(2) Data collected in the rapid-static mode should be processed according to the manufacturers'
specifications. Accuracies are similar to static surveys of a centimeter or less. This method can be used
for medium- to high-accuracy surveys up to 1:1,000,000.
f. On-the-Fly/Real-Time Kinematic Surveying. OTF/RTK surveying is similar to kinematic
surveying because it requires two receivers that record observations simultaneously and allows the rover
receiver to move. Unlike kinematic surveying, OTF/RTK surveying uses dual-frequency GPS
observations and can handle loss of lock. Since OTF/RTK surveying uses the L2 frequency, the GPS
receiver must be capable of tracking the L2 frequency during AS. There are several techniques used to
obtain L2 during AS, including the squaring and cross-correlation methods.
(1) Successful ambiguity resolution is required for successful baseline formulations. The
OTF/RTK technology allows the remote to initialize and resolve these integers without a period of static
initialization. If loss of lock occurs, reinitialization can be achieved while the remote is in motion. The
integers can be resolved at the rover within 10 to 30 seconds, depending on the distance from the
reference station. OTF/RTK surveying uses the L2 frequency transmitted by the GPS satellites in the
ambiguity resolution. After the integers are resolved, only the L1 C/A-code is used to compute the
positions.
(2) OTF/RTK surveying requires dual-frequency GPS receivers. One of the GPS receivers is set
over a known point and the other is placed on a moving or mobile platform. If the survey is performed
in real time, a data link and a processor (external or internal) are needed. The data link is used to
transfer the raw data from the reference station to the remote.
(a) Internal Processor. If OTF/RTK surveying is performed with an internal processor (built
into the receiver), follow the manufacturer's guidelines.
(b) External Processor. If OTF/RTK surveying is performed with external processors (a
notebook computer), the PC at the reference station collects and formats the raw GPS data and sends it
via a data link to the rover. The notebook computer at the rover processes the raw data from the
reference and remote receivers to resolve the integers and obtain a position.
(3) OTF/RTK surveys are accurate to within 10 centimeters when the distance from the
reference to the rover does not exceed 20 kilometers. Testing by TEC personnel has produced
accuracies of less than 10 centimeters.
PART F - PROCESSING PRECISE-POSITIONING SURVEY
DATA
5-33
EN0593
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