no 



the purpose of locating enemy submarines in wartime. Practical peacetime use 

 of echo ranging has been proposed as a device for locating schools of fish, sub- 

 merged wrecks that may be a hazard to navigation and as a direct aid to naviga- 

 tion in restricted waters. So far as I am aware, none of these functions has 

 ever been employed in a concentrated, highly developed manner by anyone. The 

 potential of echo ranging as a general research tool in marine biology and later 

 as a practical device for locating fish is perhaps one of the most exciting possi- 

 bilities for the use of underwater sound today. Several groups in this country 

 and abroad are at work on the problem. Many ideas for instrumentation are un- 

 doubtedly being carried out and this particular subject deserves far more de- 

 tailed attention for the purposes of this symposium than I am. now prepared to 

 give it. The typical echo sounder or echo ranger employs a rather high single 

 frequency sound signal which may be radiated from the same transducer which is 

 later to act as the receiver, or the radiator may be an independent transducer, 

 separated a relatively short distance from the receiving transducer. Frequen- 

 cies commonly used in this equipment range from 10 to 50 kc* depending on the 

 use to which it is put. 



The versatility of echo ranging or sounding instruments is such that it is 

 possible with complete confidence to think of research in which echo information, 

 namely the bearing, the distance to the object under study and the character of 

 the returned echo, may be analyzed over very wide limits with appropriate de- 

 sign. For example, echo ranging techniques employing a separate sound source 

 and receiver have been used successfully to measure the back scattered sound 

 from objects as small as a single large prawn at a range of about one meter. 

 On the other extreme, it has been a matter of routine to record reverberation 

 from the scattering layers in open ocean at travel times corresponding to depths 

 of 500 to 1000 fms. below the research vessel. The principal difference be- 

 tween the sort of information achievable in the one case and in the other is that 

 individuals can be distinguished at very short ranges since there the directionali- 

 ty of both the source and the receiver is sufficient whereas at considerably long- 

 er ranges the same directional properties cause the sound to be spread out 

 through a considerably larger volume so that back scattering is received simul- 

 taneously from many individuals. These directional properties are practical 

 limitations in the gear readily available at the present time. 



Commercial echo sounders are available in this country principally from 

 the Raytheon, Bendix, Bludworth Marine, Edo and Minneapolis -Honeywell Com- 

 panies. Most of the models have built in spark recorders and offer a choice of 

 ranges from about 160 feet to 600 fathoms. They are built for fishermen, 

 yachts and steamers; not for science. Echo sounders of greater depth capabili- 

 ties are not generally available in this country, but have been designed for naval 

 use or for special surveys such as those carried out by the Coast and Geodetic 

 Survey. While these contribute steadily to our knowledge of deep oceanic bathy- 

 metry they are still a far cry from the instrument needed to supply many needs 

 in oceanographic science. For example, all echo sounders are designed to have 

 a total beam width of the order of 30O so as always to point in the general direc- 

 tion of the bottom when mounted on the keel of a rolling ship. As a result such 

 a device becomes a very blunt instrument for delineating the shape of the ocean 

 floor in any but rather shallow depths. Further, in order to keep the required 

 transducer small for even such modest directionality, frequencies well above 

 10 kc must be used. These frequencies penetrate but a short distance into 

 oceanic sediments and hence are only occasionally useful for mapping the thick- 



* - Since this paper was originally presented the Minneapolis-Honeywell 

 Company has introduced a commercial combination echo ranging and echo 

 sounding device which operates at a considerably higher frequency. 



