Bruce Grubbs - Basic Illustrated Using GPS

Bruce Grubbs is an avid hiker, mountain biker, paddler, and cross-country skier who has been exploring the American West for several decades. He has used high-technology gear in the backcountry in his work as a professional pilot, an amateur radio operator, and a mountain rescue team member. Bruce holds Airline Transport Pilot and Instrument Flight Instructor certificates. He lives in Flagstaff, Arizona, and is the author of more than thirty-five books.

Other books by Bruce:

Backpacker Magazines Using a GPS

Best Easy Day Hikes Flagstaff, 2nd

Best Easy Day Hikes Sedona, 2nd

Desert Hiking Tips

Grand Canyon National Park Pocket Guide

Hiking Arizona, 3rd

Hiking Nevada, 2nd

Hiking Northern Arizona, 3rd

Mountain Biking Phoenix

Mountain Biking St. George and Cedar City

For more information, visit Bruces website at brucegrubbs.com

GPS and Accessory Manufacturers

DeLorme

GPS receivers, SPOT receivers, maps

delorme.com

Garmin International Inc.

GPS receivers and maps

garmin.com

Lowrance Electronics

GPS receivers

lowrance.com

Magellan Systems Inc.

GPS receivers and maps

magellangps.com

RAM

GPS mounts

ram-mount.com

Trimble Navigation Limited

trimble.com

Compasses

Brunton Co.

bruntonoutdoor.com

Silva USA

silvacompass.com

Suunto USA Inc.

suunto.com

Maps and Tools

ExpertGPS.com

Computer GPS and mapping software using free, open-source maps and aerial imagery

TopoFusion.com

Computer GPS and mapping software using free, open-source maps and aerial imagery

GPSfiledepot.com

Free, open-source maps for GPS

GPStracklog.com

Trail and street GPS reviews

MapTools

Plotters and tool for use with paper maps maptools.com

US Geological Survey, Information Services

mapping.usgs.gov

Chapter One

The Global Positioning System comprises twenty-four active satellites orbiting 12,000 miles above the earth. The satellites orbits are arranged so that several satellites are always in view from any point on Earth. Spare satellites and ground control stations make up the rest of the system. Though the US Department of Defense developed the system for military use, the government makes GPS available to all users without charge. Consequently, GPS is used by businesses to track parcel delivery trucks, by individual motorists to find their way to a specific street address, by ships and aircraft of all sizes, for precise survey work, timing, and many other uses.

This book focuses on using hand-held trail GPS receivers that are intended for civilian use and suitable for navigation in the backcountry and in self-propelled sports. There are many other types of GPS receiverslarge receivers intended to be mounted permanently in vehicles, tiny ones designed to be embedded in smaller devices, and credit cardsize receivers designed to plug into data-gathering computers. Specialty receivers are made for marine use, aviation, surveying, the earth sciences, and the military.

As its name implies, GPS allows a user to determine position. As described in the preface, GPS is unique among the various methods of navigation in that it can determine position very rapidly with a high degree of accuracy, in any weather and at any time of day, almost anywhere on our planet. Using radio signals transmitted by the satellites, a GPS receiver can determine position to within 33 feet (10 meters) or better. Because the GPS receiver measures position quickly and accurately, it can calculate your direction and rate of travel based on previous position fixes. It also can tell you the direction to travel to reach your destination and display this information on the screen as an electronic compass and on a detailed, moving map.

Satellite navigation is not a magic wand. Like any tool, it has limitations. A GPS receiver must have a clear view of the sky to receive signals from the satellites. Since GPS uses microwave radio signals that travel in straight lines, like light waves, trees can block the signals, as can high canyon walls. (Clouds, rain, and snow do not interfere with the satellite signals.) Sometimes poor satellite geometry can degrade accuracy or even make it impossible to get a position fix. A GPS receiver is a complex piece of equipment that can fail or be dropped and broken, and its batteries can die. In addition, the receiver is helpful only if its user knows how to operate it properly.

GPS is best used in conjunction with the older navigation tools. The position display on a GPS receiver is a meaningless string of numbers without a map to plot your location. Although you can load detailed topographic maps on many GPS receivers, you should still have a paper map with you, for two reasons. Failure of your GPS receiver would leave you without any map. And a paper map gives you an overview of the surrounding country that you cannot get from the small screen on the GPS.

Knowing the direction to a favorite spot does not help unless you have a compass to point you in that direction. In addition, a sensitive, temperature-compensated barometric altimeter can read altitude more accurately than a hand-held GPS. While many GPS receivers now have built-in magnetic compasses, the compass must be calibrated every time you change batteries or location, and once again, failure of the GPS deprives you of your compass.

The heart of GPS is precise measurement of time. Each satellite in the system carries several atomic clocks on board. The satellites transmit precisely timed radio signals that are picked up by your GPS receiver. Each signal carries precise timing information, telling the receiver exactly when the signal left the satellite. Using an on-board computer, the receiver measures time in transitthe time required for the radio signal to travel from the satellite to the receiver. The satellites also transmit a navigation signal that gives their exact position. Using this information, your receiver calculates its exact distance from the satellite and places your receiver somewhere on a spherical surface. When your receiver links up with two more satellites and computes its distance from them, the receiver then knows that it is located on the surface of three imaginary spheres. The point at which those spheres intersect is the receivers position. Acquiring a fourth satellite refines the position calculation so that altitude can be computed.

The GPS satellites in orbit require constant updates that are transmitted from ground control stations. The ground stations continuously track the satellites and calculate updated positions. Corrections are also made for the drift of the atomic clocks. This information is uplinked to the satellites to update the navigation signal. Without this continuous flow of information, the systems accuracy would degrade in a matter of days. The ground stations can also reposition satellites and replace them with orbital spares as necessary.

The DOD constantly launches new satellites, both to replace aging satellites and to improve the capabilities of the GPS system. To avoid dependency on a single system, other spacefaring nations are building satellite navigation systems of their own, including the Russian GLONASS, Chinese BeiDou-2, and European Galileo systems.

As a wilderness navigator, one direct benefit is the increasing accuracy and reliability of satellite navigation. GPS receivers now on the market can receive both GPS and GLONASS signals, doubling the number of satellites the receiver has to work with.