mean. If less than five consecutive jumps or spikes are found, the program linearly interpolates 

 between acceptable data and replaces the erroneous data values. The editing stops if the program 

 finds more than five consecutive jumps or spikes, or more than a total of 100 bad points, or the 

 variance of the voltage is below 1 x 10'^ squared volts. The statistics and diagnostics from the 

 analysis are saved. 



Sea surface energy spectra are computed from the edited time series. Spectral estimates are com- 

 puted from smaller data segments obtained by dividing the 4,096-point record into several 512-point 

 segments. The estimates are then ensemble-averaged to produce a more accurate spectrum. These 

 data segments are overlapped by 50 percent (known as the Welch (1967) method) which has been 

 shown to produce better statistical properties than nonoverlapped segments. The mean and linear 

 trends are removed from each segment prior to specdral analysis. To reduce side-lobe leakage in the 

 spectral estimates, a data window was applied. The first and last 10 percent of data points were 

 multiplied by a cosine bell (Bingham, Godfrey, and Tukey 1967). Spectra were computed from each 

 segment with a discrete Fast Fourier Transform and then ensemble-averaged. Sea surface spectra 

 from subsurface pressure gages were obtained by applying the linear wave theory transfer fimction. 



Unless otherwise stated, wave height in this report refers to the energy-based parameter fl^ 

 defined as four times the zeroth moment wave height of the estimated sea surface spectrum (i.e., four 

 times the square root of the variance) computed from the spectrum passband. Energy confutations 

 from the spectra are limited to a passband between 0.05 and 0.50 Hz for surface gag^ and between 

 0.05 Hz and a high-frequency cutoff for subsurface gages. This high-frequency limit is imposed to 

 eliminate aliased energy and noise measurements from biasing the computation of H^^^ and is defined 

 as the frequency where the linear theory transfer fimction is less than 0. 1 (spectral values are multi- 

 plied by 100 or more). Smoother and more statistically significant spectral estimates are obtained by 

 band-averaging contiguous spectral components (three components are averaged per band, producing a 

 frequency band width of 0.0117 Hz). 



Wave period r_ is defined as the period associated with the maximum energy band in tiie spec- 

 trum, which is computed using a 3 -point running average band on the spectrum. The peak period is 

 reported as the reciprocal of the center frequency (i.e., 21 = 1/frequency) of the spectral band with 

 the highest energy. A detailed description of the analysis techniques is presented in Andrews 

 (1987).2 



Results 



The wave conditions for the year are shown in Figure 9. For all four gages, the distributions of 

 wave height for the current year and all years combined are presented in Figures 10 and 11, respec- 

 tively. Distributions of wave period are presented in Figure 12. 



Multiple-year comparisons of data for Gage 111 actually incorporate data for 1985 and 1986 from 

 Gage 640 (a discontinued Waverider buoy previously located at the approximate depth and distance 

 offshore of Gage 111) and data for 1987 from Gage 141, located 30 m'south of Gage 111. 



^ M. E. Andrews. 1987. "Standard wave data analysis procedures for coastal engineering appli- 

 cations," unpublished report prepared for the U.S. Army Engineer Waterways Experiment Station, 

 Vicksburg, MS. 



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