Receive Beam Patterns Research Articles

Directional hearing sensitivity of the bottlenosed dolphin (Tursiops truncatus) in the vertical plane

The ability of the dolphin to detect pure tone signals presented from directly ahead, with noise presented from various vertical angles was determined behaviorally for pure tone frequencies of 30, 60, and 120 kHz. The animal's position at the centerpoint era 3.5-cm arc was fixed by requiring firm contact on a biteplate. Using a yes-no response procedure, vertical directional sensitivity was examined by varying the noise levels and determining masked thresholds via a tracking method of stimulus presentation. Polar plots of the threshold points for the three frequencies generally showed a narrowing of receiving beam patterns with increased frequency. Maximum sensitivity occurred between five and ten degrees above the midline of the mouth. Sensitivity dropped more sharply with increasing angle above the midline rather than below, as might be expected with an animal that hears via the lower jaw. These receiving beam patterns show close agreement with the echolocation pulse transmitting beam patterns reported by Au, Floyd, and Haun [J. Acoust. Soc. Am. 64, 411–422 (1978)]

Simulation of distributions of observed effective scattering strengths of individual fish

A knowledge of the probability distribution of effective scattering strengths of observed fish is important in determining the reliability of acoustic estimates of fish abundance. The effective scattering strength is defined here as the product of backscattering cross section of observed fish and transmit and receive beam patterns of observing sonar. The distribution depends on the geometry of ensonification and fish behavior, or joint distribution of spatial and orientation states of fish, in addition to the sonar beam patterns and fish target strength as a function of orientation. Simulation of the distribution is discussed and illustrated for the case of observation of gadoids, for which measurements of the dorsal aspect target strength functions at two ultrasonic frequencies are available, by a directional downward-looking sonar.

The effects of scattering and interaction on the beam pattern of a system of two parallel cylinders and a planar baffle

An investigation of the scattering and interaction effects on the receive beam pattern of a pair of parallel cylinders and a baffle will be presented. An incident plane wave is assumed and the effects of the baffle are included using classical image theory. The cylinders and baffle are considered to be infinite in extent and idealized boundary conditions are considered. An eigenfunction approach which was originally developed for electromagnetics [V. Twersky, J. Appl. Phys. 23, 407–414, 1952] and then adapted to acoustics [J. W. Young and J. C. Bertrand, J. Acoust. Soc. Am. 60, 1265–1269, 1976] is utilized to solve the multibody acoustic scattering and interaction problem. In addition, two simpler approaches are investigated. Numerical results will be presented for all three approaches, and the useful range for utilization of the simpler solutions will be shown.

Geometric sensitivity of frequency spreading due to acoustic scattering from wind driven water surfaces

Several recent studies have focused on the degree to which acoustic scattering from wind driven water surfaces exhibits frequency spreading which is asymmetric in any regular way. Ocean experiments, physical model studies and analytical models have so far not been entirely in agreement on this issue. Therefore a set of physical model experiments has been performed to investigate the sensitivity of frequency spreading asymmetries to variations in geometric parameters. These experiments were conducted using broadband probing signals in the model tank at Yale. Grazing angle, azimuth, projector and receiver beam pattern, acoustic frequency, and surface roughness were varied in a systematic way. The results of this series indicate that frequency spreading is in fact quite sensitive to a number of geometric parameters and that most current analytical models are inadequate to explain the detailed behavior of this phenomenon. [Work supported by NSF and Code 320, Naval Electronic Systems Command.]Several recent studies have focused on the degree to which acoustic scattering from wind driven water surfaces exhibits frequency spreading which is asymmetric in any regular way. Ocean experiments, physical model studies and analytical models have so far not been entirely in agreement on this issue. Therefore a set of physical model experiments has been performed to investigate the sensitivity of frequency spreading asymmetries to variations in geometric parameters. These experiments were conducted using broadband probing signals in the model tank at Yale. Grazing angle, azimuth, projector and receiver beam pattern, acoustic frequency, and surface roughness were varied in a systematic way. The results of this series indicate that frequency spreading is in fact quite sensitive to a number of geometric parameters and that most current analytical models are inadequate to explain the detailed behavior of this phenomenon. [Work supported by NSF and Code 320, Naval Electronic Systems Command.]

Optimum Transmit and Receive Beam Patterns for Sonata Operating Against Reverberation

Since the shape of the transmit beam pattern affects not only the strength of the echo but also the spacial correlation of the reverberation, optimum design of this pattern may improve performance. Following transmission of a narrow-band pulse, our system decides if an echo from a slowly moving target is present in the volume reverberation and noise. The target direction and range are known a priori. Our transmit pattern may be adjusted by applying amplitude weightings and phase shifts to the transducer inputs. Using a well-known reverberation model, we obtain the beam former for the Bayes optimum receiver. Once the optimum receiver for arbitrary transmit pattern has been found, further reduction in the error probabilities is obtained by the proper choice of transmit shading coefficients. As examples, we investigate line arrays with half-wavelength spacing. When the reverberation power is much greater than the noise power, the optimum transmit and receive patterns do not have their maxima in the target direction. When noise that is independent between hydrophones dominates, unshaded patterns are optimum.