Dynamic calibration for multi-beam bathymetric system based on characteristic data processing
The geometric installation error of the multi-beam bathymetric system will affect measure accuracy of the depth and location, which must be faced and resolved in the engineering survey urgently. The most important three kinds of the installation error are roll error, pitch error and yaw error. Through quantitative analysis of impact of installation error to the measure result, a dynamic calibration method has been proposed in the paper. In the method, installation errors can be obtained by analyzing bathymetric result from the characteristic terrain seafloor and the errors will be used as the parameters to calibrate other bathymetric result. Validity of the method has been proved by processing the measure data from Songhua Lake test.
Measurement error analysis of multibeam echosounder system mounted on the deep-sea autonomous underwater vehicle
The measurement error sources of the multibeam echosounder system (MBES) mounted on the deep-sea autonomous underwater vehicle (AUV) are analyzed according to the composition features of the system. By analyzing the AUV sailing poses, the installation deviation of the multibeam measuring probe and the navigation and positioning system, the depth error estimation model and the position error estimation model of MBES are established. Based on the models above, the simulation is carried out considering the installation error of MBES. The deep-sea AUV conducted a sea trial at a drilling well site in Bohai Sea with a fixed depth of 7 m above the seafloor. The pose fluctuation of the AUV is derived. By comparing with topography in the area of the well site, the validity of the depth error estimation model and the position error estimation model are tested. The results provide design considerations of the integration installation of MBES to the AUV system. They are also important for the measurement data pose processing for MBES.
Analysis on the characteristics of phase difference sequence in super wide coverage multi-beam echo sounder
The ocean is much more than 70% of the surface on the Earth, many kinds of mineral resources and natural gas exist under seafloor. Before mining for them we need detail terrain information of the seafloor. Multi-beam echo sounder is one of the current major equipments to obtain bathymetry of ocean, whose working principle is to estimate the DOA (Direction of Arrival) and TOA (Time of Arrival) of echo from each footprint on the seabed, and then to get the depth. To obtain super wide coverage of oblique incident angle, a phase detection method, such as the array separation method, is often used. The phase based detection method is to locate the zero-crossing of the phase difference curve through function fitting and then to achieve the DOA estimation of echo. In order to fit better the phase difference curve, the paper presents a theoretical analyzing of the phase difference sequence in super wide coverage multi-beam echo sounder. In this paper, based on output of FFT beam-former, a mathematical expression of phase difference sequence in multi-beam-former has been derived. The relation between the shape of the phase difference curve, the extent of non-confusion region, zero-crossing point position and the acoustical center's distance of two sub-arrays, number of sub-array's hydrophones, sloping angle of array, beam index has been discussed. Simulation based on a model assumption has been performed to verify the derived conclusions. The research results show that the theoretical mathematical expression matches simulation data and sea trial data very well.