Abstract— Part of underwater archaeologist’s work consists

in documentation of underwater sites. This is done by divers,

with deployment of markers, poles, grids, etc. over the sea-

bottom. Surveys with the traditional techniques require a

considerable effort limiting the possibilities of multiple

inspection surveys by the responsible agencies. Within the last

ten years, ISME (Interuniversity Ctr. Integrated Systems for

the Marine Environment) and SBAT (Italian Ministry of

Culture, Superintendence of Archaeological Goods of Tuscany -

Soprintendenza per i Beni Archeologici di Toscana) have

worked toward automation of the survey process. The objective

is the development of low-cost, easy-to-use and non-invasive

systems to obtain a geo-referenced augmented map of a wreck

site. During the VENUS project, funded by European

Commission - Information Society Technologies (IST) and

ended in 2010, UNIVPM – Università Politecnica delle Marche

(ISME) and SBAT has worked together providing scientific

methodologies and the technological tools for the virtual

exploration of deep underwater archaeological sites. The

VENUS project improved the accessibility of underwater sites

by generating thorough and exhaustive 2D and 3D records for

virtual exploration. UNIVPM's team and SBAT's team,

following the work done in VENUS, in the last year (2010), have

continued to develop new technologies and have validated

techniques with other archaeological institutions.

This paper presents the results obtained by UNIVPM's team

within the Breaking the Surface 2010 Workshop4 (Murter,

Croatia) in studying one famous cultural and historical heritage

site in Kornati Archipelago. Several dives made on this site and

a program of remote sensing using an AUV and an ROV with a

camera was made. In addition to these explorations, a number

of finds are been geo-localized and a final map has been created

starting from the photomosaic of the sea-bottom. To this aim,

different technological components are been developed or

integrated, including a still camera for photogrammetric

reconstruction of the site and an USBL acoustic positioning

system. Crucial to the performance of the automated system has

been the integration of the acoustic positioning system with the

photo archive in the dive state estimation algorithm, in the

design and definition of a specific data format used to store the

data; in the geo-referentiation of the estimated position and in

the determination of the geometrical features of the site. This

positioning data will be effective also in facilitating excavation

operations, allowing to focus the diving on the precise spot

1D. Scaradozzi is with Dipartimento di Ingegneria Informatica,

Gestionale e dell'Automazione, Università Politecnica delle Marche,

Ancona, Italy (d.scaradozzi@univpm.it). 2I. Radić Rossi is with the Dept. of Archaeology, University of Zadar,

Croatia (irradic@unizd.hr). 3Kruno Zubčić is with Croatian Conservation Institute, Zagreb,

Croatia, (kzubcic@h-r-z.hr). 4Breaking the Surface (BtS) is part of a larger on-going effort

within the supporting framework and infrastructure of the FP7-REGPOT-

2008-1 EU project within the FP7 Capacities scheme Developing the

Croatian Underwater Robotics Research Potential awarded to the

Universities of Zagreb, Faculty of Electrical Engineering and Computing,

Croatia.

determined by the archaeologists after the geo-referenced

surveys.

I. INTRODUCTION

The recent years have seen much study in developing

efficient subsystems for underwater applications, especially

driven by Off-Shore companies and by European

Commission in terms of research and new tools investments.

The problem of data gathering in the underwater

environment and 3D reconstruction of the underwater sites is

one of the most important challenges since different

application fields need to have enriched maps of the

underwater areas in an efficient, economic and safe way.

Practical examples of application fields are: marine

environment monitoring in order to analyze marine or

underwater building status (i.e. bridges, dams, offshore

structures, etc...); biological marine environment monitoring

and analysis (i.e. visual census, time evolutions, etc...);

survey of archaeological sites (i.e archaeological

documentation, cultural heritage protection, museum

dissemination, etc...). Taking into account: the abundance of

underwater archaeological sites that characterizes some

geographical areas (as for instance the Mediterranean Sea);

