(1) Receiver Time. This technique uses a change from one epoch to the next in the between
receiver single differences for the same satellite. This technique eliminates satellite-dependent integer
cycle ambiguities and simplifies the editing of cycle slips.
(2) Receiver Satellite. There are two different methods that can be used to compute a receiver
satellite double difference. One method involves using two between-receiver single differences and a
pair of receivers that record different satellite observations between two satellites. The second method
involves using two between-satellite single differences and a pair of satellites, but with different
receivers, which differences the satellite observations between the two receivers.
c. Triple Differencing. There is only one triple-differencing processing technique--receiver
satellite time. All errors eliminated during single- and double-differencing processing are also
eliminated during triple differencing. When used in conjunction with carrier beat phase measurements,
triple differencing eliminates initial cycle ambiguity. During triple differencing, the data are
automatically edited by the software to delete any data ignored during the triple-difference solution.
This feature is advantageous because of the reduction in the editing of data required; however,
degradation of the solution may occur if too much data are eliminated.
5-40. Baseline Solutions by Cycle-Ambiguity Recovery. The resultant solution (baseline vector)
produced from carrier beat phase observations when differencing resolves cycle ambiguity is called a
fixed solution. The exact cycle ambiguity does not need to be known to produce a solution. If a range
of cycle ambiguities is known, then a float solution can be formulated from the range of cycle
ambiguities. It is desirable to formulate a fixed solution. However, when the cycle ambiguities cannot
be resolved, which occurs when a baseline is between 20 to 65 kilometers, a float solution may actually
be the best solution. The fixed solution may be unable to determine the correct set of integers (fix the
integers) required for a solution. Double-differenced fixed techniques can effectively be used for
positional solutions over short baselines of less than 20 kilometers. Double-differenced float techniques
normally can be effectively used for positional solutions of medium-length lines between 20 and 65
kilometers.
5-41. Data Processing and Verification. Baselines should be processed daily in the field to identify
any problems that may exist. Once baselines are processed, the field surveyor should review each
baseline output file. The procedures used in baseline processing are manufacturer-dependent. Certain
computational items within the baseline output are common among manufacturers and may be used to
evaluate the adequacy of the baseline observation in the field. The triple-difference float solution is
normally listed. The geodetic azimuth and the distance between the two stations are also listed. The
RMS is a quality factor that helps identify which vector solution (triple, float, or fixed) to use in the
adjustment. The RMS is dependent on the baseline length and the length of baseline observation. Table
5-4 provides guidelines for determining the baseline quality. If the fixed solution meets the criteria in
this table, the fixed vector should be used in the test. If the vector
EN0593
5-36
Previous Page
