Source: Copernicus/ESA

Europe has launched the first satellite of what is heralded as one of the most ambitious Earth-observation programmes ever. On 3 April, a Soyuz rocket dispatched into orbit the Sentinel-1A probe, the first craft of a planned constellation of six Sentinel families set to be launched by the end of the decade. Together, the satellites will offer unprecedented long-term monitoring of the planets land, water and atmosphere.

The Sentinels will be the core of the 8.4-billion (US$11.5-billion) Copernicus programme, which is managed by the European Commission. Copernicus will also draw in data from about 30other satellites, and from ocean buoys, weather stations and air-quality monitoring networks.

The Sentinels and Copernicus have the potential to become the worlds most comprehensive Earth-monitoring system, says Zbynek Malenovsky, who studies vegetation using remote sensing at the University of Wollongong in Australia.

Copernicus was designed by the European Union (EU) and the European Space Agency (ESA) to help the European Commission and EU member states to develop environmental policies and monitor the results. Its data will be used to create services for myriad practical applications, including ice mapping, agriculture management, climate-change forecasting and disaster response. The idea is to produce images, maps and models in near real time, much as is done with weather monitoring, but for many more variables.

Unlike most previous Earth-observation missions, the Sentinels will be replaced regularly as they age. This will help to generate long-term cross-calibrated data sets of a variety of imagery and measurements, says Cathy Clerbaux, an atmospheric scientist at the LATMOS atmosphere and astrophysics research institute in Paris. Its not easy to connect data series such as measurements of pollutants, ozone or greenhouse gases when you have different instruments, and gaps between missions, she says.

The data will be free for anyone to access and use. But researchers will enjoy formal user status alongside public authorities, and will thus have privileged access, including dedicated help desks and support. Scientists are now much more integrated into the user community, and not neglected as they have been in the past, when the focus was more on the operational side, says Josef Aschbacher, head of ESAs Copernicus office. I expect scientists to be the number-one user group.

Sentinel-1A is the first of two identical satellites; 1B is set to be launched in the next 18months. Both contain a radar system that can see in darkness and through clouds, unlike the optical instruments on many satellites. This will allow them to continuously image cloudy areas such as tropical forests. They will operate in tandem, cutting down the time between flyovers of the same point on Earth (known as revisit time), and enabling quick-succession imaging to measure, for example, ground deformation from earthquakes.

Sentinels 2 to 5 will have different goals. Between them, they will use optical sensors, radiometers and spectrometers to measure everything from sea temperatures to air pollution. In addition, a Sentinel-5 Precursor satellite will be launched in 2016 to minimize the shortfall in atmospheric data-gathering following the 2012 loss of the European Envisat satellite. A sixth Sentinel, a radar altimeter that will measure sea-surface heights, is also under discussion (see Watchers in the skies).

These diverse measurements of the major components of Earth systems will make the Sentinels very valuable, says Richard Anthes, emeritus president of the University Corporation for Atmospheric Research in Boulder, Colorado. A balanced suite of Earth observations is required for observing and understanding Earth as an interconnected system, he says.

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Earth observation enters next phase