4. Record and number the vertical distance between each minimum and the succeeding 

 maximum on another data sheet, in every other column, and label these columns "relative 

 wave height." All wave lengths less than a specified magnitude will not be considered, nor 

 will the wave heights associated with these lengths. 



5. Record the wave lengths and wave heights of all waves corresponding to lengths larger 

 than the specified minimum value. The wave lengths will be taken to be the distance between 

 successive minima of the wave surface. The corresponding wave height is taken to be the 

 distance between a minimum and the succeeding maximum. 



6. Multiply each number by a given constant (scale factor) and record it in the blank col- 

 umns which are then labeled "absolute wave length" or "absolute wave height." 



Definition of Small Wave Lengths 



1. Start from the left of the record again and measure the horizontal distances between 

 all the successive minima, regardless of whether the profile is bounded by mean sea level or 

 not. Measure the associated heights. 



2. Observe the rules set forth in Steps 4 and 5 for the definition of largest wave lengths. 



PROCEDURE FOR DETERMINING THE LENGTH CUTOFF VALUE 



1. For the time and geographic location at which the stereophotographs were taken: de- 

 termine the wind field, including velocity, duration, and fetch (distance over which wind has 

 blown). 



2. With the wind data enter Pierson's Co-Cumulative Duration Spectra 8 and determine the 

 energy value E. 



3. With 3 percent of the E value determined in Step 2, enter the Co-Cumulative Fetch 

 Spectra of Reference 8 at the wind velocity determined in Step 1, and obtain a frequency 

 cutoff value f. 



4. Using the / value obtained in Step 3, determine the length cutoff value in feet by means 

 of the following conversion formula: 



3.41 



L = 



f 



5. In measuring heights and lengths from the sea surface profiles do not record any values 

 for waves whose length is less than the value L determined from Step 4 above. 



41 



