The history of the space industry in France and Europe shows that programmes as varied as Argos, Spot and Ariane have a common feature: the designers' and operators' vision of what was needed and their determination to achieve it. Originally these visions were not always very sharply-defined, but they have withstood the test of time, evolving to better match users' needs as soon as new methods and technologies become available.

As a newcomer to marine altimetry, I found 1995 both informative and inspiring. Ocean altimetry programmes from SEASAT and GEOSAT to ERS-1 and TOPEX/POSEIDON all show a magical combination of vision and determination:

• knowing which parameters, accessible from space, can teach us about the ocean,
• making sure the resources needed, such as the DORIS system, became available, and routinely obtaining ocean measurements to previously undreamt-of accuracy.

The vision and the determination grew up twenty years ago on both sides of the Atlantic, and were nurtured by an excellent blend of competition and cooperation. Let’s see some thoughts from observers and players, on both sides, over the years.

• In 1965, Henry Stommel wrote that conventional tools were completely inadequate for observing the ocean, and that the theory of current dynamics was based largely on guesswork.

• Twenty-three years later, IFREMER director Bruno Voituriez, now director of ORSTOM, wrote in an Argos Newsletter editorial that oceanography, lacking the necessary tools, lagged a long way behind other atmospheric sciences, for example. So few observations were available that oceanographic research and exploration needed to become the priority in climate forecasting. Voituriez concluded, prophetically, that space technology would give us the means to make comprehensive observations of the ocean and enhance our climate predictions. But ocean (surface) observation from space would not make in situ measurements obsolete. The former would provide worldwide coverage, the latter the third dimension such as the vertical ocean stratification. Satellites would also acquire in situ measurements from drifters, moored buoys and so on. True operational oceanography was beginning to take shape, with the establishment of ocean measurement networks similar to those used by meteorologists in atmospheric research.

• Following on in 1991, Michel Lefebvre noted that TOPEX/POSEIDON and later altimetry missions would provide continuous, homogeneous time series. Not only to observe the ocean but to derive measurements useable as quantitative constraints for numerical models.

The path from inspiration to realisation is now marked out, and we have come a long way on it. Much of the progress has been achieved by meticulous attention by the system designers and operators. The best example is perhaps the AVISO data distribution system, which does not just routinely output hundreds of thousands of high-precision quality-controlled TOPEX/POSEIDON measurements. It also adds the auxiliary data users need to get the best from the results without labouring over the data themselves. And the integrated, interactive approach of the AVISO team will be crucial as we move confidently towards the 1999 launch of TPFO/Proteus.

Today a community of research scientists, with collective overview of the fundamental questions in the earth sciences, are producing results that thrill us a little more each day. Scientific progress is reducing the element of chance, not spoiling the dream. The homogeneous measurements from TPFO and its follow-ons over twenty years will make a huge contribution to knowledge of our planet’s climate and evolution.