Aret Associates Approved for Public Release, Distribution Unlimited. Imaging Waves for Bathymetric Retrievals Dr. Steven P Anderson Senior Principal Scientist Environmental Intelligence Group Aret Associates Arlington, VA Presentation to KHOA June 18, 2013 Aret Associates Approved for Public Release, Distribution Unlimited. Who is Aret? Aret 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. Streak Tube Imaging LIDAR (STIL) Approved for Public Release, Distribution Unlimited. Aret RenderWorld scene of open ocean Aret Associates Approved for Public Release, Distribution Unlimited. Bathymetric Survey 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 A shore mounted Bathymetric Radar will provide persistent monitoring of water depths Aret Associates Approved for Public Release, Distribution Unlimited. Wave Speed, Frequency and Water Depth Wikipedia.com 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. AIR WATER GRAVITY C (WAVE SPEED) L (WAVE LENGTH) H (DEPTH) Aret Associates Approved for Public Release, Distribution Unlimited. Linear Surface Wave Dispersion Relation Frequency 1/T Wavenumber 1/L vector currents water depth gravity Linear wave dispersion assumes: small amplitude waves uniform currents depth constant H = shallow- water If we can observe the wavenumber-frequency relationship, we can invert and solve for depth and currents directly. Aret Associates Approved for Public Release, Distribution Unlimited. Depth Retrievals from Airborne Imagery Williams 1947 Capability developed during World War II. Uses a single image taken by aircraft. Assumes: monochromatic waves (single frequency) linear wave dispersion. Capability developed during World War II. Uses a single image taken by aircraft. Assumes: monochromatic waves (single frequency) linear wave dispersion. Aret Associates Approved for Public Release, Distribution Unlimited. Estimating Depth from a Single Image Williams 1947 Measure Wavelength in Deepwater L=260ft Measure Wavelength near-shore L=180ft A A B B Aret Associates Approved for Public Release, Distribution Unlimited. Estimating Depth from a Single Image (2) L=260ft deepwater T=7s L=180ft B B H= 26ft H= A A Williams 1947 Aret Associates Approved for Public Release, Distribution Unlimited. Time-Series Imagery of Ocean Waves Measure the wavelength and period information directly Aret 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 Aret Associates Approved for Public Release, Distribution Unlimited. AROSS Images of Shoaling Waves Raw imagery (camera coordinates) Registered & mapped imagery (ground coordinates) Effectively separates space & time From Duck, N.C. USACE Field Research Facility Aret Associates Approved for Public Release, Distribution Unlimited. AROSS Image Stack and 3-D Spectrum See (Dugan et al 2001; Piotrowski and Dugan 2002). 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 dashed line deepwater dispersion solid line observed dispersion AROSS data from Corps of Engineers' Field Research Facility in Duck, NC Fourier Transform Aret Associates Approved for Public Release, Distribution Unlimited. AROSS Bathymetry Retrievals AROSS Retrievals Note: Algorithm assumes linear wave dispersion 5-10% RMS Errors Comparison to Ground-truth LARC Survey Duck, N.C. USACE Field Research Facility Lighter Amphibious Resupply Cargo See Dugan et al (2001 JGR) US ONR funded Bias: < 0.25m Accuracy: 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 Bias: < 0.25m Accuracy: 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 Aret Associates Approved for Public Release, Distribution Unlimited. Wave Imagery by X-band Radar Figure from Borge et al 2004, JPO 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 Aret's Furuno radar at the Diablo Canyon X-band radar sees waves as modulations in the radar cross section Aret Associates Approved for Public Release, Distribution Unlimited. 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 to wave kinematics Provides higher spatial resolution Yields more accurate results Aret Associates Approved for Public Release, Distribution Unlimited. 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 Aret Associates Approved for Public Release, Distribution Unlimited. Thank you. Aret Associates Approved for Public Release, Distribution Unlimited. Back Up Slides Aret Associates Approved for Public Release, Distribution Unlimited. Overall bathymetric algorithm block diagram. Aret Associates Approved for Public Release, Distribution Unlimited. Phase I. Proposed radar deployment site One Island on the Bay located on the Chesapeake Bay Bridge-Tunnel. Aret Associates Approved for Public Release, Distribution Unlimited. Examples of Prior work on Radar Bathymetry Aret Associates Approved for Public Release, Distribution Unlimited. Young et al (1985, JGR) First suggestion of estimating bathymetry by using wave imaging radars Aret Associates Approved for Public Release, Distribution Unlimited. OceanWaveS GmbH, Lneburg, Germany (OCEANS 2005) Wave Monitoring System WaMoS Aret Associates Approved for Public Release, Distribution Unlimited. Paul Bell (2009) Proudman Oceanographic Lab Aret Associates Approved for Public Release, Distribution Unlimited. McNinch and Brodie (JGR 2007) Bar And Swash Imaging Radar (BASIR) Aret Associates Approved for Public Release, Distribution Unlimited. McNinch et al (2012; OCEANS) Radar Inlet Observing System (RIOS): Aret Associates Approved for Public Release, Distribution Unlimited. Hessner and Borge (2012 IGARSS) OceanWaves GmbH, Germany