Sentinel-2 L2A (Surface Reflectance)

Sentinel-2 L2A is the bottom-of-atmosphere surface reflectance product derived from the 13-band multispectral MSI instrument on the ESA/Copernicus Sentinel-2 constellation, generated by applying the Sen2Cor atmospheric correction processor to the Level-1C top-of-atmosphere reflectance data^[1][2]. L2A omits the B10 cirrus band (1375 nm) that is present at L1C, leaving 12 surface reflectance bands available for analysis^[3]; the raw sensor band count is 13, which is the value recorded in the row and reflects the total MSI band set. Spatial resolution varies by band: B2, B3, B4, and B8 are delivered at 10 m; B5, B6, B7, B8A, B11, and B12 at 20 m; and B1 and B9 at 60 m.

ESA distributes L2A through the Copernicus Data Space Ecosystem in JPEG2000 format within a SAFE container, under the Copernicus Open Access licence. The French THEIA centre produces an independent L2A product from the same input imagery using the MAJA atmospheric correction algorithm^[4], which applies a multi-temporal approach differing from Sen2Cor's single-scene MODTRAN-based correction^[1].

From Processing Baseline 04.00 (deployed January 2022), ESA introduced a +1000 digital offset to the L2A reflectance values (stored as integer reflectance x 10000 + 1000). Data processed before PB04.00 does not carry this offset. Users combining time series across the baseline boundary must apply harmonization to ensure consistency^[5][6]. ESA's Collection-1 archive reprocessing campaign applied PB05.x to the 2015-2023 historical archive^[1].

The Sentinel-2A+2B dual-satellite configuration provides a nominal 5-day global revisit at the equator. Known processing artefacts include Sen2Cor scene classification errors in which thin cirrus layers are misclassified as bright bare soil, which can result in incorrect cloud masking in semi-arid scenes^[3]. Cloud cover remains the primary operational limitation for usable acquisition density in persistently cloudy regions. Product data and STAC catalogue access are available at dataspace.copernicus.eu^[3][6].