Ole Grøn

Modelling flint acoustics for detection of submerged Stone Age sites

In accordance with the increasing industrial interests in the sea areas a two-pronged development can be observed: an appearance of new methodologies for up-to-date and costeffective management and protection of these cultural areas and environmental resources which is underpinned by a parallel development of a legislative framework. For submerged cultural heritage UNESCOs Convention on the Protection of the Underwater Cultural Heritage (UNESCO 2001) forms an important part of this administrative development. The method for acoustic detection of submerged Stone Age sites outlined in this paper will, if it can be demonstrated to work in practice, contribute to the spectrum of ongoing new technologies facilitating access to large amounts of environmental data, useful for the understanding of environmental changes such as rising sea levels and their impact on human cultural systems in prehistory. This paper mainly addresses the acoustical characterization of buried flints for Stone Age underwater archaeology. A finite element time domain method is used to simulate acoustic remote sensing in a realistic environment. The method is capable of accurately representing the complex interplay between the acoustic waves, the sediments and the flints embedded in the cultural layer. The predicted signals, once compared with in-situ measurements, provide the basis for the solution of inverse problems that can pinpoint the presence of worked flint over large areas.

Chirping for Large-Scale Maritime Archaeological Survey: A Strategy Developed from a Practical Experience-Based Approach

Archaeological wrecks exposed on the sea floor are mapped using side-scan and multibeam techniques, whereas the detection of submerged archaeological sites, such as Stone Age settlements, and wrecks, partially or wholly embedded in sea-floor sediments, requires the application of high-resolution subbottom profilers. This paper presents a strategy for cost-effective, large-scale mapping of previously undetected sediment-embedded sites and wrecks based on subbottom profiling with chirp systems. The mapping strategy described includes (a) definition of line spacing depending on the target; (b) interactive surveying, for example, immediate detailed investigation of potential archaeological anomalies on detection with a denser pattern of subbottom survey lines; (c) onboard interpretation during data acquisition; (d) recognition of nongeological anomalies. Consequently, this strategy differs from those employed in several detailed studies of known wreck sites and from the way in which geologists map the sea floor and the geological column beneath it. The strategy has been developed on the basis of extensive practical experience gained during the use of an off-the-shelf 2D chirp system and, given the present state of this technology, it appears well suited to large-scale maritime archaeological mapping.

Detecting human-knapped flint with marine high-resolution reflection seismics: A preliminary study of new possibilities for subsea mapping of submerged Stone Age sites

Seismic high-resolution Chirp profiles from the welldocumented submerged Stone Age settlement Atlit-Yam, located off Israel’s Carmel coast, display systematic disturbances within the water column not related to sea-floor cavitation, vegetation, fish shoals, gas or salinity/temperature differences, where flint debitage from the Stone Age site had been verified archaeologically. A preliminary series of controlled experiments, using identical acquisition parameters, strongly indicate that human-knapped flint debitage lying on the sea floor, or embedded within its sediments, produces similar significant responses in the water column. Flint pieces cracked naturally by thermal or geological processes appear not to do so. Laboratory experiments, finite element modelling and controlled experiments conducted in open water on the response to broad-spectrum acoustic signals point to an excited resonance response within humanknapped flint even for sediment embedded debitage, with acoustic signals within the 2–20 kHz interval. The disturbances observed in the water column on the seismic profiles recorded at Atlit-Yam are, therefore, based on these results, interpreted as resonance from human-knapped flint debitage covered by up to 1.5 m of sand. Such a principle, if substantiated by further research, should facilitate efficient and precise mapping of submerged Stone Age sites.