Principles of Operation
P/N 7010-0935
1-5
Later, the data is downloaded to a computer, combined, and
processed.
Using this technique, the spatially correlated errors—such as
satellite orbital errors, ionospheric errors, and tropospheric
errors—can be significantly reduced, thus improving the position
solution accuracy.
A number of differential positioning implementations exist, including
post-processing surveying, real-time kinematic surveying, maritime
radio beacons, geostationary satellites (as with the OmniSTAR
service), and Satellite Based Augmentation Systems (WAAS,
EGNOS, MSAS).
The real-time kinematic (RTK) method is the most precise method of
real-time surveying. RTK requires at least two receivers collecting
navigation data and a communication data link between the receivers.
One of the receivers is usually at a known location (Base) and the
other is at an unknown location (Rover). The Base receiver collects
carrier phase measurements, generates RTK corrections, and sends
this data, along with the coordinates of the reference station, to the
Rover receiver. The Rover processes this transmitted data with its
own carrier phase observations to compute its relative position with
high accuracy, achieving an RTK accuracy of up to 1 cm horizontal
and 1.5 cm vertical.
Essential Components for Quality Surveying
Achieving quality position results requires the following elements:
• Accuracy – The accuracy of a position primarily depends upon
the satellite geometry (Geometric Dilution of Precision, or
GDOP) and the measurement (ranging) errors.
– Differential positioning (DGPS and RTK) strongly mitigates
atmospheric and orbital errors, and counteracts Selective
Availability (SA) signals the US Department of Defense
transmits with GPS signals.
– The more satellites in view, the stronger the signal, the lower
the DOP number, the higher the positioning accuracy.
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