-view spectral-angular models available as look-up tables for up to 40 different Aerosol models. The retrieval includes uncertainty estimates per pixel, based on the curvature of the error metric at the minimum. Retrieval failures are filled by means of distance-weighted averaging and a climatologic background model.
Retrieved Aerosol properties and uncertainty estimates are interpolated to the full spatial resolution grid. Employing the look-up tables with the interpolated Aerosol properties as parameters yields surface reflectance and corresponding uncertainty estimates, considering uncertainty estimates at L1 and Aerosol retrieval uncertainties.
The VGT processing uses the same 18 OLCI spectral bands as the L2 processing, but only three spectral bands in the SLSTR nadir view. The calculation of the SPOT VGT spectral bands (termed spectral band mapping) is carried out by means of atmospheric correction (aerosol from climatology), hyperspectral interpolation of surface reflectance, inverse hyperspectral atmospheric correction, and convolution with VGT response functions.
The prototype Synergy processor consists of modules, which correspond to the individual processing steps. It is applicable to products of any size, because it processes data in chunks. The prototype is coded in C++ and uses the Open Multi-Processing technology to exploit multiple CPU cores.
Poster presented at the ESA Sentinel-3 OLCI/SLSTR and MERIS/AATSR Workshop 2012 in Frascati, Italy.