Abstract: Elastic wave in the seabed caused by low frequency noise radiated from ship is a so-called ship-induced seismic wave which can be used to identify the ship target in shallow sea. In order to investigate the detecting range and signal feature of ship-induced seismic wave in shallow sea with thick sandy bottom, a detecting test of seismic waves caused by random ships in inland river with thick sandy bottom is carried out with a three-component seismometer for weak seismic wave detection. The seismic waves caused by several random ships are obtained. According to the calculated time-frequency spectrum of the seismic waves, the propagation characteristics of seismic waves caused by ships in shallow water with thick sandy bottom are analyzed. The vertical component of seismic wave can propagate to a far distance compared with the horizontal component. The signal received by seismometer in far field is mainly caused by the noise radiated from the propeller because the line spectrum of the detected signal is almost the same as that of the propeller and always has a double frequency of the propeller's rotation frequency. The detecting ranges of most random ships are above 1 km based on the line spectrum of propeller.

Key words: acoustics, sandy bottom, shallow water, random ship, seismic wave, detecting test