×

You are using an outdated browser that does not fully support the intranda viewer.
As a result, some pages may not be displayed correctly.

We recommend you use one of the following browsers:

Full text

Title
International cooperation and technology transfer
Author
Mussio, Luigi

4. Method of surveying
The methods used for surveying may be classified in respect
to accessibility to antennae frame centre. In some cases it is
too hard to access to the antenna centre because of the height,
which on the other hand could be an advantage from the
visibility point of view, (such as, selecting the baselines
around the antenna).
1- Accessibility at the frame centre with GPS or DGPS
receivers.
Taking into account the considerations made above, the
possibilities of surveying are :
a- for sub-metric accuracy:
1- using one DGPS receiver at the frame centre and
then using the parameters transformation to
obtain the co-ordinates in the National system.
2- for the orientation of antenna frame, one DGPS
receiver may be used to find the reference co
ordinates of one point in WGS84 with sub
metric precision and another single frequency
receiver in fast-static mode (5-10 minutes),
allows a precise orientation. Then we can use the
symmetry and alignment to find the co-ordinates
of the frame centre.
b- for decimetric accuracy:
1- Using one dual GPS receiver at the frame centre
and processing the data respect to the nearest
permanent station or known master station. The
alternative methodology of surveying is to use
precision DGPS technique, where the phase
measurements corrections from the reference
receiver are transmitted to the remote receiver to
be incorporated into the position solution in
order to solve for the phase ambiguity (RTK).
2- for the orientation of the frame we can use the
same procedure reported above.
The sequence of work of this method have been implemented
at the BO-ASST station, (Tab. 1).
Tab. 1 - co-ordinates of the antenna frame centre of ASST-
station in the WGS84 system with relative rms in meters.
Static mode respect to Medicina permanent station
Static GPS
N
E
H
Co-ordinates
44 29 59.557
11 20 47.692
117.258
rms
0.002
0.002
0.004
differential GPS
N
E
H
Co-ordinates
44 29 59.514
11 20 47.672
118.6
rms
1.4
0.8
1.4
2- Difficult accessibility to the frame centre.
The common field work in this case is to determine one or
more external baseline using GPS technique and then use a
conventional surveying for antenna frame. Of course this
work procedure may also be done, in the case of accessibility
at the frame antenna centre.
Procedure of surveying
1- determine at least two baselines around the antenna
frame, in such a way that the zenith angle is wide
enough since the antenna frame could be very high
respect to the selected points and this could cause some
difficulties in pointing the top of the antenna frame with
classical instruments.
2- Use GPS technique (non-precision DGPS or precision
DGPS or static techniques) to determine at least one
point of the selected baselines and then fast-static
technique (single frequency receiver) may be used for
the other ends of baselines to obtain a good orientation.
The use of fast-static save time and cost, particularly in
the case of static and non-precision DGPS techniques.
In Fig. 6, we can see the local Stadio - network, where the
stations have been surveyed using both static and non
precision DGPS techniques respect to the Medicina
permanent station and to the Faculty of Engineering Tower
(known station in the WGS84).
3- Classical surveying: Theodolite, total station and MDL
are the instruments used to determine the orientation and
position of antenna elements. Which have been pointed
from stations determined with GPS:
a- using Theodolite or total station instruments. The
difficulties of using these instruments, in our case, is
to point the same target from different stations and
to use the reflectors.
b- using MDL instrument. The difficulty in using this
instrument is to determine which elements of the
antenna reflect the LASER, therefore maximum care
should be taken when operating with them.
In the Fig. 7, it is shown the classical measurements at the
antenna Stadio, by using intersection and radiation surveying
from the three reference GPS stations.
Generally, we should have to distinguish between the
precision of GPS techniques and classical techniques
(Theodolite or total station or MDL instruments). The
precision of GPS surveying (static, non-precision DGPS,
precision DGPS) to determine the co-ordinates of one point
in WGS84 and consequently into the Italian National system
depends on the technique used. In any case in order to obtain
good orientations, when using classical survey, one has to
achieve at least sub-decimetric accuracy.