Underwater Archaeological Sites Research Articles

A multi-camera system for the integrated documentation of Underwater Cultural Heritage of high structural complexity; The case study of M/S Helma wreck

High structural complexity is quite common in underwater archaeological sites and perhaps on top of the list when it comes to challenges regarding 3D reconstruction. Advances in underwater robotics and optical sensors are providing solutions for high quality data acquisition for mapping and documentation of underwater cultural heritage (UCH) sites. This paper presents a workflow for the detailed 3D reconstruction of a disintegrated shipwreck from the 1920’s in Trondheimsfjord, Norway, a wreck site of high 3D structural complexity at 55 meters depth. The work focuses on the use of seven multi-purpose optical sensors, like low-cost action cameras, omnidirectional cameras, a depth camera and an RGB camera attached to an Underwater Hyperspectral Imaging sensor, all mounted on a Remotely Operated Vehicle (ROV). The 3D reconstruction of the wreck site was carried out offline, through the implementation of a typical Structure-from-Motion pipeline. Only one camera, considered as the master camera of the system, was connected to the ROV’s control system and to the navigation sensors, hence providing georeferenced images. With the assumption that all seven cameras were moving jointly in 3D space, an approach for estimating the relative positions of the six stand-alone cameras, with respect to the master camera, was followed. The geometric configuration of the multi-sensor system allowed scaling and georeferencing of all created 3D models, and a more rapid alignment process of the big amount of collected imagery data. The presented case study highlights the advantages of multi-vision setups for UCH documentation, such as near 360° field of view with robust geometry; full 3D coverage of challenging objects of interest; the possibility of sensor’s synchronization invariant approaches, and not least minimization of maneuvering and bottom time.

A third medieval bridge on Lake Lednica, Greater Poland

Lake Lednica, Greater Poland, is one of Poland’s most important and longest-studied underwater archaeological sites. The residential centre established on an island was one of the central points in the state of the first Piasts. Previous research located two bridges to the island and discovered the largest collection of early medieval military objects in Central Europe in the lake. In the 2017 season, a third bridge was discovered on Lake Lednica leading to the small island called Ledniczka on which the layers of an early medieval settlement and clear remnants of a motte-type medieval structure are found. Three seasons of research on relics of the crossing suggest that it may have functioned in two periods: in the tenth century and at the turn of the fourteenth century. During the research, a number of military items, pottery, objects made of organic materials and fishing tools were found.

A novel method of temporary solidification and extraction of underwater fragile relics in their original state

Fragile cultural relics at underwater archaeological sites are difficult to preserve in situ over long time periods due to the effects of a complex and constantly changing surrounding environment. Thus, extracting the relics from water and preserving them in a controllable environment is of primary importance. In this paper, the technology of temporary reinforcement and extraction of underwater fragile relics with veratraldehyde followed by a process of secondary temporary reinforcement using polyethylene glycol (PEG) was studied. After investigating the melting temperature and permeability of PEGs with different molecular weights, we found that PEG-3000 is an excellent candidate as the secondary reinforcing agent for the extracted relics. In the laboratory, combined with veratraldehyde and polypropylene-fiber cloth as temporary underwater strengthening materials, and selected dispersed beaded jewelry and a broken three-dimensional crock as our research subject, we carried out an entire retrieval process—temporary stabilization and secondary temporary reinforcement, to systematically evaluate the technological aspects of safely excavating fragile underwater relics in the original state. After being extracted from water and subjected to secondary temporary reinforcement using PEG-3000, the beaded jewelry and broken crock retained their underwater shape and arrangement completely. The use of secondary reinforcing agent prevents the removal process of veratraldehyde and enclosed sediment from affecting the state of the relics.

