INVERTED ECHO SOUNDER 
by WILLARD DOW, Electronics Engineer 
and STEPHEN L. STILLMAN, Research Assistant in Engineering 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 
PART 1 - Willard Dow 
ABSTRACT 
The Inverted Echo Sounder is an instrument 
primarily designed to provide a continuous and 
precise measurement of the depth of other 
instruments, such as the velocimeter being 
lowered along with it into the sea. 
The device has also been used for detailed 
survey of the ocean bottom in deep water and 
by simple alteration of its suspension can be 
used for high powered short pulse echo ranging. 
INTRODUCTION 
Instruments are now available which are 
capable of measuring sound velocity, tempera- 
ture, and salinity to a high degree of precision. 
However, the value of these measurements is 
greatly reduced if the depth of the instrument 
is not also known simultaneously and with 
comparable precision. 
Most devices for such depth measurement 
incorporate bellows or bourdon tubes which 
although they can be made sensitive to small 
pressure changes in shallow water, become of 
necessity stiff and insensitive to such changes 
when designed to withstand the high static 
pressures of the deep ocean. 
The Inverted Echo Sounder when coupled 
to a precision recorder has provided highly 
precise depth measurements down to at least 
16,000 feet, and when perfected should 
operate considerably deeper. 
When towed close to the bottom, the 
instrument also provides a highly detailed 
survey of the area showing bottom configu- 
ration impossible to resolve with conventional 
surface echo sounders. 
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THEORY OF OPERATION 
The device consists of a high powered 
"pinger'’ as a short pulse transmitting unit 
mounted along side a sensitive fixed tuned 
receiver. Both units are connected to a com- 
mon transducer which is used both as a 
projector and as a receiving hydrophone. The 
apparatus is self-contained and battery operated. 
When submerged, the transmitter directs 
short pulses toward the surface at a one second 
repetition rate (Fig. 1). The surface reflected 
pulses are detected by the deep receiver, 
amplified and sent up via a single conductor 
oil well logging cable to the surface vessel. 
Here the signal is amplified further and applied 
to a precision graphic recorder normally used 
for echo sounding. From this record the depth 
of the instrument may be read directly.( Fig.1A) 
Although the main lobe of the transducer is 
always directed toward the surface during 
instrument lowerings, there is also a weaker 
back lobe directed toward the bottom, There- 
fore when the gear is lowered to within 600 
feet or so of the ocean floor, the bottom also 
becomes visible on the recorder chart and the 
winch can be stopped in time to avoid dragging 
instruments in the mud. 
This same back lobe is made use of in 
bottom survey operations. In this case the 
sounder is lowered to between 30 and 100 feet 
of the bottom, and towed slowly across the 
region of interest. Under these conditions 
the area covered by the transducer beam at 
any given moment is comparatively small and 
details of bottom structure may be observed 
without the ambiguity produced by side re- 
flections or the losses encountered in sound 
transmission through thousands of feet of 
water. 
