Sentinel-3C is measuring ocean height and Greenland ice elevation, with five months of commissioning to go

The Italy image shows how the release handles uncertainty when it has a reason to. The lighter blue bands along Italy's eastern coast are, according to ESA, believed by scientists to be likely sediment carried into the sea by rivers and redistributed by coastal currents ^[8].

The two measurement claims get no such treatment. ESA says the satellite's instruments have begun measuring ocean heights and the elevation of Greenland's ice sheet, and calls this an early demonstration of technology designed to monitor Earth's changing climate ^[2]. The release does not include an error estimate or a comparison with reference measurements. The judgement that both instruments are performing well in initial tests is ESA's own, about its own satellite ^[3].

ESA describes a testing and commissioning process that it expects to take another five months ^[4]. On that timetable, the early result is that the sensors return data. Returning data is a lower bar than returning data good enough to extend a climate record. A first-light image or a first altitude reading cannot show that an instrument stays comparable over years.

In our view the next check comes after commissioning. Sentinel-3 satellites carry matching sets of instruments ^[5], so Sentinel-3C's sea heights and Greenland elevations can be set against what the earlier spacecraft in the series measure. If they agree, the third satellite extends the series. We'd expect that comparison, more than any image, to be the evidence on whether the fleet is on track.