Objectives   With the gradual development of marine resources, the number of vehicles operating under the sea surface has rapidly increased, and the problem of the electromagnetic detection of underwater complex targets such as underwater vehicles needs to be solved urgently.

  Methods  Based on the total-field scattered-field source finite-difference time-domain method (TSS-FDTD) and the method of field value conversion on the sea surface, the spatial distribution of scattering fields generated by the underwater antenna array irradiation of target underwater vehicles is analyzed. The field distributions in the regions near the underwater antenna array and complex target, in the seawater and above the sea surface are obtained by calculation, and the spatial scattering fields of the three groups with different relative positions of target and source are compared and analyzed.

  Results  Through comparison and analysis, the scattering fields of the three groups in the seawater environment are clearly different, and the existence of the underwater target can be determined by observing the scattering fields. While the scattering fields of the three groups above the sea surface show little difference, the existence of the underwater target can be still determined by observing the value and energy distribution of the scattering fields.

  Conclusions  The results of this analysis can provide numerical references for detection radar with similar working frequency bands, and provide technical support for the fields of underwater vehicle detection, underwater rescue and sunken ship salvage.