TR No. 22 
proceeding against and along the center of the current from the vicinity 
of Station II to Station I. Four runs were made.proceeding with the 
current and four against (including the first, the data from which was not 
analyzed). On each run, the instant when the boat passed between the 
channel buoys was observed and recorded. 
A light southerly breeze prevailed during the time measurements were 
made; surface waves were limited to wave heights. of a few centimeters and 
therefore no wave particle motions should have. been recorded, although 
the current meter was only 1 1/2 meters below the water surface. 
DATA ANALYSIS 
Analog to Digital Conversion 
The data analysis follows the procedure given by Blackman and Tukey (17). 
Figure 12 is a block diagram indicating the process involved in obtaining data in 
digital form appropriate for computer analysis. The original data was recorded 
on 1/2 inch magnetic tape at 30 inches-sec”~ and has the waveform shown in 
figure 3 (top trace). It was reproduced at 30 inches-sec71, amplified 10 dB, 
and modified using a Schmidt trigger so that the waveform was.as shown in 
figure 3 (lower trace). A binomial counter was used to divide the original 
frequency by six thus resulting in the square wave shown in figure 4 (lower 
trace), where one cycle of the square wave corresponds to one rotation of the 
impeller or 19.61 cm advance of the current meter through the water. The 
average frequency of the original data was (at 30 inches-sec7+) 120 Hz and 
that of the modified data 20 Hz. The modified data were recorded on 1 inch 
FM magnetic tape at 30 inches-sec”™- on an Ampex FR-1100 recorder. 
The square wave data were converted, using.a Honeywell analog-to-digital 
converter, to digital data at a conversion rate of 2500 counts-sec ~ and re- 
corded on digital magnetic tape. Reproducing speed-was 7 1/2 inches-sec7; 
as a result the average frequency of the square wave was 5 Hz, and therefore 
the number of counts per square wave cycle was approximately 500. The maximum 
error in determining the period of one square wave cycle is *1 count or ap- 
proximately 40.2%. At an average towing velocity of 400 em-sec7l, this error 
corresponds to variations in velocity of 0.5 cm-sec7l. 
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