GNSS Multi-antenna Ship Attitude Compensation Technology In Complex Multi-beam Sounding Environment

Multi-beam bathymetric system has the characteristics of high efficiency and high accuracy,making it play an increasingly important role in marine surveying and mapping.In conventional measurement,multi-beam usually needs INS equipped to provide attitude information of the ship.However,in the complicated measurement environment such as abrupt change of ship speed or turning,there is a certain error in the attitude measurement of the INS,which will cause a certain depth error in the multi-beam based on the INS attitude measurement.In comparison,GNSS navigation errors do not accumulate over time and are cheaper than INS.When three GNSS antennas are used and the three antennas form a plane,the three-dimensional attitude angle of the ship can be measured by GNSS.Especially in complex measurement environment,GNSS attitude measurement still can guarantee high accuracy,which makes GNSS/INS integrated navigation become a research hotspot.Therefore,this paper focuses on ship attitude compensation under the condition of multi-beam complex sounding,the specific research work is carried out on the influence of attitude error on multi-beam,GNSS attitude measurement method and error analysis,and the construction of GNSS/INS loose combined attitude measurement method based on difference value of attitude.The main achievements and innovations made in this paper are as follows:(1)The influence of attitude error on multi-beam bathymetry and the characteristics of INS attitude error are analyzed theoretically,and verified by related experiments.Among them,the linear acceleration motion will make the attitude measured by INS produce a certain error on the pitch angle,but the error has little influence on the multi-beam sounding;the turning motion will cause a certain error on the roll angle measured by the INS,which has a great influence on the multi-beam sounding,and even leads to the distortion of the final seabed topographic map;when the sounding ship is on sideslip,the attitude of the INS will have some error on the pitch angle and the roll angle,which has the greatest influence on the multi-beam sounding and should be avoided as far as possible.(2)The attitude measurement method of GNSS three antenna is introduced in detail.Through the analysis of the MATLAB simulation experiment and the measured data,it is concluded that the attitude accuracy is related to the positioning accuracy of GNSS,the length of the GNSS baseline and the angle between the GNSS baseline.Therefore,when the GNSS positioning accuracy is certain,we can increase the baseline length and double baseline orthogonal layout to improve the accuracy of GNSS attitude measurement.PPP,PPK,and MBD are three common dynamic positioning methods for GNSS.Experiments have found that the GNSS attitude accuracy calculated by the MBD model is superior to the other two methods.(3)The accuracy of interpolation by four common interpolation methods for GNSS attitude is compared and analyzed,and a GNSS/INS loose combination attitude measurement method based on attitude difference is proposed.Experiments show that the cubic spline interpolation method can ensure that the GNSS attitude has the same high sampling rate as the INS attitude under the premise of ensuring the GNSS attitude measurement accuracy.Then,based on this,the GNSS attitude measurement accuracy is used as the threshold of the GNSS and INS attitude angle difference.And this threshold is used as a condition for the GNSS and INS attitude selection,and the reliability of the method is proved by experimental data.The combined attitude obtained by this method can effectively improve the multi-beam sounding error in the complex sounding environment and realize the smooth transition of the seabed topographic map under the complex sounding environment.