A motion error estimation method based on seafloor tracking

In marine engineering surveying, when we control a towed synthetic aperture sonar in an uniform linear state, the survey results appear with many motion errors because of the random and multi-dimensional position fluctuation of the towed platform. A motion error estimation method based on seafloor tracking is studied in order to estimate these errors. Firstly, sonar echo data is obtained by wideband signal matched filter processing from different launch positions. According to the energy amplitude mutation, characteristics of the seabed echo we can deduce the seafloor position and eliminate abnormal values due to seafloor interface stationarity. Secondly, the approximate positional change curve of the towed platform is calculated from various sensor data. Thirdly, we can intercept the echo data from adjacent arrays in the same transmission period, according to the temporal correlation of echo data near the seafloor. The residual pitch angle is estimated by the shear average autofocus algorithm. By intercepting the echo data from redundant arrays in the adjacent transmission period - and on the basis of spatial redundancy of echo data near the seafloor - it is possible to estimate the residual heave values of the towed platform by use of the redundant phase center algorithm. In the meantime, the least square method is used to fit the linear phase error of pitch angle causing by assembly technology. Finally, the motion error of the echo data in different launch positions is finely compensated. The result of simulation and sea trial proves that the method in this paper is correct in principle and provides high engineering value.