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Calibration of broadband active acoustic systems using a single standard spherical target

A new method is developed in which a single standard target is used to calibrate the system response of broadband monostatic active acoustic systems. Spheres have commonly been used to calibrate narrowband systems. A major challenge involves the resonances of the scattering by the sphere. For narrowband systems, the sphere is designed so that the acoustic frequency is between the resonances. However, this cannot be done for broadband systems as the frequencies will span multiple resonances. Our method completely eliminates the source of the resonances through pulse-compression processing of the signal. Through this processing, the echo from the front interface of the sphere is isolated from other echoes which cause the resonances. The echo from the front interface is generally weakly dependent upon frequency, making it ideal for calibrating a broadband system. The method is a generalization of what was proposed by Dragonette et al. (J. Acoustic. Soc. Am. 69,1186-1189 (1981)). The advances in this new method involve incorporation of signal processing to better isolate the echo, as well as a more accurate treatment of the scattering physics. As a result, the approach is applicable over a wide range of conditions.