118 



DEEP-WATER TRANSMISSION 



SOUND FIELD DATA 



4880 4930 4980 



SOUND VELOCITY IN FT PER SEP' 



40 



■o- o 



2000 4000 6000 



RANGE IN YARDS 



Figure 34. Sample transmission anomaly plot. 



5.4 TRANSMISSION WITH NEGATIVE 

 GRADIENTS NEAR SURFACE 



In some regions at certain times, negative tem- 

 perature gradients in the upper 50 to 100 ft of the 

 ocean are very common. Especially in coastal waters 

 and during the summer months the temperature dif- 

 ference between the surface and 30 ft frequently ex- 

 ceeds 0.3 F. Temperature patterns of this type are 

 usually highly variable. 



Many of the transmission measurements at 

 UCDWR were made with negative gradients at the 

 surface. The present section discusses these data. 

 While emphasis is placed on temperature patterns 

 for which the temperature difference from the surface 

 to 30 ft is 0.4 F or more (NAN and CHARLIE pat- 

 terns), some discussion is included of those cases where 

 the top 30 ft is isothermal but the top of the ther- 

 mocline is less than 100 ft below the surface. A more 

 rigid division of the acoustic data by the different 

 types of temperature-depth patterns is not possible, 

 since the different analyses that have been made 

 have used somewhat different classifications. 



In the following pages, a discussion will first be 



given of the general types of transmission anomalies 

 that are found with temperature gradients near the 

 surface. Subsequently, more detailed discussions will 

 be given, first for those situations where the temper- 

 ature gradient in the top 30 ft is large, about 0.7 F or 

 more, and second, for smaller gradients in the top 

 30 ft. 



Because of an almost complete lack of analyzed 

 data at other frequencies, this discussion is largely 

 confined to results obtained at 24 kc. A few results 

 obtained at 60 kc are described at the end of this 

 section. The bulk of the results come from two re- 

 ports by UCDWR, one issued in 1943^' and the other 

 in 1945.''' Use is also made of individual transmission 

 anomaly curves obtained from UCDWR which have 

 not been published. 



An examination of the transmission anomalies 

 measured with temperature gradients near the sur- 

 face shows that most of the observational curves may 

 be divided into two types. In the first of these, the 

 anomaly does not change rapidly with range at very 

 close ranges or at very long ranges, but drops very 

 rapidly at a range somewhere between 500 and 2,000 

 yd. In the second type, the transmission anomaly in- 