the fact that such sites are under the jurisdiction of local

government agencies; and that such authorities have the task

of periodically inspect all the known sites, it is clear that the

resources usually available are largely insufficient for the

accomplishment of the given tasks. Such procedure is

required also in all the operations of so-called “prevention

archeology”: in particular, in several countries (Italy amongst

these), it is required by law to carry out a seafloor

archeology investigation on any area where any work

requiring seafloor morphology changes (such is the case for

instance of harbor dredging, foundations lay-out, pier

extensions, etc.). In these cases the mapping operation, and

its repetition at each new periodic inspection, is usually

carried out by divers, taking photographs of the site, after

laying out in sites an appropriate set of calibrated markers,

grades, and/or grids to be used in the site reconstruction. The

use of photographs and subsequent 3D computer

reconstruction with photogrammetric tools is, in itself, a

great improvement, considered that until very recently most

of the site reconstruction was done by drawings made by the

archaeologists after the dive, and the geometric

measurements were taken with grades hand-held by the

divers. Since several years, it has been recognized that

advances in marine technology and oceanic engineering,

especially in measurement automation and autonomous

Geoposition data aided mosaicing for archeology sites

documentation: the islet of Bisaga (Kornati Archipelago) site case. David Scaradozzi

1, Irena Radić Rossi

2, Kruno Zubčić

3

19th Mediterranean Conference on Control and AutomationAquis Corfu Holiday Palace, Corfu, GreeceJune 20-23, 2011

TuCT4.5

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systems, can be of great benefit to the previous described

work made by underwater archaeologists. This has been the

theme of focused workshops (see for istance [1]), however,

from the published literature, most of the case-studies belong

to the two following situations: technology specifically

developed in other fields (as for instance military or off-

shore) and used in archaeological surveys; development of

special purpose, very specific, one-piece only

archaeologically oriented tools [2]. It is our opinion that

neither case is a viable way for a sustainable technological

growth of underwater archeology activities; this is because in

both cases the costs associated to the instrumentation, and/or

the complexity of the instrument operation are far above the

reachable target of responsible archeology agencies. For

instance, the work described in [2] requires a dedicated ship

with trained and skilled engineering personnel to operate the

equipment. While such a work is certainly relevant from the

technological research view point, it is hardly that such

modus operandi can be standardized and routinely used by

archaeological groups with low budgets not at least in the

short-medium term future. What is needed by the

archaeologists is a set of low-cost, easy-to-use, plug&play

technological tools and procedures that can help in reducing

the overall cost of site inspection and documentation. To be

effective, such tools and procedures have to be designed

from the start with the archaeological application in mind.

Our research group has identified the above problems since

several years [3, 4, 5], and, in the recent past, has addressed

specifically the issue of automated inspection by means of

ROV for 2D and 3D virtual reconstruction of the underwater

environment (see European projects [7], [8] and [9]). In

particular, following the work done in VENUS, in the last

year (2010), UNIVPM's team and SBAT's team have

continued to develop new technologies and have validated

techniques with other archaeological institutions. In order to

build augmented map of underwater environments it is

necessary to have optical data (coming from digital camera

and videocamera) synchronized with specific sensors, which

allow to know position and inclination at which the scene is

acquired. For these reasons, a team from Laboratory of

Modeling, Analysis and Control of dynamical Systems

(LabMACS) of Università Politecnica delle Marche

developed a low cost device, consisting of a portable sets of

sensors, controlled by a microprocessor, for acquisition of

geographic and attitude data, to complement photo and video

collected by divers or by ROVs. The UNIVPM's device

construction is based on COTS and on other custom software

tools. Basically, to map out absolute underwater position of

the diver, the device was used with USBL system that joins

together DGPS communication receiving apparatus and

acoustic underwater transceiver. In order to produce geo-

referenced and large-to-medium 2D scale maps of the

underwater explored sites with the acquired photos, a

software suite for the integration and fusion of the acoustical,

optical and platform navigation data has been developed.

This paper presents some results obtained during the

Breaking the Surface 2010 Workshop (BtS2010 - Murter,

Croatia see [http://cure.fer.hr/index.php/cure-

activities/events/realized-events]) in studying one famous

cultural and historical heritage site in Kornati Archipelago.

Several dives made on this site and a program of remote

scouting using an AUV and a ROV with a camera was made.

