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What is WAAS?

WAAS-enabled products ca 2005:
eTrex Legend
eTrex Legend C
eTrex Venture
eTrex Vista
eTrex Vista C
Foretrex 101
Foretrex 201
Geko 201
Geko 301
GPS V
GPS 15H
GPS 15L
GPS 16
GPS 17N
GPS 18
GPS 18 OEM
GPS 72
GPS 76
GPS 152
GPSMAP76
GPSMAP 76C
GPSMAP 76S
GPSMAP 76CS GPSMAP 96
GPSMAP 96C
GPSMAP 162
GPSMAP 172C GPSMAP 178C

GPSMAP 168 Sounder
GPSMAP 176
GPSMAP 176C GPSMAP 182
GPSMAP 188 Sounder
GPSMAP 196
GPSMAP 232
GPSMAP 238 Sounder
GPSMAP 276C
GPSMAP 295
GPSMAP 296
GPSMAP 60C
GPSMAP 60CS GPSMAP 2006
GPSMAP 2010
GPSMAP 3006C GPSMAP 3010C
iQue 3200
iQue 3600
Quest
Rino 110
Rino 120
Rino 130
StreetPilot 2610
StreetPilot 2620
StreetPilot 2650
StreetPilot 2660

Note: This list is not comprehensive.
WAAS system
You've heard the term WAAS, seen it on packaging and ads for Garmin® products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.

The origins of WAAS

The Federal Aviation Administration (FAA) and the Department of Transportation (DOT) are developing the WAAS program for use in precision flight approaches. Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity, and availability. WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing, and satellite orbit errors, and it provides vital integrity information regarding the health of each GPS satellite.

How it Works

WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

Who benefits from WAAS?

Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of WAAS is that it does not require additional receiving equipment, while DGPS does.

Other governments are developing similar satellite-based differential systems. In Asia, it's the Japanese Multi-Functional Satellite Augmentation System (MSAS), while Europe has the Euro Geostationary Navigation Overlay Service (EGNOS). Eventually, GPS users around the world will have access to precise position data using these and other compatible systems.

It just keeps getting better

WAAS accuracy 100 meters: Accuracy of the original GPS system, which was subject to accuracy degradation under the government-imposed Selective Availability (SA) program.
15 meters: Typical GPS position accuracy without SA.
3-5 meters: Typical differential GPS (DGPS) position accuracy.
< 3 meters: Typical WAAS position accuracy.

* All information above is courtesy of GARMIN International

Click here for "WAAS Operation: Your Questions Answered" by Joe Mehaffey & Jack Yeazel


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