RRS James Clark Ross (British Antarctic Survey) and Sentinel 3a satellite (European Space Agency, ESA)

Helping satellites to better observe our oceans

Images: JCR - A. Simpson, British Antarctic Survey, Sentinel 3a satellite - European Space Agency, ESA 

PML scientists are embarking on two new projects funded by the European Space Agency, ESA, to ensure the accuracy of satellite data that is used to observe our changing oceans, now and into the future.

Observations from space provide unique information which greatly aids understanding and management of climate change. 
 
Satellites are vitally important as they can observe vast areas of the ocean that are difficult to access and sample using traditional methods. Satellite data therefore offers a cost-effective means of providing a global coverage of oceanic conditions. However, in order for these observations to be meaningful, they need to be corroborated by measurements taken in the field.
 
To achieve this, PML scientists are involved in two new exciting international projects. The first (AMT4SentinelFRM) is led by PML, using measurements taken on the Atlantic Meridional Transect (AMT) during an annual research voyage between the UK and destinations in the South Atlantic. Drs Gavin Tilstone, Giorgio Dall’Olmo and Bob Brewin will use continuous on-board ship measurements to validate the accuracy and quality of the satellites orbiting overhead. This transect is of particular value as it covers a vast range of environments from the productive coastal regions to the desert-like gyres in the centre of the ocean, which are rarely accessed by research ships.
 
Data from Europe’s Sentinel satellites will be central to the projects. This new suite of satellites, developed by the European Space Agency, forms the heart of the European Commission’s Copernicus programme – the largest global environmental monitoring initiative ever conceived. The Sentinels carry a vast range of sensors to deliver a stream of complementary imagery and data for monitoring our land, ice, oceans and atmosphere.
 
Sentinels 1, 2a and the recently launched 3a will be utilised in the project. There has already been some spectacular imagery obtained from these satellites however scientists need to be able to prove how good the data are.
 
The Copernicus programme is unique because of the continuity of coverage overseas and oceans of global maps of phytoplankton chlorophyll, the green pigment found in plants, temperature and other sea surface properties that contribute to the air-sea flux of carbon dioxide and other climate relevant gases. Up until now, space agencies have typically launched single satellites to gather data, yet once that satellite reaches the end of its life the data stop. Through the Copernicus programme, the European Space Agency is launching a cluster of satellites to provide data to monitor our planet for the next 20 years.
 
The images received by the Sentinels are vital for PML earth observation research as they can help scientists measure the number and type of plankton in the ocean which is crucial for understanding how the ocean is changing. These plankton form the base of the food-web upon which all life in the ocean is dependent. Plankton is also important for maintaining the balance of gases in our atmosphere and sustaining life on Earth.
 
Both ESA funded projects work towards the data being classed as FRM (Fiducial Reference Measurements) which certifies that the measurements meet required conditions to ensure quality and confidence in the resulting data.
 
Dr Gavin Tilstone, Principal Investigator commented: “The satellite data is only ever as good as the high quality measurements taken at sea which we use to ground-truth them. To have confidence in the satellite data you need to have exceptionally high quality reference data. This is where AMT comes in, taking rigorous in-situ measurements”.
 
In the second of two ESA funded projects (FRM4SOC), PML will be going beyond the Atlantic working with lead partner Tartu Observatory.
 
In this project the scientists will concentrate on ensuring that the optical sensors used to ground truth the satellite data are of the highest quality using rigorous calibration procedures and protocols to ensure that these optical instruments meet the quality standards of FRMs. Comparisons will be conducted across the International community, using a range of different optical sensors under both laboratory and field conditions to ensure that all sensors meet the same high quality standards necessary for assessing the accuracy of the Sentinel satellite data.  PML will play a lead role in comparing the sensors in the ocean on fixed platforms and on-board the 27th AMT research cruise in 2017.
 
These projects will provide confidence in the satellite data that is available globally and used to improve our understanding of how the oceans are being affected by and buffer human activity.

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