A multi-scalar approach to marine survey and underwater archaeological site prospection in Murujuga, Western Australia

During the past 20,000 years approximately one-quarter of the continental landmass of Australia was inundated by postglacial sea-level rise, submerging archaeological evidence for use of these landscapes. Underwater archaeological sites can offer substantial insights into past lifeways and adaptations to rapidly changing environments, however the vast scale of inundation presents a range of challenges in discovering such sites. Here we present a suite of methods as a model methodology for locating sites in submerged landscapes. Priority areas for survey were based on palaeoenvironmental contexts determined from the onshore archaeological record. Remote sensing was used to identify seabed composition and indicators of palaeolandscapes where high potential for human occupation and site preservation could be identified in Murujuga (or the Dampier Archipelago), northwestern Australia. Target locations were surveyed by scientific divers to test for the presence of archaeological material. Application of this methodology resulted in the discovery of the first two confirmed sub-tidal ancient Aboriginal archaeological sites on Australia's continental shelf. Survey methods are discussed for their combined value to identify different classes of landscapes and archaeological features to support future underwater site prospection.

El yacimiento subacuático de Las Amoladeras, Cabo de Palos (Cartagena). Nuevos enfoques

The aim of this article is to reinterpret a well-known underwater archaeological site located at Las Amoladeras, in La Manga del Mar Menor, near Cabo de Palos. For this purpose, after a historiographical review, we have studied, contextualized and undertaken isotopic analyses of some of the most interesting material from this archaeological site, as well as a plomo monetiforme (coin-like lead token) of the same type as those recovered at Las Amoladeras and the ones that circulated in the Balearic Islands. The lead isotope analyses carried out on the afore-mentioned artefacts allow us to determine the source of the lead used in the first two objects as Cartagena-Mazarrón and the Sierra Morena respectively. However, the lead used in the manufacture of the plomo monetiforme seems to reflect a mixture of metals. Based on all the above, we interpret this site as the remains of a shipwreck dating from 50-30 bc that was carrying a cargo composed in part, if not almost exclusively, of metallic items, mostly lead objects, probably to be sold and recycled. Las Amoladeras can therefore be contextualized in a very specific historical and economic framework: that of the commercialization and reuse of the lead in late Republican Hispania.

SUNKEN ROMAN VILLA OF ANCIENT EPIDAURUS: DOCUMENTATION AND ENHANCEMENT USING VIRTUAL REALITY

Abstract. The interest in the documentation and enhancement of Underwater Cultural Heritage (UCH) is rising rapidly over the last decades. This has happened especially due to the significant technological advances, which have enabled the digital data acquisition in the hostile underwater environment. Numerous efforts have been made so far concerning the 3D digitisation and promotion of the UCH using photogrammetric methods and 3D surveys in order on one hand to document the site and on the other to develop virtual and augmented reality applications and make this part of the hidden cultural heritage accessible to people with difficulties to reach it.This paper presents the methodology, the actions and decisions that were taken for the geometric documentation, study, promotion and enhancement of the remains of a roman villa located at Agios Vlassis, in Ancient Epidaurus in Greece. The present effort focuses on the use of low-cost equipment in order to acquire the necessary digital data to produce the 3D textured model of the archaeological site and the required 2D documentation products. The methods used to produce this 3D model involve contemporary computer vision algorithms adapted to confront the challenge of processing a huge number of images and extracting useful metric information from them. Moreover, the creation and programming process of two virtual reality applications is described. By developing a virtual tour and a virtual reality application, it is hoped to raise the awareness about UCH and give prominence to different means and ways of protection and management of underwater archaeological sites.

Aboriginal artefacts on the continental shelf reveal ancient drowned cultural landscapes in northwest Australia.

