4. CONCLUSIONS 
Fig.8 Residual values of the Helmert transformation 
between static and RTK techniques data (Ischia island) 
For data processing BERNESE vers.4.0 scientific 
software has been used. In fig.9 are shown the rms 
values at 2a level of the WGS84 geographic coordinates 
of the network. 
Fig.9 RMS values of the WGS84 geographic coordinates 
of the island of Ischia network at 2a level (1998 
measurements) 
4.1 Phlegrean Fields 
Spirit leveling is, among the surveying topographic 
techniques used by the Osservatorio Vesuviano for the 
monitoring of the neapolitan volcanic area, that one 
employed since more time. Depending on the length of 
the temporal series of the acquired data, is therefore that 
one which, historically, has allowed to follow the evolution 
of the bradyseismic phenomenon during the years. The 
measurements carried out in about 25 years have allowed 
in fact to define and limit the deformation field acting in the 
Phlegrean Fields: the area of the maximum vertical 
displacement is located in the city of Pozzuoli in which 
huge uplifts have been recorded during the bradyseismic 
crises of 1969/72 and 1982/84 (with maximum values of 
about 170 cm in the first period and about 180 cm in the 
second period). The areas surrounding the center of 
Pozzuoli, in accordance with an about radial symmetry, 
can be considered more stable, with decreasing values of 
vertical deformation going away from the area of the 
maximum vertical displacement. 
From 1985 the phlegrean area is interested by a 
subsidence phase interrupted only during 1989, when a 
maximum uplift of 7 cm has been recorded at benchmark 
n.25 (see fig.2), located in the maximum deformation area 
and during 1994, with an uplift pointed out only by the 
stations of the tiltmetric network operating in the area: 
during these events seismic activity has been registered. 
In fig.11 the height variations are shown for a temporal 
interval of 13 years (January 1985/February 1998) 
referred to the above mentioned benchmark, which 
historically best represents the different phases of the 
phlegrean bradyseism: from the analysis of the figure it is 
possible to point out that in 13 years the Phlegrean Fields 
have suffered a maximum subsidence up to - 82.2 ± 0.5 
cm. The results of the measurements carried out in 
February 1998, compared with those ones of January 
1997, point out that the phlegrean area is still interested 
by a subsidence phase with a maximum value of vertical 
displacement of - 5.8 cm. 
In fig. 10 are shown the residual values of the Helmert 
transformation between 1997 and 1998 WGS84 
coordinates. 
Fig.10 Residual values of the Helmert transformation 
between 1997 and 1998 WGS84 coordinates (Ischia 
island) 
Fig. 11 Vertical displacement at benchmark n. 25 (1/85- 
2/98) Pozzuoli - Phlegrean Fields 
Again, the measurements show that the suburban areas, 
with respect to Pozzuoli, are not interested by statistically 
significant vertical displacements. Besides, the height 
variations falling outside the error limits pointed out for 
some benchmarks located along some lines of the 
phlegrean network, are due to local deformations of