A new way to find your way.

Gary Turbak of Missoula, Montana, is a freelance writer specializing in outdoor topics.

Navigating by the stars was never like this ! If there is a universal law of the woods, it is this: Know where you are. Until now, map and compass have been the tools of choice for finding one's way, but new technology promises to rewrite the maps and make the compass all but obsolete.

It's called GPS-Global Positioning System-and it involves an array of hightech satellites, computers, and sophisticated software. It also has enough down-to-earth applications to gladden the heart of the crustiest forester.

At the push of a button, GPS can tell exactly where you are- no matter where you are. It works like this: Each orbiting satellite in the U.S. government's NAVSTAR military constellation emits a radio signal that can be used by civilians. Included in this signal are the satellite's precise location and the exact time that the signal left the satellite.

On the ground, a computerized receiver calculates the satellite's distance. By doing this simultaneously for three different satellites, the computer/receiver has the information it needs to triangulate-to determine its own position by knowing the locations of other points.

The result is an instantaneous readout of the receiver's longitude and latitude. Add a fourth satellite, and the computer can calculate its elevation.

GPS has been around for several years, but the equipment was bulky, complex, weighed close to 40 pounds, and cost up to $30,000. It was usually used only for surveying and marine navigation.

Recently, however, the U.S. Forest Service asked one of its engineering facilities-the Missoula Technoloyg and Development Center (MTDC) in Montana --to see if the system might have forestry applications. The answer was a resounding "yes!"

"We needed a receiving unit that was lightweight, relatively inexpensive, and easy to use," said MTDC project leader Dick Hallman, "and we've gotten exactly that. " Working closely with several manufacturers of navigational equipment, the MTDC helped give the emerging technology almost unlimited resource management potential.

Currently, the best unit consists of a receiver the shape of a car radio, a hand-held computer about the size of an electronic calculator, and a small antenna. The whole thing fits conveniently in a daypack, weighs barely nine pounds, and sells for about $19,000.

Some experts believe that the price may eventually fall to around $1,000 and the weight to three or four pounds. There's even talk of a pocketsize model.

"In one swoop we've switched from an ancient and terribly inaccurate compass-and-pacing system to space-age technology," says Hallman. "The impact on resource management simply boggles the mind." For one thing, mapping will be revolutionized. Current forest maps are notoriously unreliable, with features sometimes "misplaced" by hundreds of yards and trail and road lengths off by a mile or more. Timber sales may be accurate only to the closest 40 acres.

Suddenly, with GPS, any location-or series of locations-can be described via longitude, latitude, and elevation. A forester driving a road or walking a trail can take a GPS reading every 100 feet or so, store the information, and later plot the points on a map (or let a computer plot them). Cutting units, timber types, and ownership boundaries can be described by coordinates, not by vague references to drainages, ridges, and other topographic features. Presto-every item on the map is exactly where it belongs.

"The system's precision is really incredible," says Forest Service engineer Tony Jasumback. "We're already getting 1-in-10,000 accuracy with handheld equipment." This means that over nearly two miles of measurement, the GPS is likely to be off by only a foot or so. By comparison, the pacing-and-compass technique has perhaps 1-in-500 accuracy. With a GPS receiver in hand, a forester can be reasonably certain of ending up within 50 or 75 feet of any preselected point--even in remote, unmarked terrain.

In addition to improved mapping, the MTDC has identified scores of resource-management uses for GPS, and the ideas are still rolling in:

An engineer can determine the coordinates of needed road repair and be certain that a work crew will return to that exact location weeks or months later.

A fire boss can measure a burn by taking readings as he walks around it.

Getting exact acreages for harvest or planting is a snap.

Spray planes no longer need a guide plane, because the pilot can always know exactly where he is.

* A new fire's location can be pinpointed immediately by an airborne GPS receiver.

*A crew can walk directly to any preselected spot-even in the dark-simply by knowing the required coordinates.

*Archaeological sites or specific wildlife habitats-such as bear dens, nesting trees, or a small marsh-can be located with pinpoint accuracy.

*Remote timber or soil samples taken by different people years apart can reliably come from the same spot.

*Supervisors can keep track of every vehicle in a fleet by monitoring their locations with GPS.

And the list goes on. "Virtually anything on earth may at some time need to be positioned," says Fred Gerlach, the University of Montana forestry professor who trains Forest Service employees to use GPS at the University's Lubrecht Experimental Forest near Missoula. This training program may be opened to private foresters this year.

Work at Lubrecht has, however, uncovered a significant problem with GPS use in the forest-canopy interference with satellite signals. "We're not sure how or why it's happening," says Gerlach. "And we don't know yet if the problem comes from the trunks or from the foliage." In addition, GPS does not work well in canyons or other places where the view of the sky is restricted. "The system isn't perfect," says Jasumback, "but we're developing procedures to correct its shortcomings.

And potential uses for GPS extend far beyond resource management. Some cars already have a GPS navigational system with a map that changes as the car moves. Aboard an airliner, a GPS receiver could prevent pilots from ever straying off course. A downed aircraft transmitting its location could lead rescue crews directly to the wreckage. A backpacker with a receiver and a map would no longer be tied to trails.

And people in the forest might never again get lost. AF