ranging equipment, but also pingers which are 
attached to cable-suspended and free instru- 
ments. The difference between the arrival 
times of the directly received and bottom 
reflected signals from this pinger indicates an 
instrument's height above bottom, (Fig. 8). 
The signal structure and timing of these arrivals 
displayed on the PGR disclose such details as 
when a corer triggers, or the attitude of a 
dredge e. g. whether or not it is kiting during the 
lowering. Cameras can be manuevered within 
their focal lengths above the bottom in water 
several miles deep. We can tell whether the 
cameras are over smooth, muddy bottom or 
rough, rocky bottom. The guesswork in these 
many operations has for the most part been 
eliminated. We no longer speculate whether 
a dredge is on bottom, a camera in focus, cable 
payed out too fast or a Nansen bottle cast 
dragged on bottom. 
Where depth must be accurately known, 
for such instruments as the Bureau of 
Standards Velocimeter, the simple pinger 
technique is not adequate 18° However, the 
additional travel path geometry provided by 
the inverted echo sounder described by Dow 19 
solves this problem. 
Navigation techniques involving acoustic 
pingers and transceivers, and sonobuoys are 
also used with the PGR. The motion of freely 
drifting pingers with precisely timed repetition 
rates can be tracked by measuring the change 
in time interval between received pings. When 
sonobuoys and acoustic transceivers are used, 
a simple travel time measurement is used to 
compute one's range from them. 
Studies of Sea Life 
Scattering layer records from the PGR 
see Fig. 9a and b, often a by-product of 
bathymetry, show the diurnal migration and 
distribution of these groups of sound 
scatterers 19 Interesting work has been done 
by lowering a sounding transducer into the 
layers to learn more of the size, population 
and movement of individual animals 14, 20, 
Echoes are read out on the highest writing 
speed of the PGR. Earlier this information was 
used to determine when to trigger an underwater 
camera; now the camera and its acoustic range 
finder are in one submersible package. 
Fish schools are studied by sounding 
and echo ranging. A PGR record from such 
a study illustrates this use of short pulses 
254 
and high resolution, Fig. 10. 
CONCLUSIONS 
Some of the salient jobs of the PGR have 
been mentioned, There is good probability’ 
that there will be more, We have not yet used 
it to measure oceanic tides, for example. 
Studies of the scattering layer and newly found 
groups of larger sea life continue. New 
advances in navigation are most encouraging 
for those studying bathymetry, for our depth 
measurement capability is all-too- often better 
than our navigation, New and more powerful 
broadband sound sources hold promise of 
making continuous seismic profiling as routine 
as echo sounding. Even without the use of new 
inverted sounders, heat probes, and other 
equipment there is without a question much 
future use for the PGR. 
ACKNOWLEDGMENTS 
The development of the recorder and 
much of the Continuous Seismic Profiler was 
carried out by WHOI under U. S. Navy Bureau 
of Ships' Contracts NObs- 43270 and NObsr-7252 
as has been previously reported. Other work 
summarized here have been supported by WHOI 
under Office of Naval Research contract Nonr- 
1367(00), and NSF grants, 
This is Contribution No. 1223 of the 
Woods Hole Oceanographic Institution, Woods 
Hole, Massachusetts. 
REFERENCES 
1, "Atlantic Submarine Valleys of the United 
States and the Congo Submarine Valley", 
Veatch, A. C. and Smith, P. A. , Geol. 
Soc. of Am. , Special Papers No. 7, 1939. 
2. "High Resolution Echo Sounding Techniques 
and their Use in Bathymetry, Marine 
Geophysics and Biology," Knott, S. T. and 
Hersey, J. B, , Deep-Sea Research, Vol. 4, 
No. 1, 1956, pp 36-44. 
