Geoscience Reference
In-Depth Information
3. When there is an ordinary tower at the point and the distance between observa-
tion stations is less than 10 km, an antenna is allowed to be installed upon the
tower, but the time of observation should be extended.
4. The pointer of the antenna should be directed to the true north. The effect of local
magnetic declination should be considered and the orientation error should be no
more than
5 .
5. The level bubble at the bottom of the antenna must be centered.
6. While installing an antenna in thunderstorm weather, the bottom of the antenna
must be grounded to avoid lightning strikes. In a thunderstorm, observation
operations should be stopped and the antenna removed.
After installation of the antenna, its height should be measured both before and
after each time interval of observation. The difference between the results of the
two measurements should be less than 3 mm. The average can be determined as the
final height of the antenna. If the difference is larger than the tolerance, we should
identify the causes, put forward suggestions, and note down the observation
records.
The antenna height refers to the height from the average antenna phase center to
the surface of the central mark of the observation station, which can be divided into
two parts. One part covers the height from the phase center to the bottom of the
antenna (i.e., the antenna reference point, ARP), which is a constant provided by
manufacturers; the other part covers the height from the ARP to the surface of the
central mark of the observation station, which should be measured by users on the
spot. The specific measurement methods can be categorized into direct measure-
ment and slant range measurement, according to the methods and types of antenna
installation. Please refer to the receiver user manual for details. The final value of
the antenna height is the sum of the heights of the parts.
Observational Operations
Observational operations are mainly aimed at capturing, tracking, receiving, and
processing GPS satellite signals to obtain the required data on positioning and
observations.
The operation of GPS receivers is highly automated. Its specific methods and
procedures of operation vary with the types and operating modes of receivers.
Detailed information is included in the attached operation manuals. During opera-
tion, observers only need to follow the instructions in the operation manual.
Generally, the following aspects should be noted:
1. Observers at each receiver should work within the regulated observation time to
ensure the realization of simultaneous observation of the same group of
satellites.
2. After correct connection of the external power supply, the cable and antenna are
confirmed, and the power can be switched on; when the receiver is in the right
preset state it can be started.
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