Xlendi, Malta

Mission director: Timmy Gambin, University of Malta





Mission report, author: Bertrand Chemisky, COMEX.

GROPLAN project is founded by the French Research Agency, with a partnership composed of the French Research Institute CNRS with the LSIS Laboratory specialized in informatics and model, the French company COMEX specialized in underwater engineering and research, and archeologists from the Malta University, CNRS Camille Jullian laboratory and Texas A&M University. GROPLAN is a project for 4 years and the Malta campaign represents the main sea campaign to collect data to be used during the project. This campaign is included in the work package 5 managed by COMEX. The MINIBEX vessel with all the equipment required to collect the 3D data on the XLEDI wreck in Malta leaves Marseille the 10 July to be ready to start the campaign the 16th.

 

Equipment:

Survey vessel



Operations have been conducted from the MINIBEX DP vessel.

General description

Minibex is a light, highly maneuverable 30 meters vessel fitted with a Dynamic Positioning system, allowing research and subsea operations down to 800m. Minibex offers an outstanding ratio between mobility, reduced crew and onboard equipment. The “DP” designed by COMEX allows the ship to remain stationary above a fixed seabed reference point, to keep a constant heading or to follow free swimming or tethered, mobile target accurately. MINIBEX is equipped to provide comfortable living conditions for 11 persons. Thanks to her high level of automation and sophisticated equipment, a multidisciplinary team can operate a wide range of underwater scientific or oceanographic equipment and subsea exploratory vehicle. While of moderate size compare to more conventional oceanographic vessels, MINIBEX offers a far higher cost/value ratio with increased mobility, reduced crew, safe handling and wide range of equipment.


  

Main characteristics of the minibex




Instruments


Surface positioning system – DGPS Subsea positionning – USBL

DGPS AG132 - TRIMBLE

HPR 410P – SIMRAD
The TRIMBLE AG132 is a DGPS with sub metric accuracy. The AG 132 can use a technology which is the combination of the beacon differential, satellite differential and WAAS/ EGNOS differential receiver.To positioning Side Scan Sonar, ROV or submarine, a subsea positioning system is required. The system used on the MINIBEX vessel is an Ultra Short Base Line (USBL) HPR 410P from SIMRAD.
A transponder is fitted close to the Side Scan Sonar Towfish or on ROV, Submarine, depending of operations. All records will geo-referenced in real time.



Submarine & ROV


SUPER ACHILLE ROV REMORA 2000
Our SUPER ACHILLE, in place on board MINIBEX, is a light observation ROV (80 kg) fitted with a Tether management system that enables it to operate quickly at a depth until 800 m. It is equipped with two video color cameras, one 3 axes working arm and a Tritech panoramic sonar. In function of needs, It can be fitted out with specific tools, to perform: research, inspection, observation, sampling, subsea movie, divers assistance, recovery of wrecks, etc…

DYNAMIC POSITIONING AND TMS : The optimal solution. Super Achille is a turnkey solution composed by:

  • • One handling hydraulic winch, a capacity of 800 m of umbilical. Breaking strength of 15 tons (diameter: 20 mm).
  • • One cage, It’s the "garage" of the ROV vehicle, thanks to which it is lowered vertically to the working depth.
  • • One ROV vehicle and its tether once at its working depth, "SUPER ACHILLE" can leave its cage on a 60m floating Umbilical.
  • • One top side unit mainly composed by control command and video monitors.
The entirety builds a Tether Management System (TMS). The TMS allowed the ROV to operate at no reachable depth in free swimming mode In shallow or middle operating depth, the TMS increase the maneuverability compared of a free swimming ROV. In fact, the length and so the weight of umbilical is greatly reduced (less inertia, courant effect…) Fitted with a “transponder”, acoustic beacon communicating with surface vessel’s USBL, the ROV can be followed by the ship navigation system. Interfaced with the vessel’s Dynamic Positioning system, it allows the ship to stay at the vertical of the vehicle and to carry out high accuracy work in total security.
Thus Super Achille is able to perform mission in hazardous environments including in the presence of sunken cables or wrecks:
In case of salvage of heavy sunken elements, The TMS can be used as powerful lifting device
Otherwise, the TMS allows the use of tools which can’t be fitted on a “free” ROV.
The latest in the range of COMEX’s innovative submarines, REMORA 2000 combines the functions and instrumentation of an oceanographic subsea vessel with the built-in amenities and eye-catching design of a recreational submarine
Its primary mission is to carry two persons down as far as 610 meters for up to 5 hours of underwater exploration in the comfort and safety of an air-conditioned cabin at atmospheric pressure.


Equipment:

  • • One hydraulic arm CYBERNETIX “SAMM” 5 axes
  • • One hydraulic arm CYBERNETIX “SAMM” 3 axes
  • • A high resolution 725 kHz scanning sonar
  • • An echosounder
  • • A complex system of cameras:
  • • Pan & Tilt camera
  • • High Definition camera
  • • Video recorder (DVCAM or HDD recorder)
  • • Reflex digital camera + flashes
  • • 4 halogen searchlights and 4 high power HMI searchlights.


ROV3D System
The ROV3D system is very high resolution optical survey system. Two types of sensors can be used, dependant of the size of the site, merging acoustical data and optical data to produce a 3-dimensional model of a large and complex underwater site.
There is two step of survey :
Production of an acoustic model by a high frequency acoustic: 3D scanner. Multiple stations around the site are merged to model the interest site. This step is done only in case of large area study.
Optical survey using 3 cameras to produce very high resolution 3D data.
These two models are merged to build a 3D reconstruction of large complex scenes, the ROV3D system can be operated by the submarine REMCRA 2000 or a ROV (ROV APAG-IE).
A navigation system based on real tine odometry process and included into the RO\/3D system give to the operator a real time trajectory of the vehicle.

