Sentinel-2A and 2B absolute calibration monitoring

TLDR

Sentinel‑2 is a Copernicus optical imaging mission that provides global, high‑resolution, multi‑spectral coverage of land and coastal areas with a five‑day revisit cycle. This paper reviews the techniques used to achieve an absolute calibration of the 13 spectral bands to better than 5 % (target 3 %) at the top‑of‑atmosphere level. The authors describe the mission’s radiometric calibration scheme, the use of vicarious calibration over natural targets such as oceans, deserts, and Antarctica, and a verification process employing in‑situ photometer measurements at La Crau (France) and Gobabeb (Namibia). The study concludes that the calibration methods yield spectral coherence, agreement across techniques, and a consistent temporal evolution of the calibration coefficients.

Abstract

As part of the Copernicus program, Sentinel-2 is the optical imaging mission designed for the operational monitoring of land and coastal areas. It offers a unique combination of global coverage with a wide field of view, a high revisit capability (5 days with two satellites), a high resolution and multi-spectral imagery.CNES, the French Space Agency, was involved in the commissioning of both Sentinel-2 satellites and is currently working in collaboration with ESA on their long-term monitoring. This paper reviews all the techniques used to ensure an absolute calibration of the 13 spectral bands to better than 5% (the target is 3%) at TOA level. After a brief description of the mission and its related radiometric calibration scheme, we show how standard vicarious calibration methods based on acquisitions over natural targets (oceans, deserts, and Antarctica during winter) are used to check and improve the accuracy of the absolute calibration coefficients. Finally, the verification scheme, exploiting photometer in-situ measurements over the La Crau plain in France and Gobabeb in Namibia, is described. The paper concludes with a summary that includes spectral coherence, agreement between the results obtained with various calibration methods and temporal evolution.