September 1, 2004  -  

Just when you think you’ve heard all the possible uses for GPS receivers – like the multibillion-dollar precise navigation technology for measuring your distance from the cup on a golf course, or to direct robotic lawnmowers – along comes another GPS idea that seems, at first, like a bit of a head scratcher. Carmanah Technologies of Victoria, British Columbia, is now offering buoy navigation lights equipped with integral GPS receivers. “Great idea,” you say. “The buoys will know exactly where they are, but how does that help navigators?”

Far from being merely another feature to fill out a spec sheet, the addition of GPS to these solar-powered navigation lights makes them more precise aids to navigation. The key is not answering the question, “Where am I?” but rather, “What time is it?”

“Where am I?” is a question voyagers ask themselves all the time (well, good ones do). Mariners use GPS receivers to determine their position. To do this, they need the signals from at least three GPS satellites to solve for the two unknowns of latitude and longitude.

There’s more to it than that, however, to properly crunch all the numbers involved, a GPS reciever also needs to know time accurately. However, even sophisticated GPS recievers are built with quartz clocks, which, by themselves, aren’t up to the task of supplying GPS-useful time. A better time is needed.

But don’t start grumbling about shoddy GPS-receiver manufacturers, the solution to accurate time is out in space, 10,000 miles up. Each GPS satellite has four atomic clocks (the various satellites have a mixture of cesium- and rubium-based timepieces). These clocks, contrary to their name, are not mini nuclear reactors, they use the dependable “energy transition” properties of cesium and rubium to provide a rock-solid oscillator – think of cesium and rubium atoms as an extremely accurate version of the pendulum in your grandfather clock. These atomic clocks would lose less than a second in a million days of operation.

A GPS receiver uses its simple quartz clock to get itself in the ballpark, and then via an impressive bit of signal processing, tunes itself to the accuracy of the atomic clocks on the satellite. It can then use atomic-based GPS time to solve for the other two unknowns of latitude and longitude. So, one of the byproducts of answering “Where am I?” is an excellent answer to “What time is it?” In addition to determining your location, a GPS receiver also gives you the accuracy of a $25,000 atomic clock for the price of a $200 GPS receiver.

Like your GPS navigation receiver, the aids to navigation lights from Carmanah Technologies also benefit from GPS time transfer. The GPS units built into the lights aren’t used to determine position. Instead of tracking three satellites to solve for time, latitude and longitude, they track a single satellite to determine accurate GPS time.

Now finally, to the question of why a navigation light needs to know time. According to Carmanah Technologies, a group of its model 701-GPS time is the perfect lighting director. Synched to the same time standard, they flash in perfect unison. “For many applications, GPS synchronized lighting makes marine navigation easier by offering improved visibility and clearer delineation of waterways and navigation hazards,” said Art Aylesworth, CEO of Carmanah. Carmanah says that lights flashing together, outlining a port entrance, say, are easier to see against shore lights.

In addition to being solar-powered, the 701-GPS and 702-GPS also use light-emitting-diode (LED) lamps rather than incandescent lamps. On March 8, 2004, the U.S. Coast Guard approved the use of LED lighting for private aids to navigation. According to Carmanah, the 700-series lights are the first solar-powered lanterns using LEDs to be designed and built under contract with the Coast Guard, making the 700 series the first to enter the U.S. Aids to Navigation System. LED lamps have the advantage of consuming less power than incandescent lamps, and LEDs last much longer.

The expanding number of products that make use of GPS is ample demonstration that it is the foremost satellite navigation system. It might not say that way, however. The European Union continues to push ahead with plans to build and launch its own satellite navigation system called Galileo. The U.S. Department of Defense has been concerned that Galileo signals could interfere with GPS signals and degrade the effectiveness of the American system.

That fear was largely laid to reset in late June, when the United States and the European Union signed an agreement that pledged the new European system and the existing American one would be “compatible and interoperable. “This furthers the idea that by the end of the decade, dual GPS-Galileo receivers may have more than 50 navigation satellites available – flashy indeed.