A TECHNIQUE FOR CALIBRATION OF MONOSTATIC ECHOSOUNDER SYSTEMS

A calibration technique has been adapted to render complete system cal ibrations of high-frequency acoustical instrumentation. This is based on standard targets; specifically, precisely manufactured spheres comp osed of tungsten carbide with 6% cobalt binder, The use of multiple sp here sizes was found to be advantageous, both as an independent check of the calibrations, and so that resonances in the sphere responses at certain frequencies could be avoided, Complete system gains and beam patterns, which include effects of bandpass filters and finite-pulse l engths, were determined by moving the spheres individually in the tran sducer far-fields. Use of this procedure ensures control over the acou stical characteristics of transducers, which may change from the time of manufacture and first testing due, for example, to platform mountin g, It also provides a direct means of measuring the sampling volume at relatively high and constant signal-to-noise ratios. Implementation o f this technique is discussed using a multifrequency sonar system as a n example.