Table 11-1 



Operational Specification of the Instruments Used in This Study 



Instrument 



Elevation 



Sample rate 



Sample 

 volume 



Calibration Coefficient 



LDV 



1, 2, 3, 4, 8, 

 and 1 6 cm 



25 Hz 



1 00 fjm x 1 

 mm 



0.92 cm/sec per 

 digitization step 



BASS 



100 cm 



1 Hz 



15 cm 



0.0207 cm/sec per 

 digitization step 



Pressure 



50 cm 



25 Hz 



3 mm port 



0.028 cm per 

 digitization step 



OFS1 



16.6 cm 

 above LDV 



10 Hz 



undefined 



Not calibrated 



OFS2 



122 cm 



10 Hz 



undefined 



Not calibrated 



the bed. Using this point as a reference, the profiler is then backed up pre- 

 programmed distances. The distances for this experiment were approximately 

 log spaced: 1, 2, 3, 4, 8, and 16 cm. Velocity was sampled and recorded in 

 90-sec segments at each of these locations above the bed. At the end of a 

 complete vertical profile, the profiler returned to the point nearest the bed, 

 and the data-collection cycle started again. Data collection was begun for 

 each run approximately three or four wave periods after start of the 

 wavemaker. 



Sampling and time reference. LDV velocity data were sampled at 25 Hz. 

 The pressure sensor was interrogated synchronously with the LDV to maintain 

 coincidence with velocity observations. For this purpose, the pressure sensor 

 analog output was digitized by the multi-channel analog-to-digital board on the 

 LDV. 



BASS samples were synchronized with the LDV as follows. Approxi- 

 mately 3 msec prior to the moment that the LDV began logging velocity (and 

 pressure) data, a "start" pulse was transmitted to the BASS electronics. The 

 BASS would then log data for 90 sec, based on its own clock. The relative 

 drift in the LDV and BASS clocks over the 90 sec, which would be the maxi- 

 mum synchronization error of the two records, was less than a millisecond. It 

 follows that these data do not contain time references to the master clock 

 maintained at the Oregon State University facility. The run numbers listed 

 with the data (Table 11-2) give the necessary cross-reference. 



Data storage. All velocity, pressure, and BASS data were stored on mag- 

 netic media and later saved as disks and tapes. These data are to remain as 

 archival sets available to other investigators. 



Experimental conditions. Successful operation of the complete instrument 

 system in a coordinated fashion began only in the fifth week of 

 SUPERTANK. Nevertheless, extensive data were obtained. The majority of 

 the data were measured under monochromatic wave conditions of 3-, 4.5-, 



Chapter 1 1 LDV in the Bottom Boundary Layer 



219 



