When I golf, I’m forever asking my wife how far it is to the pin (not that it really matters, the way I golf, but I like to keep informed). At Pelican Hill Golf Club in California, you don’t have to ask your wife. All you have to do is park your cart by your ball and hit a button, and a built-in display tells you exactly how far it is to the hole.
What makes this possible is Global Positioning Satellite technology–GPS for short. Using GPS, anyone with the correct equipment can pinpoint his or her position anywhere on Earth.
GPS is based on the ancient surveying method of triangulation. To precisely determine your location on a map, all you need to do is take bearings from two previously mapped landmarks. The point on a map where lines drawn along those bearings intersect is where you are.
GPS’s “landmarks” are satellites. There are currently 27 global positioning satellites in orbit, of which 24 are operational and three are spares. Each satellite, roughly the size of a compact car, circles the Earth every 12 hours in one of six circular orbits 20,200 kilometres up. At any time a minimum of four satellites are in the sky anywhere on Earth.
These satellites send out low-power, one-way signals. A GPS receiver–which can be as small as a credit card–measures how long it takes the signals to reach it. Since all the signals travel at the same speed–the speed of light–the receiver can use that information to determine its current altitude, latitude, longitude and even speed and direction of travel.
GPS originated with the U.S. military’s $12-billion Strategic Defense Initiative in the 1970s. It was a closely guarded military system at first, but became available for civilian use in the early 1980s, after Korean Air Lines Flight 007 was shot down by the Soviet Union for drifting into its airspace.
The military still has a better version of the system than civilians. While civilian receivers are accurate to within about 100 metres, the military version is accurate to within 10. (Both kinds of receivers often provide much better resolution than that, but that’s what you can count on.) However, over the next few years, civilian users will increasingly enjoy the same kind of accuracy military users do now.
GPS technology is already a multi-billion-dollar industry. For example, more and more cars are equipped with GPS receivers. Combined with computerized roadmaps, they can help you navigate your way through unfamiliar cities and help the service centre find you if your car breaks down. Similarly, cell phones may soon include GPS receivers, to enable 911 operators to pinpoint the location calls are made from.
Police forces are using GPS systems to keep track of their patrol cars, and in Chicago, the city tracks its buses with GPS so drivers can tell if they are ahead or behind schedule. In some places, felons placed under house arrest or strict probation are carrying GPS receivers. If the felon goes somewhere he shouldn’t, the GPS system warns him and notifies authorities.
Other recent uses have included mapping animal habitats; mapping the communities of Nicaragua’s Caribbean coast; surveying highways; mining coal; mapping meteorite impacts in the Antarctic; retracing the last flight of Amelia Earheart; reconstructing a battle from the American Indian Wars and mapping wave heights on the ocean.
The GPS system isn’t perfect. Its radio signals are subject to interference if too much of the sky is obscured by mountains, trees or buildings. But it’s better than any other existing or foreseeable method of locating position.
The growing dependence on GPS, in fact, could cause a few problems next month. At midnight between August 21 and 22, GPS system time, which counts weeks and began in January, 1980, will reach the end of Week 1023 and roll back over to Week 0. Some older equipment may have difficulty with that rollover. And yes, there are a few Y2K issues with GPS, too; while GPS components themselves are expected to work fine, some of the systems they’re embedded in might not.
Assuming all is well going into the 21st century, what else can we expect from GPS? Well, one firm envisions wristwatch-sized GPS receivers that can be used to keep track of your kids, your car, your dog, or anything else.
Soon, thanks to GPS, the age-old question, “Do you know where your children are?” might well be precisely answerable in latitude, longitude, and elevation.
