ashtech Z-FX, Operation And Reference Manual

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70 Z-Surveyor & Z-FX Operation Manual
ambiguities; it is a type of redundancy. The data processor will be made
aware if a discrepancy is found pointing to a possible problem with the data.
The kinematic method has the significant disadvantage of not having any redundant observations of
the points being established. It is similar to a radial survey, in that a bad baseline can go undetected.
Therefore, it is recommended that points established using the kinematic method be observed twice
in independent surveys. Preferably, the resurvey would include the base system being located on a
different control point. The results of the two surveys should be compared manually or, preferably,
run through a least squares adjustment.
Rapid Static Surveying
The added capabilities of dual-frequency P-code found in the Z-Surveyor and Z-FX
make this method of GPS surveying possible. The procedure for a rapid static survey
is identical to that for a static survey, the only difference being point occupation time,
thus the name rapid static. Access to more information, namely the L2 satellite
frequency and access to the more precise P-code, allows the receiver to solve for the
carrier phase ambiguities in a significantly shorter period of time compared to the
static method.
The advantage of rapid static is increased productivity, in that occupation times are
greatly reduced compared to the static method. Since occupation times are so short,
the risk of a failure (point occupation not resulting in the expected level of accuracy)
is higher than with a static survey. Accuracies of the rapid static method are
comparable to the static method.
As a general rule of thumb, if the baseline is 10km or less, the observation session length should be 10
minutes. For every 1km over 10km, add one minute of additional observation session length time.
Use the rapid static method when high productivity is required. Expect a higher
failure rate compared to static methods due to the short occupation times. Limit the
length of baselines to no more than 15 kilometers. As baseline lengths increase, so
will the need for longer occupation times. At 15 kilometers, required occupation
times will approach those of static surveys.
Performing a Rapid Static Survey
The procedure for performing a rapid static survey is nearly identical to that of a static
survey. The key difference is the amount of time required for collecting data on a
point. Since occupation times are much shorter in this method of GPS surveying,
close monitoring of the survey is more important.
A rapid static survey requires at least two GPS systems that collect data
simultaneously from several common satellites over a specific time period. One