Pierre Drap

Fine-scale genetic structure and inferences on population biology in the threatened Mediterranean red coral, Corallium rubrum

Identifying microevolutionary processes acting in populations of marine species with larval dispersal is a challenging but crucial task because of its conservation implications. In this context, recent improvements in the study of spatial genetic structure (SGS) are particularly promising because they allow accurate insights into the demographic and evolutionary processes at stake. Using an exhaustive sampling and a combination of image processing and population genetics, we highlighted significant SGS between colonies of Corallium rubrum over an area of half a square metre, which sheds light on a number of aspects of its population biology. Based on this SGS, we found the mean dispersal range within sites to be between 22.6 and 32.1 cm, suggesting that the surveyed area approximately corresponded to a breeding unit. We then conducted a kinship analysis, which revealed a complex half‐sib family structure and allowed us to quantify the level of self‐recruitment and to characterize aspects of the mating system of this species. Furthermore, significant temporal variations in allele frequencies were observed, suggesting low genetic drift. These results have important conservation implications for the red coral and further our understanding of the microevolutionary processes acting within populations of sessile marine species with a larval phase.

Underwater Photogrammetry for Archaeology

Archaeological excavations are often irreversibly destructive, so it is important to accompany them with detailed documentation reflecting the accumulated knowledge of the excavation site. This documentation is usually iconographic and textual. Graphical representations of archaeological sites such as drawings, sketches, watercolors, photographs, topography, and photogrammetry are indispensable for such documentation and are an intrinsic part of an archaeological survey. However, as pointed out by Olivier Buchsenschutz in the introduction to the symposium Images and archaeological surveys, in Arles, France, in 2007 (Buchsenschutz, 2007, Introduction page 5), even a very precise drawing only retains certain observations that support a demonstration, just as a speech retains only some arguments, but this choice is not usually explicit. This somewhat lays the foundation of this work: a survey is both a metrics document and an interpretation of the site by archaeologist.

Underwater image preprocessing for automated photogrammetry in high turbidity water: An application on the Arles-Rhone XIII roman wreck in the Rhodano river, France

ROV 3D project aims at developing innovative tools which link underwater photogrammetry and acoustic measurements from an active underwater sensor. The results will be 3D high resolution surveys of underwater sites. The new means and methods developed aim at reducing the investigation time in situ, and proposing comprehensive and non-intrusive measurement tools for the studied environment. In this paper, we apply a pre-processing pipe line to increase the SIFT and SURF descriptors extraction quality in order to solve the problem of surveying an underwater archaeological wreck in a very high condition of turbidity. We work in the Rhodano river, in south of France on a roman wreck with 20 centimeters visibility. Under these conditions a standard process is not efficient and water turbidity is a real obstacle to feature extraction. Nevertheless the mission was not dedicated to an exhaustive survey of the wreck, but only a test to show and evaluate the feasibility. The results are positive even if the main problem seems now to be the time processing, indeed the poor visibility increase drastically the number of photographs.

Harvesting effects, recovery mechanisms, and management strategies for a long-lived and structural precious coral.

Overexploitation is a major threat for the integrity of marine ecosystems. Understanding the ecological consequences of different extractive practices and the mechanisms underlying the recovery of populations is essential to ensure sustainable management plans. Precious corals are long-lived structural invertebrates, historically overfished, and their conservation is currently a worldwide concern. However, the processes underlying their recovery are poorly known. Here, we examined harvesting effects and recovery mechanisms of red coral Corallium rubrum by analyzing long-term photographic series taken on two populations that were harvested. We compared the relative importance of reproduction and re-growth as drivers of resilience. Harvesting heavily impacted coral populations causing large decreases in biomass and strong size-class distribution shifts towards populations dominated by small colonies. At the end of the study (after 4 and 7 years) only partial recovery was observed. The observed general pattern of low recruitment and high mortality of new recruits demonstrated limited effects of reproduction on population recovery. Adversely, low mortality of partially harvested adults and a large proportion of colonies showing new branches highlighted the importance of re-growth in the recovery process. The demographic projections obtained through stochastic models confirmed that the recovery rates of C. rubrum can be strongly modulated depending on harvesting procedures. Thus, leaving the basal section of the colonies when harvesting to avoid total mortality largely enhances the resilience of C. rubrum populations and quickens their recovery. On the other hand, the high survival of harvested colonies and the significant biomass reduction indicated that abundance may not be an adequate metric to assess the conservation status of clonal organisms because it can underestimate harvesting effects. This study highlights the unsustainability of current harvesting practices of C. rubrum and provides urgently needed data to improve management practices that are still largely based on untested assumptions.

We All Live in a Virtual Submarine

Our seas and oceans hide a plethora of archaeological sites such as ancient shipwrecks that, overtime, are being destroyed through activities such as deepwater trawling and treasure hunting. In 2006, a multidisciplinary team of 11 European institutions established the Venus (Virtual Exploration of Underwater Sites) consortium to make underwater sites more accessible by generating thorough, exhaustive 3D records for virtual exploration. Over the past three years, we surveyed several shipwrecks around Europe and investigated advanced techniques for data acquisition using both autonomous and remotely operated vehicles coupled with innovative sonar and photogrammetric equipment. Access to most underwater sites can be difficult and hazardous owing to deep waters. However, this same inhospitable environment offers extraordinary opportunities to archaeologists because darkness, low temperatures, and low oxygen rates are all favorable to preservation. From a visualization pipeline perspective, this project had two main challenges. First, we had to gather large amounts of raw data from various sources. Then, we had to develop techniques to filter, calibrate, and map the data and then bring it all together into a single accurate visual representation.

