The bottom detection is very important for defining an integration layer with the bottom as a reference basis during acoustic survey of demersal fish.
Therefore, we have considered theoretically elements which form bottom echoes, and have devised a stable bottom detection method namely maximum differential voltage method, which was not influenced by variable levels and waveform transformation. The method has been shown to be effective using in-situ bottom echo waveforms and computer simulation data.
A comparison between near-botton SV profiles acquired in Funka Bay Hokkaido of Japan and East China Sea, with the threshold method and maximum differential voltage method, shows that the SV obtained with the maximum differential voltage method is 4-6 dB higher within 2m from the bottom.

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