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Gordon Farquharson

Affiliate Principal Engineer

Affiliate Assistant Professor, Electrical Engineering

Email

gordon@apl.washington.edu

Phone

206-685-1505

Education

B.S. Electrical Engineering, University of Massachusetts, Amherst, 1996

M.S. Electrical Engineering, University of Cape Town, South Africa, 1996

Ph.D. Electrical Engineering, University of Massachusetts, Amherst, 2005

Publications

2000-present and while at APL-UW

Turbulence from breaking surface waves at a river mouth

Zippel, S.F., J. Thomson, and G. Farquharson, "Turbulence from breaking surface waves at a river mouth," J. Phys. Oceanogr., 48, 435-453, doi:10.1175/JPO-D-17-0122.1, 2018.

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1 Feb 2018

Observations of surface waves, currents, and turbulence at the Columbia River mouth are used to investigate the source and vertical structure of turbulence in the surface boundary layer. Turbulent velocity data collected on board freely drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys are corrected for platform motions to estimate turbulent kinetic energy (TKE) and TKE dissipation rates. Both of these quantities are correlated with wave steepness, which has previously been shown to determine wave breaking within the same dataset. Estimates of the turbulent length scale increase linearly with distance from the free surface, and roughness lengths estimated from velocity statistics scale with significant wave height. The vertical decay of turbulence is consistent with a balance between vertical diffusion and dissipation. Below a critical depth, a power-law scaling commonly applied in the literature works well to fit the data. Above this depth, an exponential scaling fits the data well. These results, which are in a surface-following reference frame, are reconciled with results from the literature in a fixed reference frame. A mapping between free-surface and mean-surface reference coordinates suggests 30% of the TKE is dissipated above the mean sea surface.

Small boat detection with along-track interferometric SAR

Balaban, M., A. Kovorotniy, Y. Goncharenko, V. Gorobets, F. Kivva, G. Farquharson, and A. Jessup, "Small boat detection with along-track interferometric SAR," IEEE Radar Conference, 8-12 May, Seattle, WA, doi:10.1109/RADAR.2017.7944356 (IEEE, 2017).

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8 May 2017

Along-track interferometric synthetic aperture radar measurements of a small fiberglass-hull boat were made in various wind and wave conditions and for different measurement geometries and boat speeds. The data collected show three different cases: 1) the boat signature is visible both in the backscattered power and interferometric phase images; 2) the boat signature is visible only in the interferometric phase image, and 3) the boat signature is not visible in either image. From a preliminary analysis of the data, we conclude that the angle between radar look direction and the nominal velocity vector of the boat significantly affects boat detection. The worst cases for detection are when those vectors are collinear or oppositely directed. The best detection cases appear to be for the case, when boat velocity vector and radar look direction are orthogonal or when the boat is stationary.

Remote measurements of tides and river slope using an airborne Lidar instrument

Hudson, A.S., S.A. Talke, R. Branch, C. Chickadel, G. Farquharson, and A. Jessup, "Remote measurements of tides and river slope using an airborne Lidar instrument," J. Atmos.Ocean.Technol., 34, 897–904, doi:10.1175/JTECH-D-16-0197.1, 2017.

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24 Apr 2017

Tides and river slope are fundamental characteristics of estuaries, but they are usually undersampled due to deficiencies in the spatial coverage of water level measurements. This study aims to address this issue by investigating the use of airborne lidar measurements to study tidal statistics and river slope in the Columbia River estuary. Eight plane transects over a 12-h period yield at least eight independent measurements of water level at 2.5-km increments over a 65-km stretch of the estuary. These data are fit to a sinusoidal curve and the results are compared to seven in situ gauges. In situ– and lidar-based tide curves agree to within a root-mean-square error of 0.21 m, and the lidar-based river slope estimate of 1.8 × 10−5 agrees well with the in situ–based estimate of 1.4 × 10−5 (4 mm km−1 difference). Lidar-based amplitude and phase estimates are within 10% and 8°, respectively, of their in situ counterparts throughout most of the estuary. Error analysis suggests that increased measurement accuracy and more transects are required to reduce the errors in estimates of tidal amplitude and phase. However, the results validate the use of airborne remote sensing to measure tides and suggest this approach can be used to systematically study water levels at a spatial density not possible with in situ gauges.

More Publications

Inventions

Conformal Series-Fed Electronically Squinted Aperture-Couple Patch Array Antenna

Record of Invention Number: 46904

Gordon Farquharson

Disclosure

7 Apr 2014

Shipborne Ocean Wave Measurement System

Record of Invention Number: 46763

Gordon Farquharson, Bill Plant

Disclosure

11 Dec 2013

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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