Waveguide invariant in shallow water is an attractive topic in recent three decades.The interference phenomena of direct wave of radiated noise of underwater target and reflection wave from sea surface and sea bottom can be considered as a typical case of shallow water waveguide. The interference striation pattern of direct wave and its reflection is the effective and comprehensive figure for better understanding the essence of shallow water waveguide invariant.

LI Qihu, WANG Lei, WEI Chonghua, LI Yi, MA Xuejie and YU Haichun of of Institute of Acoustics, Chinese Academy of Sciences presented the theoretical analysis of interference phenomena generated by direct wave of radiated noise of underwater target and its reflection wave from sea surface and sea bottom.

They showed that the interference wave resulted by sea surface reflection will produce striation pattern centered at high frequency band. But the interference of nulling frequency resulted by sea bottom reflection may be at low frequency or high frequency, it strongly depends on the acoustic behavior of sea bottom. The relationship between main parameters of interference striation pattern and target, receiver, and environment is derived. It is shown that the interference striation have the shape of hyperbolic curve. The equation set of the hyperbolic curve and its asymptotic line is presented.

This research result was published on the recently issued Chinese Journal of Acoustics (2011, Vol. 30,No.1, pp:73-80).