Thales Z-Max Operation And Application Manual page 290

Step 2. Are base and rover tracking at least 5 common satellites?
Although the rover receiver is capable of computing a position with only 4 common
healthy satellites with the base, the rover will not attempt to fix ambiguities unless 5
common healthy satellites are observed. Fixing ambiguities is a required process for
the rover system to compute highly precise RTK positions. Your field application
software will inform you if you currently have a fixed ambiguity solution or a float
ambiguity solution. Your field application software will also inform you which satellites
are being tracked by the base and which are being tracked by the rover and whether
or not these satellites are healthy. If you find that your solution will not fix, look to
determine if the base and rover are indeed tracking at least 5 common healthy
satellites.
Not tracking at least 5 satellites
1. Check satellite availability.
a. Use the Mission Planning software to check satellite availability for your
current location and time.
b. Look for the number of satellites higher than 15° above the horizon.
c. Ensure at least 5 healthy satellites are available.
d. If not, you will need to perform your survey at another time.
e. Go to step 3 below if the problem is not yet resolved.
2. Move base or rover if sites have satellite obstructions.
a. If your base or rover site has any obstructions higher than 15° above the
horizon, the obstructions may be blocking essential satellites. If
obstructions exist at the base or rover, move the system to an open area.
Tracking at least 5 satellites
Go to step 3 below.
Step 3. HDOP & VDOP Values Too High for Precision Requirements?
Dilution of Precision (DOP) values give a quality indication of the satellite geometry at
any given time. Satellite geometry is important to the precision of an RTK solution. In
fact, the DOP value is used as a multiplier in the computation of position precision.
For example, in the computation of horizontal RMS (HRMS), an estimated precision
value is multiplied by the HDOP at that given time to produce HRMS. The larger the
HDOP value, the larger the HRMS value. The same relationship holds for VDOP and
VRMS. Therefore, poor satellite geometry will result in poor solution precision. The
smaller the DOP value, the better the geometry and solution precision. Your field
application software supports the ability to view current DOP values. If your precision
Troubleshooting 267