The National Institute of Oceanography of Eng- 
land reports good results at ship speeds up to 
7 knots using a multiple crystal arrangement in 
a plastic oil filled hose. EG&G markets an 
effective hydrophone with towing fish, the 
rocket hydrophone (see Figure 4 ). Braincon 
Corporation also markets a special "V"'=Fin 
lollipop hydrophone which is suitable for use 
with the thumper system. 
Fs 
Figure 4. E.G.&G. Rocket Hydrophones. 
IV. SONAR RECORDER 
The thumper has been successfully recorded 
with a number of systems. Excellent results 
have been obtained by using the Alden Precision 
Graphic recorder and the EG&G Model 250 Sonar 
Recorder, both of which use Alden Alfax paper. 
These recorders work on the same principle of a 
resilient negative helix electrode and a posi- 
tive moving loop electrode, which provides high 
accuracy and resolution. 
The EG&G Sonar Recorder was designed spe- 
cifically for use with the Sonar Thumper and 
EG&G's Sonar Pinger. Figure 5 shows the Sonar 
Recorder in operation on a contract job for the 
U. S. Corps of Engineers. The recording unit 
is compact and versatile and emphasizes sim- 
plicity and ease of operation. Three recording 
speeds are provided to give basic full-scale 
sweeps of 50 fathoms, 200 fathoms and 800 
fathoms. A record gating system allows presen- 
tation of the first, second, third, or fourth 
sweep after keying; thus the 0-50, 50-100..., 
0-200, 200-400..., 0-800, 800-1600... fathom 
intervals can be recorded, depending on water 
depth and scale desired. A middle keying 
feature is also provided to give greater scale 
flexibility. 
Sweep accuracy is .005% derived from an 
internal tuning-fork oscillator. Recording cin 
be either full wave, positive half wave, or 
negative half wave. Connections are provided 
for independent headphone monitoring and oscil- 
loscope display of the signal being recorded. 
The paper feed speed is controlled by a sepa- 
286 
rate shunt wound motor with continuously vari- 
able speed control. An event marker line can 
be recorded either with a panel-mounted button 
or remotely. 
Amplifier response can be selected to give 
either a broad band for thumper recording or 
12-!-locycle peaked response for pinger record- 
ing. A built-in RC filter can be cut in for 
reducing high- or low-frequency noise on the 
broad-band response, A separate variable 
filter can also be used to provide fine control 
of frequency response. 
The seis- 
the tape 
recorder at the right for experimental replay. 
Figure 5. Sonar Recorder at left. 
mic returns were also recorded on 
V. ELECTRICAL POWER REQUIREMENTS 
The power requirements for the thumper 
seismic system can be supplied by a ship's gen- 
erator or auxiliary generator. A voltage fluc- 
tuation may be noticeable when the thumper is 
fired because of the high peak currents. There- 
fore it is recommended to run the thumper on a 
separate generator, if possible, to avoid volt- 
age fluctuations to the recorder. 
Many generators are available for sale or 
rental which are suitable for powering the 
thumper. A portable unit with a minimum of 2 
kilowatts, 110 volts or 220 volts, 60-cycle a.c. 
is perfectly adequate for the standard thumper. 
The larger thumper units require somewhat 
larger generators. For example, a 5000-watt- 
second unit with a firing rate of 2.5 secs 
requires a 4-kilowatt generator or larger. 
VI. FIELD SURVEY PROCEDURES 
Assuming that a specific program with de- 
sired coverage has been outlined, an experimen- 
