CHAPTER T 



SEISMIC PROFILING SYSTEMS 



T-1 Seismic Profiling Systems. — Seismic 

 profiling systems are used to map acoustically 

 the geologic structures buried beneath the ocean 

 floor. These systems consist of a repetitive 

 broad-band sound source and compatible receiv- 

 ing, amplifying, filtering, and recording equip- 

 ment. The sound source and the hydrophones 

 are towed behind the ship, and the data are 

 recorded aboard the ship on a special graphic 

 recorder. Several seismic sound sources, hydro- 

 phone arrays, and receiving systems are in use 

 at the U.S. Naval Oceanographic Office, and the 

 state-of-the-art is undergoing constant modi- 

 fication. 

 The sound sources include the following : 



1. The Boomer is an electro-magnetic sound 

 source. Discharge of a capacitor bank establishes 

 eddy currents in a set of parallel plates, result- 

 ing in rapid repulsion between the plates and 

 generation of a shock wave in the water (fig. 

 T-1). 



2. The Sparker is an acoustic pulse generator 

 which produces a small controlled underwater 



explosion by discharging a capacitor bank across 

 spark electrodes, causing the water to vaporize 

 into steam and generating a shock wave in the 

 water (fig. T-2 and T-3) . 



3. Other sound sources that are under devel- 

 opment include gas and compressed air guns 

 and the line source. The gas and air guns work 

 by discharging a bubble into the water through 

 special valves, and the line source consists of 

 elongated coils of cable that operat« by repul- 

 sion as do the boomers. 



Figure T-2. Sparker acoustic pulse generator (EG&G 

 Model 267 Sparkarray). 



Figure T-1. Boomer sound source (EG&G Model 238). 



Figure TS. The "bared cable" sparker acoustic pulse 

 generator. 



T-1 



