The Long Arm Of Radar

By Bruce van Voorst/Bangor

What is the best vantage point for spotting a drug-smuggling plane crossing the Caribbean? Strangely enough, one good place to be is Bangor, Me., a city thousands of kilometers north of the smugglers' favorite routes. Last week in Bangor the U.S. Air Force showed off the operations center for a new radar system that can "see" up to 3,300 km (2,000 miles), or nearly ten times as far as conventional radar. Built by General Electric, the OTH (for over-the- horizon) radar system was originally developed to give the U.S. military an early warning of any approaching Soviet bombers. But in these days of easing tensions between East and West, the Pentagon is excited about the role that the radar can play in the war against drug trafficking.

Able to cover a swath of sky from Iceland to the northern coast of South America, the OTH radar can monitor a smuggler's plane from soon after it takes off in, say, Colombia until it reaches the U.S. When a technician in Bangor sees an unscheduled flight over the Caribbean, the information will be relayed - to the Pentagon's Joint Task Force Center in Key West, Fla. An Air Force fighter will follow the suspect plane, and officers of the Customs Service and the Drug Enforcement Administration will be alerted to the mystery craft's course so that they can be on the scene when it lands. Says Air Force Colonel Jack Lenz, the OTH project manager: "Only suicidal smugglers would try to beat this."

All radar operates by sending out radio beams and listening for echoes as the signals bounce back from distant objects. The range of conventional radar is limited by the earth's curvature, since the signal must follow a straight line. Standard ground-based systems work for about 80 km (50 miles), and airborne equipment for 320 km (200 miles). OTH radar gets around the limit by sending beams up to the ionosphere, an atmospheric layer of charged atoms that begins some 75 km (46 miles) above the earth's surface. The signals are reflected by the ionosphere over the horizon, where they hit objects and bounce back to the ionosphere and then back to the radar system.

The idea behind this radar is not new; shortwave radio signals have long been bounced off the ionosphere. But developing reliable over-the-horizon radar proved tricky because the composition of the ionosphere is always in flux, making it more like a mass of moving clouds than a smooth reflecting mirror. The OTH radar overcomes this problem by using computer power: the software enables technicians to chart constantly the intensity and thickness of the ionosphere, telling operators where conditions are best and which radio frequencies to use for maximum performance.

To be effective, the OTH radar system had to be huge. The signals are sent from three transmitting antennas, each more than 1,095 meters (3,600 ft.) long, in Moscow, Me. Some 175 km (110 miles) away, in Columbia Falls, are three receiving antennas, each stretching nearly 1,520 meters (5,000 ft.). The whole system is controlled by 28 of Digital Equipment Corp.'s powerful VAX computers located at the operations center in Bangor.

And that is only the beginning. The OTH radar in Maine will soon be joined by similar installations in North Dakota, California and Alaska. Together, the radar systems will be able to look out for millions of square kilometers from every part of the U.S. coastline. That promises to complicate the life of any drug smuggler trying to sneak into American skies.

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CREDIT: TIME Diagram by Steve Hart

CAPTION: LOOKING OVER THE HORIZON