First images from Sentinel-3B

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In early May the first images from the new Sentinel-3B were released. This case takes a quick tour though some of the elements visible in the imagery.

First images from Sentinel-3B
Date & Time
08 May 2018 09:33 UTC
True Colour

By Mark Higgins (EUMETSAT)

On 8 May a True Colour image based on the red, green, and blue bands of the OLCI instrument, was released it was centred on southern Sweden and showing parts of the North Sea and the Baltics (Figure 1, top right, click to expand).

OLCI is the ocean and land colour instrument — it is tuned to help scientists see variation at sea and on land. In the sea west of Denmark, north of Germany and the Netherlands there is an area of pale blue (Figure 2).

Figure 2
Figure 2: Sentinel-3 OLCI True Colour, 8 May 09:33 UTC

This is most likely a coccolithophore bloom, a species of phytoplankton which build armour from calcium carbonate. This is the same substance that makes up chalk and is the reason these blooms are easily identifiable due to their white colouration. The swirling pattern is caused by the ocean currents and winds.

Just off the German/Polish coast a small area of slightly green waters can be seen (Figure 3). This shows up better if the colour scale is changed slightly (lower right-hand panel in Figure 3). The green colour indicates that this is likely a bloom of another species of phytoplankton — perhaps cyanobacteria or another species containing green pigments.

Figure 3
Figure 3: Sentinel-3 OLCI True Colour, 8 May 09:33 UTC

Coastal effects can also be very clearly seen. In the North Sea, off the coast of Germany, we can see the flows of the rivers into the sea - and the transport of sediments (brown coloured waters) near the coast.

Figure 4
Figure 4: Sentinel-3 OLCI True Colour, 8 May 09:33 UTC

OLCI is not only used to study the seas but also inland waters. As can be seen in the example from the lakes in southern Sweden (Figure 5). There is variation in the colour of the water in the lakes, due to the different water flowing into the lakes; different amounts of sediment and algae, and the amount that the wind stirs up the lake contents.

Figure 5
Figure 5: Sentinel-3 OLCI True Colour, 8 May 09:33 UTC

One of the reasons we can see so much of the different water regions in this image is the lack of clouds.

In the Eastern Baltic the thin cirrus clouds show up very clearly, as do the contrails left by aircraft crossing the Gulf of Riga (Figure 6).

Figure 6
Figure 6: Sentinel-3 OLCI True Colour, 8 May 09:33 UTC

EUMETSAT has particular responsibility for products for the atmosphere and oceans but OLCI is also useful for land monitoring. In Figure 7 we can clearly see variation over the land surface. The image is centred on Hamburg, the Elbe river is clear. Forests and the yellow crops are also easy to see.

Figure 7
Figure 7: Sentinel-3 OLCI True Colour, 8 May 09:33 UTC

These are just a few of the first images from the OLCI sensor aboard Sentinel-3b, over time this instrument, along with its sister aboard Sentinel-3a, will provide more and more data for scientists, governments, and businesses, to help understand how our Earth functions and our impacts on it.

Related content

Terra MODIS True Color RGB, 8 May 10:45 UTC, also showing phytoplankton.

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