ROV3D system The software suite include:

  • • Red time quality control
  • • Control / Command
  • • Data management
  • • 3D visualization tools — multiscale representation
  • • Interpretation tools, measurement tools, automatic recognition tools
  • • Export standard formats
Scaled results:

  • • Dense point clouds until 20 millions of points (format: ply, obj....) with colour information
  • • 3D mesh with texture projected (format ply, obj, 3ds.)
  • • Resolution of 1/10mm in very high resolution mode.
  • • 3D visualization tools — multiscale representation



Objectives & methodology

The objectives of the campaign are defined with Timmy GAMBIN from Malta University and Jean-Christophe SOURISSEAU from French institute CNRS – Camille Jullian laboratory.

The first objective is to produce a very high resolution 3D model of the Xlendi wreck using the last ROV3D system developed by COMEX and LSIS laboratory of the CNRS. This system is operated by the REMORA submarine as describe in this report.
The second objective is to recover 4 pieces from the wreck
At least, a large area with many amphora will be surveyed to produce a model on which we can identify the different artifacts.



Operations description

Xlendi wrech

Over the past years, local heritage authorities in Malta have conducted a number of systematic remote sensing surveys off the coasts of the Maltese Islands. One such collaborative project resulted in the discovery of a well-preserved ancient shipwreck. From initial studies conducted on the site it was established that the site is datable to circa 7th century BC at a depth of 125 m. This shipwreck may offer new and significant information about Phoenician seafaring and trade in the central Mediterranean during the archaic period. To date, little is known about the earliest contact of Phoenician mariners with the Maltese islands. Most archaeological evidence stems mainly from funerary evidence. This discovery may be considered as one of the best-preserved archaeological sites in Malta datable to the early Phoenician period. The use of a remote operated vehicle, side scan sonar and a sub bottom profiler enabled the discovery, study and assessment of this deepwater shipwreck. Preliminary photomosaics were created and video footage obtained. Importantly, it was also established that the bulk of the cargo still remains buried in the sediments.



The Xlendi Bay is localized in the South in Gozo Island in Malta, in the middle Xlendi Side Scan Sonar mosaic data (Timmy Gambin)


Recently discovered, the Xlendi wreck on approximately 120m depth shows on the top part a freight well preserved, composed by amphorae and millstones which reminds off a 12 – 14 meters by 4-5 meters vessel. Some images evoke a second level of amphorae. The exam of the first level shows a mixed freight and the vessel seems entire.

From the information the archaeologist have, the ship wreck is dated between the end of the VIIIe century and the middle of the VIIe century before J-C.

This configuration is perfect for a photogrammetry studies, in fact, the photogrammetry will permit to provide a 3D reconstitution of the first level, in order to pick up amphorae and millstone to provide studies on.

The operation was composed:

  • ROV observation to determine the 3D acquisition protocol of the ship wreck
  • Photogrammetry data acquisition from REMORA 2000
  • From the first rapid photogrammetry processing data, identification of the millstone and amphorae to be recovered.

  • Here a report on the first considerations relative to the cargo (report in French)

    Xlendi orthophoto


    3D photogrammetry – ROV3D SYSTEM FROM R2K.

    Pilot Y. Tchernomordick – Co-Pilot and ROV3D: B. Chemisky
    The REMORA 2000 equipped with ROV3D system has been deployed for the first survey the 17/07/2014 at 10:30am
    The survey begun at 11:00, 8 passes E-W and 6 passes N-S and the record finished at 12:20.
    The camera has been disposed at the vertical of the site.
    The second survey has been done the 18/07/2014, the camera has been disposed at +22.5° and the survey begun at 11:29 and finished at 12:25. 10 transects E-W and 8 transects N-S

    Another record has been done on isolated amphorae on the North West boundary on the shipwreck. This record has been made in closed photogrammetry procedure.

    KEY NUMBERS
    On site results: Mosaic Low resolution: about 24 hours: 664 photos – 23 Millions pts – 20 Millions faces
    Post process results: 829 photos – 27 Millions pts – 30 Millions faces
    All data: 2 831 photos HR & 28 310 photos HD in two dives 01:20 & 00:54

    R2K dive for scientist observation

    The 18th of July, Timmy Gambin has been co-Pilot to realize a scientific observation of the Xlendi wreck.
    The 20th of July, Jean-Christophe Sourisseau has been co-Pilot to realize a scientific observation of the Xlendi wreck.



    Amphorae and millstone recovery

    From the first photogrammetry process in low resolution, the material to recover has been identified by the scientist on board, Timmy Gambin and Jean-Christophe Sourisseau.
    The 19 of July, the aim was the recovery of amphorae and millstone.




    Sample 1: Millstone recovery; Sample 2-3-4: Amphorae recovery                     Photo of the millstone recovery



    sample 2 amphorae recovery



    sample 3 amphorae recovery




    sample 4 amphorae recovery




    All samples have been secured by divers at 25 meters depth before being on board.

  • September 2014 report : "Sea report on the mission in Malta" -in French-
  • GROPLAN
    Ontology and Photogrammetry ; Generalizing Surveys in Underwater and Nautical Archaeology