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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

Pulse compression for an X-band marine wave-sensing radar

Mower, J.M., G. Farquharson, B. Frazer, and J.G. Kusters, "Pulse compression for an X-band marine wave-sensing radar," Proc., MTS/IEEE OCEANS, 27-31 October 2019, Seattle, WA, doi:10.23919/OCEANS40490.2019.8962784 (IEEE, 2020).

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20 Jan 2020

As part of the Office of Naval Research's Environmental and Ship-Motion Forecasting project, we have developed a four-antenna vertically-polarized coherent X-band radar to measure the orbital Doppler velocities of the sea-surface. This Advanced Wave-Sensing Radar (AWSR) initially used a gated CW pulse to radiate the scatterers using a traveling-wave tube amplifier (TWT) in full-saturation. To improve the performance of the system under low wind conditions, we implemented a pulse compression scheme to increase the average transmitted power. In this application, the range-sidelobes associated with compressed waveforms was required to be less than 40dB. Nonlinear FM chirp were considered but these waveforms require larger time-bandwidth products than the near-range requirements of the wave-sensing application would allow. A weighted linear FM chirp was chosen but linearization of the pulsed TWT is required. In this paper we will demonstrate the AWSR pulse-compression scheme detailing the waveform generation, real-time IF correlation and averaging, and digital predistortion.

Phase calibration of an along-track interferometric FMCW SAR

Deng, H., G. Farquharson, J. Sahr, Y. Goncharenko, and J. Mower, "Phase calibration of an along-track interferometric FMCW SAR," IEEE Trans. Geosci. Remote Sens., 56, 4876-4886, doi:10.1109/TGRS.2018.2841837, 2018.

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1 Aug 2018

We introduce a phase calibration scheme for an interferometric frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) to correct range-dependent phase errors in FMCW SAR interferograms. We demonstrate that the receiver filters operating on the FMCW beat frequency signal account for most of the phase mismatch between the different receiver channels. The scheme presented estimates the phase error in each channel. We present results of the scheme for three estimation approaches (curve fitting, joint least squares, and maximum likelihood) for two different phase models. The results are quantified by computing the reduction in spectral energy associated with the phase mismatch. We find that phase error can be reduced by 14 dB using the approach.

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.

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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