SENTINEL-2 Level-1C is an orthoimage product, i.e. a map projection of the acquired image using a system DEM to correct ground geometric distortions. Pixel radiometric measurements are provided in Top-Of-Atmosphere (TOA) reflectances. The SENTINEL-2 instrument acquires measurements at 12 bits. These measurements are converted to reflectances and stored as 16 bit integers in the S2 product. The transformation of reflectances in 16 bit integers is performed according to the following equation:
L1C_DN = ρ * QUANTIFICATION_VALUE - RADIO_ADD_OFFSET
The L1C product's metadata includes the values for the QUANTIFICATION_VALUE and RADIO_ADD_OFFSET.
The No Data value is represented as 0 in the L1C product.
Level-1C products are resampled with a constant GSD (Ground Sampling Distance) of 10 m, 20 m and 60 m according to the native resolution of the different spectral bands.
Level-1C products are routinely geometrically refined. However, they can be processed without refinement on an "as required" basis (e.g. where they might be required for cal/val purposes). These products can be identified by the presence of a dedicated flag in the metadata.
Level-1C processing includes:
- geometric corrections:
- sub-pixel multi-temporal registration between images
- resampling using a 90m Copernicus DEM (or 30 m Copernicus DEM for the Collection 1 products)
- radiometric processing
- conversion to reflectance
-
preview image generation and masks generation (defective pixels, clouds and land/water).
Since December 2016, Level-1C products are provided in single Tile format. A single Tile is a 110 km by 110 km squared orthoimage in UTM/WGS84 projection and containing 13 spectral bands in JPEG2000 (*.jp2) format. Tiles can be fully or partially covered by image data. Partially covered tiles correspond to those at the edge of the swath.
Neighbouring Tiles overlap each other by 10 Km.
Figure 1: Example of Level-1C Tiled Product
The quality indicator and the auxiliary data are provided within the metadata.
Note that one Level-1C tile including all bands is approximately 500 MB in file size.
The Level-1C product has a SAFE format. This groups together several types of file:
- a product metadata file in XML format that describes the physical organization and the content of the product
- a manifest.safe file which holds the general product information in XML
- a GRANULE subfolder, including image data for the given tile in JPEG2000 format as well as quality indicators (quality masks, quality reports, etc.)
- a DATASTRIP subfolder containing information at datastrip level
- an AUX_DATA subfolder containing the set of auxiliary files that can be embedded in the product
- a rep-info subfolder containing the XSD schemas describing the product components
- an INSPIRE XML file, that is a metadata file based on INSPIRE Metadata regulation
- a HTML subfolder containing a product presentation file allowing to display easily the main content of the product.
Figure 2: Level-2A Product physical format