Sentinel-2

Sentinel-2 is a twin-satellite Earth observation mission developed by the European Space Agency (ESA) as part of the European Union's Copernicus programme. Comprising Sentinel-2A (launched 23 June 2015) and Sentinel-2B (launched 7 March 2017), the mission provides high-resolution multispectral imagery with 13 spectral bands, up to 10-metre spatial resolution, and a combined revisit time of 5 days at the equator (2–3 days at mid-latitudes). With its free, full, and open data policy, Sentinel-2 has become the workhorse of civilian Earth observation — the most widely used source of free multispectral satellite data in the world.

The mission was designed to support land monitoring services including agriculture, forestry, land-cover change detection, and disaster mapping, but its versatility has made it indispensable across dozens of application domains, from urban planning to coral reef monitoring.

Each Sentinel-2 satellite carries a Multi-Spectral Instrument (MSI) — a pushbroom sensor that images a 290 km swath as the satellite moves along its sun-synchronous orbit at 786 km altitude. The MSI records reflected sunlight in 13 spectral bands grouped by spatial resolution: four 10 m bands (Blue at 490 nm, Green at 560 nm, Red at 665 nm, and NIR at 842 nm), six 20 m bands (three Red Edge bands at 705/740/783 nm, Narrow NIR at 865 nm, and two SWIR bands at 1610/2190 nm), and three 60 m atmospheric bands (Coastal Aerosol at 443 nm, Water Vapour at 945 nm, and Cirrus at 1375 nm).

Data is distributed as Level-1C (top-of-atmosphere reflectance in UTM/WGS84 tiles) and Level-2A (bottom-of-atmosphere surface reflectance, atmospherically corrected using the Sen2Cor processor). L2A products include a Scene Classification Layer that flags clouds, shadows, water, and snow. For most analytical workflows — especially time-series monitoring and spectral index calculation — L2A is the recommended starting point.

As an optical sensor, Sentinel-2 cannot image through clouds — a significant constraint in tropical and high-latitude regions where persistent cloud cover can leave gaps lasting weeks or months. The 10 m spatial resolution, while excellent for free data, is insufficient for applications requiring individual object identification. The 5-day revisit is too infrequent for monitoring rapidly changing phenomena like tidal patterns or daily urban activity. The 60 m atmospheric bands have limited direct analytical value and exist primarily to support atmospheric correction.

Sentinel-2 emerged from ESA's recognition in the early 2000s that Europe needed its own high-resolution, multispectral monitoring capability. Sentinel-2A reached orbit on 23 June 2015, launched by a Vega rocket from Kourou. Its twin, Sentinel-2B, followed on 7 March 2017, halving the revisit time from 10 to 5 days. The decision to include three red-edge bands — absent from Landsat — was driven by the European agricultural community's need for detailed crop monitoring, and this has proven to be one of the mission's most significant differentiators. The free and open data policy transformed the mission's impact far beyond what traditional restricted-access satellites could achieve. Sentinel-2C was launched in September 2024 to maintain constellation continuity, with Sentinel-2D planned to follow.