Taking planet Earth’s temperature

The most recent addition to Europe’s fleet of Copernicus ocean-monitoring satellites has begun sending images back to Earth and the results have experts excited.

Thursday, 10 May 2018

Image - Sentinel-3B First Images - 5 - W Europe

The visible channels of the radiometer on board Copernicus Sentinel-3B, launched on 25 April, have been switched on and the instrument sent its first images of a low over the UK and Ireland (yes, Ireland really is there, under the cloud) and the Bay of Biscay, Spain. The image was taken at 10:51 UTC on Wednesday 9 May (Figure 1, top right, click to expand).

The image shows interesting cloud features off the west coast of Spain, Portugal and northern Africa, and a trough through the Gibraltar area.

A lovely, cloud-free image of the holiday favourite, the Red Sea, was taken at 07:38 UTC on 9 May (Figure 2). Patches of vegetation are shown in red and are particularly evident along the Nile River, on the left-hand side of the image. On the right, sand features in Saudi Arabia appear in whitish and yellowish hues.

Figure 2

The Sea and Land Surface Radiometer (SLSTR) measures the energy radiating from the Earth’s surface in nine spectral bands, including visible and infrared. The thermal channels will be switched on once the instrument has completed outgassing water vapour, and the infrared channels have been cooled to the operating temperatures.

Experts are meeting at the Darmstadt headquarters of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) this week to examine the data being sent back to Earth from the satellite as each of its instruments is switched on.

Sentinel-3B is currently flying in tandem with its twin, Sentinel-A, which was launched in 2016, so that their observations can be cross calibrated. The spacecraft are part of a series of Sentinel satellites under the umbrella of the EU’s Copernicus programme, which takes a continuous “health check” of our planet.

Accuracy and quality

EUMETSAT sea surface temperature expert Anne O’Carroll said expectations for Sentinel-3B had been high, given the outstanding quality of the flow of data received over the past two years from Sentinel-3A.

“The greater accuracy and higher quality of data delivered by the SLSTR is owed to its design,” O’Carroll said.

“The instrument takes a dual view of its path as it orbits the Earth and has two infrared sources on board which are able to continually compare and calibrate the measurements.

“The data we receive from Sentinel-3B SLSTR will increase the coverage of high-quality information we already have from Sentinel-3A. These data help with improvements to weather forecasts such as the accuracy of hurricane path predictions and related warnings, and climate monitoring, and are designed to be used as a reference for other satellite sea surface temperature missions.”

In addition to providing the temperature of the sea and land surface, dedicated channels on the SLSTR will search for fires. This will help to map carbon emissions from burnt biomass and to assess damage and estimate recovery of burned areas.

The Sentinel-3 mission

The successful launch of Sentinel-3B represents the full deployment of the Sentinel-3 mission, which requires a two-satellite constellation to provide the coverage required by users of the data.

The European Space Agency (ESA) and EUMETSAT both have key roles in the mission. ESA is currently undertaking the commissioning phase of the spacecraft and, once that is completed, EUMETSAT will take over routine operations.

EUMETSAT will process and disseminate the marine-related data and ESA will do the same for the land-related data.

The Copernicus Marine Environment Monitoring Service, operated by Mercator Ocean, is a major user of the marine data stream.

“High precision sea surface temperature data from Sentinel-3A and -3B SLSTR observations will be key to improving upper ocean monitoring activities of the Copernicus Marine Environment Monitoring Service,” Mercator Ocean Scientific Director Pierre Yves Le Traon said.

This will happen after the calibration and validation phase, when Sentinel-3B is moved to its final orbit.

Image - Logos - Copernicus - Sentinel-3B

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