Virtual exploration of underwater archaeological sites: visualization and interaction in mixed reality environments

This paper describes the ongoing developments in Photogrammetry and Mixed Reality for the Venus European project (Virtual ExploratioN of Underwater Sites, http://www.venus-project.eu). The main goal of the project is to provide archaeologists and the general public with virtual and augmented reality tools for exploring and studying deep underwater archaeological sites out of reach of divers. These sites have to be reconstructed in terms of environment (seabed) and content (artifacts) by performing bathymetric and photogrammetric surveys on the real site and matching points between geolocalized pictures. The base idea behind using Mixed Reality techniques is to offer archaeologists and general public new insights on the reconstructed archaeological sites allowing archaeologists to study directly from within the virtual site and allowing the general public to immersively explore a realistic reconstruction of the sites. Both activities are based on the same VR engine but drastically differ in the way they present information. General public activities emphasize the visually and auditory realistic aspect of the reconstruction while archaeologists activities emphasize functional aspects focused on the cargo study rather than realism which leads to the development of two parallel VR demonstrators. This paper will focus on several key points developed for the reconstruction process as well as both VR demonstrators (archaeological and general public) issues. The first developed key point concerns the densification of seabed points obtained through photogrammetry in order to obtain high quality terrain reproduction. The second point concerns the development of the Virtual and Augmented Reality (VR/AR) demonstrators for archaeologists designed to exploit the results of the photogrammetric reconstruction. And the third point concerns the development of the VR demonstrator for general public aimed at creating awareness of both the artifacts that were found and of the process with which they were discovered by recreating the dive process from ship to seabed.

A photogrammetric process driven by an Expert System: A new approach for underwater archaeological surveying applied to the 'Grand Ribaud F' Etruscan wreck

The present paper focuses on a new tool dedicated to the survey and the representation of archaeological and architectural heritage. The tool is based on a photogrammetric process related to an expert system that handles a knowledge base coming from the field of archaeological or architectural expertise. The system was tested on an archaeological field: the Etruscan amphora, Py4. The first step of the photogrammetric survey was presented in VAST 2001 [Drap, Long, 2001]. In this paper we present a new symbolic approach to manage the data surveyed. The use of an Expert System gives us a higher level of abstraction by the insertion of a new abstract layer between surveyed data and the model to compute. The presence of a great number of amphorae on the site of Grand Ribaud F, the Etruscan wreck located in Hyères, France, together with the archaeologists survey needs of the wreck, led us to the development of the system. We add also a persistence mechanism for the data, structured in XML. A Web site allows access to all the excavation data. (http://GrandRibaudF.gamsau.archi.fr) The project is articulated in several phases: • Development of the theoretical model: for each identified object, a geometrical description offers a complete set of geometrical primitives, which are the only objects that can be potentially measured, and a theoretical representation of the object. • Photogrammetric measurement being highly incomplete (the object is seen only partially or is in part deteriorated), the Expert System determines the best strategy to inform all the geometrical parameters of the studied object, starting from taken measurements and the default data as defined in the architectural model and the geometrical model. • The resulting object is thus based on a theoretical model, dimensioned more or less partially by a photogrammetric measurement. At the time of the photograph exploitation, the operator can choose the number of attributes of the object, which are regarded as relevant to measure. The choice of attributes is revisable in time, for example at the time of a second series of measurements. The system can be used to position in space some objects of catalogue after a scale phase. If measurement is more complete, in addition to positioning in space, the system allows an analysis of how the measurements vary from the theoretical model and, from there, a study of these deformations or erosions. These, in turn, allow one to question the initial model. The whole developments of the project are written in Java and use the expert system Jess, available on the WEB.

Underwater Photogrammetry for Archaeology. What Will Be the Next Step

Since 1973 archaeology and computer science have developed close ties in Marseille. Two departments (computer science and archaeology) from the French National Centre for Scientific Research (CNRS) in Marseille started working together and laid the cornerstone of the Computer Applications and Quantitative Methods in Archaeology (CAA) community. Marseille also has the advantage of being located in a very interesting place on the Mediterranean Sea and being the home to several famous laboratories, such as the French Cultural Heritage Department (DRASSM) or private companies like COMEX. In 1980 they performed a series of explorations of a deep-sea wreck with the help of COMEX and DRASSM. In this paper we present new advances in underwater photogrammetry for archaeology based on forty years of experience. The survey described in this article does not only discuss the acquisition of 3D points in difficult conditions but also linking archaeological knowledge to the surveyed geometry. This approach needed to com...

ROV-3D: 3d underwater survey combining optical and acoustic sensor

ROV 3D project aims at developing innovative tools which link underwater photogrammetry and acoustic measurements from an active underwater sensor. The results will be 3D high resolution surveys of underwater sites. The new means and methods developed aim at reducing the investigation time in situ, and proposing comprehensive and non-intrusive measurement tools for the studied environment. In this paper, we are presenting a new method of 3D surveys which are dedicated to high resolution modeling of underwater sites. The main met constraints in situ are taken into account and this method leads to a precise 3D reconstruction. Some examples will present both the main obtained results and their limitations. We will end with the perspectives and the necessary improvements to the method, so as to automate the multimodal registration step.

Underwater archaeological 3D surveys validation within the removed sets framework

This paper presents the results of the VENUS european project aimed at providing scientific methodologies and technological tools for the virtual exploration of deep water archaeological sites. We focused on underwater archaeological 3D surveys validation problem. This paper shows how the validation problem has been tackled within the Removed Sets framework, according to Removed Sets Fusion (RSF) and to the Partially Preordered Removed Sets Inconsistency Handling (PPRSIH). Both approaches have been implemented thanks to ASP and the good behaviour of the Removed Sets operations is presented through an experimental study on two underwater archaeological sites.