This article reports Australia’s first confirmed ancient underwater archaeological sites from the continental shelf, located off the Murujuga coastline in north-western Australia. Details on two underwater sites are reported: Cape Bruguieres, comprising > 260 recorded lithic artefacts at depths down to −2.4 m below sea level, and Flying Foam Passage where the find spot is associated with a submerged freshwater spring at −14 m. The sites were discovered through a purposeful research strategy designed to identify underwater targets, using an iterative process incorporating a variety of aerial and underwater remote sensing techniques and diver investigation within a predictive framework to map the submerged landscape within a depth range of 0–20 m. The condition and context of the lithic artefacts are analysed in order to unravel their depositional and taphonomic history and to corroborate their in situ position on a pre-inundation land surface, taking account of known geomorphological and climatic processes including cyclone activity that could have caused displacement and transportation from adjacent coasts. Geomorphological data and radiometric dates establish the chronological limits of the sites and demonstrate that they cannot be later than 7000 cal BP and 8500 cal BP respectively, based on the dates when they were finally submerged by sea-level rise. Comparison of underwater and onshore lithic assemblages shows differences that are consistent with this chronological interpretation. This article sets a foundation for the research strategies and technologies needed to identify archaeological targets at greater depth on the Australian continental shelf and elsewhere, building on the results presented. Emphasis is also placed on the need for legislation to better protect and manage underwater cultural heritage on the 2 million square kilometres of drowned landscapes that were once available for occupation in Australia, and where a major part of its human history must lie waiting to be discovered.

Challenges for the Protection of Underwater Cultural Heritage (UCH), from Waterlogged and Weathered Stone Materials to Conservation Strategies: An Overview

Despite the growing attention to Underwater Cultural Heritage (UCH) in Europe and worldwide, the efforts in wholly enjoying underwater archaeological assets and sites are still remarkable; hence, the need for innovative research and solutions that are suitable for raising knowledge on the subject. In this way, this paper wants to be a review for highlighting all of the developments, potentials, and results achieved in the last decade to reach a good protection of UCHs related to the study of stone materials, degradation processes, and the new methods for protection/consolidation directly in situ. The present work is focused on the analysis of the main results obtained from several studies conducted to date, providing additional guidelines for operators in the UCH sector (i.e., restorers, archaeologists, conservation scientists, geologists, etc.). Such guidelines will be a very useful key factor in enhancing knowledge, management, protection, and promotion of underwater sites. In particular, the purpose of this paper is to provide an analysis of the state of the art on both consolidated techniques for studying materials coming from seawater and innovations in the field of protection and consolidation of UCH against biofouling, the main cause of damage in underwater environments.

Temporary consolidation and packaging of fragile cultural relics at underwater archaeological sites to maintain their original state during extraction

The flexible sponge/epoxy composite can wrap underwater artefacts in any shape and forms a protective shell after curing, thus effectively wrapping and reinforcing the artefacts. However, the hydroscopicity of the sponge itself limits the underwater application of the sponge/epoxy composite. In this study, a novel polyurethane sponge was prepared by modified with super‐hydrophobic multi‐wall carbon nanotubes (SH‐MWCNTs@PU sponge). Compared with the pristine PU sponge, the water‐contact angle on the surface of SH‐MWCNTs@PU sponges increased from 103.3 ± 1.82 to 152.6 ± 1.54o, and oily epoxy resin was able to cover the surface completely. The study shows that when SH‐MWCNTs@PU sponges/epoxy resin composite material is used underwater, it prevents both water from entering the sponge and also the inside epoxy resin from overflowing into the water. Moreover, the composite materials have excellent toughness after reinforcement under water (flexural strength = 3.56 MPa) and the soft sponges can be moulded to wrap any type of underwater artefacts. In the laboratory, when taking a broken, three‐dimensional blue‐and‐white porcelain pot as a research subject, the entire retrieval process—temporary stabilization, packaging, extraction and reinforcement material removal—was simulated to evaluate systematically all the technological aspects of safely excavating fragile underwater relics.

