82 THE NAVY OCEAN ENGINEERING PROGRAM 



Bottom-reflection processes are being studied by means of theoretical 

 models to determine the influences of composition, layering, roughness 

 and acoustic frequency on reflection losses. Experimental measurements 

 are being made at sea to provide accurate data and new techniques for 

 measuring bottom roughness, reverberation, and reflectivity, and to deter- 

 mine relationships between these properties. 



In addition to these major advanced development programs, various sup- 

 porting programs are leading to innovations in underwater acoustics. Im- 

 proved acoustic data collection and analysis techniques are being developed. 

 Airborne acoustic survey methods are under evaluation for the rapid col- 

 lection of acoustic propagation and reverberation data. Various acoustic 

 data collection techniques have been developed for deep and shallow water, 

 and, more recently, acoustic transmission measurements are being made 

 from deep research vehicles. 



Measurements of the acoustic and other properties of the ocean are 

 being made to investigate environmentally induced amplitude fluctuations 

 of acoustic signals as a function of range and frequency. Physical properties 

 are measured by means of buoyed current and thermistor arrays. The lat- 

 eral variability of acoustic and sediment properties is being investigated in 

 a variety of physiographic provinces using seismic reflection methods and 

 deep research vehicles. 



Considerable work is underway in the acoustics programs to investigate 

 biological scattering. Experiments are being conducted to determine the 

 abundance and distribution of the organisms populating the deep scattering 

 layers and to determine their effect on sound propagation. These experi- 

 ments are revealing that biological scattering is dependent on season, time 

 of day, acoustic frequency, and geographic location. 



Accomphshments in the exploratory development area include: 



1. The derivation of a mathematical model which explains the nature 

 of the acoustic field and the propagation loss in subsurface ducts (this 

 model is known as the Normal Mode Theory). 



2. The development of techniques for performing real-time shipboard 

 analysis of the propagation and echo-ranging data. 



3. Development of programs for computing propagation loss by ray or 

 wave theory. 



4. Experiments to measure bottom-reflection loss, reverberation levels, 

 ambient noise levels and characteristics, submarine target strength, sound 

 velocity profiles, etc. 



