The OLCI/Sentinel-3A L1 Reduced Resolution Top of Atmosphere Reflectance, S3A_OL_1_ERR is generated from the data aquired by the Ocean and Land Colour Instrument (OLCI) on board European Earth Observation satellite mission, SENTINEL-3. The OLCI is a push-broom imaging spectrometer that measures solar radiation reflected by the Earth at a ground spatial resolution of around 300m, over all surfaces, in 21 spectral bands. OLCI is based on the imaging design of ENVISAT's Medium Resolution Imaging Spectrometer (MERIS). It has a 1270km wide swath.

For more information about the instrument and the mission, visit "Sentinel Online" at https://sentinel.esa.int/web/sentinel/home.

The S3A_OL_1_ERR is a Level-1B product. This is composed of an information package map, called a manifest, 22 measurement data files, and seven annotation data files. The 21 measurement data files (one for each band) consist of Top Of Atmosphere (TOA) radiances, calibrated to geophysical units (W.m-2. sr-1 Micro meter-1), georeferenced onto the Earth's surface, and spatially resampled onto an evenly spaced grid. Seven annotation files provide information on illumination and observation geometry, environment data (meteorological data) and quality and classification flags. Both measurement data files and annotation data files are written in netCDF 4 format. The manifest file is in XML format and contains metadata associated with the instrument and the processing. The S3A_OL_1_EFR is generated in Earth Observation (EO) processing mode and all parameters in this product are provided for each re-gridded pixel on the product image and for each removed pixel.

The OL_1_EFR product package is described below:

Element name Description Manifest.safe SENTINEL-SAFE product manifest Oa##_radiance.nc Radiance for OLCI acquisition bands 01 to 21 Time_coordinates.nc Time stamp annotations Geo_coordinates.nc High resolution georeferencing data Quality_flags.nc Classification and quality flags Tie_geo_coordinates.nc Low resolution georeferencing data Tie_geometries.nc Sun and view angles Tie_meteo.nc ECMWF meteorology data Instrument_data.nc Instrument data

note: Oa## represents all the OLCI channels (Oa1 to Oa21).

For more information about the product, read the SENTINEL-3 OLCI User Guide at https://sentinel.esa.int/web/sentinel/user-guides/sentinel-3-olci