CIPA 2003 XIX 11 ' International Symposium, 30 September — 04 October, 2003, Antalya, Turkey
location where the present archaeological structures could be
found. Actually, as over an inhomogeneous and/or anisotropic
ground, the calculated resistivity will vary, data inversion will
be necessary to get a real electric image of the ground (Ward,
1990). In comparison to the magnetic prospecting, the
instruments necessary for a geoelectric survey are decidedly less
expensive. Nevertheless time required for this kind of
investigation is much longer.
2.1 Data acquisition
As regards the magnetic measures, an optical pumping
magnetometer (Geometries G858) in gradiometer configuration,
was used. The sensors were set to a fixed distance equal to 1.2
m and the inferior one to 0.25 m from the ground. In general
single square areas of 30X30 m 2 were surveyed. Data were
acquired in the bi-directional mode along profiles 0.5 m apart
with an average sampling step of one datum/0.125 m. After
interpolating operations regular high resolution grid were
obtained with a 0.25X0.125 m cell.
The electric profiles were performed by using a dipole-dipole
array (AM=MN=NB=lm) and employing a modern computer
assisted georesistivimeter (Net Sistemi EW 24/410). Each
profile, 20 meters long, has a constant separation of 5 m from
the others and yields a network of 105 experimental data
points until a pseudo-depth of 4 m.
2.2 Data processing and visualization
In all the three magnetic surveys the row data were first
visualized as 8 bit raster images to identify the presence of
those unwelcome disturbances commonly known in literature
with the name of spikes, stripes and zig-zag (e.g. Scollar et al.,
1990; Eder-Hinterleinter et al., 1996).
Spikes are mainly due to the accidental failure of the sensors
produced by thermal or mechanic shocks as well as the presence
of ferrous modern material lost in the ground such as rods,
wires, studs, etc.. This can cause some non systematic errors of
measure shown in a magnetogram as isolated anomalies either
positive or negative. For the de-spiking step a GESD method
was applied to non interpolated data (Ciminale and Loddo,
2001). Spikes were identified and flagged through a statistic
comparison with other neighbouring data within opportunely
chosen sub areas. Once having been labeled, they were removed
from the data set. Stripes predominately occur in the
magnetogram when data are collected in the bi-directional
mode. To reduce striping effect each line was simply set at zero
mean. Positioning errors, different lengths of parallel profiles
and the technical specifications of the magnetometer often
cause, especially in bi-directional surveys, a strong zigzag
pattern. This displacement effect has been minimized through a
procedure based on the computation of the cross-correlation
function between the magnetic profiles considered three at a
time (Ciminale and Loddo, 2001).
After having attenuated these effects with DIP techniques, the
data processing was completed through filtering operations in
order to reduce the background noise present in the three
surveys. Finally contrast stretching procedure helped in
emphasizing the magnetic anomalies.
Electric data were simply visualized as filled contour plot. In
thus case it was considered not useful to apply any inversion or
processing to the data because the depth of the searched
structures was already known due to nearby excavations.
Moreover the primary aim of the survey was the detection of the
archaeological target for which a significant contrast in
resistivity with the subsoil was expected.
3. RESULTS AND DISCUSSIONS
3.1 Kyme (Turkey)
Figure 2. Part of the high-resolution magnetic mosaic obtained
at Kyme. The light gray features are already excavated
structures.
Kyme, one of the most ancient cities of the Aegean coast of the
Anatolia, was founded around the 1050 B.C. by people who
come from the "Fricio Locrico" and assimilated the natives
"Pelasgi" in the first city core (Strabone, XII, 4,3). Immediately
after its foundation, Kyme became the center of trading in both
the Aegean and the Eastern Mediterranean seas. Here Kyme
established its most ancient colony, Cuma in Campania (Italy).
Despite having already been discovered as far back as the 18 th
century, Kyme became an object of study, albeit sporadic, only
after the second half of the 19 th century. The University of
Catania (Italy) has been systematically studying the
archaeological site since the 1982 (Lagona, 1993). Annual
excavations have brought to the light several ruins, among
which the majority of the port area (IV B.C.), a theatre (I B.C. -
180 A.D.), a defence wall and a tetrastyle temple devoted to
Iside (IV A.D.) and a medieval citadel (XII-XIII A.D.).
Nevertheless, the most part of the site is still completely
unexplored while the excavations proceed only in summer
months. The contribution that the archaeologists expected from
the geophysical survey, was the identification of those areas
with a more probable archaeological content.
During two summers (1999-2000) 37000 m were surveyed.
Because of the articulated morphology and the presence of
natural and artificial obstacles (threes, dried walls, cultivations,
pylons, etc...) it was impossible to investigate the site with
continuity. The final result is the high-resolution magnetic
mosaic (Ciminale, 2003) a part of which is shown in Figure 2.
The data processing allowed to point out many anomalies with
an archaeological meaning. Unfortunately the discontinuity of
the survey affected the interpretation. Often in fact signals
abruptly break off. Furthermore a background noise, due to the
outstanding presence of potsherd and bricks spread into the
