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High-Accuracy Data Collection
10
Principles of carrier phase data collection
This section outlines some of the underlying principles of carrier phase data collection
that apply to the different carrier phase techniques, H-Star technology, and carrier
phase postprocessing.
Carrier lock
To achieve the target accuracy, carrier phase data collection depends on maintaining
carrier lock. Carrier lock is achieved when the receiver is continuously locked onto and
tracking the carrier measurements on a minimum number of satellites. The minimum
number of satellites required to maintain carrier lock depends on whether you are
logging static or dynamic GNSS positions. When logging, you must maintain lock on at
least five satellites.
Events that cause loss of carrier lock include anything that might interrupt the
reception of the satellite signal, such as interference from tree canopy or buildings.
Lock is also lost when you disconnect from the receiver or turn off the receiver. When
lock is lost, the TerraSync software displays a notification message and adjusts any
accuracy estimates to reflect the degradation in accuracy due to loss of lock. In difficult
conditions, code processing may be better than carrier techniques.
Initialization
For RTK, carrier lock must be achieved and maintained on five satellites until the
receiver can generated a fixed carrier solution. This process is known as initialization.
On today's RTK receivers, it can be less then 10 seconds with a short baseline and open
sky conditions. On older receivers, initialization may take a few minutes.
While carrier lock is maintained, centimeter-level accuracy is also maintained. When
carrier lock is lost the receiver must re-initialize. During initialization no positions are
output from the survey RTK receiver.
Carrier blocks
For postprocessing techniques, the TerraSync software records blocks of carrier data
throughout the data file. Carrier blocks are periods of carrier phase logging over which
carrier lock is maintained. Figure 10.1 on page 242 shows how the number of satellites
being continuously tracked affects the length of the carrier blocks.
TerraSync Software Getting Started Guide
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