For the last few days, you may recall, Weather Eye has been reporting live from inside the Arctic Circle, from the Norwegian island Spitzbergen as near the North Pole as makes no difference. And what could tempt anyone to brave these frozen, barren wastes, to suffer disorientation from the midnight sun with intermittent blizzards, and risk attack by hungry polar bears? The answer is weather satellites.
"Polar-orbiting" satellites travel around the globe from pole to pole, about 500 miles above the ground, following as it were the lines of longitude. They photograph the whole globe, bit by bit from directly overhead, as the Earth revolves on its axis underneath.
Now it is obviously convenient if when taking images, a polar-orbiting satellite is deployed in such a way that the ground beneath it is always bathed in sunlight. Ideally, then, the north-south track of the satellite should shift westwards with the daily sun. This arrangement, a so-called near- polar sun-synchronous orbit, can be relatively easily achieved, and it is precisely what EUMETSAT, the European Organisation for Meteorological Satellites, proposes a year or two from now with Metop-1.
But this clever, sun-synchronised solution makes it difficult to retrieve the pictures from the satellite. A ground station in Ireland, for example, could receive pictures from the satellite as it passes overhead, but six hours later the spacecraft's southward swoop will take it over Canada. To collect data at all the different longitudes would require a string of ground stations dotted around the world at frequent intervals along, say, the 50th parallel.
The solution lies in the fact that the lines of longitude converge towards both poles. Polar-orbiting satellites, therefore, always pass near the North Pole every 100 minutes as they circle around the Earth. If it is arranged, therefore, for the satellite to store the images it takes throughout an orbit, all the pictures can be down loaded in one go to a single ground station near one or other of the poles.
In the case of EUMETSAT and Metop-1, a ground station will be built on the island of Spitzbergen, whose ultra-northern location makes it uniquely suitable for receiving data from a polar-orbiter. From there, the information will be relayed by other means to forecasting offices all around the world.
And that's why I am here. A EUMETSAT meeting has been arranged in Spitzbergen so participants can view the site, on top of a local mountain, where the ground station will be located.