TM Wo. 377 

 CHAPTER III 

 DATA PROCESSING AND ANALYSIS 



Meaningful measurements of wave motions depend to a grea"C extent upon uhe 

 reliability of the sensing device. Instrumentation characteristics, such as 

 response time, precision, and accuracy of measurement, must be known if the 

 value and limitations of the data are to be fully realized. No less important, 

 however, is the method used for data analysis. Without careful and critical 

 evaluation of the data, valuable information may be lost; or, more importantly, 

 biased or even wrong conclusions may be drawn. 



The observational data on wave motions are derived from several different 

 types of measurements made with various instruments. First and foremost are 

 the measurements of surface wave motions using the wave meters discussed in 

 chapter II. A single series of observations was made in Narragansett Bay; 

 the bulk of the measurements were made in the open sea at the Buzzards Bay 

 Entrance Light Station (BBELS) Since these primary observations were made 

 to determine the character of the relatively high frequency motions of waves 

 and, hopefully, to provide information regarding the energetics inherent in 

 the surface layers, the analysis of these data is somewhat extensive. 



The remaining observations were of a supplementary nature and provide 

 background information to more fully analyze and better discuss the wave 

 data. These measurements include : free surface electronic wave staff 

 observations, conventional horizontal current measurements, wind speed and 

 direction records, tidal amplitude, and numerous visual estimates of wave 

 parameters and weather conditions 



Table III-l, which includes both primary and supplementary measurements, 

 shows the various types of data acquired and the requirements for data analysis, 

 The first three columns list the variables measured, the location and series 

 identification number, and the instrument used. The time interval ^ T is the 

 frequency of sampling of the data. The period T is the total span of time 

 during which the data were obtained,. 



This chapter contains a discussion of the data processing procedures-- 

 from raw data handling through to final analysis and presentation of spectra- 

 used to analyze the results of the various observations. 



Processing of Wave Particle Velocity Observations 



Raw Data Preparation — The data output from the various wave meter systems 

 (OMDUM I, II and III, and LMDUM i) discussed in chapter II was essentially 

 identical » 'The preparation of the raw data, from these instruments can there- 

 fore be discussed together. Figure III-l is a diagram delineating the processing 

 procedures. Also included in the diagram is a description of the manner of 

 processing the free surface elevation data provided by the U. S. Army Corps of 

 Engineers Wave Staff System, which is mounted on the Buzzards Bay Entrance 

 Light Station, 



