cause an electrical short between them. They were calibrated prior to instal- 

 lation by creating an electrical short between the two cables at known dis- 

 tances along the cable and recording the voltage output. Electronic signal 

 conditioning amplifiers are used to ensure that the output signals from the 

 gages are within a 0- to 5-V range. Gage accuracy is about 1 percent, with a 

 0.1 percent full-scale resolution. (Full scale is 9.4 m for Gage 625 and 

 8.5 m for Gage 645.) These gages are susceptible to lightning damage, but 

 protective measures have been taken to minimize such occurrences. A more com- 

 plete description of the gages' operational characteristics is given by Grogg 

 (1986). 

 Buoy gages 



43. Two Datawell Laboratory for Instrumentation (Haarlem, The 

 Netherlands) Waverider buoy gages (Gage 630 located 6 km and Gage 640 located 



1 km from shore) , measure the vertical acceleration produced by the passage of 

 a wave. The acceleration signal is double-integrated to produce a displace- 

 ment signal which is transmitted by radio to an onshore receiver. The manu- 

 facturer states that wave amplitudes are correct to within 3 percent of their 

 actual value for wave frequencies between 0.065 and 0.5 Hz (corresponding 

 15- to 2-sec wave periods) . The manufacturer specifies the error can increase 

 to 10 percent for wave periods in excess of 20 sec. 



Digital Data Analysis and Summarization 



44. Thompson (1977) and Harris (1974) describe the procedure used for 

 analyzing and summarizing the digital wave data contained in this report. The 

 procedure is based on a Fast Fourier Transform (FFT) spectral analysis of 

 4,096 data values (1,024 sec sampled at 4 Hz) for each file processed. 



45. The program computes the first five moments of the distribution of 

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

 "jumps" and "spikes" and for the data points out of the 0- to 5-V range. 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 errone- 

 ous data values. If more than 5 jumps or spikes in a row or a total of 



100 bad data points for the file are found, the program stops interpolating 



30 



