A YEAR or so ago, meteorologists around the world received a nasty jolt. Omega, they were told, will shortly be discontinued, meaning that unless they make alternative arrangements, the supply of information about winds and temperatures in the upper atmosphere will more or less dry up.
Omega is a radionavigation system originally designed far guiding aircraft, but is now widely used by meteorologists to track their hydrogen balloons. These carry a little package called a radiosonde, which contains instruments to measure the temperature, pressure and humidity of the surrounding air as the ensemble rises gently through the atmosphere. The instruments in turn are linked to a radio transmitter, and the frequency of the transmitted signal varies with different values of these elements.
But for these data to be useful, it must be known where they relate to in the atmosphere. And indeed the motion of the balloon itself also provides valuable information about the speed and direction of the wind at various levels.
In the old days it was followed using radar, and successive "fixes" at, say, 60-second intervals allowed the operator - or later a computer to calculate the wind. Since the early 1980s, however, Omega has been used for - this purpose, pinpointing the position of the radiosonde at regular intervals and allowing the speed and direction of the upper-level winds to be computed.
Omega is a ground system, based on eight transmitting stations at strategic sites around the world. In the last few years, however, the satellite-based Global Positioning System, or GPS, has become widely available and the authorities see no further need to continue funding Omega.
But GPS has a major disadvantage for meteorologists: although it provides a more accurate "fix" on the position of a balloon at any time, it is more complex, and each radiosonde - several of which are sent aloft each day at every - station, and usually not recovered - is significantly more expensive than those currently in use for Omega.
Some meteorological services propose to take the plunge and bear these costs by using GPS to track their radiosondes. Others, however, mainly in Europe, are looking at the Loran-C radionavigation system as a possible alternative.
Loran-C, like Omega, is ground-based; indeed you may recall that there is some controversy at present about the possible siting of a Loran-C transmitter on the coast of Co Clare. For the meteorological community, however, the system has the advantage of being just as accurate as Omega, and once the expense of converting to the system has been borne, the daily costs are comparable.