## 2 EO Satellite and In Situ Observations for Earth Surface
### Copernicus Sentinels
A highly sensitive Ocean and Land Colour Imager (OLCI) delivering multi-channel wide-swath optical measurements for ocean and land surfaces. With 21 bands (compared to the 15 on Envisat's MERIS) and a design optimised to minimise sun-glint, OLCI marks a new generation of measurements over the ocean and land attaining a resolution of 300 m over all surfaces. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Sentinel 1** & **Launch Date** & **ESM Relevance** \\ \hline Sentinel 1A & 3 April 2014 & aggregate \\ Sentinel 1B & 25 April 2016 & aggregate \\ Sentinel 2A & 23 June 2015 & aggregate \\ Sentinel 2B & 7 March 2017 & aggregate \\ Sentinel 3A & 16 February 2016 & direct \\ Sentinel 3B & 25 April 2018 & direct \\ Sentinel 5P & 13 October 2017 & direct \\ Sentinel 6 & 2020 (expected) & direct \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Copernicus Sentinels launch dates and relevance in modelling application (aggregate use refers to composites in space and time, while direct use refers to single observation). Figure 1: Copernicus Sentinels 1 to 6 (left to right). A dual-view Sea and Land Surface Temperature Radiometer (SLSTR) delivering accurate surface ocean, land, and ice temperature, with an accuracy better than 0.3 K. SLSTR measures in nine spectral channels and two additional bands optimised for fire monitoring. SLSTR has a spatial resolution in the visible and shortwave infrared channels of 500 m and 1 km in the thermal infrared channels. The swath of OCLI and nadir SLSTR fully overlap. Sentinel-3A and 3B were launched in February 2016 and April 2018, respectively. Full performance will be achieved once both Sentinel-3A and 3B will be in routine operations at the end of 2018, with a revisit time of less than two days for OLCI and less than one day for SLSTR at the equator. The satellite orbit provides a 27-day repeat for the topography package, with a 4-day sub-cycle (defined as the minimum number of days after which the ground track of the satellite nearly repeats itself within a small offset). The Sentinel-3 ground segment systematically acquires, processes and distributes a set of pre-defined core data products to the users (see [[https://earth.esa.int/web/sentinel/missions/sentinel-3/data-products](https://earth.esa.int/web/sentinel/missions/sentinel-3/data-products)]([https://earth.esa.int/web/sentinel/missions/sentinel-3/data-products](https://earth.esa.int/web/sentinel/missions/sentinel-3/data-products))). An example of the sensor capability is given in Figure 2 for land surface temperature, vegetation state (chlorophyll index) and snow cover. Figure 2: Sentinel-3 derived kilomet-scale products for Earth System Modelling. **(top)** SLSTR Land Surface Temperature monthly composite for September 2016 (Credit: D. Ghent, University of Leicester) **(middle)** OLCI Terrestrial Chlorophyll Index April–May 2017 (Credit: University of Southampton–J. Dash/Brockman Consult (S3-MPC)) **(bottom panel)** SLSTR Snow Extent Product, 5–10 April 2018 (Credit: ENVEO). Copyright: All figures contain modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO.