IfM^k 1 



f|hvi^ 



^— CONTINUOUS 

 /PRESSURE RECORD 



WVv 



fT SAMPLES COLLECTED BY WAVE QAQE 



\iii^hM4^k 





1,024 

 OR 



NO SAMPLES 



1,024 

 OH 



NO SAMPLES 





2..-M8 

 SAMPLES 



TAKEN 



2.048 

 SAMPLES 



TAKEN 





2HROR4 HR, ETC 



SHROR 4 HR, ETC 















Figure 30. Example of continuous wave pressure record and wave burst sampling of 

 pressure data 



It is beyond the scope of this report to discuss details of the above procedures. 

 This section will summarize some aspects of data collection, quality control, 

 analysis, and terminology. Because of the complexity of the subject, the 

 reader is referred to Bendat and Piersol (1986), Horikawa (1988), the Shore 

 Protection Manual (1984), and Weaver (1983) for additional references. 



Data collection planning 



A continuous time series of raw pressure values plotted with time along the 

 x-axis is shown in Figure 30. Because it is impractical and too expensive to 

 collect data continuously throughout the day, discrete time series or "bursts" 

 are collected at predetermined intervals (often every 2, 4, or 6 hr; Figure 30). 

 Wave bursts typically consist of 1,024 or 2,048 consecutive pressure, U- 

 velocity, and V-velocity 1 samples. At a sampling frequency of 1 Hz, these 

 produce time series of 17.07 min and 34.13 min, respectively. Clearly, it 

 would be desirable to acquire wave bursts frequently, but the sheer amount of 

 data would soon overwhelm an analyst's ability to organize, interpret, and 

 store the records. A researcher who plans a data acquisition program must 

 balance the need to collect data frequently versus the need to maintain gages 

 in the field for an extended period. There is a temptation to assume that as 

 long as the gages are at sea, they should be programmed to collect absolutely 

 as much data as possible. However, data management, analysis, and 



82 



Orthogonal horizontal water velocity measurements. 



Chapter 5 Analysis and Interpretation of Coastal Data 



