Data obtained from the measurement of backscattering of sound from the ocean bottom at 16 locations around the coast of the United States of America are presented. Data are given as a function of grazing angle and frequency for mud, sand, and gravel. The range of frequency was 12.5 to 290 kc/sec and the range of grazing angle was 1.0 ø to 90 ø. Backscattering increased with grazing angle according to the sin and sin", depending on the value of angle and the type of sediment. Backscattering increased with frequency according to the 1.6 power for some locations. It is concluded that a knowledge of the particle structure of the bottom is useful in estimating the reverberation level.

An experimental study of the scattering of acoustic energy from solid metal spheres in water has been carried out in the frequency range 50–150 kc and with a range of sphere sizes from 1 to 7 in. in diam, giving values of ka (acoustic radius) from 4.1 to 57. Data are presented which show the scattered pulse formation for pulses which are short compared to the sphere and for pulses which are long compared to the sphere as a function of frequency, of scattering angle, and of sphere composition. The study shows that the spheres cannot be treated as rigid bodies since an appreciable amount of energy penetrates the surface and results in a complicated echo structure for the scattered signal. The back-scattered target strength of spheres for short pulses (and considering only the surface-reflected pulse) is essentially constant with frequency for large ka, and is slightly less than the theoretical value for rigid spheres. For pulses which are long compared to the transit time across the sphere, the target strength fluctuates as much as 30 db for small changes in frequency. For short pulses the angular distribution of the scattered energy is fairly uniform over the back 180°, but this is not true for long pulses.

This paper presents the results of an experimental investigation of several passive sonar targets of the types used for calibration, marking, and tracking. Targets studied include spheres, spherical lenses, triplanes, icosahedrons, biconics, and some composite types designed to have specific frequency responses. It is concluded that, of the targets investigated, only the accurately made sphere and spherical lens are suitable for use as calibration standards under the condition of the target being supported by a flexible line. The various corner reflector configurations are suitable for marking, navigation, and tracking. The feasibility of designing passive targets with a specified frequency response is demonstrated.

This paper presents the results of an experimental investigation of the scattering of acoustic energy from finite circular cylinders in water. Photographs are shown of the pulses scattered in the backward direction in the plane normal to the longitudinal axis and in the plane containing the longitudinal axis of a cylinder. The echo structure exhibits characteristics dependent upon the corners of the cylinder where there is a sharp change in the slope of the projected area and discontinuities between air, brass, and water. The photographs of pulses returned from the cylinders in the plane normal to the longitudinal axes imply the existence of surface waves which travel around (the) circumferences of the cylinders. Distribution-in-angle diagrams of acoustic energy scattered in the plane perpendicular to the longitudinal axes of solid and hollow air-filled cylinders were taken for changes in cylinder length, changes in pulse length, and changes in acoustic radii. Length modes of vibration do not affect significantly the energy scattered perpendicular to the longitudinal axis. When pulses, which are long compared to the diameter of the cylinder, are used, the scattered energy distribution is dependent upon the composition and the acoustic radius of the cylinder.

This paper presents the results of an experimental investigation of the scattering of acoustic energy from finite circular cylinders in water. Solid and hollow brass cylinders were used as targets. Distribution-in-angle diagrams of acoustic energy scattered in the plane perpendicular to the longitudinal axis of the cylinders are shown for changes in finite cylinder length, changes in pulse length, and changes in frequency. Pulse photographs are presented to describe the echo structure of solid and hollow cylinders. Photographs are shown of the pulses scattered in the backward direction in the plane normal to the longitudinal axis of the cylinder and in the plane containing the longitudinal axis of the cylinder. The change in echo structure is presented as a function of pulse length and frequency. The echo structure exhibits characteristics dependent upon the sharp corners of the cylinder where there is a large change in slope and a discontinuity between brass and water. The photographs of pulses returned from the cylinders in the plane normal to the longitudinal axis describe the existence of surface waves which travel around the circumferences of the cylinders. (This work was partially supported by the Bureau of Ships.)