Study on Reburial Method for The Preservation of Copper Artifacts at The Underwater Archaeological Site

Study on Reburial Method for The Preservation of Copper Artifacts at The Underwater Archaeological Site

A submerged 7000-year-old village and seawall demonstrate earliest known coastal defence against sea-level rise

We report the results of underwater archaeological investigations at the submerged Neolithic settlement of Tel Hreiz (7500 – 7000 BP), off the Carmel coast of Israel. The underwater archaeological site has yielded well-preserved architectural, artefactual, faunal and human remains. We examine and discuss the notable recent discovery of a linear, boulder-built feature >100m long, located seaward of the settlement. Based on archaeological context, mode of construction and radiometric dating, we demonstrate the feature was contemporary with the inundated Neolithic settlement and conclude that it served as a seawall, built to protect the village against Mediterranean Sea-level rise. The seawall is unique for the period and is the oldest known coastal defence worldwide. Its length, use of large non-local boulders and specific arrangement in the landscape reflect the extensive effort invested by the Neolithic villagers in its conception, organisation and construction. However, this distinct social action and display of resilience proved a temporary solution and ultimately the village was inundated and abandoned.

Performance evaluation of underwater image pre-processing algorithms for the improvement of multi-view 3D reconstruction

<p class="Abstract">3D models of submerged structures and underwater archaeological finds are widely used in various and different applications, such as monitoring, analysis, dissemination, and inspection. Underwater environments are characterised by poor visibility conditions and the presence of marine flora and fauna. Consequently, the adoption of passive optical techniques for the 3D reconstruction of underwater scenarios is a highly challenging task.</p>This article presents a performance analysis conducted on a multi-view technique that is commonly used in air in order to highlight its limits in the underwater environment and then provide guidelines for the accurate modelling of a submerged site in poor visibility conditions. A performance analysis has been performed by comparing different image enhancement algorithms, and the results have been adopted to reconstruct an area of 40 m<sup>2</sup> at a depth of about 5 m at the underwater archaeological site of Baiae (Italy).

Building Knowledge and Connections: The Success of the UNESCO International Capacity Building Training Programmes for Cultural Heritage Management of Underwater Archaeological Sites

Many countries do not have sufficient professional capacity to manage its underwater cultural heritage (hereafter UCH) or fulfil its research objectives. To address this situation, which is acute in some countries, since 2009 UNESCO has, in partnership with heritage organisations, facilitated professional training in a number of locations, notably Argentina, Colombia, Croatia, Cuba, Jamaica, Kenya, Madagascar, Mexico, Spain, St. Eustatius, Thailand and Vietnam. Although there are similarities these courses differ in length, content, and sometimes emphasis. What many have in common is the application of teaching units taken from the training syllabus developed in Thailand from 2009, and published as UNESCO’s Training Manual for the UNESCO Foundation Course on the Protection and Management of Underwater Cultural Heritage in Asia and the Pacific. Organisers and trainers have learned important lessons; most importantly that successful training courses comprise more than the sum of the individual teaching components. In particular those international courses that bring together participants from different cultures present their own challenges, not just differences in language, but also other considerations. This paper, using examples from the courses listed above, will illustrate the structure and organisation of UNESCO’s Foundation Course that not only helps to fulfil the specific goals of the professional training, but leaves a lasting legacy that continues to change attitudes to the management and protection of UCH.

Enhancing learning and access to Underwater Cultural Heritage through digital technologies: the case study of the “Cala Minnola” shipwreck site

The paper presents the digital technologies developed in the VISAS project and their application to the underwater archaeological site of Cala Minnola (Levanzo Island, Italy) that preserves the remains of a Roman ship. Following the basic principles defined by UNESCO for the protection of the Underwater Cultural Heritage the VISAS project has led to the development of innovative digital technologies for a more engaging and educational exploitation of the submerged archaeological sites.In particular, the paper describes a virtual diving system that allows users to perform, outside of the submerged environment, a virtual exploration of the Cala Minnola shipwreck site. Moreover, an augmented diving system provides, through an underwater tablet, a geolocalized multimedia guide for the divers that visit the underwater archaeological site. Both digital technologies allow users to perform an entertaining and interdisciplinary learning experience by receiving archaeological, historical, and biological information of the specific submerged site.

