V. EXPERIMENTAL PROGRAM 



OBSERVATIONAL PLATFORM 



The equipment described in Section III requires a 

 reasonably stable supporting surface to work properly. It 

 would not be possible to use this equipment on a ship. On 

 the other hand, the time delay suffered if samples were 

 taken at sea and brought back to the laboratory would be 

 highly undesirable. 



The NEL Oceanographic Research Tower off Mission 

 Beach, San Diego, is well suited for cavity measurements, 

 and a program was therefore initiated to develop equipment 

 suited for this research facility. 40 ' 41 



The tower is situated 0. 8 nautical mile off the shore 

 in approximately 59 feet of water. The shoreline off 

 Mission Beach is completely unobstructed from the influ- 

 ences of the open ocean. The influence from man-made 

 contamination is therefore at a minimum. The main deck 

 of the platform is 24 feet above the water level, and acts 

 as foundation for an instrument house of 13 by 13 feet in 

 plan section. This leaves an outside passageway around 

 the house about 4-§ feet wide. Space inside the house 

 was not available, so the instrumentation had to be placed 

 outside in the passageway. The tower is quite stable, but 

 the action of waves on the tower supports causes a slight 

 oscillation. The main influence was from the wind, which 

 often would spoil a reverberation measurement by creating 

 ripples on the surface of the water in the cavity. Measure- 

 ments were impossible whenever very "noisy" equipment 

 was in use such as compressors and heavy winches, but 

 the cavities worked well when the conditions were favorable. 



The present field data collection began May 1960 and 

 continued through the summer until the tower was closed 

 down in September 1960. 



60 



