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Kristin Zeiden

Research Scientist/Engineer - Senior






B.S. Astrophysics, University of California, Los Angeles, 2011

Ph.D. Oceanography, University of California, San Diego, 2021


2000-present and while at APL-UW

Calibration and Processing of Nortek Signature1000 Echosounders

Bassett, C., and K. Zeiden, "Calibration and Processing of Nortek Signature1000 Echosounders," Technical Report, APL-UW TR 2307, Applied Physics Laboratory, University of Washington, Seattle, December 2023, 40 pp.

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27 Dec 2023

The five-beam Nortek Signature series acoustic Doppler current profilers (ADCPs) include a vertical beam that can be operated as an echosounder. These echosounders record an echo intensity level as a function of range in hundredths of a decibel. While these recorded levels provide valuable qualitative information about scattering from the water column, without calibration the units’ recorded echo intensities cannot be linked quantitatively to scattering processes. In this report we summarize calibration results for six Nortek Signature1000 units. The echosounders were calibrated in the field while deployed on 4th generation Surface Wave Instrument Floats with Tracking (SWIFTs) by suspending 38.1-mm tungsten carbide spheres with 6% cobalt binder below. Here, we summarize the equations used to process Nortek Signature series echosounder data, general calibration procedures for echosounders, the methodology used to calibrate the six units, the results of the calibrations, and uncertainties and recommendations for future work. In addition, we present post-processed, calibrated echosounder data from a deployment of the SWIFTs equipped with the Signature1000s in Mobile Bay, Alabama.

Estimating profiles of dissipation rate in the upper ocean using acoustic Doppler measurements made from surface following platforms

Zeiden, K., J. Thomson, and J. Girton, "Estimating profiles of dissipation rate in the upper ocean using acoustic Doppler measurements made from surface following platforms," J. Atmospheric. Ocean. Technol., 40, 1383-1401, doi:10.1175/JTECH-D-23-0027.1, 2023.

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13 Oct 2023

High resolution profiles of vertical velocity obtained from two different surface-following autonomous platforms, Surface Wave Instrument Floats with Tracking (SWIFTs) and a Liquid Robotics SV3 Wave Glider, are used to compute dissipation rate profiles ε (z) between 0.5 and 5 m depth via the structure function method. The main contribution of this work is to update previous SWIFT methods (Thomson 2012) to account for bias due to surface gravity waves, which are ubiquitous in the near-surface region. We present a technique where the data are pre-filtered by removing profiles of wave orbital velocities obtained via empirical orthogonal function (EOF) analysis of the data prior to computing the structure function. Our analysis builds on previous work to remove wave bias in which analytic modifications are made to the structure function model (Scannell et al. 2017). However, we find the analytic approach less able to resolve the strong vertical gradients in ε (z) near the surface. The strength of the EOF filtering technique is that it does not require any assumptions about the structure of non-turbulent shear, and does not add any additional degrees of freedom in the least-squares fit to the model of the structure function. In comparison to the analytic method, ε (z) estimates obtained via empirical filtering have substantially reduced noise and clearer dependence on near-surface wind speed.

Vorticity in the wake of Palau from Lagrangian surface drifters

Zeiden, K.L., D.L. Rudnick, J.A. MacKinnon, V. Hormann, and L. Centurioni, "Vorticity in the wake of Palau from Lagrangian surface drifters," J. Phys. Oceanogr., 52, 2237-2255, doi:10.1175/JPO-D-21-0252.1, 2022.

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1 Sep 2022

Wake eddies are important to physical oceanographers because they tend to dominate current variability in the lee of islands. However, their generation and evolution has been difficult to study due to their intermittency. In this study, 2 years of observations from Surface Velocity Program (SVP) drifters are used to calculate relative vorticity (ζ) and diffusivity (k) in the wake generated by westward flow past the archipelago of Palau. Over 2 years, 19 clusters of five SVP drifters ~5 km in scale were released from the north end of the archipelago. Out of these, 15 were entrained in the wake. We compare estimates of ζ from both velocity spatial gradients (least squares fitting) and velocity time series (wavelet analysis). Drifters in the wake were entrained in either energetic submesoscale eddies with initial ζ up to 6f, or island-scale recirculation and large-scale lateral shear with ζ ∼ 0.1f. Here f is the local Coriolis frequency. Mean wake vorticity is initially 1.5f but decreases inversely with time (t), while mean cluster scale (L) increases as Lt. Kinetic energy measured by the drifters is comparatively constant. This suggests ζ is predominantly a function of scale, confirmed by binning enstrophy (ζ2) by inverse scale. We find KL4/3 and upper and lower bounds for L(t) are given by t3/2 and t1/2, respectively. These trends are predicted by a model of dispersion due to lateral shear. We argue the observed time dependence of cluster scale and vorticity suggest island-scale shear controls eddy growth in the wake of Palau.

More Publications

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