In addition to these explorations, a number of finds are been

geo-localized and a final map has been created based on the

photomosaic of the sea-bottom.

The paper is organized as follows. In the next section the

classical way to study archaeological sites was recalled with

the improvement made by the new strategies and tools. In

Section 3 the description of the equipments, data gathering

systems and associated processing tools to map the

archaeological site are described. In Section 4 a case study as

an example is reported.

II. METHODOLOGY USED IN THE ARCHAEOLOGICAL SURVEY

The overall aim of underwater archeology, like its terrestrial

counterpart, is to improve the knowledge of the past. The

goals are obtained according to the increase of information a

new study could provide. For example, the study of shipping

trade, sea ways, or naval architecture at a given epoch. The

objective in this context is mainly prevention. Precious

underwater archaeological sites, for example the ship

wrecks, are continuously jeopardized by activities such as

trawling or robbing that destroy the surface layer of the site.

In order to protect archaeological sites, a systematic

recording and mapping is proceeded, sponsored by cultural

heritage public institutions. An accurate documentation has

to be provided at each stage of the methodology. The

evaluation of the achievement of the objective is performed

by the evaluation of the quality of the produced

documentation.

Here, the traditional underwater archeology methodology for

studying the sites is presented in order to introduce a

technological innovation in the documentation process (see

VENUS wp3r1 final document). This study is performed

according to the site, the scientific goals, the means at

disposal and follows different steps.

1. Choice of the site.

This first step is crucial, it is performed by comparing

several information coming from different sources: reports

made by divers or fishermen in reporting the presence of

artifacts and historical sources, geographic information,

geologic information, morphology, nature of the sediment of

the seabed, biologic aspects and meteorological information.

2. Site location.

When the site is chosen a sub-area is delimited according to

the concentration of artifact materials. This site is precisely

2D geo-referenced by the spherical coordinates: that is

longitude and latitude of one point with a GPS in the surface.

3. Cleaning the archaeological site.

The recognition of artifacts may be poor because they may

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be covered. Dredges and/or crane are used for removing

organic materials like algae, dead “posidonia” or sand and

mud in order to improve the recognition of artefacts within

the site.

4. Positioning the site.

A preliminary observation of the site is performed by the

archaeologists in order to have a general view of the site:

positions of the artefact's, relative orientation of the objects (

the ones with respect to the others), shape of the seabed,

position of the flora and if there is enough light for

photosynthesis. In order to position the site a buoy geo-

referencing the site is located.

5. Cataloging.

Before surveying the site, the objects are numbered and

labeled, for example, with small PVC tablets.

6. Positioning a referencing system on the sea-bottom.

A referential system is established by geo-referencing an

origin point and two axes. The origin and the axes are fixed

by divers with buoys, moorings and halliards. Within the

traditional methodology the choice of these landmarks is

very important since it is used for referencing the position of

the discovered artifacts. There are several referencing

systems, however the measures are manually performed

according to linear measurement or linear measurements

with angles. According to the density of the archaeological

material a reference system (grid, square, triangle, base line)

is installed on the site. The most conventional technique is to

place an orthogonal quadratic grid of 2 x 2 meters or 4 x 4

meters, of nylon cables, metal or PVC tubing. From this grid

a sub-area is defined in squares creating lattices which help

the divers and the archaeologists to find their bearings and to

label the artifacts. Different points of the squaring are

marked by moorings for helping the divers to easily locate

the objects and the archaeologists to more easily register the

position of the objects for mapping the area. This procedure

could only be performed in case of shallow water and, in any

case is very time consuming and expensive.

7. Surveying the site

The traditional method technique for surveying and well

documenting an archaeological site is manual according to

linear measures or linear and angular measures and there are

several methods [12]. In the case of the site of Bisaga, the

manual surveying has been carried out by triangulation. After

selecting three points on the objects, the divers have

measured by tape measure the Cartesian coordinates of these

points with respect to the reference system of the

archaeological site. The archaeologists usually perform scale

drawings of the objects with simple pencils and whiteboards.

Photo and video documents of the site, taken by divers

following the lattices of the marked area, could help for

surveying the site.

