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February 16, 2016
Sentinel-3: A New Window on the Changing State of Our Oceans

Climate change is much discussed, says Dr Simon Keogh of the Met Office, and to inform the conversation the Met Office uses historical scientific data including sea-surface temperature records, based on data from the Along Track Scanning Radiometer (ATSR) series of satellite instruments. These instruments, designed and built in the UK, provided accurate infrared measurements of the Earth’s thermal emissions – including the heat signature emitted by the world’s oceans – until the untimely demise of ESA’s ENVISAT satellite in April 2012. Since the loss of ENVISAT, scientists have been eagerly awaiting ESA’s Sentinel-3 mission and hoping that it will provide high-precision data that will continue the ocean temperature record begun by ESA’s earlier satellites.

This post coincides with today’s Sentinel-3 mission launch which will be carrying the most sensitive instrument to measure sea-surface temperatures for many years. This instrument is known as the Sea and Land Surface Temperature Radiometer or SLSTR and it has special significance for Dr Simon Keogh, who leads the Met Office Satellite Data Products and Systems group. He said: “I spent the early part of my career working on sea-surface temperature measurements on a ship in the Bay of Biscay and English Channel as part of the ATSR validation effort. A lot has changed in the last 20 years, but the importance of the integrity of our sea-surface temperature records has remained paramount.”

ATSR-1 thermal image of the English Channel and North Sea and ATSR-1 thermal image of the Mediterranean Sea (Imagery courtesy of Rutherford Appleton Laboratories)

Left: An ATSR-1 thermal image of the English Channel and North Sea (showing in yellow and orange). Right: An ATSR-1 thermal image of the Mediterranean Sea showing highly variable surface temperature patterns between the Balearic Islands and the North African coast (bottom). (Imagery courtesy of Rutherford Appleton Laboratories)

To understand the need for the precision SLSTR delivers, we must understand what scientists are looking for in the climate data records. They can’t wait 100 years to see what the climate will be like, so instead they’re looking to confirm much smaller temperature changes over recent decades – decades when we have been measuring sea temperatures so precisely from space. That’s why the data gap between ATSR and SLSTR needs to be a short as possible. These series of satellite instruments provide indisputable, hard evidence of what is going on with the world’s ocean temperatures.

Sea-surface temperatures are important because the ocean is actually a vast heat sink or ‘thermal reservoir’. The ocean absorbs sunlight into its upper layer, storing it as heat and then transporting it around the world in vast currents. Energy is also exchanged between the ocean and atmosphere and sea ice. This redistributed energy drives ecosystems and physical and chemical cycles. It’s this coupling between the sun and the ocean that makes our Earth habitable. You can think of the ocean as the Earth’s ‘solar panel’, absorbing sunlight and transforming it into energy that ultimately powers the rest of the planet’s life-support systems. Of course, the land also absorbs sunlight too but only at the surface where the energy is held less effectively. Satellites like Sentinel-3 are needed to provide a global picture of what is happening with our oceans.

Dr Keogh adds: “Our scientists’ interest in sea-surface temperatures doesn’t stop at monitoring our climate over a period of decades. This information drives ocean and weather models to predict future events. The Met Office OSTIA sea temperature and ice analysis is used to generate our world-leading weather forecasts. Accurate sea temperatures from satellites and other platforms are blended to provide a global snapshot of the temperature of our oceans.”

global sea surface temperature from the Met Office OSTIA analysis

An example of global sea surface temperature from the Met Office OSTIA analysis.

Sentinel-3 is important to the Met Office not only for the climate scientists wanting to know what will happen in future but also for today’s meteorologists interested in what the weather will be doing in the coming week. The Sentinel-3 project comprises two satellites (3A and 3B) to be launched about a year apart. This pairing is due to provide an accurate continuation of the ATSR sea-surface temperature records for the coming decade, ensuring the continued integrity of our climate records.

EUMETSAT will be operating Sentinel-3 and providing the marine data, while the European Space Agency will be providing the land data. If you’d like to know more about Sentinel-3, which is scheduled for launch at 17:57 GMT today, please visit the European Space Agency web site here: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-3.

The marine data from Sentinel 3 will be distributed by EUMETSAT. More details about EUMETSAT’s role can be found here: http://www.eumetsat.int/website/home/Satellites/FutureSatellites/CopernicusSatellites/Sentinel3/index.html

For more information about the Met Office ocean forecasting activities please visit our research web site: http://www.metoffice.gov.uk/research/weather/ocean-forecasting

Biography:   Dr Simon Keogh leads the Met Office Satellite Data Products and Systems group. He is a member of a United Nations WMO expert team on Satellite Utilisation and Products and is the UK delegate to EUMETSAT’s Operations Working Group.

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