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SPR survey for archaeological researches: the site of Himera
by
Pietro L. Cosentino
CFTA Department, University of Palermo
Coauthors: P. Capizzi,G. Fiandaca, R. Martorana, P. Messina, L. Romano
Nowadays SPR survey are typical for investigation of buried archaeological remains. Nevertheless many aspects of these surveys are continuously improved with a considerable increasing of the resolution power and global reliability of the obtained results. One example is given in this paper.
The old town of Himera was build near the mouth of Northern Imera river (Northern Sicily) in the 648 b.C. as a Greek colony, and was destroyed by Carthaginians in the 409 b.C., during a cruel battle that caused definitive abandonment. The urban order of the city, realized in the VI century b.C., is the purpose of our study.
The investigation has been carried out in the Buonfornello’s coastal plain, where the town was planned following a very regular urban order. The structure of the town was constituted by blocks, about 40 m large, roughly oriented in the N-S direction, which are generally separated by roads 6 - 6.20 m large. Now the down part of the Himera archaeological area is about 18 of 35 hectares.
The used geophysical techniques is impulsive high-frequency electromagnetism (reflection SPR tomography). SPR surveys has been carried out using two GSSI systems (SIR System 2 and SIR3000), two 400 MHz antennas and the following acquisition setup: Range = 100 ns (investigated depth ~ 4 m); Frequency band pass (100 – 800 MHz); Horizontal Stacking = 3; Sample/Scan = 1024; Bits/Sample = 16; Scans/Second = 64. The wavelength, according to the central frequency of the antenna (400 MHz) and to the mean wave propagation velocity in the ground (about 0.087 m/ns), is about 20 cm.
In the ten investigated areas (namely L1 to L6 and P1 to P4) the profiles have been acquired in the following way:
- L1 area is 19x79 m sized. In this area 20 profiles along longitudinal direction (NNW-SSE) and 80 profiles along transversal direction (ENE-WSW) have been spaced 1 m apart each other;
- In the L2 zone, 1x62 m, 2 profiles along longitudinal direction (NNW-SSE), 1 m spaced;
- In the L3 zone, 27x82 m, 15 profiles along longitudinal direction (NNW-SSE) and 42 profiles along transversal direction (ENE-WSW), 2 m spaced;
- In the L4 zone, 1x11 m, 2 profiles along transversal direction (ENE-WSW), 1 m spaced (in this case an alternative range of 50 ns has been used);
- In the L5 zone, constituted by 2 areas of 3x5 m separated by a 0.6 m step, 4 profiles along longitudinal direction (NNW-SSE) and 6 profiles along transversal direction (ENE-WSW), 1 m spaced;
- In the L6 zone, 45x5 m, 16 profiles along longitudinal direction (NNW-SSE) and 5 profiles along transversal direction (ENE-WSW), obtaining a grid of 3x1 m;
- In the P1 zone, 50x50 m, 51 profiles along longitudinal direction (NNW-SSE) and 51 profiles along transversal direction (ENE-WSW), 1 m spaced;
- In the P2 zone, 50x50 m, 26 profiles along longitudinal direction (NNW-SSE) and 26 profiles along transversal direction (ENE-WSW), 2 m spaced;
- In the P3 zone, 50x50 m, 26 profiles along longitudinal direction (NNW-SSE) and 26 profiles along transversal direction (ENE-WSW), 2 m spaced;
- In the P4 zone, 50x50 m, 26 profiles along longitudinal direction (NNW-SSE) and 26 profiles along transversal direction (ENE-WSW), 2 m spaced.
The acquired data have been successively processed using a standard procedure included in the Reflex-Win software. In particular, background removal, band pass frequency filter (150-750 MHz), horizontal and vertical stacking and envelope have been applied to original data. Furthermore, the processed data have been used to obtain slice representation. For each area 10 slices (0.25 m spaced in depth) have been calculated. The maps obtained using profiles acquired along perpendicular directions have been constructed separately and compared. Their discrepancies gave same additional information about the structures, considering the depolarizing effects of the reflecting surfaces. The representation of integrated maps allowed us to highlight geometrical forms imputable to archaeological buried structures.
Preliminary archaeological assays, carried out after the geophysical investigations, showed several structures predicted by SPR surveys.
REFERENCES
Capizzi P., Cosentino P.L., Messina P., Miraglia D., Romano L. e Vassallo S. (2003) – Indagini georadar nel sito archeologico di Himera. Atti Del 22° Convegno G.N.G.
Date received: September 13, 2004
Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caon-48.