Ice explorer

Deutsche Welle: Professor Wingham, what was your immediate reaction to the successful launch of CryoSat-2?

Duncan Wingham: Four and a half years ago, CryoSat-1 failed. This was something of a blow to us and we had to work very hard to recover it. As we watched the launch, all of us who'd been involved first time round were particularly nervous because we knew that actually these things can fail. But it didn't do so... it was a very very happy affair and I'd say I still feel extremely buoyant, I feel a very happy man.

One of the main missions of the satellite, as we understand it, is to assess the volume of the ice in the Arctic - something that's apparently very hard to do from space. Why is that?

Well, it's technically very difficult to do. The ice is only a few meters thick and what we are measuring is actually the difference in height between the ice and the water that it floats in. So this is only a few tens of centimeters and we have struggled to do this in the past because it is simply a quite difficult thing to achieve.

And this in spite of the fact that satellites have been used for some time now to trace the extent of ice coverage?

That's right. For a very long time now, I think since 1979, we have had satellites that have taken pictures of the surface and so we can see what area the ice is occupying. But, equally, the ice area doesn't tell us as much as we'd like to know because the ice is in fact moved around each year by the wind. So, if you actually want to know literally how much ice there is, then you need to measure the thickness as well.

We understand that radar altimeters flown on previous missions have not had the resolution to calculate thickness. What makes the ones on CryoSat-2 different?

We've used an old principle, you could say, for a new task. We have added the old historical capability, what we would describe as a synthetic aperture capability, and this produces a much more finely focused spotlight on the earth than has been the case in the past, and so by adding this capability to the heritage of previous satellites, we've been able to just really concentrate the energy in a small space.

And could you explain, in simple terms, how the altimeter actually calculates the thickness of ice?

Yes, we simply emit a short burst of radio waves, they travel down to the surface and bounce off and a very small amount of the energy is received again at the satellite. So we can time this round-trip extremely precisely, and this tells us the distance between the satellite and the surface that the energy is bounced off. Then by locating the satellite very precisely we can just subtract one number from another, and we can find out exactly where the surface is relative to the center of the earth.

In scientific terms, how is the process of calculating the thickness of marine ice different from calculating that of ice sheets that overlie Greenland and Antarctica?

What the satellite is actually doing is simply measuring the distance between the surface of the ice and the center of the earth. If the ice is floating, as it is in the Arctic, and by measuring both the ice and the sea and looking at the difference between those, we can determine the thickness of the floating ice. With the continental ice sheets, we cannot measure the thickness because the radar won't penetrate the great depth of ice - it's several kilometers thick - but what we can do is monitor the height, the elevation, of the ice over a period of time. And if this changes, then it tells us that the ice is thinning.

Some experts are saying that CryoSat will also be enormously important to complete the picture that scientists have had - in the satellite era, at least - of the decline in Earth's ice cover. What is it exactly that sets this mission apart?

It's partly exactly the radar that I've described. We've designed this radar to do this task specifically and so while earlier instruments have given us, I would say, a tantalizing glimpse of what could be possible if we flew the right hardware - and this time we have the right radar. But the other point is that previous satellites have been in orbits which have been close to the pole but have left uncovered the top 10 degrees of latitude of the world. And so this time we have put the satellite in a truly polar orbit: It will actually go to the poles and so we will see the whole whereas before we had a partial picture.

It's no longer in doubt that the ice cover on Earth is diminishing. It's clear that we're looking at parameters like thickness, the speed with which this event is taking place, as well as perhaps the larger regions where that's happening. What other parameters are we there?

As you say, we know that things are happening but we have a very, very limited idea about what the consequences of those changes are and a very limited idea of what the speed of those changes are. We are interested in how much ice from the continents is flowing into the sea - this immediately impacts global sea level. In the Arctic, the question is a bit more subtle and, therefore, in a sense, more important. We are looking at the amount of freshwater which is being added to the ocean by the melting ice. So by flying closer, we not only understand in more detail what is happening at the poles, we can start to measure what the implications of that are for lower latitudes, and in particular, the latitudes where you and I, at least, live.

Having provided the means with which to make these assessments, once the readings come home from the satellite and once the information is out there in the public sphere, what is it that scientists like you are hoping your efforts will achieve?

I think in the public sphere, first, scientists' primary responsibility is to tell people what is actually happening. Of course, in the last year or so, we have understood that there is a group of the public that doesn't want to know what is actually happening. But this doesn't alter the fact of the matter. So our first responsibility is to inform people as accurately as we can. But the other aspect of this and the question everybody wants to know, is 'what will happen?' And it turns out that the climate system is extremely complex and it's in fact quite difficult to make predications about the climate system. And that is why we need these very detailed measurements in order to make these kinds of predictions more precise than they are today.

The US space agency, NASA, has also been trying to put an ice-monitoring satellite in space. Can the launch of CryoSat-2 be seen as ESA taking the lead in this field?

To be honest, I don't think that's how I'd describe it. In fact, CryoSat was predated by a NASA mission called ISAT, and ISAT itself was predated by the earlier CryoSat mission, which unfortunately failed. The crucial distinction is that in Europe we are using a radar technology, which, in fact, Europe is truly the best in the world at, whereas the American approach is to use an optical laser technology. What of course all of us know is that if we had even more money than we've spent already, we would be flying both kinds of instrumentation on the same satellite. But, in fact, we have a very constructive situation where the Americans and NASA are pursuing one kind of solution and we are pursing the other kind of solution. And certainly amongst the scientists we all appreciate that if we share this data, we win, basically.

You talked about expenditure and funding there. Europe has reportedly doubled the spending on Earth observation in the past few years. Surely space scientists like you view this as a very encouraging trend?

Well, there is no question that Europe in its totality has increased very significantly its funding for Earth observation, in space and indeed it is now the largest single activity that uses space in Europe. There is no question that this is a reflection of the understanding of the impact and importance of satellites in understanding our environment and the effect that we are having on it. Of course, speaking as a scientist, I would simply say that more is better, of course.

Interview: Ranjitha Balasubramanyam (as)
Editor: Kate Bowen