HANNA: DESIGN OF TRANSMISSION LOSS EXPERIMENTS 



impulse response spectrum for discrete source-receiver geometries. 

 There is much interest, however, in the behavior of a CW signal 

 radiated by a continuously moving source; the behavior is deter- 

 mined most directly by the use of towed CVJ projectors. In this 

 case, the spectrum of the impulse response is sampled at a single 

 frequency (with some narrowband resolution) as a function of the 

 changing source-receiver geometry. Even though the narrowband 

 sampling may be produced continuously in time (as, say, the output 

 of an analog filter) , the practical question arises as to how often 

 [in time] should this output be sampled to give transmission loss 

 as a function of changing geometry. The answer is simple and obvious: 

 often enough to adequately represent the underlying continuous curve. 

 If, however, one must set up an automatic sampling system, it is 

 necessary to estimate in advance the character of the transmission 

 loss as a function of changing geometry, just as in the case of 

 impulsive sources it is necessary to estimate the spectrum of the 

 impulse response. 



This point is illustrated in the next two figures. First, in 

 Figure 6 are shown an estimated transmission loss curve and its 

 experimentally determined counterpart for nearly axis-to-axis 

 propagation in the Mediterranean. The calculation was performed 

 using the parabolic equation program as implemented at the Acoustic 

 Environmental Support Detachment; this calculation was carried out 

 with a range resolution of 0.1 nm which was adequate to sample the 

 rapid variations of the loss with range. The data were taken at 

 approximately 5 nm intervals using a time average equivalent to a 

 range interval of 0.05 nm. Although the data are not inconsistent 

 with the calculation (and, thus, suggest that the real-world trans- 

 mission loss has character comparable to that of the estimated loss) , 

 it is clear that the dependence of the actual transmission loss on 



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