Minimize Auxiliary Data Files (ADFs)

Auxiliary data is all other data (i.e. excluding direct measurements from the instrument and information on platform orbital dynamics) necessary for product processing and generation.

ADFs, such as the Digital Elevation Model (DEM) or the Global Reference Image (GRI), that are used in the generation of Level-1 products, are verified before use to ensure the processing chain is not compromised. The GRI enables the automatic creation of Ground Control Points (GCPs) for Level-1C processing.

For SENTINEL-2, auxiliary data is composed of:

  • On-Board Configuration Data (OBCD), comprised of on-board configuration parameters and payload and platform characterisation data
  • On-Ground Configuration Data (OGCD), which, for Level-1 products, is composed of Ground Image Processing Parameters (GIPP) and includes the DEM, GRI and processors versions.

Each OBCD and OGCD file is identified by the type of data, applicability date, version number and the satellite to which it is applicable (SENTINEL-2A, SENTINEL-2B or both). Any update of one or other of the files will result in the other being updated at the same time. All auxiliary data used for Level-1B and Level-1C processing can be identified in the metadata accompanying the product.

In addition to the Level-1B auxiliary data, the Level-1C auxiliary data also includes meteorological parameters, temporally and spatially interpolated from raw ECMWF global forecast data sets:

  • Total Column Ozone (TCO3) [kg/m2]

  • Total Column Water Vapour (TCWV) [kg/m2]

  • Mean Sea Level Pressure (MSLP) [hPa].

The Level-1C meteorological auxiliary data are resampled and distributed on the Level-1C tiles. Grid points are provided in latitude/longitude using the WGS84 reference system.


ECMWF Ozone

Within Level-1C products, in addition to Total Column Water Vapour (TCWV) and Mean Sea Level Pressure (MSLP) auxiliary data, Total Column Ozone (TCO3) auxiliary data is also provided. Expressed in units of kg/m2, TCO3 corresponds to the vertical integrated ozone content.

TCO3 is used in the context of atmospheric corrections, to correct ozone gaseous absorption affecting TOA measurements, and forms part of the On-Ground Configuration Data (OGCD) provided for onward processing (i.e. to Level-2A).

The input data content is provided by ECMWF and is derived from temporal and spatial interpolation of the raw global forecast dataset. This data is then resampled to conform to the Level-1C grid and information requirements. Grid points are provided in latitude/longitude using the WGS84 reference system.


Total Column Water Vapour

Sentinel-2 Water Vapour

One of the parameters included in the Level-1C auxiliary data is the Total Column Water Vapour (TCWV) expressed in kg/m2. This parameter corresponds to the vertically integrated water vapour. TCWV is used in the context of atmospheric corrections, to correct water vapour gaseous absorption affecting TOA measurements.

TCWV data is derived from ECMWF input data resampled and distributed in grid information tiles with the same dimensions as the Level-1C tiles. Grid points are provided in latitude / longitude using the WGS84 reference system.


Mean Sea Level Pressure (MSLP)

One of the parameters embedded in the Level-1C auxiliary data is the Mean Sea Level Pressure (MSLP) expressed in hPa. This parameter corresponds to the atmospheric pressure at sea level.

The MSLP is used in the context of atmospheric corrections to correct TOA measurements for Rayleigh scattering.

It is derived from temporal and spatial interpolation of the raw ECMWF global forecast dataset. This dataset is updated daily. MSLP data is resampled and distributed in grid information tiles with the same dimensions as the Level-1C tiles. Grid points are provided in latitude/longitude using the WGS84 reference system.

More information on these ECMWF inputs can be found at European Centre for Medium-Range Weather Forecasts.