As Mohinder Grewal prepared for a new school year, the California State University, Fullerton, the professor had a good story to tell students about how his summer went.

His specialty, a technology called the Wide Area Augmentation System, or WAAS, was approved by the Federal Aviation Administration in July to help pilots fly airplanes in thick fog and awful weather.

WAAS is one of several burgeoning uses of the Global Positioning System, which relies on 24 satellites to find the position of a person, place or thing anywhere on Earth within 100 meters. Grewal is an expert in one GPS application and an enthusiastic user of others.

"I grew up with this," said Grewal, who has taught classes on GPS for 29 years and published his first book on WAAS in 1993.

Along with the industry, Grewal has excitedly watched the uses for GPS expand, from surveyors using GPS to measure property lines to golfers using the technology to figure out the distance to the next hole.

BMW, Acura and Lexus offer navigation systems as a standard in higher-end vehicles, not to mention the General Motors OnStar system, which combines GPS tracking with concierge services for drivers searching for the nearest hotel or reporting a stolen vehicle. Parents can now buy GPS-equipped watches to keep track of their children. Outdoor enthusiasts use GPS devices for "geocaching" games and to help lost hikers find their way to civilization.

Laptops and digital organizers are now available with GPS receivers inside. By 2005, cell phones will have a locating device, such as a GPS chip, so 911 operators can locate callers through an "e911" service.

"Consumer awareness (of GPS) has really only been in the last two to three years" said Glen Gibbons, founder and editor of GPS World magazine. "It's showing up in things like geocaching, the e911, GM's OnStar System. ... We live with cars and cell phones. If you put GPS in them, people become familiar with it."

Treasure hunts

While automobile navigation systems continue to be the largest use of GPS devices among consumers, geocaching has attracted many fans. In the game, "cachers" hide objects and then post the location's latitude, longitude and clues on a Web site.

"There's a lot hidden" in Orange County, said Rodney Goehring, a Huntington Beach resident who has played the game with his girlfriend, Dawn DeShazo, for almost two years. "We enjoy being outside, mountain biking and hiking. We'll look for geocaches along the way. Pretty much every trail is going to have one around here."

DeShazo, who estimates she's found about 120 caches in two years, takes her GPS unit along when she travels for business.

"It's a reason to get outside," she said. "There are a lot of places we would never have gone otherwise."

As of Friday, the Geocaching.com Web site tracked 66,966 caches in 184 countries. Caches usually contain goofy items, such as toys and useless objects. When a cache is found, players are supposed to take away an item and leave something in its place.

The rise of geocaching has improved the sales of handheld GPS devices, said Lonnie Arima, vice president of worldwide sales and marketing of consumer products for San Dimas-based Magellan, which specializes in GPS devices.

"Based on feedback we receive directly from geocachers and from postings in geocaching chat rooms, we are certain that geocachers account for a growing customer base and numerous sales of Magellan handheld GPS receivers," Arima said.

Aviation

A more recent GPS development is WAAS, which is expected to change the way pilots fly in the fog.

At most small airports, pilots can't land unless they can see the ground. In bad weather, pilots aren't allowed to fly lower than 600 feet unless they can see the landing strip. One way to get around this is for an airport to install a precision instrument landing system, which uses radio frequencies and transmitters, and allows planes to fly as low as 200 feet without seeing the landing strip.

But at $3 million, many community airports can't afford the technology. WAAS offers a much cheaper alternative at about $12,000 per plane. With it, the FAA allows pilots to fly as low as 250 feet before sighting the runway.

"GPS works in any weather but ion storms," said Grewal, referring to an atmospheric disturbance that occurs when solar radiation gives the air an electric charge.

WAAS uses ground-based sensors that correct inaccuracies of GPS satellites, which can wander slightly off course or produce imprecise readings because of atmospheric changes.

WAAS is so precise that it will open up many small airports in all types of weather, said Warren Morningstar, vice president of communications for the Aircraft Owners and Pilots Association.

Still to come sometime in the future is the more precise WAAS Phase II, which will allow pilots to land without ever seeing the ground.

Emergency calls

Cell phones can be frustrating - or fatal - for callers in an emergency who can't tell 911 operators exactly where they are. Because users are constantly moving, there's no way to determine their location, unlike a traditional phone.

In 1996, the U.S. government passed the enhanced 911, or e911 law, requiring cell-phone companies to implement a system to locate emergency cell-phone callers by 2005. Some companies installed equipment that determines the caller's general position in relation to the closest cell-phone tower. Others, such as Verizon and Sprint, opted for putting a GPS chip in each cell phone.

Sprint was one of the few companies to meet an October 2001 federal deadline for having technology that can pinpoint a caller's location to within 160 to 330 feet.

"Right now, with your Sprint (cell phone), they can approximate where you are," based on which cell tower you're connecting through, says Stephanie Walsh, Sprint's spokeswoman.

Fifteen models of Sprint phones now include a GPS chip, but it won't be put to use until the entire 911 operator service is upgraded to handle such tracking, she says.