The aim of this research is to establish a measurement system to acquire 2-D sound scattering field by an underwater target. In the system, A 3-DOF (degree of freedom) block is remotely orientated by Borland C++ Builder programming language and the batch-processing for signals is used to estimate strength by programing language, Matlab. The process of experiment is simplified by standard operating procedure and the safty of facilities is controled by monitor. Based on the improvements above-mentioned, we can develop an more automatical system to save time effectively, better work conditions, reduce personnel cost, and acquire more objective outcomes. We set up experiment in an water tank of dimension 4mx3.5mx2 m, located in National Sun Yat-sen University, and choose a copper sphere of diameter 60 mm as target. The projector and receiver both are iTP-192k transducer with directivity and frequency response at 192k Hz. In order to measure the 2-D scattering field at 1 m from target without strong boundary interference, projector transmits 64 sine waves at 3.8 Hz and receiver changes direction by block and rotating mechanisms. The effects of direct signal in forward scattering field can be reduced by modified signal process according to Ding (JASA, 101(6), pp.3398-3404, 1997). The difference between actual and theoretical magnitude, based on Hickling (JASA, 34(10), pp.1582-1592, 1962), is 2~3 dB in most of backward scattering region and parts of forward scattering region (30¢X~60¢X and 300¢X~330¢X), and 5~10 dB in else forward scttering range. Generally speaking, that experimental result displays symmetrical distribution corresponds with theory and indicates the design of mechanism, software and procedure in this study practicable and useful for further research in the future.

The research aims to design an experimental testing mechanism and process for measuring the scattering strength and the pattern induced by an underwater target. The experimental data are to compare with existing theoretical results to insure the integrity of experimental design. The experiment is conducted in a water tank of dimension 4m x 3.5 m x 2m. The main work is to measure the sound field scattered by a copper sphere of diameter 60mm. There are two types of sources employed in this analysis: one is omni-directional, 70kHz CTG-0708 transducer, and the other is directive, 192 kHz iTP-192k transducer. Both transducers transmit sine waves with the pulse lengths roughly equal to 0.143 msec (equivalent to 10 waves) and 0.333 msec (equivalent to 64 waves), respectively. The scattering field theory is based on the formulation developed by Hickling (JASA, 34, 1962, pp.1582-1592). The experimental process has demonstrated that it is more difficult to measure the forward scattering field than the backward scattering field, due to the fact that the forward scattering field is likely to be mingled with the direct waves. To deal with this problem, the treatment developed by L. Ding¡]JASA, 101,1997, pp.3398-3404¡^has been invoked, in that the direct waves may be filtered by phase shift. This procedure requires the special concern on synchronism of sound source in order to avoid the variation of scattering signals. The comparison between experimental and theoretical results shows that the discrepancy in the forward scattering sector is within 3 to 4 dB, while in the backscattering sector, it is within 1 to 2 dB; however, generally speaking, the variation of the curves show a good agreement. These results indicate that the design of this experiment is basically practicable, and with further improvements, it could be applied to measure other underwater targets. As a whole, the thesis is composed by basic theory deduction, experimental instrumentation, mechanism design, and experiment data analysis. The emphases place on the design and observation of the scattering experiment, data analysis, and further improvement.

The aims of this research are to design an experimental testing mechanism and process for measuring the scattering strength and the pattern induced by an underwater target. The experimental data are to compare with existing theoretical results to insure the integrity of experimental design. The experiment is conducted in a water tank of dimension 1.8 m x 1.8 m x 1 m. The main work is to measure the sound field scattered by a copper sphere of diameter 60mm. There is one type of directive source employed in this analysis: 192 kHz iTP-192k transducer as the receiver and projector. The transducer transmits sine waves with the pulse duration roughly equal to 0.143 msec (equivalent to 64 waves). The scattering field theory is based on the formulation developed by Hickling (JASA, 1962, pp.1582-1592). In order to get more precise measurement results, this research designs a high strength and accurate mechanism with a ball-ring and aluminum workpieces. The mechanism can be used to measure target scattering signals circularly with same radius. The experimental process has demonstrated that it is more difficult to measure the forward scattering field than the backward scattering field, due to the fact that the forward scattering field is likely to be mingled with the direct waves. The comparison between experimental and theoretical results shows that the discrepancy in the backward scattering sector is within 3 to 4 dB; however, generally speaking, the variation of the curves show a good agreement. These results indicate that the design of this experiment is basically practicable, and with further improvements, it could be applied to measure other underwater targets. As a whole, the thesis is composed by basic theory deduction, experimental instrumentation, mechanism design, and experiment data analysis. The emphases place on the design and observation of the scattering experiment, data analysis, and further improvement.The aims of this research are to design an experimental testing mechanism and process for measuring the scattering strength and the pattern induced by an underwater target. The experimental data are to compare with existing theoretical results to insure the integrity of experimental design. The experiment is conducted in a water tank of dimension 1.8 m x 1.8 m x 1 m. The main work is to measure the sound field scattered by a copper sphere of diameter 60mm. There is one type of directive source employed in this analysis: 192 kHz iTP-192k transducer as the receiver and projector. The transducer transmits sine waves with the pulse duration roughly equal to 0.143 msec (equivalent to 64 waves). The scattering field theory is based on the formulation developed by Hickling (JASA, 1962, pp.1582-1592). In order to get more precise measurement results, this research designs a high strength and accurate mechanism with a ball-ring and aluminum workpieces. The mechanism can be used to measure target scattering signals circularly with same radius. The experimental process has demonstrated that it is more difficult to measure the forward scattering field than the backward scattering field, due to the fact that the forward scattering field is likely to be mingled with the direct waves. The comparison between experimental and theoretical results shows that the discrepancy in the backward scattering sector is within 3 to 4 dB; however, generally speaking, the variation of the curves show a good agreement. These results indicate that the design of this experiment is basically practicable, and with further improvements, it could be applied to measure other underwater targets. As a whole, the thesis is composed by basic theory deduction, experimental instrumentation, mechanism design, and experiment data analysis. The emphases place on the design and observation of the scattering experiment, data analysis, and further improvement.

Rough surface scattering is a problem of interest in underwater acoustic remote sensing applications. To model this problem, a fully three-dimensional (3D) finite element model has been developed, but it requires an abundance of time and computational resources. Two-dimensional (2D) models that are much easier to compute are often employed though they don’t natively represent the physical environment. Three quantities have been developed that, when applied, allow 2D rough surface scattering models to be used to predict 3D scattering. The first factor, referred to as the spreading factor, adopted from the work of Sumedh Joshi [1], accounts for geometrical differences between equivalent 2D and 3D model environments. A second factor, referred to as the perturbative factor, is developed through the use of small perturbation theory. This factor is well-suited to account for differences in the scattered field between a 2D model and scattering from an isotropically rough 2D surface in 3D. Lastly, a third composite factor, referred to as the combined factor, of the previous two is developed by taking their minimum. This work deals only with scattering within the plane of the incident wave perpendicular to the scatterer. The applicability of these factors are tested by comparing a 2D scattering model with a fully three-dimensional Monte Carlo finite element method model for a variety of von Karman and Gaussian power spectra. The combined factor shows promise towards a robust method to adequately characterize isotropic 3D rough surfaces using 2D numerical simulations. / text