8. Restitution : mapping.

While the surveying is performed underwater, the restitution

is performed back to ground. According to manual surveying

method, a map, that is a 2D representation of the underwater

site, is produced in a form of gradually improved sketch.

This map aims at obtaining very accurate graphical

representations of reality. The map is firstly carried out

reporting the origin and the axes of the reference system then

the Cartesian coordinates of the objects with respect to the

reference point.

9. Exploration.

The production of a map of the whole site and work done

during each campaign, helps for further explorations,

investigations and interpretations. The methodical

exploration of the site leads to the identification of new

objects and to the systematic recording of the referenced and

identified objects especially in previous maps. After the

methodical exploration of the surface layer, intrusive

excavation, stratum by stratum, is continues inside the grid.

Silt and sediments can be removed using water dredges. The

recovery of artifacts from underwater sites destroys the

archaeological context, which remains preserved only in the

notes (typically on the archaeologist's notebook), drawing,

and photographs made by the archaeologists in the field.

Careful recording is necessary, and documentation is crucial

during all the stages of the investigation.

In the above described methodology we studied the

possibilities to introduce engineers, data manager experts

and new technologies to make the process more efficient and

accurate in the documentation phases. In particular,

computer scientists and engineers are been introduced

directly into the line of the site's study since the first day of

field work. With the use of the AUVs or ROVs (when the

economic resources allow it), acoustic positioning systems

and improved photo-camera we obtain a very precise geo-

referenced map or 2D geo-referenced reconstruction of a

large area of the seabed instead of the sketches after each

survey day. Such maps, obtained by optical, acoustical and

position data correlation is important because it is not

dependent from the memories of the diver who has visited

the site and also because it can be inserted in real time on

GIS tool and, later, with appropriate filtering, in 3D virtual

reconstruction of the site. In the figure 1 the introduced

technology and the, consequent, output documentation

during the classical site analysis phases are presented.

Modifying the classical way to proceed and directly use the

gathered data for the daily improvement of the maps will

create a sort of self-assessed work cycles.

Figure 1. Classical site analysis phases and the

introduced technology.

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The maps will contribute to understand whether some data

are missed or more areas are to be investigated. In this way

archaeologists can dynamically change the plans during the

campaign, optimizing costs and time. Figure 2 shows a

typical work cycles with the final map produced. This self-

documented cycles are more useful in case of day by day

digging and consequent 3D layers reconstruction of the site.

Figure 2. Typical work cycles for producing augmented

map in archaeological campaign.

In the Bisaga case study both traditional and innovative

techniques of acquisition have been used. The next section

provides a brief description of the technological tools used

during the site studying phases, subsequently, a brief

description of the survey methods and data processing,

developed within VENUS and used in BtS2010, are

presented. In particular are described: calibration, collection

of photographs using divers and geo-referencing

photographs method for 2D map reconstruction. In the last

part, the archaeological context and partial results obtained,

are presented.

III. TOOLS FOR ARCHAEOLOGICAL SURVEYS ON SUBMERGED

SITES

The considered scenario has been witness of the combined

use of divers equipped with acoustic and optical sensors. In

particular, a first team of divers has been used for performing

preliminary, large scale acoustic surveys and explorations,

while a second and third teams has been used for collecting

data of photogrammetric type. In the second dive two divers

guide the photographer maintaining desired heading and

depth along predetermined trajectories or paths, while

activating USBL and cameras in accordance with pre-

specified programs, recording navigation data. The third dive

is devoted to carry on the transponders over artifacts to be

geo-localized. The work will aim at developing (semi-)

automatic procedures which help the operators in governing

the sensory apparatus in gather the photos over the area of

interest. The tasks must be completed with an evaluation of

performances by means of adequate output indicators. The

last work concerns integration of all navigation data in a

scheme to increase precision in navigation positioning, self-

localization and image photogrammetry. The output

indicator of this tasks usually is the success of the

photographer in guiding the photo camera along

predetermined trajectories taking care of geo-referencing the

acquired data. It is clear that the need of getting precise

positioning increases as the dimension of the area covered by

a single acoustic or optic image decreases. Therefore, a

precision indicator will be given by the ratio between (a

parameter which expresses) the positioning error and (a

parameter which expresses) the dimension of the area

covered by a single acoustic or optic image (as an example

of this type of work the Deliverable 6.5 of VENUS project

can be considered).

