The signal from the filter is applied to the logarithmic type amplifier. Here, low 

 level signals receive a higher gain than high level signals so that weak reflections 

 may be recorded along with strong signals. The output from the amplifier passes 

 to the level control and printing circuits where a means of selecting the smallest 

 signal to be displayed and/or recorded Is provided. 



The Recording Unit starts each cycle of operation and makes a record of 

 signals received. The recording paper passes between a flat blade and a revolving 

 drum that Is wound with a single helix of wire. The pulse of acoustic energy Is 

 transmitted at the instant when a point connecting the blade and the wire Is at 

 the top of the paper; the zero depth position. The drum rotates at a rate so that 

 each inch from the top of the paper represents 8 1/3 milliseconds of travel time. 

 On the assumption that the velocity of propagation of the signal through seawater 

 is 4800 ft/sec, each Inch down the recording paper equals 20 feet of depth to a 

 reflecting horizon. When a signal is detected by the hydrophone a spark passes 

 between the blade and the wire on the rotating drum, at the point of contact, and 

 a mark is made on the electrosensitive paper. The paper is 10 inches wide and 

 lined in Increments of 1/2 inch, each representing 10 feet of depth. 



The Precision Power Unit provides the regulated power necessary to drive the 

 recording drum at the precise speed needed for synchronization of the system. 



C. Instrument Capabilities and Recordings 



Bottom penetration of the acoustic signal under favorable conditions of water 

 depth and bottom type is 100 feet to perhaps a maximum of 200 feet . Soft mud 

 bottoms permit the greatest signal penetration whereas clean sands and gravels 

 reflect nearly all of the signal . The use of the instrument is believed to be limited 

 to water depths of less than 700 feet. Although the Instrument is limited in pene- 

 tration capability, its usefulness is demonstrated by Its high resolution of bottom 

 and subbottom features. This high resolution is not equaled by instruments with 

 greater penetration capability. 



The resolution capabilities of subbottom profiling instruments are dependent 

 upon the frequency and pulse duration of the acoustic signal . It is possible to de- 

 tect subbottom discontinuities as thin as 1/2 wave length of the acoustic signal . 

 For the Sonoprobe, the wave lengths In water are 1 .6 and 0.8 feet for the 3 kc, and 

 the 6 kc.slgnals, respectively . The short pulse durations permit only a single cycle 

 of a 3.8 kc. wave to be transmitted at each pulse. In practice the resolving power 

 of the Sonoprobe is 1 to 3 feet (McClure, et.al ., 1958, Moore, 1960). 



The calibration velocity of the instrument is 4800 ft/sec; therefore, the depth 

 of the bottom and the layers beneath the bottom will be recorded at their true 



