Patent attributes
In an under water detection for detecting the phase difference of an echo by two reception beams according to a split beam method, the difference Δθ between the phase difference of an echo detected by first and second reception beams formed in some direction and the phase difference of the echo detected by first and second reception beams which is formed in a direction rotated from the former direction concerned by a predetermined angle is detected by a phase detector. A reliability judging unit judges whether the difference Δθ detected by the phase detector is within a predetermined range or not. If the difference Δθ is within the predetermined range, an echo is displayed on a display unit. If the difference Δθ is not within the predetermined range, the echo is displayed with a specific color tone or the echo is not displayed.
