time spent and the cost of conducting the survey are significantly reduced. The achievable accuracies
typically equal or exceed third order.
(1) Stop-and-go surveying is performed similarly to a conventional EDM traverse or electronic
total station radial survey. The system is initially calibrated by performing either an antenna swap with
one known point and one unknown point or by performing a static measurement over a known baseline.
This calibration process is performed to resolve initial cycle ambiguities. This known baseline may be
part of the existing network or can be established using static GPS-S procedures. The remote roving
receiver then traverses between unknown points as if performing a radial topographic survey. Typically,
the points are double-connected, or double-run, as in a level line. Optionally, two fixed receivers may
be used to provide redundancy on the remote points. With only 1 1/2 minutes at a point, production of
coordinate differences is high and limited only by satellite observation windows, travel time between
points, and overhead obstructions.
(2) During a stop-and-go kinematic survey, the rover station must maintain satellite lock on at
least four satellites during the survey period (the reference station must be observing at least the same
four satellites). Loss of lock occurs when the receiver is unable to continuously record satellite signals
or the transmitted satellite signal is disrupted and the receiver is not able to record it. If satellite lock is
lost, the roving receiver must reobserve the last control station surveyed before loss of lock. The
receiver operator must monitor the GPS receiver when performing the stop-and-go survey to ensure loss
of lock does not occur. Some manufacturers have now incorporated an alarm into their receiver that
warns the user when loss of lock occurs.
(3) Survey site selection and the route between rover stations to be observed are critical. All
sites must have a clear view (a vertical angle of 15^ or greater) of the satellites. The routes between
rover occupation stations must be clear of obstructions so that the satellite signal is not interrupted.
Each unknown station to be occupied should be occupied for a minimum of 1 1/2 minutes. Stations
should be occupied two or three times to provide redundancy between observations.
(4) Although the antenna swap procedure can be used to initialize a survey before to a stop-and-
go survey, it can also be used to determine a precise baseline and azimuth between two points. An
unobstructed view of the horizon must be maintained at both occupied stations and the path between
them. A minimum of four satellites (although more than four satellites are preferred) and a maintainable
satellite lock are required. One receiver or antenna is placed over a point of known control and the
second receiver or antenna is placed a distance of 10 to 100 meters away from the other receiver. The
receivers at each station collect data for about 2 to 4 minutes. The receiver or antenna locations are then
swapped. The receiver or antenna at the known station is moved to the unknown site while the other
receiver or antenna is moved to the known site. Satellite data are again collected for 2 to 4 minutes, and
the receivers are swapped back to their original locations. This completes one antenna swap calibration.
If satellite lock is lost during the procedure, the procedure must be repeated.
EN0593
5-30
Previous Page
