SYN Level-2 Format

SENTINEL-3 Synergy SYN L2 format

The SYN Level-2 product is composed of five different packets, all available to the user except the VGK product:

  • SY_2_SYN includes surface reflectances and aerosol parameters over land and on a 300m resolution
  • SY_2_VGP includes TOA reflectances on 1 km VEGETATION-like product
  • SY_2_VGK includes surface reflectances and NDVI for spectral VGT channels
  • SY_2_VG1 includes 1 day synthesis surface reflectance and NDVI on 1 km VEGETATION-like product
  • SY_2_V10 includes 10 day synthesis surface reflectance and NDVI on 1 km VEGETATION-like product.
  • SY_2_AOD includes global aerosol characteristics over land and sea at 4.5 km super-pixel resolution

As for Sentinel-3 products, all these packages are composed of one information package map, also called a manifest, and several measurement and annotation data files.

The manifest file is written in XML format and gathers general information concerning the product and processing. The measurement and annotation data files are written in netCDF 4 format, and include dimensions, variables and associated attributes.

The SY_2_SYN package includes 29 measurement data files and nine annotation data files.

The first 26 measurement files provide Surface Directional Reflectances (SDR) and their associated error estimates for all OLCI channels (except Oa13, Oa14, Oa15, Oa19 and Oa20) and all SLSTR solar channels (except S4 dedicated to cloud detecton), nadir and oblique view. As files are projected on the OLCI image grid, one specific file is dedicated to the removed pixels. The last two provide aerosol optical thickness at 550 nm and the aerosol Angstrom exponent, also projected on the image grid of OLCI reference channel.

The annotation files are described in the following:

  • angles and geographical information for OLCI and SLSTR tie-points (on nadir and oblique view) provided on dedicated tie-point grids
  • geolocation for the OLCI reference channel
  • time of measurement for each line of the OLCI reference channel
  • geophysical atmospheric data, derived from the OLCI meteorological annotation file
  • global flags, computed during Level-1 processing but also during OLCI and SLSTR processing, provided on the OLCI image grid
  • Synergy Aerosol Model Index Number data file (SYN_AMIN) provided on the OLCI reference image grid (note that this aerosol model is currently fixed to the continental model)
  • all annotation data associated with removed pixels

The SY_2_VGP, SY_2_VG1 and SY_2_V10 packages are designed as SPOT continuity products. They include respectively four and five measurement data files in addition to eight and nine annotation data files.

The measurement data files included in SY_2_VGP provide VEGETATION TOA reflectance for each defined spectral band, i.e. B0 for 450 nm (central wavelength), B2 for 645 nm, B3 for 835 nm and MIR for 1665 nm. The reflectances are indexed by number of columns, line by latitude and longitude dimension. Their geographical positions are also included in these files

The annotation data files included in SY_2_VGP provide, for sub-sampled columns and lines, in addition to their geographical position, solar/ viewing azimuth and zenith angle (respectively referenced as saa, sza, vaa, vza), aerosol optical thickness at 550 nm (ag), total column ozone (og) and water vapour (wvg) and the status flags (sm).

The SY_2_VG1 and SY_2_V10 packages include similar files to the SY_2_VGP packages but VG1 provides the single best value for TOA reflectance at the four specific channels over 1 day period and V10 provides the maximum value composite over a 10-day period at the four channels.The composite method is based on the “maximum-NDVI value” approach.

In addition, the Normalised Difference Vegetation Index (NDVI) is provided in a measurement file and the synthesis time data (tg) is provided in an annotation data file.

The SY_2_VGK product is similar in content and in projection to the SY_2_VGP product. The only exception is that included radiometric measurements are surface reflectance (i.e. aerosol corrected) and that this product is also providing NDVI and time.

The SY_2_AOD product is a global aerosol product, including only one measurement file. This file, common to ocean and land area, provide aerosol optical thickness and surface reflectance for 6 different radiometric bands on a 4.5 km resolution. Other aerosol characteristics like dust fraction, single scattering albedo, … are provided for each super-pixel(defined as a combination of 15*15 300m OLCI image pixel). These super-pixels are described in the SY_2_AOD product by providing geographical position of each corner and position of their center.

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