ensonification image
GGE 3353 - Imaging and Mapping II :
Submarine Acoustic Imaging Methods

Instructors : John E. Hughes Clarke

Fall Term (September - December 2010)
Monday - Wednesday - Friday 1330 -1420 E4

(last updated September 2010)

(1) To instill a burning desire to map the oceans
...failing that ...

To ensure that the students have covered the minimum material requirements embedded in the Canadian Land Surveyors (CLS) accreditation.

(2) : to appreciate the similarities and differences between submerged acoustic imaging techniques and atmospheric electromagnetic imaging.

(3) : to be able to design the most effective submarine survey given specific clients needs

(4) : to be knowledgeable about currently available, state-of-the-art acoustic survey systems. Includes the theory, application and processing requirements.


Introduction - Course Overview

The outline of the course is described along with the timetable. Inter-class clashes will hopefully be resolved. The requirements for course assessment and marking will be described.  Identification of the student body. The relationship of this course to:

will be explained. What is Acoustic Imaging. Why it is important for a graduate of the Geodesy and Geomatics Engineering program to have an understanding of the principles and applications of submarine acoustic imaging. What job opportunities there are : Private Companies, Government Agencies, Research opportunities.
  • PPT Slides (zipped set of gif's)
  • Typical Applications of Submarine Acoustic Imaging

    A series of real examples for which submarine acoustic imaging is required will be described. These will include examples from:

    The accuracy, resolution and coverage requirements for each application will be compared and contrasted.

  • PPT Slides (zipped set of gif's)
  • Physical Oceanography A - a description of the water masses and processes that drive worlds oceans 

    A description of the typical water masses and the processes that drive their circulation in the following environments:

    in high, mid and low latitude locations. Including a description of the circulation, currents, tidal regimes and wave climate and influence of weather on those environments. How these parameters influence the planning (instrument choice), execution and results of acoustic surveys.
  • PPT Slides (zipped set of gif's)
  • Physical Oceanography B - physical properties of seawater and their effect on acoustics 

    Measurement of temperature, salinity, density, attenuation and sound speed . The instruments, the empirical relationships. And the effect of these physical properties on the propagation of sound in the ocean. Typical ocean wave spectra and their influence on vessel motions.

  • PPT Slides (zipped set of gif's)
  • Marine Geology A - a description of the sediments that make up the floors of the Oceans

    A description of the typical scales of relief and the types of seabed material type commonly found in the following submarine environments:

  • PPT Slides (zipped set of gif's)
  • Marine Geology B -  physical properties of marine sediments and their effect on acoustics

    Measurement of :

            of typical marine sediments.

    The effect of these properties on the reflection and scattering of sound at the sediment water interface.- Surface and Volume Scattering
    Reflection and Refraction - The Critical Angle

  • PPT Slides (zipped set of gif's)
  • Acoustic Sources and Receivers

    Method for generating  and sensing acoustic energy in water.
    Description of acoustic signals, amplitude, frequency and phase
    The choice of frequency - range issues.
    Dimension and beam width - directivity (an introduction, more in angular resolution later).
    Arrays - line, disk, barrel and spherical.

  • PPT Slides (zipped set of gif's)
  • Propagation and Refraction (2 lectures)

    Source level , spherical (and  cylindrical) spreading and attenuation (absorption and scattering). Typical Ocean noise spectra
    Harmonic Mean concept, modelling a stratified ocean.
    Snells Law, approximation of a water mass by constant layers or constant gradients.

  • Propagation: PPT Slides (zipped set of gif's)
  • Refraction: PPT Slides (zipped set of gif's)
  • Range Resolution (2 lectures)

    CW Pulse and Chirp. The concept of bandwidth and its effect on range resolution. Convolution and deconvolution, Auto-Correlation. Matched Filters, extracting signal from noise. Single beam bottom de. Single beam bottom detection issues.

  • Lecture I: PPT Slides (zipped set of gif's)
  • Lecture II: PPT Slides (zipped set of gif's)
  • Angular Resolution (2 lectures)

    Directionality and Beam Forming.  Line and Circular arrays. Discretely sampled apertures. The relationship between wavlength and array dimension.
    Weighting or Shading. Using the Knudsen sources as type examples. Nearfield and farfield. Focussing.