A. Operative needs in documentation of a site

The major activities that define the work of underwater

archeologists include: Pre-analysis of the area, search area

definition, mission design, local survey, documentation,

excavation, post-analysis and final documentation. Interest of

the methodology here presented is concentrated on the

phases prior to the excavation phase. The work must

concentrate first in order to study a suitable robotic systems

for data gathering. The kind of data one wants to get

consists, essentially, of a set of geo-referenced pictures of

photogrammetric quality and, possibly, of acoustic images of

the site. Geo-reference should be accurate enough to allow a

complete reconstruction of the site with a specified level of

precision. As in others EU project (see VENUS,

UPGRADE, EPOCH Network), for the output format

coming from a survey, here the team has selected the

JPEG/EXIF structure. In this way a set of files in

JPEG/EXIF format are recorded which can be accessed on

line (at the end of the dive) by the archaeologist. The

association processes is performed accounting for the fact

that data are not acquired at synchronous timestamps: every

sampled low quality picture is associated with the high

quality photograph and the acoustic response that exhibits

the closest timestamp; the association of the other data such

as geo-referenced coordinates or attitude data require

supplementary calculations which include averaging,

interpolation or filtering procedures. The merged data sets

deliver more information than if the data sets were viewed

individually, thus it can be said that the system exhibits a sort

of economies of scope where the whole has more value than

the sum of the parts. In order to increase portability and

usability, the same information has also been structured in a

different, alternative way, following the XML format. The

XML file contains the data of the various sensors, ordered in

a coherent way, and a set of pointers to the various images.

The final enriched maps are made by SIFT algorithm

enhanced with camera position and attitude information, the

data is in GeoTIFF format.

B. Mission preparation and design

Before starting the underwater surveys, all equipment need a

first stage of preparation and tuning. During this phase the

sensors are tuned (in order to erase bias and other mission

specific errors) and the camera is calibrated. The camera

calibration in multimedia photogrammetry is a problem that

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has been documented for almost 50 years. The problem is

not obvious, the light beams refract through the different

diopters (water, glass, air) and introduces an error which is

impossible to express as a function of the image plane

coordinates alone. Using a digital camera, it was chosen a

simple way to do that: a camera calibration grid (as in Figure

3) was photographed from 8 points of view under an

incidence of more or less 45°.

Figure 3. Camera calibration phase.

In order to minimize errors before described, a custom tool,

developed with LabVIEW Vision Toolkit basing on

PhotomodelerTM calibration software, has been made. The

tool recognizes in all the photographs the vertex of all the

circles and produces a high number of observations related

to the triangle vertex on the calibration grid.

C. Geo-referenced DATA acquisition

The optical and acoustic data acquisition with the underwater

photographer takes place as a succession of linear transects

above the area of interest as specified by the archaeologists

at the survey design stage. Position and orientation of the

diver (or of any other instrument carrying acquisition

devices) often need to be referenced in an absolute reference

system. During the surveys, divers carry on a transponder,

used by the transceiver for diver tracking. Another

transponder is put on the sea bottom in the mission reference

point (on Bisaga site: the point is A in the figure 5) and the

last of 3 transponders used is moved on the finds in order to

geo-localize them with repeated dives. During the Bisaga

mission within each transect, the diver has been commanded

to dive at 1 knot speed with an average distance from the

seabed of about 2m; in this way, with the available

equipment, each optical frame covers a seabed area of about

2.5m2. These sets of frames provide a complete coverage of

a 1.5m wide corridor, assuring an overlap of about 60%

between two consecutive frames. The photographer position

is always on-line monitored and memorized for post

processing operations by a Ultra Short Base Line (USBL)

acoustic system (i.e. Sonardyne Scout system, operating in

the acoustic frequency range 35 – 55 KHz, with repetition

rate of 1 Hz). Depending on the mission these data were

integrated with DGPS information and compared with the

mean of the fixed known position on the sea-bottom so to

obtained geo-referential data. During all the mission it is

very important to put one acoustic transponder for the USBL

system at fix position on the sea-bottom in order to

triangulate all position data with the filtered position of the

center of the site or the measurement point common to all

campaigns. The reference transponder was equipped to

operate continuously during the experiment period; since the

supporting ship was not stationed permanently at the

experimental site, but was reaching the site in the morning

and leaving it in the evening, logging of the fixed

transponder position was obviously possible only when the

ship was on site.

