146 



SHALLOW-WATER TRANSMISSION 



numerical example, assume that a total number of 26 

 runs were obtained on 4 days. If the numbers of runs 

 on these four days were 7, 7, 6, and 6, then the value 

 of K for this case would be 4.0. If, on the other hand, 

 two of the four days contributed 12 runs each, and 

 the other two days only one run apiece, K would be 

 found to equal 2.3. 



The results in Tables 1 and 2 indicate that SAND, 

 ROCK, and STONY are well-reflecting bottom types; 

 they lead to values of i?4o in excess of 2,000 yd in the 

 great majority of cases, regardless of refraction con- 

 ditions. CLAY also appears to be a well-reflecting 

 bottom, although it should be emphasized that all the 

 CLAY runs by UCDWR were made at a single loca- 

 tion off San Francisco, and that a generalization of 

 the results obtained should be based on a more ade- 

 quate sample. In this method of analysis, no sys- 

 tematic dependence on hydrophone depth can be dis- 

 covered, although the samples for deep hydrophones 

 are mostly too small for the results to be considered 

 conclusive. Transmission over STONY bottoms ap- 

 pears somewhat better than over any other type of 

 bottom. 



For the classification MUD, it is apparent that the 

 dependence of ^40 on the conditions of refraction is 

 similar to the situation in deep water. The WHOI 

 SAND-AND-MUD data resemble the MUD data 

 in this respect. The R40 ranges are long when the water 

 is isothermal, and short when the sound beam is bent 

 downward by negative temperature gradients. In the 

 classification SHALLOW MIKE, there is some evi- 

 dence of layer effect over the poorly reflecting bot- 

 toms. Layer effect is much weaker, if present at all, 

 for SAND, ROCK, and STONY bottoms. There is 

 also some evidence that in the case of MUD bottoms 

 the transmis.sion for the deep hydrophone is better 

 than for the intermediate and shallow hydrophones. 

 The transmission results obtained by UCDWR and 

 by WHOI appear to be in fair agreement with each 

 other except for the SAND-AND-MUD bottoms. 

 In this classification, the transmission observed by 

 WHOI is significantly poorer than the transmission 

 observed by UCDWR. This disparity is not too sur- 

 prising in view of the fact that the SAND-AND- 

 MUD classification covers a wide variety of bottoms, 

 namely, all those bottoms in which very fine particles 

 are mixed with sand grains and in which the per- 

 centage of sand grains lies between 10 and 90 per 

 cent. It appears reasonable to assume that the SAND- 

 AND-MUD bottoms investigated by UCDWR con- 

 tained a larger percentage of sand grains and were 



B MEDIAN AND QUARTILE CURVES 

 BASED ON UCDWR DATA 



MEDIAN CURVES SHIFTED 

 AND SUPERIMPOSED TO 

 COINCIDE AT 1500 YARDS 



\ 



^ 



1000 



2000 

 RANGE IN YARDS 



Figure 3. Comparison of WHOI and UCDWR trans- 

 mission data over sand with downward refraction. 



harder, on the average, than the SAND-AND-MUD 

 bottoms investigated by WHOI. 



The value of ^^40 is a useful parameter for the 

 description of transmission; but in view of the fre- 

 quent nonlinearity of the transmission anomaly 

 range curve, no single parameter can be relied on to 

 adequately characterize the transmission from very 

 short to very long ranges. A more adequate method 

 for describing a sample of transmission curves is the 



