Figure 6-4. 



Example of OBS array; AO, BO, or CO. Longshore displacement 

 from current meters is less than 20 cm 



Experiment Procedures 



Sequence of events 



A typical data run was conducted after all OBS heights above the bottom 

 had been measured and recorded. The OBS data logging system was started 

 approximately 15-30 sec prior to the official start time of a run to record the 

 "clear-water" offset of each OBS. Data collection continued for approximate- 

 ly 15-30 sec after the official stop time of the run to record whether the clear- 

 water offset had changed during the run. Comments on wave conditions, 

 difficulties encountered, or noteworthy events observed during the run were 

 logged into notebooks. Divers were men deployed to measure OBS heights 

 above the bed, describe bed configuration (ripples, plane, etc.), and readjust 

 the OBS stacks such that the lowermost sensor was set to z = 3.5 cm, in 

 preparation for the next run. These pre- and post-run instrument elevations 

 were recorded in the logbooks. 



Sampling and time reference 



All data were recorded on a personal computer (PC) located in the 

 SUPERTANK Principle Investigator room at the WRL. All data channels 

 were simultaneously sampled at a 10-Hz rate. The time of each data sample 



112 



Chapter 6 Suspended Sediment Concentration 



