Calibration of Quantitative Echo Sounders by Using Echo from Water Tank Surface.

In order to get reliable results from surveys by quantitative echo sounders, an accurate calibration of the sounder is necessary especially for the transmitting and receiving system. Therefore, we investigated a new method of simple and accurate calibration by utilizing the echoes from the water surface of an experimental water tank. We show that the method can easily calibrate the equivalent beam width of surface scattering by application of the property that the backscattering strength of the surface of water is 0dB. In case of a sharp beam, we show that the equivalent beam widths for surface scattering and volume scattering are nearly the same. Moreover, it is possible to perform an overall calibration of the transmitting and receiving system, including the equivalent beam width and the transmitting and receiving sensitivities, thus producing a more reliable result than the method in which each factor is measured separately.