Len Zedel's Home Page

Associate Professor, Memorial University of Newfoundland


Course Web Pages: P4300


Gros Morne summit in March!

Background

I received my B.Sc. degree in physics from the University of Victoria, Canada in 1982, my M.Sc. degree in physics from the University of Victoria, Canada in 1985. At that point, I took a period of time off studies and worked as an Experimental Scientist at the CSIRO Marine Laboratories in Hobart, Tasmania. At CSIRO, I configured and developed the data acquisition system for one of the early RD Instruments, Acoustic Doppler Current Profilers on the RV Franklin. I returned to Canada in 1987 and began work on my Ph.D. at the University of British Columbia Oceanography Department. Working with the IOS Ocean Acoustics group my thesis research involved the use of acoustics to study near surface ocean processes. After graduating in 1991, I took up a position as a Research Associate with Dr. Alex Hay at Memorial University of Newfoundland (MUN), in St. John's, NF studying sediment transport processes using acoustic systems. I accepted a post of Assistant Professor in the Dept of Physics and Physical Oceanography at MUN in 1996.

Research activities involve the exploration of oceanographic processes through the use of acoustic systems. The revolution in electronics and computing capabilities provide many opportunities for instrument development in oceanography. Current interests include; the processes responsible for ambient sound in the ocean, the use of coherent Doppler sonar for high resolution water velocity profiling, the suspension of sediment in the nearshore zone, and the application of acoustic systems to fisheries acoustics. I believe that it is fundamental that any instrument development be motivated by scientific need and not simply by technological capability.


I can be reached at:

Dr. Len Zedel
Dept of Physics and Physical Oceanography
Memorial University of Newfoundland
St. John's, NF
Canada, A1B 3X7

Phone: (709) 864-3106
Fax: (709) 864-8739


Oceanographic Acoustics

Even in the clearest water, light does not penetrate more than about 100 m in the ocean and radio waves are similarly blocked by sea water. Sound however can carry great distances underwater (signals have successfully been transmitted half way around the world). As a result, where applications such as radar use radio waves in the atmosphere, similar systems in the ocean must use sound. The recent revolution in small, high performance computing systems is making many new applications of underwater acoustic systems possible. My research activities involve the exploration of these new applications to make contributions to oceanographic studies. It is fundamental that any instrument development be motivated by scientific need and not simply technological capability


Recent Research Results


Fishmass: Fisheries Acoustics

The technique of fish detection using sonar systems is well developed. Echo integration allows for efficient surveys of fish biomass and more recent developments based on split-beam and dual-beam technology allow for the counting (and sizing) of individual fish targets. These sonar techniques combined with conventional ship trawl surveys provide a snapshot in time of fish or biomass distribution. Also important is a knowledge of fish movements over extended time periods; with conventional systems this information requires frequent (and expensive) ship surveys.

An alternative approach to acquiring long-term time series of fish motion would be to deploy a moored, internally recording instrument. It is important to note that simple fish detection in a self-recording instrument is not sufficient; it is necessary to determine the net motion of fish to distinguish between a resident population and a migration. This capability would provide a cost-effective method to monitor fish complimenting the existing ship based spatial surveys. Example applications in Canadian waters include the monitoring of Northern Cod on the east coast, and the various salmon species on the west coast. Many similar applications exist wherever fish are known to form well-defined migrations.

Tests of such a system monitoring the motion of herring have been undertaken along the coast of Norway. The following figure provides an example of the migration speed of a school of these herring. For more information on this project, go to the Fishmass web page.

Zedel, L., F.Y. Cyr-Racine, 2009: Extracting Fish and Water Velocity from Doppler Profiler Data. ICES Journal of Marine Science, 66, 1846-1852.

Tollefsen, C.D.S., L. Zedel, 2003: Evaluation of a Doppler sonar system for fisheries applications. ICES Journal of Marine Research, 60, 692-699.

Zedel, L., R. Patro, T. Knutsen, 2005: Fish behaviour and orientation dependent backscatter. ICES Journal of Marine Science, 62, 1191-1201.

Zedel, L., T. Knutsen, R. Patro, 2003: ADCP Observations of Herring Movement. ICES Journal of Marine Science, 60, 846-859.

Tollefsen, C.D.S., L. Zedel, 2003: Evaluation of a Doppler sonar system for fisheries applications. ICES Journal of Marine Science, 60: 692-699.


Dopbeam: Coherent Doppler Sonar

The study of nearshore sediment transport poses many challenges to accurate observations. One of the key areas of difficulty results from instrumentation disturbing the flow field. Dopper current profiling avoids this problem by making measurement remotely. Working jointly with Dr. A.E. Hay of Dalhousie University, a short range fully coherent Doppler sonar system has been developed. This 1.7 MHz system provides velocity profiles over a range of 1 m with 0.7 cm depth resolution at a rate of 30 profiles/second with accuracy of order 1 cm/s (in the vertical direction).

Dillon, J., L. Zedel, and A.E. Hay, 2012: On the Distribution of Velocity Measurements from Pulse-to-Pulse Coherent Doppler Sonar. {\it in press}, IEEE J. Oceanic Eng.

Hay, A.E., L. Zedel, R. Cheel, J. Dillon, 2012: On the Vertical and Temporal Structure of Flow and Stress within the Turbulent Oscillatory Boundary Layer Above Evolving Sand Ripples, {\it in press} Continental Shelf Research.

