The several K^ values along the envelope were averaged to determine the 

 K^ for the envelope. 



b. Automated Method. An automated method of determining wave reflec- 

 tion coefficients was developed as part of this study. At times it is 

 difficult to identify the location of the node and antinode on a wave 

 envelope in intermediate or shallow water, particularly for conditions of 

 low wave reflection. The automated method eliminates the subjective 

 aspect of determining the location of nodes and antinodes. Because the 

 automated method uses all wave heights of the envelopes and not just the 

 extreme values, it is statistically more meaningful. 



(1) Description of the Method. Figure 13 shows one wavelength 

 of an idealized wave envelope for a sinusoidal wave and partial reflection. 

 The reflection coefficient is the ratio of the reflected wave height to 

 the incident wave height, and in both methods the incident wave height is 

 an average height of measured waves. In the manual method the incident 

 wave height is the average of the two extremes, the nodes and antinodes 

 of the envelope; i.e.. 



[Hr] 



Hi + He 



I-l MANUAL 



In the automated method the incident wave height is the average of all 

 waves; i.e., 



Th 1 - Hi + H2 + . ■ . + He 

 i^J-l AUTOMATED — 2 ~ ' 



The carriage must be moved at a constant speed to gather unbiased data. 



In the manual method the reflected wave height is the difference of 

 the two extreme heights divided by 2; i.e., 



TH 1 - Hi - H5 

 1-% J MANUAL '^ — - • 



An exact procedure arrives at basically the same number in the auto- 

 mated method. The difference between the average wave height and the 

 individual wave height is plotted versus distance along the envelope. In 

 an ideal case where the wave shape is sinusoidal and the carriage is moved 

 at a constant speed, this curve would be a sine curve, with a maximum 

 value at the antinode of the envelope and a minimum at the node of the 

 envelope. The amplitude of the sine wave is the height of the reflected 

 wave: 



[H/?] AUTOMATED = Hi - tij^yg = Hjiyg - H5 = -i-^ ^ . 



Ideally, the two methods would produce the same value, 



32 



