Non-Directional Wave Buoy at 17 m Depth at USACE Field Research Facility 1980-1996

USACE / FRF has maintained wave buoys around the 17 m and/or 20 m depth contour since 1980. Over the years, we have used three different types of waverider buoys manufactured by Datawell B.V. (Haarlem, Netherlands). From 1980 until 1996, we used non-directional buoys, first the 0.7 m hull diameter design and then the 0.9 m hull diameter design. The buoys operate by recording the output of an accelerometer suspended in fluid and gimbaled (Hippy-40). For data prior to September 1986, data were recorded at 2 or 4 Hz and record lengths were either 34 or 17 minutes, respectively. Collection intervals were either three hours or six hours. From September 1986 to November 1996 data was collected hourly. Frequency spectra were computed using the Welch method with 50% overlapped ensembles [1]. From the end of 1996 onward, we have maintained 0.9 m hull diameter Directional Waverider MkII and MKIII buoys [2] that, in addition to vertical acceleration, also measure two orthogonal components of horizontal acceleration. From Feb 1997 to May 2005, time series were collected at 1.28 Hz and cross-spectral analysis was performed on shore [3, 4]. Between May 2005 and May 2013, directional Fourier coefficients computed on-board the buoy and transmitted onshore. Since May 2013, data analysis has been manged through the Coastal Data Information Program (CDIP), UCSD San Diego, CA. Data are transmitted via an Iridium satellite link at half-hour intervals. Two dimensional (2D) frequency-direction spectra are computed using an Iterative Maximum Likelihood Estimator (IMLE) method [5]. […]