20 
SURVEY AND ADJUSTMENT OF THE ALTIMETRIC NETWORK FOR MONITORING GROUND VERTICAL 
MOVEMENTS IN THE AREA OF PISA 
G. Caroti (*) 
(*) Department of Civil Engineering - University of Pisa, Italy 
ISPRS Commission VI, Working Group 3 
KEYWORDS: GPS, Levelling, Subsidence 
ABSTRACT 
For many years periodic controls of the Pisan plain have been undertaken to monitor vertical movements of the ground. 
In 1997 new campaigns of geometric levelling were scheduled in a CNR-ENEL research project for subsidence control in a wide 
area of the Pisan Plain. 
The author reports the study carried out for setting up the network and the outcome of the measuring surveys performed in autumn- 
winter 1998-99, the analyses of which allow the formulation of hypotheses on the trend of the phenomenon studied, in a specific 
place corresponding to a significant benchmark. 
1. INTRODUCTION 
The area studied includes part of the Old Town, the nearby 
residential areas and the northern stretch of the Pisan plain, 
outside the city center. 
A good part of this area is covered by the great levelling 
network set up in the past years on Pisan territory by various 
organization to monitor the vertical movements of the ground 
(today the altimetric control network covers an area of approx. 
430 km 2 and stretches for about 460 km). 
In order to study the area from an altimetric viewpoint and to 
monitor and analyze the vertical movements of the ground, use 
was made of precise stretches of national high precision 
levelling lines converging on or coming out of the Pisa node set 
up by the I.G.M. and surveyed by the same in 1951. With 
respect to Pisa, these lines are oriented respectively toward 
north, east, south, the first and the third approximately parallel 
to the coast (Aurelia highway), the second stretching along the 
river Arno (fig. 1). 
Subsequently, local precision levelling lines were surveyed. 
These were carried out, not at the same time, by Public or 
Private organizations. 
These lines not only made it possible to identify a common 
altimetric reference (the I.G.M. 31/8 benchmark (1951) of 
Migliarino Pisano) to use for future levelling campaigns too, but 
also to standardize the distribution of benchmarks in the Pisan 
Plain, as well as to connect the plain altimetrically to the 
surrounding mountains and their rocky outcrops. 
Of these new levelling lines, particular mention is made of the 
one stretching along the sides of the Pisan mountains consisting 
of numerous I.G.M. benchmarks dating back to 1920; 
particularly interesting is the horizontal and vertical benchmark 
(15-III-C) found on the building of the health Spa center in San 
Giuliano Terme. This line has been subsequently used also to 
define a relative altimetric reference: for this purpose it has been 
repeatedly linked with the I.G.M. benchmark of Migliarino 
Pisano in order to highlight its present progressive increase in 
negative vertical movements compared to that of S. Giuliano 
Terme. 
Figure 1 
2. NETWORK MEASURING 
In 1997, during the planning of the altimetric control network 
for the CNR-ENEL research project, aiming to check 
subsidence in a wide area of the Pisan Plain, use of the 
historical background material was taken into account.