III. SAMPLING INFORMATION AND SUMMARY DESCRIPTIONS 



1. Digital Wave Data . 



Routinely, four digital records per day at times near 0100, 0700, 1300, and 

 1900 e.s.t. are obtained from the CERC wave gages. Each record is 20 minutes 

 long with a sample frequency of four data points per second. Thompson (1977) 

 describes the method used to analyze the digital data records. Monthly summa- 

 ries of significant wave height and peak spectral period are available for 

 dissemination. 



For the pressure-wave gage, the surface pressure record is attenuated with 

 depth. In order for the pressure record sensed by the gage to reflect surface 

 conditions, linear wave theory is used to compensate for the hydrodynamic at- 

 tenuation; Esteva and Harris (1970) provide a discussion of the compensation 

 technique used by CERC. These data are sampled at 4 hertz for a 20-minute per- 

 iod as are the other wave sensors. 



The FRF wave data are summarized in the standard CERC monthly wave data 

 summary format which consists of (a) a listing of the significant wave height 

 and peak spectral wave period by day and time (Fig. 29), (b) a joint distribu- 

 tion of significant wave height versus peak spectral period (Fig. 30), and (c) 

 a graph of the significant wave height and peak spectral period versus time 

 (Fig. 31). When requested, the spectral energy distribution as a function of 

 wave frequency can be printed or plotted (Fig. 32). 



2. Current Meter Data . 



The current meter data are obtained as x and y components of velocity four 

 times a day for 20 minutes at a frequency of four data points per second. The 

 statistical package is designed to treat the data exactly like wave height in- 

 formation. Consequently, for each current component the mean of the data 

 record, the standard deviation, and the spectral energy distribution are com- 

 puted. The only summarization is in the form of Figure 29 where a listing of 

 the mean current, standard deviation, and peak spectral period as a function 

 of the day and time is generated. 



3. Conductivity and Temperature Data . 



The conductivity and temperature gages are read once daily and the data are 

 recorded as notes on the CERC Littoral Environmental Observation (LEO) forms 

 for the pier end LEO site. The LEO visually observed data are summarized by 

 computer after the data have been punched on cards. An analog recorder (in- 

 stalled in April 1980) is used for continuously recording the water conduc- 

 tivity and temperature. 



4. Monthly Tide Summaries . 



The paper tapes and strip-chart records are sent to the NOS, Rockville, 

 Maryland, where monthly tabulations of hourly tide heights and high and low 

 water level summaries are prepared. Copies of the tabulated summaries are for- 

 warded to CERC. Tidal datums at the FRF are computed by the NOS entice. An 

 example of the NOS hourly and high and low water summaries for 1 month of data 

 is shown in Figure 33. 



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