SUMMARY 



OBJECTIVES 



The general objectives during the past three years for the bottom-interaction 

 program were to: 



1. Determine, study, and predict those characteristics (or properties) of the sea 

 floor affecting sound propagation and the prediction of sonar and surveillance performance 



2. Place these properties in a fonn usable by underwater acousticians and 

 engineers 



3. Produce geoacoustic models of the sea floor as required for experimental, 

 predictive, or theoretical work 



4. Develop accurate and efficient methods for coupling geoacoustic models to 

 standard propagation models. 



RESULTS 



• It was determined that the following properties were required for geoacoustic 

 models of the sea floor which are intended to support underwater acoustics studies: 



1. Thicknesses of sediment and rock layers 



2. Compressional wave (sound) velocity and attenuation profiles and 

 gradients through the layers 



3. Density profiles and gradients through the layers 



4. Shear wave velocity and attenuation profiles and gradients through the 

 layers 



5. Additional elastic properties (e.g., Lame's constants) 



6. Bathymetry in any insonified area to get slope, relief, topography, and 

 water depths 



7. Properties of the overlying water mass (as from Nansen casts and 

 velocimeter lowerings) 



• Laboratory measurements of sound velocity and associated properties in 

 sediment cores continue to be valuable data. These measurements permit correction of 

 laboratory sound velocity and density to in situ values and prediction of sound velocity 

 and density due to interrelations between common proportion (e.g., sound velocity versus 

 mean grain size or porosity). Revised tables of properties (and regression equations of 

 their interrelations), separated into the main environments and sediment types, greatly 

 facihtate predictions of various properties. New measurements in over 400 samples of 

 calcareous sediments allow, for the first time, realistic predictions of sound velocity and 

 density in this sediment type. 



