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Improving GPS results using continuous processing strategies


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Nguyen, Lau Ngoc 2000 , 'Improving GPS results using continuous processing strategies', PhD thesis, University of Tasmania.

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The establishment of the International GPS Service for Geodynamics (IGS) in
1994 and the rapid development of its high quality products have opened promising,
new capabilities for the global GPS positioning community. Two important products
of the IGS are the precise satellite ephemerides and the precisely-determined
locations of many permanent tracking sites distributed over the entire globe. In
addition, we can obtain high quality RINEX data from the global tracking network
on a daily basis.
The combination of a multi-purpose regional GPS network and the nearby IGS
fiducial stations, along with the use of IGS precise ephemerides, can provide results
in a well-defined global reference frame with maximum accuracy and minimum
computational burden. We are fast moving towards the situation of having multi
purpose GPS networks containing medium length baselines (up to 1000 km), which
require the highest accuracy level of positioning. As a general rule of thumb, the
common-mode errors due to ionospheric, tropospheric and orbital uncertainties
increase with baseline distance. This therefore introduces a range of problems in the
processing of medium length baselines, such as ambiguity resolution, vertical
precision associated with the treatment of the tropospheric delay, etc.
The results from GPS processing can be used for many different applications,
such as in the fields of glaciology, volcanology, oceanography, meteorology, etc.,
and so we increasingly require a high degree of flexibility and innovation in our GPS
processing techniques.
The aim of this thesis is to improve our processing techniques over medium
length baselines making use of permanent stations, such as the IGS fiducial stations
and the IGS precise ephemerides. A processing technique is required that exploits the
continuity of the GPS data and that is able to satisfy various high precision GPS
applications (at the 1 part in 107 level or better). We suggest a new approach for GPS
processing, the so-called continuous processing approach, rather than the classical
processing that pertains to batch least squares adjustment.
For a continuous processing methodology, we have to resolve a number of related
matters, such as cycle slip detection and repair; outlier detection; the use of
sequential least squares adjustment, incorporating between-epoch correlation and the
necessary modification of the unknown vector and cofactor matrix to maintain the
continuity of data processing under the influence of a satellite combination change;
ambiguity resolution, and estimation strategies of tropospheric delay.
We demonstrate the efficiency of the new technique using several different high
precision GPS applications in geodynamics. Three studies were undertaken using
data from a tide gauge network within Australia, the Northridge earthquake event in
North America, and a study of the motion of the Amery Ice Shelf in Antarctica.
The results from using the continuous processing approach developed in this
thesis are in good agreement with previous studies but yield additional insight into
some of the physical processes, such as the motion of the Amery Ice Shelf. The
utilisation of improved stochastic modelling of measurements and the continuous
nature of the processing increases the effectiveness and reliability of outlier detection
and ambiguity resolution. The posteriori variance factor is also improved by up to
30%. With greater flexibility in the monitoring of complicated movements of
stations, the new technique will prove to be a very promising tool for high precision
applications involving regional GPS networks.

Item Type: Thesis - PhD
Authors/Creators:Nguyen, Lau Ngoc
Keywords: International GPS Service for Geodynamics, Ephemerides, Global Positioning System, Artificial satellites in navigation
Copyright Holders: The Author
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Copyright 2000 the author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2000. Includes bibliographical references

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