To acquire a received signal with broadband width and a high signal-to-noise ratio (SNR) by using a time reversal (TR) method for target ranging, we had developed a sensitivity-compensated amplitude- and frequency-modulated (SC-AFM) signal. The SC-AFM signal has two-order sensitivity compensation to ensure the TR reference transmitting a signal with one-order sensitivity compensation. In that previous work however, the phase distortion of sensitivity was not taken into account in the calculation of the second-order compensation. In the present study, considering the possibility that the phase distortion could unexpectedly influence the shape of the time-domain TR reference signal, we propose a phase-aware SC-AFM signal and studied its ability to enhance the transmitting energy of the TR reference signal and thus improve the accuracy of target ranging. The experimental results show that by using the phase-aware SC-AFM signal,(i) the normalized power of a received signal of its direct wave is enhanced to approx. 0.41 dB,(ii) the SNR of compressed signals for distance measurement is improved to an average of >0.4 dB, and (iii) the accuracy of distance measurement is improved by >3%. Although these quantitative results would depend on the experimental set-up and conditions, they indicate that the phase-aware SC-AFM signal’s efficiency can be expected for higher-accuracy target ranging.
Passive acoustic monitoring (PAM) has been introduced to monitor rockfish populations and distributions. We conducted water tank experiments to determine whether the white-edged rockfish (Sebastes taczanowskii) is soniferous and to confirm whether its sound properties are appropriate to adopt the PAM method. We observed two types of sound production by white-edged rockfish. The pulse durations of the Type 1 and Type 2 sounds were 0.017±0.003 s and 0.071±0.034 s, respectively, and their peak frequencies were 456.0±54.9 Hz and 116.3±28.1 Hz. These results suggest that white-edged rockfish produce sounds specific to their species and that it would therefore be possible to estimate the fish population by PAM.