12 Apr 2023
 | 12 Apr 2023
Status: this preprint is currently under review for the journal ESSD.

Measurements of Nearshore Waves through Coherent Arrays of Free-Drifting Wave Buoys

Edwin John Rainville, Jim Thomson, Melissa Moulton, and Morteza Derakhti

Abstract. Along coastlines, surface gravity wave breaking occurs in complex spatial and temporal patterns that significantly impact erosion, scalar transport, and flooding. Numerical models are used to predict these processes, but many models lack sufficient evaluation with observations during storm events. To fill the need for more nearshore wave measurements during extreme conditions, we deployed coherent arrays of small-scale, free-drifting wave buoys named microSWIFTs. The result is a large dataset covering a range of conditions. The microSWIFT is a small wave buoy equipped with a GPS module and Inertial Measurement Unit (IMU) used to directly measure the buoy’s global position, horizontal velocities, rotation rates, accelerations, and heading.We use an Attitude and Heading Reference System (AHRS), 9 degrees-of-freedom Kalman filter to rotate the measured accelerations from the reference frame of the buoy to the Earth reference frame. We then use the corrected accelerations to compute the vertical velocity and sea surface elevation. The measurements were collected over a 27-day field experiment in October of 2021 at the US Army Corps of Engineers Field Research Facility in Duck, NC. The microSWIFTs were deployed as a series of coherent arrays, meaning they all sampled simultaneously with a common time reference, leading to a robust spatial and temporal dataset during each deployment. We evaluate wave spectral energy density estimates from individual microSWIFTs by comparing them with a nearby acoustic waves and currents (AWAC) sensor. We also compare significant wave height estimates from the coherent arrays with the nearby AWAC estimates. A zero crossing algorithm is applied to each buoy time series of sea surface elevation to extract realizations of measured surface gravity waves, yielding 116,307 wave realizations throughout the experiment. These measurements spanned offshore significant wave heights ranging from 0.5 meters to 3 meters and peak wave periods ranging from 5 to 15 seconds over the entire experiment. These data are available at (Rainville et al., 2023) and will be used as a validation dataset for wave-averaged and wave-resolving models and will be used to investigate nearshore wave dynamics.

Edwin John Rainville et al.

Status: open (until 06 Jul 2023)

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Edwin John Rainville et al.

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Measurements of Nearshore Waves through Coherent Arrays of Free-Drifting Wave Buoys (UW_drifters) Edwin Rainville, Jim Thomson, Melissa Moulton, and Morteza Derakhti

Edwin John Rainville et al.


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Short summary
Measuring ocean waves nearshore is essential for understanding how the waves impact our coastlines. We designed and deployed many small wave buoys into the nearshore ocean over 27 days in Duck, North Carolina, USA, in 2021. The wave buoys measure their motion as they drift. In this paper, we describe how we use the measurements from the buoys to measure nearshore wave properties. We find that the buoy measurements are accurate and reliable compared to other nearby instruments.