The use of Copernicus Sentinel-3 data for research and societal needs

ESA launched Sentinel-3 (S3A) in February 2016, followed by S3B in April 2018, and the launch of S3C is now planned for mid-2023. Each S3 satellite is equipped with the Ocean Land Colour Instruments (OLCI). The operational mission is commissioned by ESA until 2030 and is part of the EU´s Copernicus program.

It is based on the legacy of ESA’s ENVISAT programme (2002-2012) with its Medium Resolution Imaging Spectrometer (MERIS).

The main advantage of MERIS and OLCI is their improved spatial (300 m) and spectral resolution when compared to other ocean colour sensors, allowing for enhanced monitoring of coastal and inland waters.

With already two OLCI instruments in Space, the temporal coverage has already increased to about one image per day over the Baltic Sea, and the frequency will be even higher once S3C is launched.

This constellation will allow to better resolve phenological cycles and to detect exceptional events, and thus to improve the monitoring the effects of climate change.The data from MERIS and OLCI can be used for the retrieval of various optical in-water constituents (e.g. Chlorophyll-a (Chl-a), suspended particulate matter (SPM) and coloured dissolved organic matter (CDOM).

These optical constituents can be used to monitor water quality, and to assess environmental changes over time, given that appropriate algorithms are employed and the data are validated.Our areas of interest are optically-complex, high CDOM waters such as the Baltic Sea, the Gulf of Bothnia and Lake Vänern.

The main hypothesis is that climate change leads to an increase in precipitation in Northern Europe, and generally to more frequent storm events.

These events cause increased erosion and run-off of humic substance and particulate matter into lakes and coastal waters.

Some of the water products from ocean colour data (such as Chlorophyll-a and reflectance) have already been adopted as essential climate change variables by the World Metrological Organization (WMO).

Besides this, turbidity and humic substances can also act as important indicators of climate change events (indicating e.g. increased frequency of torrential rainfall followed by flooding events).We will use some of our own regional algorithms developed in previous SNSA projects as well as other published algorithms and products from the Ocean Colour Climate Change Initiative portal (Ocean Colour – CCI) to evaluate long-term trends in ocean colour (OC) e.g. from 1998-2021.

The latter still remains to be validated in these highly absorbing waters, and the uncertainties will be described.Another important part of the project is to improve the use of satellite data for societal needs.

Our Group is member of EUMETSAT’s Sentinal-3 Validation team with focus on optically-complex waters (high CDOM waters).

We validate state of the art processing schemes and algorithms (adapted for coastal and inland waters) and products, and assess their uncertainties.

We will support the Ocean Colour Thematic Assembly Centre (OC-TAC) of the Copernicus Marine Environment Monitoring Service (CMEMS) with validation data for the OLCI Neural Network Swarm (ONNS). Besides this, we provide bio-optical training to the key marine monitoring groups in Sweden.

One of the objectives of this project is to provide continued expert support to SMHI in the setting-up of state-of-the-art Sentinel-3 validation procedures for SMHI’s pilot project within the Swedish Space Data Lab.

This will be done via joint workshops and a number of joint validation campaigns and personal consultations.The planned research project addresses UN´s global environmental Goal 13 "Climate action" as well as Goal 14 "Life below water".

The project also addresses several of the Swedish environmental goals, e.g. "Reduced climate impact", "A balanced sea" and "No eutrophication".

We have already set up collaborations with end-users, i.e. the Swedish Agency for Water and Coastal Management, and the County Boards in Stockholm and Norrbotten.