• 29 cm ■ 



14cm 



transducer 

 face 



power and 

 signal connector 



Figure 9-1. OSU Acoustic Concentration Profiler 



Benthic Acoustic Stress Sensor. Flow field hydrodynamics are measured 

 non-invasively, also in profile and within 1.5 m of the bottom, by the Benthic 

 Acoustic Stress Sensor (BASS), developed at the Woods Hole Oceanographic 

 Institution (Williams 1990). BASS is an acoustic time-of-travel velocimeter 

 with transducers arranged on four vertically aligned rigid frames and can fully 

 resolve velocities in three dimensions. BASS can measure at high enough 

 speeds to provide the velocity data needed to resolve turbulent-scale fluctua- 

 tions within the flow. Also, the vertical profile of measurements allows for 

 better estimates of the shear stresses near the bottom, which can ultimately be 

 correlated with the amount of sediment within the water column. 



Four pairs of acoustic transducers for each BASS sensor array are mounted 

 facing each other at 45-deg (0.79-rad) angles on the support rings of a 34-cm- 

 long by 12-cm-diam cylindrical stainless steel frame as shown in Figure 9-2. 

 The four transducer pairs are arranged so that their acoustic beam axes are 

 coincident at the center of the cylindrical volume. Four BASS frames are 

 attached end to end, and the transducer coaxial cables are individually secured 

 to different struts of the BASS frame. The cables from each BASS sensor 

 array frame are wrapped together with PVC spiral wrap to keep the cables 

 protected and immobilized in one bundle. The cables transmit and receive 

 signals from the BASS electronic circuitry, which is housed in a specially 

 designed pressure canister. The electronic system controls sampling rate and 

 processing of data for serial transmission to an external data storage device. 



Chapter 9 The Ohio State University Measurements 



155 



