Abstract
We investigate how suitable ground penetrating radar (GPR) and geoelectrics are to prospect the remains of submerged wooden archaeological constructions in the water column. For this purpose, we determined the contrasts of electric resistivity and dielectric permittivity from measurements on present-day wood samples, serving as simplified approximations of water saturated and undegraded archaeological wood. As common substitutes of hard and soft construction wood, we investigated oak and spruce wood. The electric resistivity and dielectric permittivity were determined with increasing moisture content from small-scale electric and GPR measurements using a Wenner alpha array and a 2 GHz Palm antenna in a watering experiment. In a water-saturated state, resistivity values of <270 Ωm and relative dielectric permittivity values of >20 were observed. The anisotropy effects and deviations of the wood species were seen to be up to 30%. On the basis of this, the relative material contrasts of wood with respect to fresh water, sand, and clay were calculatedand compared to values found in the literature for seismic contrasts. Geoelectric, GPR, and seismic measurements show contrasts of 0.3 to 0.8, −0.4 to 0.2, and −0.24 to 0.35, depending on the surrounding material and structural orientation of the wood. The highest contrasts were found for wood in fresh water, followed by clayey and sandy subsoils. On the basis of the determined contrasts, analytical calculations were performed showing that an object of 0.5 m diameter can be detected at depths between 0.5 m and 1.5 m with geoelectrics (Schlumberger) and at depths between 0.5 m and 3 m with ground penetrating radar measurements (400 MHz).
Highlights
In recent years, the geophysical prospection of archaeological targets has been extended to amphibious terrains and shallow water environments
Them to seismic material contrasts based on the work of [11]; Inhomogeneities result from differences in the raw density, irregular water absorption of wood (iii) On the basis of the determined contrasts, we performed analytical calculations to investigate the during the experiment, and anisotropic axes because of different structural orientations, among other depth penetration and applicability of the electric tomography resistivity tomography (ERT) and ground penetrating radar (GPR) methods for the prospection of wooden things
The experiment was terminated at a final wood moisture content of 100% for oak and of 130% for spruce wood
Summary
The geophysical prospection of archaeological targets has been extended to amphibious terrains and shallow water environments. Current research issues include prospecting anthropogenic harbor installations [1,2,3] and geoarchaeological indications of harbor environments [4,5], as well as archaeological objects submerged due to sea-level variations or river relocations [6]. A major construction material used in the past was wood, which was used for building ships, buildings, jetties, etc. Using locally available wood species, wooden buildings in Central Europe were often made of oak. The properties of individual wood species were used for specific components, e.g., of ships. Ship wrecks often consist of a variety of hard and soft woods [7,8,9]
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