sea-surface elevations, then edits the digital data file by checking for data 

 points out of the 0- to 5-V range or "jumps" or "spikes." A Jump is defined 

 as a data value greater than 2.5 standard deviations from the previous data 

 value, while a spike is a data value 5 standard deviations or more from the 

 mean. If less than 5 jumps or spikes in a row are found, the program linearly 

 interpolates between acceptable data and replaces the erroneous data values. 

 If more than 4 jumps or spikes in a row or a total of 100 bad data points for 

 the file are found, the program stops interpolating and editing. At this 



point, the program analyzes the data and prints a flag indicating there is a 



2 

 problem with the file. If the variance is less than 0.001 m , the record is 



not analyzed. After editing, the first five moments of the distribution of 



sea-surface elevations are again computed. A cosine bell data window is 



applied to increase the resolution for the energy spectrum of the file; use 



of the data window is discussed by Harris (1974). After application of the 



data window, the program computes the variance spectrum (energy spectrum) 



using the FFT procedure. After the data files are analyzed, the results are 



eliminated for files flagged as bad or appear inconsistent with simultaneous 



observations from nearby gage sites. Frequently, the spectrum and/or 



distribution function of sea-surface elevations are examined to determine if 



the data are acceptable. After the analysis results are edited, monthly 



summaries of wave heights and periods are generated for inclusion in summary 



reports. 



44. Unless otherwise specified, "wave height" means the energy-based 



parameter FL (defined as four times the standard deviation of the sea- 



o 

 surface elevations). 



45. The wave period T^ is defined as the period associated with the 

 maximum energy in the spectrum. This is resolved by partitioning the spectrum 

 into frequency bands of equal width and determining the band with the maximum 

 energy density. The period reported is the reciprocal of the center frequency 

 (e.g., Tp = 1 /frequency) of the spectral band. Since the spectral bands are 

 equal frequency width, namely 0.010742 Hz (e.g., 11/1,024 sec), the analysis 

 provides uniform resolution in frequency. However, the resolution in period 

 is not uniform since the period intervals become larger for lower frequencies. 

 Because of the convention of reporting the period at the center of the inter- 

 val, only a discrete set of period values is possible (Table 1), The wave 

 periods used in this report have been rounded to the nearest second before 



23 



