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Appendix
All of these error sources have an important characteristic in common; the
amount and direction of the error at any given time does not change rapidly.
Therefore, two GPS receivers that are sufficiently close together will observe
the same fix error, and the size of the fix error can be determined.
Non-Correctable Errors
Non-correctable errors cannot be correlated between two GPS receivers that
are located in the same general area. Sources of non-correctable errors
include receiver noise, which is unavoidably inherent in any receiver, and
multipath errors, which are environmental. Multipath errors are caused by
the receiver "seeing" reflections of signals that have bounced off of
surrounding objects. (The ProMARK X antenna and the Magellan exterior
antenna have been designed to minimize the effects of this problem. The
submeter antenna is multipath-resistant; its use is required when logging
carrier phase data.) Neither error can be eliminated with differential, but they
can be reduced substantially with position fix averaging.
Error Source
Correctable with Differential
Clock (Space Segment)
Ephemeris (Control Segment)
Ionospheric Delay (Atmosphere)
Tropospheric Delay (Atmosphere)
Selective Availability (if implemented)
Non-Correctable with Differential
Receiver Noise (Unit)
Multipath (Environment)
Total User Equivalent Range Error
(all sources)
Navigational Accuracy (HDOP=1.5)
A-6
ERROR SOURCES
TOTAL
TOTAL
ProMARK X
Approx.
Equivalent Range
Error (RMS)
3.0 meters
2.7 meters
8.2 meters
1.8 meters
27.4 meters
28.9 meters
9.1 meters
3.0 meters
9.6 meters
30.5 meters
45.8 meters
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