Il
olutions:
d (b) for
10000
0)
olutions
0.255m
—--.l
10000
2300)
lutions
0.223m
method, accurate to a couple of centimetres. This baseline
can therefore be used together with the phase delta position
solution to create a precise trajectory for validation of
different LRD positioning solutions. Figure 5 show the
differences between the precise trajectory and code DGPS
position solutions of two horizontal components. It is noted
that the noise of DGPS positioning solutions based on
ionosphere-free pseudoranges is as high as tens of metres
and the standard deviations for latitude and longitude
components are 9.384m and 7.348m respectively.
Comparing to the nominal figures of 2-5 metres for DGPS
standard deviations, these STD values are considered quite
high. Nevertheless, as shown in Figures 6 and 7, the
accuracy of 20~30 centimetres in horizontal components
can be achieved by the proposed filtering approach after
about 10 minutes of the continuous tracking time. These
figures clearly show the asymptotical stability of the filtering
solutions. Not surprisingly, the figures also show the biases
for the smoothing solution are -14 cm and 16 cm in latitude
and longitude respectively, which may have been caused by
the range-dependent systematic errors such as un-modelled
troposphere biases and GPS broadcasting orbital errors as
addressed previously.
5. CONCLUSIONS
Integer ambiguity resolution for long-range dynamic or
kinematic positioning is difficult to achieve by using
ionosphere-free carrier phase measurements. However, if
the cycle slips and data gaps can be detected and removed
successfully, the decimetre dynamic positioning may also be
achieved without ambiguity resolutions. This is achieved by
the long range dynamic GPS positioning method
described in the paper. The method includes two strategies.
First, it uses the phase combinations of ¢;.; and 79 to
detect and remove the cycle slips and short data gaps very
efficiently. Secondly, it introduces Kalman filtering
approach to the linear dynamic system to reprocess the
phase-delta-position solutions and code position solution for
achieving decimetre accuracy in real time. This requires on
ambiguity resolution. The real time solutions are uniformly,
asymptotically stable. The established particular. LRD
System is robust and reliable to use. The tests results have
shown that the method for the detection and repair of cycle
slips is efficient for the data gaps of up to 60 seconds for
aircraft dynamic environment. Although the noise level of
DGPS positioning solutions based on ionosphere-free
pseudoranges reaches as high as tens of metres in this test,
71
20~30 centimetre accuracy in each component has been
achieved by the proposed filtering approach. The smoothing
solutions show the errors of -14 cm and 16 cm in latitude
and longitude respectively, possibly due to range-dependent
systematic errors such as un-modelled troposphere biases
and GPS broadcasting orbital errors. In conclusion, the
experimental results have confirmed the achievable
decimetre accuracy on line (real-time) and off-line 1ppm
accuracy of the proposed long range dynamic processing
system.
REFERENCES
1. CHEN, D., Development of A fast Ambiguity Search
Filtering (FASF) Method for GPS Carrier Phase
Ambiguity Resolution, PhD Dissertation, The University
of Calgary, 1994.
2. CANNON, E., Dynamic Real Time Precise Positioning,
ION GPS -95 Tutorial, Palm Spring, September, 1995.
3. DELOACH, SR, D. WELLS & D. DODD, Why On-
the-Fly, GPS World, May, 1995.
4. DONG, D.N, & Y. BOCK, Global Positioning System
network Analysis with Phase Ambiguity Resolution
Applied to Crustal Deformation Studies in California,
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5. FENG,Y.& KUBIK, On the internal stability of GPS
Positioning Solutions, Submitted to — Manuscripta
Geodaetica, 1994.
6. FENG, Decimetre-Accuracy DGPS Achieved Without
On-The-Fly Ambiguity Resolutions, Conference
Proceedings of Satellite Navigation Technology: 1995
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7. HAN, S. & C. RIZOS, A suggested procedure for On
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9. HOFMANN-WELLENHOF, B., HLICHTENEGGER,
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996
