b. Instrument mounting is moved into place so that the bottom of the 

 BASS frame is roughly 2.5 cm above the bottom to prevent scouring 

 around the frame. The vertical plumb of the mounting is checked, 

 guy wires are tightened, and cables from the instruments to the signal 

 conditioning and microprocessor hardware on the cart are immobi- 

 lized. 



c. Power cables and data transmission lines are connected from the elec- 

 tronic and microprocessor hardware on the cart to the PC's outside the 

 channel, and equipment is powered up. 



d. A test run of the instruments is made checking data on the PC's and 

 the oscilloscope. BASS output is examined for capacitive drift due to 

 partial immersion of the sensor cables running up from the instrument 

 mounting through the water surface to the electronics. The profile of 

 signals from the ACP is checked for proper background gain level and 

 also to ensure that the instruments are positioned properly relative to 

 the bottom. 



e. Instruments are started before the wave run begins to observe the 

 "spin-up" period of the suspended sediment. At this time a 10-min 

 sample of the wave run data is written to a floppy disk which is then 

 copied into PC2 where the data can be examined. 



/. Data from the ACP, BASS, and pressure sensor are continuously col- 

 lected and written to the hard disk of PCI during the whole wave run. 

 During this time a grab sample of the sediment-water mixture is col- 

 lected using a Niskin bottle sampler from over the side of the channel 

 just shoreward of the ACP. 



g. Following completion of wave generation, a few more minutes of data 

 are taken to obtain an idea of the settling characteristics of the 

 suspended material. Data collection is ended and the instruments are 

 turned off. Power and data transmission lines to and from the power 

 supply and PC's are disconnected, and the instrument mounting is 

 raised to prevent dragging on the bottom as the offshore cart is moved 

 towards the wave paddle to facilitate the beach profile survey. 



h. Data files are then copied to a properly named file designating the 

 wave run. At the end of each day the saved files are copied onto two 

 different magnetic tapes, one a backup and the other a working copy. 



Calibration and zero reference 



ACP. The procedure with which the ACP is calibrated is complicated and 

 is fully discussed in Libicki, Bedford, Lynch (1989) and Libicki (1986). The 

 method uses a model of the various parameters that influence reflected 

 acoustic intensity, and data collected by the transducer, based on the active 



164 



Chapter 9 The Ohio State University Measurements 