  • Lecture I: PPT Slides (zipped set of gif's)
  • Lecture II: PPT Slides (zipped set of gif's)
  • Beam Steering : Time, Phase and FFT methods (2 lectures)

    An alternate approach to passively estimating the elevation angle for a given time of arrival is to actively constrain the elevation angle within which the echo might fall. Introducing the idea of handling the signal at each element of a line array separately. Introducing time delays and phase delays.  FFT beam forming, looking at the instantaneous signal across the array - the relationship between spatial wavelength and angle. Why a steered beam forms a cone rather than a tilted plane.
    Introduce narrow beam formation using the product of two orthogonal line arrays - the Mills Cross.

  • Lecture I: PPT Slides (zipped set of gif's)
  • Lecture II: PPT Slides (zipped set of gif's)
  • Horizontal Positioning Requirements

     How accurate do we need to be? By analysing the spatial resolution of sonar systems, the required positioning accuracy will be assessed.
    Compare these accuracies with those achievable through the "many modes of GPS". Pointer toward GGE4042 - (go ask Dave/Marcelo).
    Intro. to the ships reference frame. Intro to submerged positioning methods, USBL, SBL, LBL, LUSBL - common achievable accuracies as function of range and angle. Relate frequencies used  back to achievable ranges and range resolution.

  • PPT Slides (zipped set of gif's)
  • Vertical Positioning Requirements  - Long Period (2 lectures)

    : Overview  datums and enough tides to get through CCLS. Mean sealevel. Choice of low water. Tidal ranges. Driving forces behind tides. Principal tidal frequencies, their relative importance. Spectral analysis of tide time series. Prediction of tides. Typical tide measuring devices.

  • PPT Slides (zipped set of gif's)
  • Vertical Positioning Requirements - Short Period

    Heave Sensors and the future with RTK.  The bandwidth limitation of heave sensors.  Long period heave artifacts. Choice of  high pass filter time constants and damping coefficients. Causal filters. Delayed heave output. The response of a heave sensors to a step function. The problem of speed, trim, loading changes.  The importance of heave sensor location. Induced heave. AC and DC coupled lever arms.

  • PPT Slides (zipped set of gif's)
  • Orientation (Roll, Pitch and Heading) Measurement (1 lectures)

    The required accuracies needed in the three axes. The update rates needed, given typical ocean wave spectra and roll and pitch excursions. Introduction to inertial sensors (accelerations and angular rates). The vertical gyro algorithm, and limitations of the same. Use of aiding speed and heading information. Aided inertial navigation.  The problem of time delays. The problem of alignment, static biases and inter-axis crosstalk.

  • PPT Slides (zipped set of gif's)
  • Single Beam  and Sidescan Surveying - Single Beam Method (2 lectures)

    Explain the traditional model for single beam and sidescan surveying. Contrast the needs of nautical charting and engineering surveys.

    Using what we now know about range and angular resolution, decide what accuracies we should achieve using a single beam as a function of : depth, bottom slope and bottom wavelengths. Describe Boom Systems, Check Lines, Interlines - Shoal Exams. Explain Bar Checks, use of harmonic sound speed, integration of heave sensors. Phasing, sweep rates, range settings. First introduction to the application of heave, draft , lever arms etc....

    Describe the traditional use of chart scale as a control on survey line density. How this is modified by the requirement of sidescan target detection.
    Introduce sidescan concept. Discuss operational issues that would affect survey execution:

    The method for picking the first arrival from a single beam trace. Comparing and contrasting solutions with long and short pulselengths. The effect of bottom type on bottom pick.  What wavelengths you can resolve. What you are missing.
  • PPT Slides (zipped set of gif's)
  • Sidescan Imaging (3 lectures)

    Introducing the sidescan method and image geometry. The effect of towfish altitude on image quality - grazing angle and distribution of beam pattern. Dual frequency systems. Common fish instrumentation (depth, heading, roll, pitch, altitude). Depressor Fins, depressor weights, tow body geometry.  The trade off of range and resolution.  What is a focussed sidescan? The trade off of speed and towcable length. The problem of towbody positioning. The advantages and disadvantages of fixed mountings (for shallow water).
    Picking the first arrival. Slant Range correction, the limitations of the flat seafloor assumption. The problem of water column echoes (off vertical). The deep scattering layer. Beam pattern removal, destriping, despeckling. Contrast stretching, optimising for target/edge detection v. regional sediment distribution.

    The means of recognising short wavelength targets from sidescan images.  The problem of sidescan orientation.  The problem of multiples and  the changing geometry of multiples with towfish depth. The use of cast shadows as a estimator of scale. Limitation of the same.

