Objectives   Measurement of acoustic characteristics of underwater targets is usually affected by the sea surface, seabed and external noise sources. It is difficult to obtain the free-field acoustic radiation characteristics of the targets. In order to solve the problem in acquiring the free-field acoustic radiation characteristics of the underwater targets in a half space whose boundary is the sea surface or the seabed where there is noise source,

  Methods   the sound field recovery method based on the boundary element method is utilized, taking the typical underwater cylindrical shell as example, the free-field acoustic radiation characteristics of the cylindrical shell affected by the sea-surface/seabed or affected by both the sea-surface/seabed and external noise sources are separately recovered.

  Results   The numerical simulation result shows that sea surface/seabed and external noise sources could greatly affect the measurement of the radiation sound field of an underwater target. But the sound power of recovery sound field separated by sound field recovery method based on the boundary element method is consistent with the sound power of free field. At the same time, the sound pressure, the directivity and other characteristics of field point are basically the same.

  Conclusions   Therefore, the free-field acoustic radiation characteristics of the underwater targets could be effectively obtained by sound field recovery method based on boundary element method.