Imaging waves for bathymetric retrievals
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Imaging Waves for Bathymetric Retrievals. Dr. Steven P Anderson Senior Principal Scientist Environmental Intelligence Group Areté Associates Arlington, VA Presentation to KHOA June 18, 2013. Who is Areté?. Streak Tube Imaging LIDAR (STIL). Areté “ RenderWorld ” scene of open ocean.

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Imaging Waves for Bathymetric Retrievals

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Imaging waves for bathymetric retrievals

Imaging Waves for Bathymetric Retrievals

Dr. Steven P AndersonSenior Principal ScientistEnvironmental Intelligence Group Areté AssociatesArlington, VA

Presentation to KHOAJune 18, 2013

Who is aret

Who is Areté?

Streak Tube Imaging LIDAR (STIL)

Areté “RenderWorld” scene of open ocean

  • “Areté Associates is an advanced science and engineering company that provides innovative solutions to the most challenging technical problems faced by the United States.”

    • Founded in 1976 and employee-owned.

    • 320 employees at seven locations.

  • Core competencies:

    • First-principles physical modeling of signatures, environments, and sensors.

    • Ruggedized sensor development.

    • Comprehensive field experiment design and execution.

    • Delivering operational products to end users.

Approved for Public Release, Distribution Unlimited.

Bathymetric survey

Bathymetric Survey

A shore mounted Bathymetric Radar will provide persistent monitoring of water depths

  • Multi-beam sonar is widely utilized for precision bathymetry;

    • However, swath width/area coverage is limited in shallow water

  • Lidar effective for shallow-water bathymetry at large coverage rates

Wave speed frequency and water depth

Wave Speed, Frequency and Water Depth



  • Ocean surface waves are powered by gravity

  • When water surface is displaced up (or down), gravity acts to drive the wave forward

  • Our own personal experience tells us that waves slow down as they approach a beach where they eventually break

  • Dispersion Relationship:

  • the mathematical relationship between

    • wave speed - c

    • wave period - T

    • wave length – L

    • And water depth - H.





Linear surface wave dispersion relation

Linear Surface Wave Dispersion Relation

water depth



Linear wave dispersion assumes:small amplitude wavesuniform currentsdepth constant

H = ∞



If we can observe the wavenumber-frequency relationship, we can invert and solve for depth and currents directly.


Depth retrievals from airborne imagery

Depth Retrievals from Airborne Imagery

  • Capability developed during World War II.

  • Uses a single image taken by aircraft.

  • Assumes:

    • monochromatic waves (single frequency)

    • linear wave dispersion.

Williams 1947

Estimating depth from a single image

Estimating Depth from a Single Image

Measure Wavelength in Deepwater




Measure Wavelength near-shore


Williams 1947

Estimating depth from a single image 2

Estimating Depth from a Single Image (2)

H= 26ft

H= ∞






Williams 1947

Time series imagery of ocean waves

Time-Series Imagery of Ocean Waves

Measure the wavelength and period information directly

  • Areté developed the Airborne Remote Optical Spotlight System (AROSS) to collect time series imager of ocean waves

  • Spot-dwell EO imager – digital camera(s) with navigation control system to maintain pointing at virtual target on the water

See Dugan et al (2001 JGR)

US ONR funded

Aross images of shoaling waves

AROSS Images of Shoaling Waves

From Duck, N.C. USACE Field Research Facility

Effectively separates space & time

Raw imagery (camera coordinates)

Registered & mapped imagery (ground coordinates)

Aross image stack and 3 d spectrum

AROSS Image Stack and 3-D Spectrum

dashed linedeepwater dispersion

solid lineobserved dispersion

Fourier Transform

Example image stack (data cube)

2-D slice through the 3-D spectrum for shoaling waves

Note the broadening of the observed dispersion relationship associated with wave shoaling

AROSS data from Corps of Engineers' Field Research Facility in Duck, NC

See (Dugan et al 2001;Piotrowski and Dugan 2002).

Aross bathymetry retrievals

AROSS Bathymetry Retrievals

AROSS Retrievals

Note: Algorithm assumes linear wave dispersion

Comparison to Ground-truthLARC Survey

5-10% RMS Errors

Lighter Amphibious Resupply Cargo

Bias: < 0.25m


  • 1m RMS for depths 2-10m

  • 10% of water depth>10m-15m

  • Resolution:

    • 128 m for depths 2-6m

    • 256 m for depths 6-15m

  • See Dugan et al (2001 JGR)

    US ONR funded

    Duck, N.C. USACE Field Research Facility

    Wave imagery by x band radar

    Wave Imagery by X-band Radar

    Areté'sFuruno radar at the Diablo Canyon

    • Advantages:

      • All weather

      • day-night

      • unlimited dwell

    • Challenges:

      • Maritime Radars designed to minimize “clutter”…. thus low, signal to noise ratio for wave imaging

      • Limited resolution, especially at range

      • High elevation needed to maximize range

    X-band radar sees waves as modulations in the radar cross section

    Figure from Borge et al 2004, JPO

    Advancing the bathymetry algorithm

    Advancing the Bathymetry Algorithm

    • Challenge:

      • Develop an advanced algorithm to improve accuracy and resolution over existing capability and deliver a near-realtime solution.

    • Goal:

      • Resolution | 2-3 times water depth

      • Accuracy | 0.25 m (or 2.5% water depth>10m)

    • Approach:

      • Leverage new understanding of nonlinearities in the wave dynamics.

      • Use state-of-the-art computers to accelerate computations

    • Technical Challenges:

      • Develop an universal solution

        • Wave field is dynamic; conditions never exactly repeatable

        • Individual radar systems have their own specifications

      • Creating an meaningful “error-metric”

        • Provide an indication of confidence along with depth measurement

    Develop a new bathymetry algorithm that:

    • Better matches data towave kinematics

    • Provides higher spatial resolution

    • Yields more accurate results

    Development plan

    Development Plan

    • Phase I.

      • Collect radar data in operational relevant location

      • Demonstration depth retrievals using existing capabilities

      • Develop and demonstrate new algorithm that accounts for non-linear wave dynamics to provide higher resolution and more accurate results

    • Phase II.

      • Implement and test “error-metric”

      • Refractor software and optimize for speed

      • Design and fabricate a prototype system

      • Field test prototype system

    Thank you

    Thank you.

    Back up slides

    Back Up Slides

    Overall bathymetric algorithm block diagram

    Overall bathymetric algorithm block diagram.

    Phase i proposed radar deployment site

    Phase I. Proposed radar deployment site

    • One Island on the Bay located on the Chesapeake Bay Bridge-Tunnel.

    Examples of prior work on radar bathymetry

    Examples of Prior work on Radar Bathymetry

    Young et al 1985 jgr

    Young et al (1985, JGR)

    First suggestion of estimating bathymetry by using wave imaging radars

    Oceanwaves gmbh l neburg germany oceans 2005

    OceanWaveS GmbH, Lüneburg, Germany(OCEANS 2005)

    Wave Monitoring System WaMoS

    Paul bell 2009 proudman oceanographic lab

    Paul Bell (2009) – Proudman Oceanographic Lab

    Mcninch and brodie jgr 2007

    McNinch and Brodie (JGR 2007)

    Bar And Swash Imaging Radar (BASIR)

    Mcninch et al 2012 oceans

    McNinch et al (2012; OCEANS)

    Radar Inlet Observing System (RIOS):

    Hessner and borge 2012 igarss

    Hessner and Borge (2012 IGARSS)

    OceanWaves GmbH, Germany

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