D. Image acquisition and information synchronization

In order to make accurate 2D and 3D virtual reconstructions,

starting from photos, it is needed to know the inclination of

video devices, when the diver takes each photo. A low cost

device, linked to a photo camera, capable of saving its

relative orientation during each data collecting process, and

info coming from acceleration, real time clock and heading

sensors value was made. The master device is a Microchip

16bit DsPIC microcontroller: its input ports are connected to

a light sensor and to the other sensors. They are COTS

components that are connected to the DsPIC thanks to the

I2C standard bus. The acceleration sensor used is a 3 axis

digital sensor. This sensor can be used to measure static and

dynamic acceleration on different axes. It can be used as a

tilt sensor or to track the velocity profile of the diver. The

heading sensor, used in the project, is a digital magnetic

compass specifically designed for microcontrollers. This

compass can be used as a digital sensor to detect deviation

from magnetic north pole (photocamera heading). The

heading sensor can be used, also to track a certain heading or

follow paths with reference to magnetic north, and it allows

to obtain the correct inclination from the data given by the

accelerometer. This compass uses an orthogonal two-axis

magnetic sensor. The Real Time Clock is suitable for data

logging operation, because with time (hh:mm:ss) and date

(dd:mm:yy) it allows to synchronize static position of the

camera with the photo shot. A preliminary calibration of

sensors is important in order to use them correctly, to remove

an eventual bias factor: to do that, each sensor was studied

and suitable algorithms were developed. Simple software for

monitoring sensors in static conditions and elaborating their

characteristics useful to know during the mission, were

developed in LabVIEW. Then, specific drivers were realized

for each sensor, to integrate them in the system.

E. Virtual reconstruction in 2D maps

The kind of data coming from the previous steps consists,

essentially, of a set of geo-referenced pictures in

photogrammetric quality: they can be used to construct both

2D and 3D models of the explored area in a virtual

environment, with a specified level of precision. Firstly,

thanks to the data acquired by USBL system, the dive path

was plotted, like in figure 4. Besides, after the dive, with the

data set coming from the developed tools, it was possible to

view a partial reconstruction of the area with the

photomosaicing tools SMuS. SMuS is a software suite for

real time photomosaicing from underwater photos and video

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frames of a surveyed area; it can produce an output like the

figure 6. This information and data coming from the

photographic campaign were merged into a virtual

reconstruction of the 3D scene or viewed in a GIS (Global

Information Service) to design new missions. In fact, all data

can be stored in a relational database and a set of LabVIEW

tools allows to wrap objects from the database and to

produce a VRML or X3D representation.

Figure 4. Geo-referenced DATA acquisition.

IV. EXPERIMENTAL RESULTS: THE ISLET OF BISAGA

(KORNATI ARCHIPELAGO) SITE CASE

Some of the most famous cultural and historical heritage

sites in Croatian waters lie in depths unreachable by regular

sport divers. One significant group of deep wrecks

comprising 6 ships which sank during the First and Second

World Wars is concentrated along the western side of the

island of Pag. In addition to several tri-mix dives made on

these sites, a program of remote sensing using sidescan and

multibeam sonar has been partially completed. In 2005, the

French diving company Comex (Marseille) sponsored a deep

water survey of the area to the northwest of the island of Vis

where the famous Battle of Lissa took place in 1866. During

the survey the Re d’Italia was discovered and documented

with the help of a submersible and remotely operated vehicle

(ROV) with a camera. In addition to these explorations, a

number of finds raised by fishermen and a study of ancient

seafaring routes testify to the probable existence of a great

number of shipwrecks from periods ranging from prehistory

to modern times. Although trawling has disturbed some of

the sites, systematic recording of deep water shipwrecks

would contribute greatly to the research, protection and

preservation of Croatia's underwater cultural heritage.