    Interpretation of common features in sidescan image data. :

    Reduction of sidescan intensity information to make an estimate of bottom backscatter strength.  More limitations of flat seafloor assumption.. Use of BS in sediment classification.
  • PPT Slides (zipped set of gif's)
  • Bathymetric Sidescans, the first step toward Oblique Sounding
    Methods toward estimating elevation  angle. Interference patterns. Lloyds Mirror effects.
    Measuring inter-row Phase.  Interferometry. 2 row and 3+ row  cases. Solving for the elevation angle.
    The problem of common-range ambiguities - the nadir region and inward facing slopes.

  • PPT Slides (zipped set of gif's)
  • Multibeam Geometry : introduction and overview of available systems

     Use of beam steering to constrain elevation angle and cope with common-range ambiguities.
    Common implementations. Flat arrays, tilted arrays, curved arrays. An overview of modern examples.

  • Lecture: PPT Slides (zipped set of gif's)
  • Extra material (overview of modern systems): PPT Slides (zipped set of gif's)
  • Multibeam Integration

    Describing the full set of measurements needed to determine the location of a single bottom strike of one beam of a multibeam ping. The need for transmit and receive array mount orientations (within ship reference frame SRF). The need for SRF orientation at time of transmit and receive of that particular beam.  The proper use of array -relative steering angles (intersection of cones). Calculating the effective elevation of the array in the water column for start of ray tracing, The azimuth and depression angle of the ray and its path.

  • Reading material
  • Multibeam Field Calibration

    Introduction to angular misalignments between motion reference unit and multibeam echosounder. Introduction of patch test as method of estimating angular misalignments. Survey line geometries that isolate effects of patch test variables.

  • PPT Slides (zipped set of gif's)

    Multibeam Bottom Detection

    Methods for selecting a slant range given a specific azimuth and depression angle. Amplitude, phase and BDI methods . The influence of beam footprint on minimum resolvable dimension. The effect of features smaller than the beam smaller than the beam footprint. The influence of beam spacing across track (equi-distant, eqi-angular) on spatial resolution. The influence of speed, motion and ping-rate on along track density.

  • PPT Slides (zipped set of gif's)
  • Multibeam Active Motion Compensation

    Active motion stabilisation strategies for Roll, Pitch and Yaw.
    Real Time use of RPY. The problem of time synchronisation. The problem of forward predictors.
    Given that the vessel is continually varying its orientation about the local level and the mean track, strategies for stabilising the coverage.

  • PPT Slides (zipped set of gif's)
  • Survey Planning : Single beam and Swath Bathymetry (2 lectures)

    depth, swath width performance envelope of common swath sonar frequencies. A review of controlling factors

    Coping with a depth dependent swath. The use of dynamically varying angular sectors to maintain fix sectors to maintain fixed swath widths. The choice of angular sector based on required accuracy and target detection capability. The line spacing and line direction constraints imposed by simultaneously operating sensors (seismic profilers, current profilers, gravity and magnetic sensors).

    Survey rational :

    Coastal and Continental Margin
                    Choice of sonar, feature detection requirement.

  • PPT Slides (zipped set of gif's)

  • Slides for lectures below are currently not available.

    Multibeam Backscatter Imaging

    The differences between sidescan time series mapping and within-beam backscatter extraction. Ability to cope with common slant range. Ability to avoid multiples. Data reduction for source level, receiver fixed gains, time-varying gains, spherical spreading, attenuation, ensonified area and beam pattern. Backscatter Strength.
    The role of grazing angle in the appearance of features. The calcuation of grazing angle accounting for beam vector, refraction and bottom slope. The limitation on slope estimation due to spatial resolution.

    Current Meters : Mechanical, Electromagnetic and Acoustic Doppler .

    Explain mechanical (vane, impellor)  and electromagnetic (S4) and acoustic doppler instruments. The need for current measurement. Measurement over a tidal cycle. Bottom tracking, bottom mounted, integration of roll  and pitch.

    if there is time and interest, although strictly it should be covered elsewhere in Imaging and Mapping (I).


    The official TA for GGE3353 for 2010 is Travis Hamilton. He can be contacted at : t.hamilton@unb.ca or found in D49 (Go down stairwell beside E1A one floor, door is on the right)


    The course assessment will be based :



    Sample midterm and final exam questions given during the first offering of this course.
    Old midterms and finals

    last modified: September 9th, 2010 by Travis Hamilton .