8.2.1
Introduction to Ambiguity Resolution
What is ambiguity
resolution?
 A means of improving
the
accuracy of GPS surveying ...
The mathematical
process of
converting ambiguous ranges
(integrated
carrier phase) to unambiguous
ranges of millimetre
measurement precision
...
For conventional
GPS
surveying, corresponds to converting
real-valued
ambiguity parameter values to the likeliest integer
values ...
For modern GPS
surveying,
corresponds to discriminating the likeliest
set of
integer values from many alternative sets
... |
Determining the value of the unknown initial (integer)
ambiguity for
a GPS double-differenced phase solution is an important task
of GPS phase
reduction software. Ambiguity resolution is probably
the most uniquely
identifiable characteristic of high precision GPS
positioning.
Two scenarios for ambiguity resolution can be
distinguished:
- In the case of conventional static GPS
surveying, as developed
since the early 1980's, the lengths of the
observation sessions are sufficient
to ensure a reliable ambiguity-free
solution, and the successful resolution
of the ambiguities to their
integer values is a useful "bonus".
- For modern GPS surveying techniques (section 5.5.1), ambiguity resolution is a critical
operation, and if not successfully carried out, the integrity and reliability
of the baseline solution can be degraded significantly.
Considerable R&D has therefore
been invested in developing ambiguity
resolution techniques for modern GPS
surveying. Before considering the strategies
developed specifically for
"rapid static" and "kinematic"
techniques (including
some dual-frequency procedures -- section
8.4.1),
it is useful to study the steps involved in ambiguity resolution
for
conventional -- long observation session -- GPS surveying.
GENERAL OVERVIEW OF
AMBIGUITY RESOLUTION
Several steps in the
ambiguity resolution process can be identified:
- Define the
apriori values of the ambiguity
parameters.
- Use a search
algorithm to identify likely
integer values.
- Employ a decision-making algorithm to
select the
"best" set of integer values.
- Apply ambiguities to the new (ambiguity-fixed)
solution.
Each of these are discussed in the following
sections.
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© Chris Rizos, SNAP-UNSW, 1999