Some Aspects of Reflection of Dolphin FM Signals (Whistles) in an Experimental Tank

Abstract

Reflections of FM signals (whistles) of two Black Sea bottlenose dolphins (Tursiops truncatus) from the boundaries of a tank many times smaller than the spatial extent of the signals were recorded for the first time. It is shown that dolphins produce whistles with sound pressure levels (about 2 Pa) only slightly exceeding (by 3–8 dB) the acoustic noise amplitudes of the tank. It has been established that as they propagate, FM signals are repeatedly reflected from the tank boundaries; the shape of the emitted signal is distorted as a result of interference with signals reflected from the boundaries of the tank and acoustic noise. In contrast to the time domain, the FM signal spectrum is more resistant to interference; therefore, the signal-to-noise ratio of the spectral power densities (SPD) of the same signals and their reflections reaches 30–40 dB. The results indicate the advantages of analyzing FM signals and their echoes in the spectral domain.