An approach to high-accuracy target ranging by using an ultrasonic pulse echo with pulse compression is discussed. To acquire a receiving signal with a broader bandwidth and flatter spectrum, we proposed an AM-sensitivity-compensated signal, which was calculated by inversing the spectrum of the ultrasonic response function containing the sensitivities of the transmitter and receiver. Furthermore, to acquire a receiving signal with higher signal-to-noise ratio, we propose an FM-sensitivity-compensated signal, which is a signal with an identical amplitude and a spectral amplitude property that compensates for the unevenness of the receiving signal brought forth by the ultrasonic transfer function. The FM-sensitivity-compensated signal is calculated by non-linear frequency modulation according to the spectral amplitude of the AM-sensitivity-compensated signal. In this study, we examined the accuracy of target ranging in water experimentally by using an FM-sensitivity-compensated signal with pulse compression. The result verifies that the target ranging by using an FM-sensitivity-compensated signal is efficient even when the signal-to-noise ratio is low.

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