OLCI Chlorophyll-a

Chlorophyll from satellite is an estimation of the concentration of the phytoplankton pigment, chlorophyll-a, in the ocean surface and is used as a proxy for the amount of phytoplankton in the surface water. This measurement has many applications in marine ecology, from ecosystem modeling, to fisheries management, and monitoring of water quality, to name only a few applications.

CoastWatch provides chlorophyll-a products in near-real time from the Ocean and Land Colour Instrument (OLCI) on-board the European Sentinel-3 satellites, courtesy of the European Union's Copernicus satellite program. These data offer a spatial resolution advantage over other satellite missions because of their 300 m spatial resolution, as opposed to a typical 1 km spatial resolution of ocean color products from other satellite sensors.

Sentinel-3 is a multi-instrument and multi-satellite mission to measure sea- and land-surface temperature, ocean and land color and sea-surface topography. The Sentinel-3A satellite was launched on 16 February 2016. Sentinel-3B was launched on 25 April 2018 with the same instruments. See the European Space Agency (ESA) Sentinel-3 website for more information. The Sentinel-3 satellites have a mid-morning local overpass time (roughly 10 AM local time).

The Ocean and Land Colour Instrument (OLCI) is based on heritage from ESA's Medium Resolution Imaging Spectrometer (MERIS) instrument on the Envisat satellite, designed for measuring visible and thermal infrared radiances. OLCI has 21 bands at wavelengths from 400 nm to 1020 nm, a spatial resolution of 300 m, and a swath width of 1270 km. With both Sentinel-3 satellites in orbit, the combined swath width of the two OLCI instruments allows near global coverage to be obtained on a daily basis.

Chlorophyll-a compares well between Sentinel-3A/OLCI and Sentinel-3B/OLCI. The data have been compared to in-situ measurements for both clear and optically complex water. Significant differences in uncertainty exist between these water types. Users are cautioned that coastal and lake chlorophyll-a values from OLCI may exhibit large uncertainties.

For more information on the ocean color algorithms, atmospheric correction, and product uncertainty, please consult the EUMETSAT Ocean Colour Service website. In particular, the Sentinel-3 OLCI Ocean Colour Processing Baseline contains periodically updated Product Notices with important quality information.

CoastWatch converts ESA's chlorophyll-a swath data (Level-2) into mapped gridded files (Level-3), including mapped swaths and daily composites. CoastWatch obtains the EUMETSAT operational data on a near real-time basis and has not yet obtained reprocessed collections. As such, the quality of the data as stored at CoastWatch will vary over the time series.

• See the Data Access page for data offerings by region.
• Or use Direct Download to retrieve files by time-interval and region: HTTP, FTP