112 



Can the SOFAR installations be readily used to investigate water masses and 

 similar large-scale phenomena also? In part, the answer lies in the ability of 

 the investigator to disentangle the many effects which are integrated into the 

 signal as it proceeds along its transmission path. 



Received signals possess fair clues about the total length of path tra- 

 versed and the direction also may be roughly inferred. However, no profound 

 changes have been observed to occur when the length of the path is increased on- 

 ly by an annount sufficient to place the origin of the explosion from one side of a 

 water mass boundary to the other. In other words, the intermass region be- 

 tween two large and distinct oceanic masses does not leave a large imprint in the 

 signal when the transmission path in the intermass region is relatively short. 



Since a high percentage of the transmission time for a SOFAR signal is 

 spent in traversing the part of the ocean below the depth of minimum acoustic 

 velocity, the use of SOFAR for the study of near-surface currents does not ap- 

 pear promising. 



The installed SOFAR stations will be useful in studying oceanographic 

 changes only after some reliable correlation is established between just detecti- 

 ble signal variations and measured changes in the physical state of the trans- 

 mission path. No adequate means is yet available for describing simply the 

 physical state of the path, especially where it traverses several thousand miles. 



Echo-ranging equipment with high resolution in the time coordinate is 

 the second acoustic tool to which I invite attention. Occasionally, the equip- 

 ment presents scattering information from which unusual physical conditions 

 may be inferred. Figure 1, shown through the courtesy of Mr. L. R. Padberg 

 of U.S. Navy Electronics Laboratory, is a reproduction of a scattering record 

 of the type recognized as different from the usual. The abscissa represents 



time after the emission of a short pulse 

 signal, or the equivalent range from the 

 echo-ranging ship to the scatterers. 

 The ordinate represents the distance the 

 ship moves along its course while taking 

 the scattering observation. The black- 

 ness of the trace is indicative of the 

 strength of the signal, the blacker the 

 tracei" the higher the strength. 



The light bands which are ar- 

 ranged in striking manner at particular 

 ranges may be explained as a destruc- 

 tive interference in which some of the 

 energy returned by the scatterers ar- 

 rives via a direct water path and the 

 rest by a path which includes one sur- 

 face reflection. On the basis of this 

 assumption and from the known geome- 

 try and equipment paranaeters, it is de- 

 duced that: the scatters are contained 

 in a plane layer parallel to the ocean 

 surface, the mean depth of the layer is 

 about 300 yards, and the thickness of 

 the layer is probably less than 5 yards. 

 The depth of the ocean at the location 

 was 400 fathoms and reflections from it 

 are ruled <-,ut by additional evidence. 



I I 



I 2 3 



RANGE TO THE SCATTERERS 

 (IN THOUSANDS OF YARDS) 



Fig. 1. Chemical recorder trace 

 showing interference patterns re- 

 sulting from scattering layer. 



