GPS Solution - How to increase the accuracy of your location

Calibration

Electronic compasses need to be calibrated whenever you change batteries. If your GPS Tracking Device has an electronic compass, follow your user guide’s instructions to calibrate it. Usually, this requires being outside, holding the GPS unit flat and level, and slowly turning in a circle twice.

Altimeter

The elevation or altitude calculated by a GPS receiver from satellite data isn’t very accurate. Because of this, some GPS units have altimeters, which provide the elevation, ascent/descent rates, change in elevation over distance or time, and the change of barometric pressure over time. (The rough-and-ready rule is that if barometric pressure is falling, bad weather is on the way; if it’s rising, clear weather is coming.) Calibrated and used correctly, barometric altimeters can be accurate within 10 feet of the actual elevation. Knowing your altitude is useful if you have something to reference it to, such as a topographic map. Altimeters are useful for hiking or in the mountains.

On GPS units with an electronic altimeter/barometer, calibrating the altimeter to ensure accuracy is important. To do so, visit a physical location with a known elevation and enter the elevation according to the directions in your user’s guide. Airports are good places to calibrate your altimeter or get an initial base reading; their elevation is posted for pilots to calibrate their airplanes’ altimeters. If you’re relying on the altimeter/barometer for recreational use, I recommend calibrating it before you head out on a trip.

Increasing accuracy

Some GPS receivers have features that allow you to increase the accuracy of your location by using radio signals not associated with the GPS satellites. If you see that a GPS receiver supports WAAS or Differential GPS, it has the potential to provide you with more accurate location data.

WAAS

Wide Area Augmentation System (WAAS) combines satellites and ground stations for position accuracy of better than three meters. Vertical accuracy is also improved to three to seven meters. WAAS is a Federal Aviation Administration (FAA) system, so GPS can be used for airplane flight approaches. The system has a series of ground-reference stations throughout the United States. These monitor GPS satellite data and then send the data to two master stations — one on the west coast and the other on the east coast. These master stations create a GPS message that corrects for position inaccuracies caused by satellite orbital drift and atmospheric conditions. The corrected messages are sent to non-NAVSTAR satellites in stationary orbit over the equator. The satellites then broadcast the data to GPS receivers that are WAAS enabled.

GPS units that support WAAS have a built-in receiver to process the WAAS signals. You don’t need more hardware. Some GPS receivers support turning WAAS on and off. If WAAS is on, battery life is shorter (although not as significantly as it is when using the backlight). In fact, on these models, you can’t use WAAS if the receiver’s battery-saver mode is activated. Whether you turn WAAS on or off depends on your needs. Unless you need a higher level of accuracy, you can leave WAAS turned off if your GPS receiver supports toggling it on and off. WAAS is ideally suited for aviation as well as for open land and marine use. The system may not, however, provide any benefits in areas where trees or mountains obstruct the view of the horizon. Under certain conditions — say, when weak WAAS satellite signals are being received or the GPS receiver is a long way from a ground station — accuracy can actually worsen when WAAS is enabled.

WAAS is only available in North America. Other governments are establishing similar systems that use the same format radio signals such as

1. European Euro Geostationary Navigation Overlay Service (EGNOS)

2. Japanese Multi-Functional Satellite Augmentation System (MSAS)

Differential GPS

Surveying and other work that demands a high level of precision use Differential GPS (DGPS) to increase the position accuracy of a GPS receiver. A stationary receiver measures GPS timing errors and broadcasts correction information to other electronic tracker that are capable of receiving the DGPS signals. Consumer GPS receivers that support DGPS require a separate beacon receiver that connects to the GPS unit. Consumers can receive DGPS signals from free or commercial sources. Unless you’re doing survey or other specialized work, you really don’t need DGPS capabilities. For consumer use, the increased accuracy of DGPS has mostly been replaced with WAAS.

Coast Guard DGPS

DGPS signals are freely broadcast by a series of U.S. Coast Guard stations in the United States. Whether you can receive these Coast Guard broadcasts depends on your location.

Commercial DGPS

DGPS services are offered commercially for the surveying market. You can rent or purchase electronic and radio equipment for gathering precise location information in a relatively small area.

Antennas

Well, yes, electronic tracking device has to have an antenna to receive radio signals to do you any good. Several types are available, each with its advantages.