fish, plankton, and properties of surface and bottom. It 

 is therefore desirable to employ a measurement technique 

 that requires a relatively small sample when studying the 

 medium since difficulties from inhomogeneities then can 

 be avoided, and cause and effect can be established. It 

 is also desirable to be able to undertake the measurements 

 as soon after sampling as possible, to keep changes in the 

 water at a minimum. The first requirement was met by 

 using a soft or compliant wall cavity method developed at 

 the U. S. Navy Electronics Laboratory, and the second 

 requirement was satisfied by using NEL's oceanographic 

 tower off Mission Beach, San Diego, California, as the 

 supporting operations facility. 



