Geology Reference
In-Depth Information
Figure 15.1
Example of a hand-held Personal Digital Assistant (PDA) and
global positioning system (GPS) receiver that can receive real-time differ-
ential GPS (DGPS) corrections via satellite to provide 2-5 m locational
accuracies. It is equipped with WiFi and Bluetooth for easy email and data
exchange.
15.2.3 Practical considerations in using DGPS
Differential GPS data can be obtained in a number of ways:
1.
A dedicated base station may transmit corrections via a radio link for
real-time corrections, or be used to post-process the field data if real-
time corrections are not required.
2.
A government-operated SBAS (
Satellite-Based Augmentation System
)
such as WAAS (
Wide Area Augmentation Service
) in the United States
or EGNOS (
European Geostationary Navigation Overlay Service
)in
Europe can be used to provide real-time differential corrections. The
GPS instrument shown in Figure 15.1 has a built-in radio receiver,
allowing these corrections to be applied in real time.
3.
A subscription can be bought for a commercial differential service such
as Omnistar. Omnistar's dual-frequency, carrier-phase H-Star technol-
ogy can achieve sub-30-cm accuracies in real time provided that at least
2 minutes of uninterrupted satellite signal (satellite lock) have been
recorded. Lock must be maintained on a minimum of five satellites.
4.
Carrier-wave RTK techniques provide centimetre accuracies in real
time if carrier lock is maintained, but no position at all if it is lost. Post-
processing can provide accuracies of 30 cm to 1 cm using data acquired
