analysis of the acoustic properties of the materials. These acoustic- 

 physical property relationships are discussed in subsequent sections. 



DATA INTERPRETATION - QUANTITATIVE 



Reflection Coefficient 



Breslau (1965), Faas (1969), and others have indicated that a corre- 

 lation exists between the reflective and geologic properties of the sea- 

 floor. Smith and Li (1966) have suggested, however, that care should be 

 exercised when attempting to identify sediment tvpe from its reflecting 

 properties, particularly in regions where the sediments may contain a 

 substantial amount of gas. 



This section attempts to summarize recent developments in relating 

 the reflection coefficient of the bottom to its sediment or rock type. 

 Knowledge of these quantitative relationships allows the geologist or 

 marine engineer to infer certain properties of the bottom material from 

 a study of the recorded trace or, if a more comprehensive analysis is 

 desired, to use computer data processing techniques to draw quantitative 

 conclusions. The marine construction engineer can make a preliminary 

 estimate of an area's load supporting capabilities, especially if the 

 profiling survey is combined with a limited coring or boring program. 



A layered model of the seafloor is composed of strata that are 

 defined in terms of their acoustic impedance (equation (3)). For the 

 case of the incidence of an acoustic wave on a specular reflector, the 

 reflection coefficient is 



»-£ 



p 2 /pi + 



/vi 2 /v 2 2 - 



sin 2 6 



/l - sin 2 6 





/V 1 2/v 2 2 _ 



sin 2 





A - sin 2 6 (5) 



where 8 = angle of incidence from the normal to the 

 surface (degrees) 



For normal incidence, 6 is equal to zero; thus equation (5) reduces to 



= p 2 v 2 - pi v i _ z 2 - z r 



R p 2 V 2 + pjV-l Z 2 + Z 1 (6) 



which was given earlier as equations (2) and (A). 



The relationship between losses of acoustic signals attributable to 

 the seafloor and the reflection coefficient is given by the equation for 

 acoustic bottom losses as follows: 



