345
could become a protocol of management of all the
quarries in the Lombardia Region (about one hundred).
1. The Survey
The survey is divided in two phases: in the first it has
been organized and realized a network to move from the
local system to the Italian Geodetic Datum, in the second
it has been realized the survey of the detail.
1.1 The realization of the network to support the
survey of the different quarries
The choice to adopt the GPS instrumentation is justified
by the advantages respect to the traditional methodology
which consists in the use of the total station to connect
the vertices materialized inside the quarry surface to the
vertices belonging to the Italian Geodetic Datum. GPS
system allows a standardization of the procedures of
datum, which are independent from the typology of the
quarry and, in part, from the disposition in the territory of
the vertices of the reference network.
The procedures and methodologies here tested in the
different case-studio can be generalized to the all cases
of quarry survey.
It has been defined an approach to carry out an agile
survey system: this approach can be easy realized and
verified with the instruments and software of data
processing today available in sale.
To guaranty the precision requested in the GPS network
it must be used a static approach with the analysis of the
differences of phases of the carrier wave.
The characteristics of the instrumentation and the
modality of use are described as follows.
GPS receiver.
It must be used the double frequencies, L1/L2, receivers
with registration of the “C/A” code on the carrier L1. The
double frequencies receivers allow to minimize the
influence of the ionospheric component: the course of the
electromagnetic wave between the satellites and the
receivers isn’t the same.
To obtain the contemporary evaluation of three
independent baselines were implied 4 receivers with
double frequencies antennas.
The receivers have to be programmed with a cut-off angle
of 15 degree and with a sampling rate of 15 sec.
It is also necessary that at least 4 satellites must to be
always contemporary viewable with GDOP (Global
Diluition of Precision) ^ 5.
The Session of measuring (the time interval in which the
receiver are contemporary working) depends on the
distance length of the baseline, and, on the hypothesis of
5 satellites, the time acquisition is 15 sec.
Particularly for each receiver 5 difference of phases
relative to the 5 satellite are measured: from these
differences of phases are determined the differences
between the two receivers and the different satellites, and
trough these are obtained the five double differences; of
these observations only four can be considered as
independent. For this reason in one minute 16
observations must be considered .
To assure a good local redundancy, in order to allow in
the adjustment the localisation of the observations
affected by eventual rough errors, the number of
baselines which converge to each vertices must be ^3.
Generally the scheme of the survey will be composed by
a four side polygon of which are measured 6 baselines to
each point (the common side between the two four side
polygon is determined two times).
To maintain an equal time of observation among the
different sessions, the polygon was built with an almost
regular length of baselines.
The contemporary use of four GPS allows to survey, for
each session of measure, 3 independent baselines; the
determination of each polygon is made with 2 sessions of
measure that requires the repositioning of the antennas
on the vertices. The high of the antenna must be acquired
measuring in three different positions the slope distance
between the vertices and the three position of the ground
plane.
Once completed the survey of each four side polygon the
two queues receivers must move forward while the others
have to remain fixed. The other vertices of the network
(and the secondary GPS vertices) can be surveyed
through independent session of measure and connected
to each one on the 3 vertices of a four side polygon.
This schema requires 3 fixed receivers on three vertices
of the 4 side polygon and a third mobile receiver. On
these points it is possible to make two session
consequently, repositioning the GPS antenna as
explained.
The vertices of the network must be materialized in the
way to remain in good conditions in the time. A good
quality of monographs, containing pictures and the point
co-ordinates have to be made.
1.1.1 The survey of the fist order vertices
The co-ordinate system to which refer the vertices of the
network is the Gauss-Boaga system (Italian National
Datum): Cartesian co-ordinate Est-North and for the
height respect to the medium sea-level. It is possible to
determine the last one applying the corrections to the
ellipsoid height coming from the satellite measures with
the data, locally estimated, of the undulation of the Geoid
or using the corrections estimated using the benchmark
of the IGM (Istituto Geografico Militare) network or the
Verano Brianza
