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ACOUSTICAL IMAGING OF BURIED SEAFLOOR WASTE: CHALLENGES FOR AUTONOMOUS UNDERWATER VEHICLES

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Title: RISK ASSESSMENT OF BURIED SEAFLOOR WASTE: ACOUSTICAL IMAGING BY COORDINATION OF AUTONOMOUS VEHICLES Author: Andrea Caiti Last modified by – PowerPoint PPT presentation

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Title: ACOUSTICAL IMAGING OF BURIED SEAFLOOR WASTE: CHALLENGES FOR AUTONOMOUS UNDERWATER VEHICLES


1
ACOUSTICAL IMAGING OF BURIED SEAFLOOR
WASTE CHALLENGES FOR AUTONOMOUS UNDERWATER
VEHICLES
  • A. Caiti
  • ISME Interuniv. Ctr. of Integrated Systems for
    the Marine Environment,
  • DSEA Dept. Electrical Systems Automation,
    Univ. of Pisa, Italy

2
Overview
  • Motivation the SITAR project
  • Inspection of buried waste by multiple-view
    measurement of the acoustic scattered field
  • Experimental configuration within SITAR
  • Beyond SITAR use of (semi?)autonomous vehicles
    for scattering measurements
  • Lyapunov-like control techniques

3
SITAR Seafloor Imaging and Toxicity Assessment
of Risk caused by buried waste
  • Acoustical imaging, biotoxicology, decision
    support systems
  • EU funded project, partners
  • - Universities of Trondheim, Stockholm (2), Bath
  • - Swedish Defence Res. Est., Ecole Navale (Brest)
  • - Swedish Environmental Prot. Ag., ECAT Lithuania
  • - Kongsberg Defence Aerospace
  • - ISME

4
SITAR project motivations
  • Toxic dumping in shallow and close seas
  • forbidden by the London Convention (1975)
  • covert practice after 1975
  • partial or complete burial of pre-London dumpings
  • even for known sites, lack of information for a
    rational risk assessment

5
Toxic waste dumping a case study
  • Chemical munition waste dumped in the Baltic Sea
    after WW-II
  • 65.000 Tons of munition and warfare agents,
    including mustard gas and other arsenic compounds
  • Containers state preservation from perfectly
    preserved to totally corroded
  • Quantity of buried containers unknown

6
Risk assessment of dumping sites needs
  • Maps of containers distribution at the site
    (localization)
  • State of preservation, exact location,
    orientation of each container (inspection)
  • Characterization of biological effects
    (bioassessment)

7
Risk assessment of dumping sites available tools
  • localization side-scan sonar
  • inspection cameras (from ROVs)
  • bioassessment concentration measurements and
    acute toxicity analysis
  • Lack of tools for localization and inspection of
    buried waste
  • Lack of tools for bioaccumulated toxicity
    evaluation

8
SITAR developments
  • localization a parametric side-scan sonar
    (bottom penetration, 3-D imaging capabilities,
    development of associated visualization tools
    needed)
  • inspection multiple view measurements of the
    scattered 3-D acoustic field
  • bioassessment relative measurements of in-situ
    bioaccumulated toxicity

9
Multiple view measurement of the scattered field
  • reconstruction of 3-D object characteristics from
    2-D slices of the scattered field
  • scattering strength as a function of grazing
    angle and scattering angle (figures from Hovem
    Karasalo, 2000 tank experiment, acoustic source
    500 kHz)

10
Acoustic eigenrays
11
Model prediction capabilities arrival times
12
Model prediction capabilities scattering strenght
thick line experimental data thin line model
predictions
13
Multiple view scattering measurement minimal
requirements
  • 2-D scattering angle sampling ? 20 at each
    transmitted grazing angle
  • Directional source/receivers, transmission at
    20-40 kHz (wavelenghts 4-8 cm)
  • Acoustic pingers (?100 kHz) to assess
    source/receiver relative position (? max
    source/receiver distance ?40 m)
  • Azimuthal sampling? 30

14
SITAR experimental configuration
15
SITAR experimental configuration
  • Useful for test-of-concept experiment
  • Evident drawbacks for repeated inspections of a
    large number of containers
  • Beyond SITAR explore the possibility of multiple
    view scattering measurements with (semi?)
    autonomous vehicles in cooperation

16
Beyond SITAR
17
Requirements
  • directional acoustic pingers on both
    source/receivers vehicles for relative
    positioning control (attitude and distance)
  • bi-directional acoustic communication
  • station keeping capabilities
  • movement from one position to another as a task
    accomplished in three subtasks

18
Subtask 1 align with desired relative angle
  • From current position and attitude, move upward
    until detection of the transmitted signal, at
    fixed attitude
  • Choose maximization of the received acoustic
    energy as stopping criterion

19
Subtask 2 attitude correction
  • From reached position, the receiving vehicle
    changes attitude to align with the transmitted
    signal
  • Choose maximization of the received acoustic
    energy as stopping criterion

20
Subtask 3 distance correction
  • Keeping the attitude fixed, move to the desired
    distance x
  • Use time-of-flight measurements to estimate the
    distance
  • Requires clock synchronization between the
    vehicles

21
Control Lyapunov functions
22
A Control Lyapunov Function (CLF) approach to
subtasks execution
  • Easy case subtask 3
  • Let e x - x be the measured distance error
  • Pure kinematic model (but plenty of space for
    robust design, backstepping, change of
    coordintaes ...)

23
The more difficult cases subtasks 12
  • Basic idea apply the same CLF approach
  • However, in subtasks 12, the error cannot be
    measured
  • Define a tentative CLF V in terms of the measured
    acoustic pressure level
  • Move in steps in the directions minimizing V
    (somehow similar to other approaches proposed in
    visual feed-back applications)

24
Example subtask 2
25
Subtask 2 conditions and requirements
  • What does it mean as ???? It depends on
    source/receiver beam pattern and signal to noise
    ratio
  • Step-by-step exploration of the admissible
    configuration space
  • Communication and synchronization among
    source/receiver vehicles

26
Conclusions
  • Motivations and goals of the SITAR project
    development of tools for inspection of buried
    toxic waste
  • Multiple view scattering measurements with
    semiautonomous vehicles in cooperation
  • Use of CLF advantages and drawbacks

27
References
  • I. Karasalo, J.M. Hovem, Transient bistatic
    scattering from buried objects, in Experimental
    Acoustic Inversion Methods for exploration of the
    shallow water environment, Caiti, Hermand, Jesus
    and Porter (Eds.), Kluwer, 2000
  • M. Aicardi, G. Casalino, G. Indiveri, New
    techniques for the guidance of underactuated
    marine vehicles, IARP Workshop Underwater
    robotics for sea exploration and environmental
    monitoring, Rio de Janeiro (Brazil), October
    2001.
  • A. Caiti (coordinator), SITAR Description of
    Work, available on request contacting
    caiti_at_dsea.unipi.it
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