by the sensor must be known. Figure 25 shows that the response of the 

 B-7 current meter is phase-dependent, and the lag (and scatter) increas- 

 ing toward lower frequencies. 



An extensive calibration test has been completed by National Oceanic 

 and Atmospheric Administration (NOAA) , National Oceanographic Instrumen- 

 tation Center (NOIC) on the B-10 current meters. A later evaluation of 

 the meters will be expanded to include prototype waves, environmental 

 tests, response to vibration, and virtual mass effects. Results of the 

 calibration test show a nearly true cosine response of the B-10 meters 

 (Fig. 26). 



The wave gage was calibrated statically, applying compressed air to 

 the pressure transducer. The output voltage was then recorded as a 

 function of pounds per square inch units of pressure. 



b. Field Tests . Calibration of the circuitry is important in collect- 

 ing good data. The following steps are observed before each deployment 

 of the sea sled: 



(1) Check power supply voltage output; 



(2) calibrate current meter pulse to analog conversion 

 circuitry with a 16-hertz source (16 hertz = 1 knot) ; 



(3) check radio frequency output from voltage controlled 

 oscillators; 



(4) check radio frequency input to discriminators; 



(5) check wave gage voltage output; 



(6) check directional response of current meters; and 



(7) record offset. 



To verify that the performance of all current meters are identical 

 under field conditions, the sensors are mounted side by side on one of 

 the spars (Fig. 27) and towed offshore. Consequently, data are recorded 

 for 3 to 4 orientations of the sled (with respect to the base line) , thus 

 evaluating if any differences in voltage output or phase are present in 

 the meters . 



IV. EXPERIMENTAL DESIGNS 



Three experimental designs for the measurement of coastal currents 

 and the corresponding operations are discussed in this section. 



1. Continuous Surveys Along Shore-Normal Profiles . 



a. Rationale and Needs . The purpose of surveying flow properties 

 along a profile is threefold: (a) To record the variation in current 

 magnitude near the surface or on the surface with distance from shore; 

 (b) to record the spatial structure of currents near the boundary and 



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