An Integrated Analytical Approach to Define the Compositional and Textural Features of Mortars Used in the Underwater Archaeological Site of Castrum Novum (Santa Marinella, Rome, Italy)

This paper aims to carry out an archaeometric characterization of mortar samples taken from an underwater environment. The fishpond of the archaeological site of Castrum Novum (Santa Marinella, Rome, Italy) was chosen as a pilot site for experimentation. The masonry structures reached the maximum thickness at the apex of the fishpond (4.70 m) and consisted of a concrete conglomerate composed of slightly rough stones of medium size bound with non-hydraulic mortar. After sampling, for a complete characterization of selected mortar fragments, different and complementary techniques (stereomicroscopy, polarizing optical microscopy, and X-ray powder diffraction analysis) were carried out in order to: a) define the minero-petrographic features; and b) investigate their state of conservation. The obtained data allowed the determination of the main constituents of mortars from a compositional point of view. The raw materials, in fact, were quite homogeneous, as well as the ratio in which they were mixed, confirming the typical "recipe" used in Roman times to manufacture hydraulic-type mortars by adding pozzolana. At the same time, it was possible to identify the various degradation processes we were interested in, namely, biological colonization (bio-fouling) that develops differently according to environmental conditions. Based on characterization phase results, the research will help to develop adequate techniques for intervention (innovative tools and methods for the protection of underwater cultural heritage) with particular regard to cleaning and consolidating procedures to be carried out directly in situ.

THE ENHANCEMENT OF UNDERWATER CULTURAL HERITAGE ASSETS USING AUGMENTED REALITY (AR)

Abstract. Τhe development in the fields of Underwater Cultural Heritage (UCH) management and Maritime Archaeology, yields an interdisciplinary and creative academic framework, such as the Information and Communication Technologies (ICT) sector that has been proved to build intelligent systems and applications. However, the ways to fully make use of these technologies are still being explored, as their potential have not been exploited yet. Underwater archaeological sites, semi (/or fully) submerged settlements, ancient ports and shipwrecks, unlike land sites, are not accessible to public due to their special (sub) marine environment and depth. In this paper, an innovative research idea of using Augmented Reality (AR) for maintaining the memory and the information of underwater archaeological sites, is presented. Although the “artificial” visual documentation cannot replace the authentic values of the underwater tangible heritage, the AR technology can contribute to the protection of the intangible properties and the conquered knowledge of the past of a place. This research work will focus, among other case studies, on the (semi) submerged fortifications and their contiguous contents of the acropolis of Halai in east Lokris, Greece. Hence, along with the climate change that may lead more antiquities covered by water during the following years, the advances in the communication field and the up-coming 5G and cloud technologies will make the idea fully applicable, contributing to the enhancement of the coastal and the underwater archaeological remains.

DOCUMENTATION AND MONITORING OF UNDERWATER ARCHAEOLOGICAL SITES USING 3D IMAGING TECHNIQUES: THE CASE STUDY OF THE “NYMPHAEUM OF PUNTA EPITAFFIO” (BAIAE, NAPLES)

Abstract. The preservation status of an underwater cultural site can be determined as the combination of two primary factors, namely the site physical integrity, which results from the past and present interaction of the site itself with the biological/chemical agents located in the surrounding environment, and the exposure of the site to human-related threats. Methods to survey underwater archaeological sites have evolved considerably in the last years in order to face the challenges and problems in archaeological prospection, documentation, monitoring, and data collection.This paper presents a case-study of an archaeological documentation campaign addressed to study and monitor the preservation status of an underwater archaeological site by combining the quantitative measurements coming from optical and acoustic surveys with the study of biological colonization and bioerosion phenomena affecting ancient artefacts. In particular, we present the first results obtained in the survey and documentation campaign carried out during the spring – summer 2018 in the “Nymphaeum of Punta Epitaffio” located in the Marine Protected Area - Underwater Park of Baiae (Naples).

