All ESA satellites are built with a well-defined purpose in mind. In the case of Sentinel-1, the main objective has always been to provide routinely and systematically high-quality radar images to the Copernicus services in support of applications ranging from the monitoring of the marine and polar environments to support in crisis situations such as natural disasters. However, an end-user does not necessarily know or even need to know the details of the design of the satellite. My role has been to draft and manage the high-level guidelines – in ESA jargon, called ‘mission requirements’. These guidelines link the needs of the users with the detailed design of the Sentinel-1 mission.

Continuity of measurements has played a big role in the definition of the mission. Many, if not most, of the current Copernicus services that will use Sentinel-1 data are initially developed using radar images from previous ESA satellites such as ERS-1, ERS-2 and Envisat, and supported by ESA service development programmes. Only later, were these services integrated into the European Copernicus framework.

However, in meeting users’ needs we have also integrated many of the lessons learned from the previous missions. In particular, the need for consistent conflict-free operations has meant that ESA designed a ‘one-mode-fits-all’ instrument mode called the interferometric wide swath mode. This meets most, if not all, user needs as it includes both a large swath on the ground of 250 km, a resolution of 5×20 m per pixel and can also acquire ‘colour’ images with more information using different wave polarisations.

This is done in several ways. First, through the design of the satellite itself, as well as through detailed testing of the instrument during the build phase. Secondly, in orbit this will be complemented by other calibration activities using ground- based calibration devices such as transponders and corner reflectors.

Lastly – and given my role perhaps most interestingly – we have had several measurement campaigns using either airborne radar data or spaceborne data from other satellites to simulate Sentinel-1 images ahead of launch. These have been very useful to convince the user community, and ourselves, that the satellite design choices made at the beginning of the programme were the correct ones – and will lead to high-quality useful radar data for the services.

The number of modes, at least for large-area radar images, are actually restricted to only two main modes, which is much less than most other spaceborne radar missions. This was a deliberate choice to enable the simplified and conflict-free operation of the satellite and to ensure that users receive the data that they need. The modes themselves include the best possible compromise between frequent coverage, which requires large image swaths taken by the satellite, and maintaining the highest possible resolution.

The day-to-day management of Sentinel-1 will be transferred to my colleagues working at ESA’s Centre for Earth Observation in Frascati, near Rome. However, I will continue to be involved as part of the feedback loop on the mission design choices and I will continue to monitor the evolving needs of the user community for future developments of the Sentinels. I am also involved in dedicated studies looking at the scientific use of the mission.

The mission design drivers of Sentinel-1 will definitely benefit the development of new science capabilities. The long-term availability of Sentinel-1 data, for instance, benefits applications that require long-term consistent time series of data such as climate change studies. I also expect that the frequent revisit of the satellite will support applications where land is changing in a dynamic fashion. For instance, we know that agricultural crops change very quickly, so that Sentinel-1 is likely to play an important role in crop monitoring.

Despite being in the business for many years I'm still amazed by the fact that Sentinel-1 travelling at 7 km/s at roughly 700 km above Earth’s surface can measure subsidence or surface movements down to several millimetres. For the rest, I enjoy meeting the users of Sentinel-1 data and bridging the gap between their needs and the design of the satellite itself.