A MOORED OCEANOGRAPHIC DATA ACQUISITION SYSTEM^ 



by 



William C. Green and Leon deVilleneuve 

 Institute of Marine Science, University of Miami 

 #1 Rickenbacker Causeway, Miami, Florida 33149 



INTRODUCTION 



In order to correlate ambient noise in the sea with surface disturbances, 

 a permanently moored oceanographic environmental sensing system to measure 

 certain environmental factors has been installed one mile west of North 

 Bimini, Bahamas (Fig 1). It was designed for this location where the water 

 is 100 feet deep with a sandy bottom. The water currents are of variable 

 direction with velocities of to 3 knots. These waters, which are generally 

 navigated by small craft, lie in the hurricane belt (Fig 2) . 



SYSTEM 



The environmental factors being measured are wind speed and direction, 

 wave height, current speed and direction, water temperature and ambient noise. 

 The sensors measuring these parameters are sequentially sampled by a submerged 

 commutator selector, converted to a frequency analog and transferred by cable 

 to tape recorders on shore. The data are then processed by computers for 

 analysis (Fig 3) . 



Because the requirements for mounting the different sensors vary so 

 widely, two platforms were installed to support them. The anemometer and 

 wave height sensors were mounted on a spar buoy and the current speed, 

 current direction meter and temperature sensors were mounted on a submerged 

 buoy. 



SPAR BUOY 



The spar buoy (Fig 4), fifty-five feet long and one foot in diameter, 

 floats with fifteen feet of its length exposed above the water. It is fabri- 

 cated of three sections of polyvinyl chloride pipe filled with high density 

 expanded polyurethane. The pipe joints are reenforced with steel collars 

 and the buoy is externally guyed with stainless steel wire to minimize flex- 

 ing. A disc-shaped counterweight, to dampen vertical motion due to surface 

 waves, is suspended 27 feet below the spar. The buoy is secured at its 

 center of pressure by horizontal tether wires fastened to the mooring lines 

 of two large floats (Fig 5) . The horizontal wires have no vertical force 

 components due to currents and therefore, tilting and vertical excursion of 

 the buoy due to currents is minimized. The two floats, 30 feet away from, 

 and on opposite sides of the buoy, are in line with maximum expected currents. 



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