PRECISION POTENTIAL OF UNDERWATER NETWORKS FOR ARCHAEOLOGICAL EXCAVATION THROUGH TRILATERATION AND PHOTOGRAMMETRY

Abstract. Given the rise and wide adoption of Structure from Motion (SfM) and Multi View Stereo (MVS) in underwater archaeology, this paper investigates the optimal option for surveying ground control point networks. Such networks are the essential framework for coregistration of photogrammetric 3D models acquired in different epochs, and consecutive archaeological related study and analysis. Above the water, on land, coordinates of ground control points are determined with geodetic methods and are considered often definitive. Other survey works are then derived from by using those coordinates as fixed (being ground control points coordinates considered of much higher precision). For this reason, equipment of proven precision is used with methods that not only compute the most correct values (according to the least squares principle) but also provide numerical measures of their precisions and reliability. Under the water, there are two options for surveying such control networks: trilateration and photogrammetry, with the former being the choice of the majority of archaeological expeditions so far. It has been adopted because of ease of implementation and under the assumption that it is more reliable and precise than photogrammetry.This work aims at investigating the precision of network establishment by both methodologies by comparing them in a typical underwater archaeological site. Photogrammetric data were acquired and analysed, while the trilateration data were simulated under certain assumptions. Direct comparison of standard deviation values of both methodologies reveals a clear advantage of photogrammetry in the vertical (Z) axis and three times better results in horizontal precision.

4D modelling of low visibility Underwater Archaeological excavations using multi-source photogrammetry in the Bulgarian Black Sea

This paper introduces the applicability of underwater photogrammetric survey within challenging conditions as the main tool to enhance and enrich the process of documenting archaeological excavation through the creation of 4D models. Photogrammetry was being attempted on underwater archaeological sites at least as early as the 1970s’ and today the production of traditional 3D models is becoming a common practice within the discipline. Photogrammetry underwater is more often implemented to record exposed underwater archaeological remains and less so as a dynamic interpretative tool.Therefore, it tends to be applied in bright environments and when underwater visibility is > 1 m, reducing its implementation on most submerged archaeological sites in more turbid conditions. Recent years have seen significant development of better digital photographic sensors and the improvement of optical technology, ideal for darker environments. Such developments, in tandem with powerful processing computing systems, have allowed underwater photogrammetry to be used by this research as a standard recording and interpretative tool. Using multi-source photogrammetry (5, GoPro5 Hero Black cameras) this paper presents the accumulation of daily (4D) underwater surveys carried out in the Early Bronze Age (3300 BCE) to Late Ottoman (17th Century AD) archaeological site of Ropotamo in the Bulgarian Black Sea under challenging conditions (< 0.5 m visibility). It proves that underwater photogrammetry can and should be used as one of the main recording methods even in low light and poor underwater conditions as a way to better understand the complexity of the underwater archaeological record.

Waves and wrecks: A computational fluid dynamic study in an underwater archaeological site

The modification of waves by shipwrecks and the resulting scour play important roles in shipwreck site formation, and conservation of archaeological sites. The oscillatory flow induced by waves and its interaction with the hull structure at a historic shipwreck site was analyzed using a two phase 2D model based on the Reynolds averaged Navier-Stokes equations and shear stress transport (SST) k-Omega turbulence model, with inputs from field-based bathymetric survey. The relative importance and seasonal variation in hydrodynamic processes were investigated (flow velocity increase, coherent structures and vortex shedding, turbulence and steady current induced by the non linearity of waves). Results demonstrate that frictional velocity and flow increase dominate morphological change in the low wave energy period (LEP), whereas turbulent shear stress and large coherent structures dominate scouring in the high wave energy period (HEP). Furthermore, flow acceleration around the hull structure and recirculation cells originated by wave non-linearities become more prominent in the HEP, modifying the trajectory of the shedding vortex and increasing its capacity to transport sediment. The results demonstrate, for the first time, that computational fluid dynamics is a valuable tool in assessing the wave structure interaction in full scale and realistic morphological conditions at complex shipwreck sites.