Either amplitude based methods or phase based methods are usually used in multibeam bathymetry system and chosen in practical measurement by ad hoc criteria. The errors of the detection are often caused by choosing wrong detection method. In this paper a modified muhiple subarrays amplitude-phase united detection method is proposed , which uses both the amplitude and phase of echo from bottom. This new method not only realizes the super-wide swath coverage, but also improves the detection performance by using the phase differences among subarrays in place of phases of subarrays to estimate the phase slope image. Experimental results are also analyzed and discussed to demonstrate the effectivity of the proposed approach. Document code: A Article ID: 1671 -9433(2005)02 -0039 -05 1 ~TRODUCTION Bathymetry is the measurement of depths of water in oceans, seas, rivers and lakes. Muhibeam sonars are one of the presently major equipments to collect bathymetric data, whose working principle is to estimate the DOA( direction of arrival) and TOA (time of arrival) of echo from each footprint on the bottom, and then to get the depth. The echo from near-normal incident angle is strong and short, and centralizes on the beam axes. The DOA estimation of echo from each footprint is obtained from the amplitude of the output of conventional beamformer, such as the traditional FFT (fast Fourier transform) beamformer, which can provide high resolution effectively in these areas because of the large effective size of receiving array E17. For echo from oblique incident angle, with the effective size of receiving array reducing, the spatial resolution given by FFT beamformer is lower than that of near-normal incident angle. The amplitude based bottom detection metrod,such as FFT detection method or Weighed Mean Time (WMT) detection method, is not suitable here due to the low cross track resolution and long echo duration. To obtain super wide coverage of oblique incident angle, phase based detection method I2-33 , such as array separation method, is applicable. The phase based detection method is locating the zero-crossing of the phase difference curve through function fitting and then achieve the TOA estimation. The traditional method of TOA and DOA estimation of echo uses amplitude based detection methods for the near-normal incident angle, and uses phase based detection methods for the oblique incident angle. Since the practical terrain is variable and complicated, and the type of the bottom echo is not known a priori, several kinds of detection methods are used simultaneously and the best one is chosen by certain optimum or ad hoc criteria.The mentioned traditional estimation methods just either use the amplitude or phase of the echo. It is difficult to bring forward a so-called optimum or ad hoc criteria to judge which method is better, and some avoidable errors are often caused by choosing the wrong bottom detection method. In addition, several detection methods operating real-time need larger scale hardware cost. Multiple subarrays...
