![]() While the error analysis is mainly aimed at phase response, the limits of the classical amplitude-only standard-target calibration are also revisited. Sources of ambiguity are examined in terms of system, medium and target uncertainties. Calibration accuracy is examined by comparison to theoretical results. ![]() Acoustic scattering from target spheres is predicted with full-wave modal solutions. This approach minimizes the impact of range uncertainties in the calibration process. Frequency domain data processing is used, with target phase measured as a phase angle difference between two frequency components. ![]() The technique is an extension of the widespread standard-target sonar calibration method, based on the use of solid metallic spheres as standard targets. A sonar system phase calibration method, which includes both the amplitude and phase response is proposed. This thesis investigates the incorporation of target phase into sonar signal processing, for enhanced information in the context of fisheries and acoustical oceanography. An experiment is included to illustrate the method and statistical properties of the measurement are discussed. Using this measured estimate of the wavenumber corresponding to the propagating wave, the Newton-Raphson gradient method is applied (inserting the estimated wavenumber into to the theoretical dispersion curve equation for wave propagation in a fluid-loaded plate,) hence resulting in an estimate of the shear wave speed. Once the data is in the wavevector-frequency domain, the propagation wavenumber of each specific wave type can be estimated by fitting a circle to each collection of spectral peaks. The temporal domain measurements are transformed into the frequency domain using a Fourier transform, then, the spatial domain measurements are transformed into the kx,ky wavevector domain using two Fourier transforms. The submerged plate is mechanically shaken and a scanning laser vibrometer is used to measure normal velocity on one surface. This paper develops an inverse method to estimate, in water, the shear wave speed in an isotropic, thick, elastomeric plate. This model assumes single-layered panels. The sound speed is typically determined to an accuracy of +/- 30 m/s, as judged from a propagation-of-error calculation. Four (or fewer) adjusted parameters accommodate the measurements over the stated frequency decade, even for samples that exhibit significant dispersion. The sound speed and attenuation determination technique employs least-squares fitting of a causal model to the measurements. After the stated 20 min settling time, however, the phases return to the values obtained prior to rotation, or after temperature stabilization, to within +/- 1/2 deg. Temperature stabilization within the medium as well as the material is also required before measurements can take place. These differences are distributed randomly across frequency. ![]() For example, rotating the panel 10 degrees, then immediately returning to the original position, causes the observed phases to differ by up to 10 deg from those obtained prior to the disturbance. It was observed that a "settling time" of approximately 20 min is required to obtain reproducible phase measurements if the experiment is disturbed even slightly. Although the methods were developed over the frequency decade 10-100 kHz, they are not limited to that band. Presented also is a procedure for determining the phase speed and attenuation of the panel material. A technique for measuring the change in phase produced by the insertion of a panel between a projector and receiver is described. ![]()
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