SUPERSONIC TRANSMISSION 



149 



2000 

 RANGE IN YARDS 



3000 



4000 



Figure 6. Transmission over ROCK for shallow and deep hydrophones. 



Transmission appears to be better out to 2,000 yd for 

 STONY bottoms than for any other type of bottom, 

 but deteriorates rapidly from 2,000 yd on out. The 

 wide spread between the median and quartile curves 

 is an indication that these bottoms are acoustically 

 less uniform than SAND or ROCK bottoms. 



Figures 8 and 9 show two typical transmission 

 anomaly plots, which were obtained over a ROCK 

 and over a STONY bottom respectively. These runs 

 were carried out in the presence of pronounced 

 negative gradients from the surface of the sea down 

 to well below the depth of the projector. The ray 

 diagrams, which are shown in the upper parts of the 

 figures, indicate that in deep-water transmission con- 

 ditions would be confidently predicted to be poor. 

 Because of the well-reflecting bottom, however, the 

 observed transmission is comparable to that in a 

 deep mixed layer in deep water. 



MUD bottoms were originally defined as bottoms 

 in which the average particle was too small in size to 

 be classified as SAND. However, evidence accumu- 



lated indicating that from an acoustic point of view 

 there are two different types of bottoms which are 

 composed of very small particles. These two types of 

 bottom can be characterized by their consistency as 

 soft and as plastic, and they have been designated in 

 this analysis as MUD and as CLAY. Some evidence 

 concerning the difference in acoustic properties of 

 these two types of bottoms has been collected and 

 published by WHO!.* This evidence for separating 

 MUD bottoms into MUD and CLAY was apparently 

 borne out by the analysis of the transmission data 

 obtained by UCDWR, but doubts as to the correct 

 classification of the CLAY samples involved detract 

 from the value of this evidence. 



Figure 10 shows median and quartile transmission 

 curves over MUD in the presence of negative gradi- 

 ents, separated according to hydrophone depth. It 

 appears that the quartile spread is appreciably re- 

 duced for the shallow and deep hydrophone depths 

 by this separation. Regardless of hydrophone depth, 

 the transmission anomaly at 3,000 yd is approxi- 



