Practical considerations in the amplitude and phase calibration of sonar systems in laboratory water tanks using the standard target method

The standard target method is a well-established procedure for calibrating scientific sonar systems, mainly in the areas of fisheries and acoustical oceanography. An extension to include target phase as well as amplitude has been proposed, based on complex deconvolution and frequency-domain calculations. Previous studies have investigated the factors that undermine the accuracy of the calibration process, thus degrading the performance of the acoustic instrument. In this work, the stability and repeatability of a broadband sonar system capable of measuring amplitude and phase is assessed. The system response obtained is evaluated in terms of its long and short-term statistical behaviour. Fixed targets, including a large metal reflector, are used for extended measurements aimed at the study of echo fluctuations. Also, the performance of a widely-used calibration target, namely tungsten carbide spheres with 6% cobalt binder, is revisited. Its reliability is compared to that of tungsten carbide spheres with nickel binder, which have superior corrosion resistance. Using the coefficient of variation as the main statistical parameter, distinct trends are identified in the acoustic returns, with a potential connection to corrosion processes.