How to map submerged Stone Age sites using acoustics (some experimental results)

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Abstract

A central problem for maritime archaeology has been to find survey methods that facilitate efficient and precise mapping of Stone Age sites on the seabed down to the lowest sea level (approximately – 140 m) during glacial periods, as well as sites embedded in sea-floor sediments. As predictive landscape modelling has proved to be inadequate for this task, a different approach based on direct detection is required. The observation of an acoustic phenomenon associated with man-made flint debitage – but not naturally cracked pieces of flint – has opened a window for development of an alternative and efficient direct mapping method. This paper discusses the development of the idea, as well as experimental documentation of the principle on which it is based. It includes a preliminary analysis of how far away on each side of the transducer flint debitage emits an acoustic response, and consequently the required distance between sailing lines for a comprehensive survey to be undertaken at a specific depth.

About the authors

Ole Grøn

University of Copenhagen

Author for correspondence.
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researcher of Department of Geosciences and Natural Resource Management

Denmark, Copenhagen

Lars Ole Boldreel

University of Copenhagen

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doctor, associate professor of Department of Geosciences and Natural Resource Management

Denmark, Copenhagen

Jean-Pierre Hermand

Université libre de Bruxelles

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professor of Acoustics & Environmental Hydroacoustics Laboratory

Belgium, Brussels

Hugo Rasmussen

Danish Nitro-Electro

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engineer

Denmark, Copenhagen

Antonio Dell’Anno

Università Politecnica delle Marche

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doctor, associate professor of Department of Life and Environmental Sciences

Italy, Ancona

Deborah Cvikel

University of Haifa

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doctor, researcher of Leon Recanati Institute for Maritime Studies

Israel, Haifa

Ehud Galili

Israel Antiquities Authority

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doctor

Israel, Atlit

Bo Madsen

Museum of Eastern Jutland

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candidate of sciences

Denmark, Randers

Egon Nørmark

Aarhus University

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head of laboratory of Department of Geoscience

Denmark, Aarhus

References

  1. Knapp W.R. Some Talk About Angles / (ed.) M. Lynn, Flint Knapping. Articles, Tips, and Tutorials from the Internet. 3rd Edition. 2010. P. 163-164.
  2. Grøn et al. - in prep.
  3. Grøn O. Our grandfather sent the elk - some problems for hunter-gatherer predictive modelling. Quartär 59. 2012. P. 175-188.
  4. Grøn O. The «fishing-site model» - a method for locating Stone Age settlements under water, or the opposite? // Norwegian version published in Norsk Maritimt Museum, Årbok 2014. P. 235-244.
  5. Rasmussen H. Unpublished report on the acoustic resonance characteristics of flint debitage. 1982.
  6. Hermand J.-P., Grøn O., Asch M., Ren Q. Modelling flint acoustics for detection of submerged Stone Age sites. Proc. OCEANS’11 MTS/IEEE Kona Conf. (Oceans of Opportunity: International cooperation and partnership across the Pacific), Institute of Electrical and Electronics Engineers, IEEE, Sept. 2011. 9 p.
  7. Hermand J.-P., Tayong R. Geoacoustic characterization of Stone Age cultural layers: Preliminary FE modelling. OCEANS - Bergen, 2013 MTS/IEEE, 6 p.
  8. Grøn O., Nørgård Jørgensen A., Hoffmann G. Marine Archaeological Survey by High-Resolution Sub-Bottom Profilers. Norsk Sjøfartsmuseum, Årbok. 2007. P. 115-144.
  9. Grøn O., Boldreel L.O. Chirping for Large-Scale Maritime Archaeological Survey: A Strategy Developed from a Practical Experience-Based Approach. Journal of Archaeology Volume 2014, Article ID 147390. 11 p.
  10. Dencker J. Marinarkæologiske Forundersøgelser. Amager Strandpark NMU j.nr. 2322 & Italiensvej NMU j.nr. 2322. Nationalmuseets Marinarkæologiske Undersøgelser. 2004.

Supplementary files

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2. Figure 1 – Prediction of the total pressure field resulting from the insonification of a flint blade embedded 5 cm into a cultural layer. The simulated acoustic source and hydrophone are placed above the seabed, symmetrically about the flint piece, with an incidence angle of 5°. The sea-floor model consists of thin layers of sand and mud overlying the cultural layer, a thin underlying sand layer and moraine substrate. The red curve is the returned signal spectrum with no flint embedded in the cultural layer, while the black curve is the spectrum with a flint blade embedded. The resonance frequency is 10,6 kHz.15 [7]

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3. Figure 2 – The 48 sailing lines at the experimental site off Skovshoved Harbour. The 12 m long blue line marks the position of the linear string of samples placed on the seabed. The six yellow rectangles mark the buoys used to control the boat’s approach to the target. Coordinates in UTM zone 33

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4. Figure 3 – Examples of the flint debitage samples placed on the seabed in the experiment. A – sample 1, B – sample 4, C – sample 6, D – sample 7

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5. Figure 4 – Record of significant acoustic haystack features at the submerged Stone Age site at Atlit-Yam, Israel

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6. Figure 5 – Line 38 cutting across the line of targets resulting in an acoustic response that is approximately 7 m wide at its base

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7. Figure 6 – Line 13 running parallel to the line of targets showing a difference in the height of the ‘haystack’ feature

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Copyright (c) 2017 Grøn O., Boldreel L.O., Hermand J., Rasmussen H., Dell’Anno A., Cvikel D., Galili E., Madsen B., Nørmark E.

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This work is licensed under a Creative Commons Attribution 4.0 International License.

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