During the International Interdisciplinary Field Training of

Marine Robotics and Applications (September 27 - October

3), and in particular for Breaking the Surface 2010 event the

archaeologists team has been oriented to a sites which are

reachable by divers and submersible vehicles. In the Bisaga

Islet case study various techniques of data acquisition both

traditional and Remotely Operated Vehicle (ROV) was been

used.

A. Choice of the site

The choice of Bisaga Islet was made by crossing different

sources of information. Volunteer divers reported the

presence of anchors and canons on the site of Bisaga and

declared the site to the “authority” several decades ago.

Since then the site has been heavily looted. The

archaeological survey during the BtS2009 confirmed the

presence of 3 anchors, 6 canons and a lot of small scattered

finds still present on the seabed within an area of 15 x 30 m.

B. Site Localization.

The localization of the site has been performed using both

local traditional referencing system using DGPS and

absolute referencing system from the ROV and AUV

combining USBL, SONAR and DGPS. The cleaning has

been carried out by first removing the dead posidonia from

the site and a thick layer of sediment that several types of

anchors and cannons have been identified by volunteer

divers during previous explorations. The divers then brushed

visible finds since they were covered by algae and marine

organisms. In deep underwater archaeological sites, blasters

are generally used for cleaning; however the presence of

flora and fauna decreases with depth and it could be possible

to skip this stage for such excavations.

C. Preliminary observation

A preliminary observation by the archaeologists focused on a

homogeneous group of 3 anchors and 6 canons of about the

same type which became the starting point of any further

investigation and allowed them to select a 15 x 30 meters

area for exploration. As final result of the preliminary

observation the draft presented in the figure 5 was produced.

Figure 5. Draft of the site and survey dives design.

D. Restitution: mapping of a part of the site

During the few days over the site in BtS2010 and following

the preliminary draw of the site the archaeologists choose to

map the South part of the site. At the site's depth divers can

normally operate so that manual survey procedures could be

take place: according to the archaeologists decision the

chosen zone was structured with 6 graded bars (2 of 2m, 2 of

1.6m and 2 of 1.5m). The zone delimited by the bars was

then surveyed by the photographer with the custom

electronics, sensors and USBL transponder. The dive

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partner was essential for guiding the photographer toward

the archaeological zone at new raw of photo survey (see the

planned survey lines in the figure 5).

During the surveys time another teams reached the reference

points “A”, “E”, “I”, “J” and put there the other USBL

transponders for a measurement necessary time. At the end

of the 2 day mission we obtain the latitude, longitude and

depth of the referenced point measured by previously

archaeological campaign and the points “I” and “J” clearly

visible on the 2D mosaic for geo-positioning the final map

and using it in a commercial GIS or Google Earth (see Fig.

6).

Figure 6. 2D Map in GeoTiff of the South part of the site.

V. CONCLUSION

The work done so far in the framework of the Research

Project VENUS has shown the great potential of USBL and

underwater robotics in the field of underwater archeology,

providing tools and innovative methodologies for exploring

sites for gathering large amount of informative data and for

processing them, in order to facilitate study and

dissemination and to ensure preservation. By making the

scientific exploration of underwater archaeological sites

easier and more viable, the results obtained in the project

will help archaeologists to get new information and to

enlarge knowledge. In the Bisaga site the use of acoustic

position system, in particular of an USBL system, as part of

a system engineering design and procedures devoted to the

2D mosaicking a geo-referenced map of cultural heritage site

has been presented, together with some examples from the

field. Future work will include new field experiments for

validating and tuning the developed methods, as well as

study for enhancing their applicability and efficacy in the

exploration of sites located in deep water. Moreover, the

activity pursued in VENUS and after will may open the way

to the study and development of intervention techniques that,

in the future, may allow archaeological excavation and

documentation in deep water solely by means of robots and

unmanned vehicles.

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