."54 HERSBY [chap. 4 



is burned and torn to shreds!). McClure et al. (1958) report logarithmic com- 

 pression for the Sonoprobe ; Beckmann et al. (1959) report time-variable gain 

 (TVG) for the sub-bottom depth recorder, and recent forms of compression 

 circuitry in the seismic profiler include an adjustable clipper or, alternatively, 

 approximately logarithmic output. 



F. Special Data- Processing Techniques 



The Field Research Laboratory of Socony Mobil Oil Company reports 

 success with a magnetic drum compositor which retains and delays up to 16 

 successive between-pulse wave trains allowing them to add together before 

 recording. The wave trains are automatically matched at the trigger pulse of 

 the sound source. Correlated echoes are enhanced much more strongly than 

 random noise components. The electro-sensitive papers have a somewhat 

 similar action if the paper is moved so slowly through the recorder that suc- 

 cessive stylus-sweeps overlap. Other correlation techniques that have been 

 studied recently are gradually being introduced into seismography ; the basic 

 method of regular repetition of pulse-and-recording while the system moves 

 slowly over the structure under study is well designed for their profitable 

 application. 



G. Recorders 



The graphic recorders in use divide into dry paper and wet paper, and into 

 stylus- and hehx-recorders. There have been several produced commercially 

 that will serve, but those most in use today are the Alden ^ (wet paper and 

 helix-recorder), the Westrex^ (dry paper and stylus) and the ^luirhead^ 

 (wet paper and helix-recorder). All are facsimile recorders which have been 

 adapted. The Alden and Westrex are described by Knott & Hersey (1956) and 

 Luskin et ah (1954) respectively. 



Multiple-channel recording is sometimes useful as in the simultaneous 

 recording of low- and high-frequency bands discussed above (see Filters). 



In conventional graphic recording of echo-soundings, individual oscillations 

 are not resolved ; the correlation presented is that of envelope matching 

 (Fig. 4). Pulses filtered to emphasize low frequencies during continuous reflec- 

 tion profiling have been recorded to resolve individual oscillations either by 

 half-wave rectification or high time resolution. Thus phase correlations can be 

 made. Phase correlation recordings are illustrated in Figs. 5 and 19 by half- 

 wave rectification, and in Fig. 21(b) by full-wave rectification and high resolution. 

 In Fig. 6 full- wave and half- wave rectification are compared during a profile. 

 Here echo sequences stand out more clearly when half-wave rectification is 



^ Alden Products Company, Brockton, Massachusetts. Product known as "The Precision 

 Graphic Recorder". 



2 Westrex Company. Product known as the "Precision Depth Recorder". 



3 Muirhead Instruments Inc. Product kno^vn as the "Facsimile Depth Recorder". 



