5.5.4 Modern GPS Surveying: Field Procedures

"STOP & GO" GPS SURVEYING TECHNIQUES


Centimetre accuracy positioning during very short static observation periods (<1minute) ... receiver moves carefully from point to point ...


This is a true kinematic technique because the receiver continues to track satellites while it is in motion. It is known as the "stop & go" (or semi-kinematic) technique because the coordinates of the receiver are only of interest when it is stationary (the "stop" part), but the receiver continues to function while it is being moved (the "go" part) from one stationary setup to the next. There are in fact three stages to the operation:

 


The technique is well suited when many points close together have to be surveyed, and the terrain poses no significant problems in terms of signal disruption (usually an audible signal is emitted by the receiver when it has lost lock on the satellites). The survey is carried out in the manner illustrated in the Figure 2 below, and the ambiguities reinitialised using any of the techniques shown in Figure 3.




Figure 2. Field procedure for the "stop & go" surveying technique.




Figure 3. A variety of reinitialisation techniques for "stop & go" or "kinematic" surveys.

 

One particular negative characteristics of this technique is the requirement that phase lock must be maintained by the roving receiver as it moves from site to site. This requires special hardware mounts on vehicles if the survey is carried out over a large area.

An additional requirement is that the stationary reference receiver must continue to track all the satellites being tracked by the roving receiver. The accuracy attainable is about the same as for the "rapid static" technique. As with the "reoccupation" technique, the receiver must have the ability to handle data files from several different sites. The software then has to sort out the recorded data for the different sites, and to differentiate the "kinematic" or "go" data (not of interest) from the "static" or "stop" data (of interest). It can be implemented in real-time if a communications link is provided to transmit the "carrier-range" data from the reference receiver to the roving receiver(s).

 

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© Chris Rizos, SNAP-UNSW, 1999