Global Positioning System Accuracy - Troxler Enhanced RoadReader Plus 3451 Manual Of Operation And Instruction

GLOBAL POSITIONING SYSTEM ACCURACY

As described earlier, the Model 3451 is equipped with a global
positioning system (GPS) receiver that provides accurate
information on the location (latitude and longitude) of the gauge.
This information is stored with each gauge measurement. The GPS
receiver used in the Model 3451 has Wide Area Augmentation
System (WAAS) capabilities, which provides accuracy to within 3 m
(10 ft). However, the accuracy is dependent upon the user's location
and other factors as described below.
The global positioning system (GPS) is a satellite-based navigation
system that consists of 24 satellites and a network of ground stations
that monitor and control those satellites. The satellites orbit the earth
at an altitude of approximately 11,000 miles, and constantly
transmit signal information back to earth. A GPS receiver uses this
information to determine its location.
To determine its latitude and longitude, a GPS receiver must receive
the signals from at least three satellites.
On average, the receiver used in the Model 3451 gauge is accurate
to with 15 m (approximately 50 ft) when receiving GPS data alone.
However, the WAAS capabilities can increase the accuracy to
within 3 m (10 ft), as shown in Table 1–1.
The accuracy of GPS information can be affected by a number of
atmospheric forces and other conditions. The Wide Area
Augmentation System (WAAS) corrects for these factors by placing
GPS receivers at 25 known, precisely surveyed locations, called
reference stations, across the United States. The reference stations
determined a measured distance to each satellite using the signals
received from the satellites. For each satellite, the stations compare
the measured distance to the actual range (as calculated from its
known position) to determine a differential correction for each
satellite
Model 3451 1–5