Precise target strength pattern measurement in an indoor tank

Abstract

A precise target strength measurement system in an indoor tank is constructed. A target is rotated in pitch plane by a computer controlled stepping motor and measurements are done automatically from the start to the end. Echo data in the range between -50 and 50 degrees are stored at intervals of 1 degree on the hard disk built in an oscilloscope. Spreading loss and absorption loss are compensated for in a software to calculate precise target strength. Because all echo sounders with both output terminals of transmitting trigger signal and of echo signal are available as a transmitter and receiver of this system, precise target strength measurements are possible at any frequency for many kinds of physical models and fish. Target strength patterns of several prolate spheroidal models precisely made of expanded polystyrene are measured, and the results are compared with the exact theory of a soft prolate spheroid scattering model to ascertain accuracy and precision of the measurements. The experimental results agreed very well with the theoretical results and the correlation coefficients are almost unity.