Hay, A.E., L. Zedel, J. Dillon, 2012: Observations of the Vertical Structure of Turbulent Oscillatory Boundary Layers Above Fixed Roughness using a Prototype Wide-band Coherent Doppler Profiler: 2. Turbulence and Stress, J. Geophysical Research Oceans, 117, DOI: 10.1029/2011JC007114.

Hay, A.E., L. Zedel, J. Dillon, 2012: Observations of the Vertical Structure of Turbulent Oscillatory Boundary Layers Above Fixed Roughness using a Prototype Wide-band Coherent Doppler Profiler: 1. The Oscillatory Component of the Flow, submitted to J. Geophysical Research Oceans, DOI: 10.1029/2011JC007113.

Dillon, J., L. Zedel, and A.E. Hay, 2012: Simultaneous Velocity Ambiguity Resolution and Noise Suppression for Multi-Frequency Coherent Doppler Sonar, Journal of Atmospheric and Oceanic Technology, 29, 450-463.

Dillon, J., L. Zedel, and A.E. Hay, 2011: Asymptotic Properties of an Autocorrelation Coefficient for Coherent Doppler Sonar. Journal of Atmospheric and Oceanic Technology, 966-973.

Zedel, L., and A.E. Hay, 2010: Multi-Frequency, Pulse-to-pulse Coherent Doppler Sonar. IEEE Journal of Oceanic Engineering. DOI: 10.1109/JOE.2010.2066710

Zedel, L. 2008: Modeling Pulse-to-pulse Coherent Doppler Sonar, Journal of Atmospheric and Oceanic Technology, 25, 1834-1844.

Smyth, C.E., L. Zedel, A.E. Hay, 2002: Coherent Doppler profiler measurements of near-bed suspended sediment fluxes and the influence of bedforms. Journal of Geophysical Research, 107, C8, 19.1-19.20.

Zedel, L., and A.E. Hay, 2002: A Three Component Bistatic Coherent Doppler Velocity Profiler: Error Sensitivity and System Accuracy. IEEE Journal of Oceanic Engineering, 27, 717-725.

Zedel, L., A.E. Hay, 1998: Direct Observations of Wave Induced Sediment Flux and Turbulent Velocities in a Wave Flume. to be presented at ICCE in Copenhagen.

Zedel, L., A.E. Hay, R. Cabrera, and A. Lohrmann, 1996: Performance of a Single Beam, Pulse-to-Pulse Coherent Doppler Profiler. IEEE Journal of Oceanic Technology, 21, 290-297.

Zedel, L., A.E. Hay, 1996: Acoustic Doppler Velocity Observations in a Turbulent Particle Laden Jet. submitted to Journal of the Acoustical Society of America.

Zedel, L., A.E. Hay, 1995: Coherent Acoustic Profiling of Sediment Suspension Under Waves. in Proceedings of the 1995 Canadian Coastal Conference - October 18-21, Dartmouth.

This figures provides an example of Dopbeam data collected during trials in the NRC prototype scale wave flume facility. 7 s of Dopbeam data are shown collected during a run of 50 cm height waves of 3.5 s period. a) horizontal velocity, b) vertical velocity, c) suspended sediment concentration. Height is indicated on the vertical axis in cm, colour scale values are indicated in panels on right.


OASIS: Ocean Ambient Sound System

The OASIS system measures wind speed and direction from an acoustic instrument package positioned several hundred meters beneath the ocean surface. When waves brake at the ocean surface they generate sound just as breaking waves make sound in the air. It has been established that the sound level is proportional to wind speed and these sound levels have been used to estimate wind speed. Knowledge of wind speed is of course of interest but of equal importance is knowledge of wind direction. Wind direction can be inferred from beneath the ocean surface by considering the behaviour of near surface drift currents. These currents are normally difficult to measure because of complications associated with surface waves. It is however possible to measure these currents remotely using Doppler sonar technique.

Zedel, L., 2001: Using ADCP Background Sound Levels to Estimate Wind Speed. Journal of Atmospheric and Oceanic Technology, 18, 1867-1881.

Zedel, L., L. Gordon, S. Osterhus, 1999: Ocean ambient sound instrument system: Acoustic Esimtation of Wind Speed and Directionfrom a Sub-Surface Package. submitted to, Journal of Oceanic and Atmospheric Technology.

Zedel, L., G. Crawford, L. Gordon, 1996: On the determination of wind direction using an upward looking ADCP. Journal of Geophysical Research, 101, C5, 12163-12176.

Scatter plots between observed wind speeds and OASIS wind speed estimates using ambient sound at a) 2 kHz, b) 4 kHz, c) 8 kHz, and d) 16 kHz: the standard deviation (wind speed - oasis speed) for these estimates are 1.5, 1.4, 1.4, and 1.9 m/s respectively. Data are hourly samples from the OWS Mike in the Norwegian Sea starting May 17, 1996 and lasting for 40 days.


This figure compares anemometer wind direction measurements with estimates made using the OASIS system. Near surface current structure is used to estimate wind direction. Data points represent 12 hour averages and are for the 80 day period starting April 16, 1997. Data were collected in the North Atlantic Ocean (close to Ocean Weather Station Mike).


Last Updated on January, 2009 by Len Zedel.