Instruction manual

Page C-4 Z-12 Real-Time Sensor Operation and Reference Manual
measurements and reduce the sensor noise and multipath. After locking to a satellite,
the rms noise of the sm oothed pseudo-range is reduced with the square root of n
where n is the number of measurements.
Satellite Geometry
The recommended satellite geometry is to have the RZ Sensor (both base and rover)
track at least 5 common satellites above the elevation mask angle with the PDOP
(Position Dilution of Precision) less than 4. Of course, the more satellites the
receivers track, the better. The best performance can be obtained with the receivers
tracking 8 satellites with a PDOP of 2 or less.
Maintaining Lock to the Satellites
During the operation of the Real-time Z system, it is recommended that continuous
lock to the GPS satellites be maintained for best performance. Having uninterrupted
data from the satellites provides faster ambiguity resolution and better position
accuracy, since more data can be used. Therefore, make sure to place the GPS
antennas (for both the base and remote stations) so that they have a good view of the
whole sky. Do not mount them near any large obstructions. However, since it is
understood that tracking satellites continuously is sometimes not possible due to
obstructions such as bridges and trees, the Real-time Z system can still recover from
these situations and provide the best accuracy possible.
Carrier Phase Integer Ambiguities
For carrier phase differential, the integer cycle ambiguities are initially estimated as
float numbers. At this stage the position accuracy converges from the meter level to
submeter level. The integer ambiguity search process is also launched from epoch to
epoch. Once the integer ambiguities can be fixed into integer values, centimeter-level
position accuracy can be achieved.
Data Link Related Errors
Radio Link Dropout
When the rover does not receive the DBEN or RTCM messages, it will continue to
compute its CPD position for about thirty seconds if Fast CPD is on. However, the
three-dimensional position error (sigma) will increase during this period. When the
DBEN messages are re-acquired, the sigma will immediately drop to the value before
the radio link drop out. If Fast CPD is off, CPD position computation will stop within
seconds of losing the DBEN messages. For best results in the field, Fast CPD should
be left on, and the base radio antenna should be located as high as possible with a line
of site to the rover.