INTRODUCTION 



Critical placement of underwater equipment on the 

 sea floor for long-term studies has traditionally been a 

 source of concern for scientists and engineers engaged in 

 investigation of the marine environment. Mooring tech- 

 niques have been unable to satisfy the needs created by the 

 complex instrumentation presently in use. For example, 

 large tripods with legs imbedded in clumps of concrete, 

 weighing as much as 2000 pounds, have been used to posi- 

 tion thermistor beads, acoustic equipment, and other 

 oceanographic devices at relatively stable points above the 

 sea floor. Positioning of these tripods at desired locations 

 has proved to be a tedious, expensive operation, requiring 

 the services of a large vessel equipped with winches and 

 booms. Once emplaced, the concrete clumps are suscep- 

 tible to wave scouring which, in short periods of time, 

 changes the position of the equipment relative to the sea 

 floor. Thus, any job requiring a large number of these 

 installations becomes virtually impossible. 



An alternate method of anchoring small equipment to 

 the bottom which has been in use by NEL for some time, is 

 to physically inject sections of pipe into the sediments 

 using high-pressure water. This method, commonly 

 referred to as "jetting, " is performed by divers using 

 SCUBA or shallow-water diving equipment. When several 

 feet of pipe are buried in the sea floor in this manner, 

 scouring action is considerably reduced, if not entirely 

 avoided, and the protruding pipe becomes a stable, rela- 

 tively permanent mooring to which a variety of instruments 

 can be mounted or tethered. 



The Marine Environment Division of NEL is charged 

 with the responsibility to study oceanographic factors that 

 contribute to the use of underwater sound in naval opera- 

 tions. Internal waves are known to alter sound fields in 

 the sea. Consequently, many studies conducted on the 

 NEL oceanographic tower depend on adequate field mea- 

 surements of naturally occurring internal waves. Ideal 



