DESIGN OF TRANSMISSION LOSS EXPERIMENTS 



J. S. Hanna 



Office of Naval Research 

 Code AESD 



The conceptual design of transmission loss measurements is 

 discussed. The concern here is not with the hardware 

 implementation of a desired measurement, but with the 

 definition of what is to be measured given everything we 

 know about the medium, the acoustic sources, and the 

 available processing techniques. 



The cyclical effort of the past in which models were used 

 to interpret data, and the data in turn used to refine 

 models, is drawn upon to illustrate some general proper- 

 ties of the impulse response of the ocean. Given these 

 general properties, the following topics are addressed: 



1) The nature of sound sources (impulsive and continuous 

 wave) and the limitations each imposes upon our 

 ability to measure the spectrum of the ocean's 

 impulse response 



2) The selection of a signal processing scheme (analog 

 or digital) , given the expected nature of the impulse 

 response and the properties of the sound sources 



3) Examples of measurements which, in some cases have 

 and in others have not permitted meaningful interpre- 

 tation of the results; these examples illustrate 

 common problems and the way they can be avoided. 



INTRODUCTION 



The objective of any transmission loss experiment is to measure 

 a particular property of the ocean environment, namely its effect on 

 the transmission of an arbitrary signal between two points. This 

 seemingly obvious statement is worth making because some measurements 

 have been conducted in a way which has inextricably confused the 

 properties of our measurement system (source and signal processor) 

 with those of the medium. 



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