Sentinel-3: connect color, temperature and surface height

Sentinel-3 supplies systematic observations of oceans, land, ice and atmosphere. Sentinel-3A launched in 2016, followed by additional members of the family. ESA and EUMETSAT divide responsibilities for the mission and its land and marine products. The program builds on earlier environmental observing experience while supporting services that need repeated, comparable information.

Its payload combines the Ocean and Land Colour Instrument, a Sea and Land Surface Temperature Radiometer, a radar altimeter and a microwave radiometer. These are complementary instruments, not four interchangeable cameras. Color, emitted thermal radiation and radar travel time describe different aspects of a scene; the product selected must match the physical question.

The Hurricane Matthew image shown here came from Sentinel-3A in October 2016. It is a false-colour thermal-infrared view, with the source’s temperature scale preserved. Very cold cloud tops around the storm’s eye appear differently from warmer parts of the scene. The colors encode the measured thermal signal and its interpretation, rather than the visible colors a person would see.

A fictional reader might mistake a red region for flames or assume the cold cloud-top value is the temperature at the sea surface below it. Both conclusions skip the measurement geometry. Where clouds block the view, thermal radiation can describe the cloud top instead of the underlying surface. The location, instrument and displayed scale must travel with the image.

Sentinel-3’s optical, thermal and altimetric measurements pass through different processing chains. The microwave radiometer helps correct atmospheric effects on altimetry; it is part of the support needed for a reliable height product. Combining instruments is valuable precisely because each contributes information the others do not provide in the same way.

For a fictional coastal study, ask separate questions about water color, surface temperature and height. Select the appropriate products and check their acquisition times, resolution and quality. A clear temperature pattern cannot supply a missing height measurement, even if both are plotted over the same coastline. The shared spacecraft makes coordination useful without erasing the differences among its observations.