| The ultra-short baseline positioning system is an important and commonly used positioning and navigation system with the advantages of small size,easy installation,easy calibration,etc.It has been practically applied in many maritime military and civil fields,but there are positioning errors in the ultra-short baseline positioning system due to its own scale,working sea conditions,processing accuracy and other factors.Therefore,it is necessary to make a comprehensive analysis of the working error of the ultra-short baseline positioning system and its influence mechanism by various factors.The correlation between the positioning accuracy and various factors influencing the error is sorted out by combining the working principle of the ultra-short baseline positioning system,and the influence mechanism and degree of each factor are quantitatively analyzed by simulation calculation.The main work of the thesis includes:(1)The positioning principle of the ultra-short baseline positioning system is described,each parameter affecting the ultra-short baseline positioning accuracy is studied,and the factors affecting each parameter are briefly analyzed and summarized,the effect of time delay difference and ship attitude is simulated and studied,and the time delay estimation technique affecting the accuracy of the parameters of the time delay estimation value is described,leading to various error factors in the positioning process.(2)The various error factors in the ultra-short baseline positioning process,including ocean noise,base array shape,base array installation error,transducer distortion error,and hydroacoustic channel response error,are sorted out and studied in detail,and the influence mechanism of each factor is explored,and the degree of influence of each factor is analyzed from the perspective of time delay estimation.Marine environmental noise affects the waveform of the received signal and influences the time delay value of the system.The accuracy of time delay estimation differs for different transmit signals.The speed of sound error not only affects the slant distance of the target,but also affects the measurement angle of the system.The ship attitude affects the azimuth and pitch angle of the target.the GPS error only affects the absolute geodetic coordinates of the target.The transducer distortion will cause distortion of the transmitted signal,and the hydroacoustic channel will produce propagation loss and multipath effect,affecting the waveform structure of the received signal.(3)Lake tests were conducted to verify the influence mechanism of the hydroacoustic channel through signal transmission and reception in the field.The experimental results show that the time domain waveform of the received signal varies greatly in the hydroacoustic channel due to the noise of the water environment and the multipath effect,and that the waveform structure of the signal changes when the source is above the thermocline compared to when the source is below the thermocline,with smaller direct waves and larger multipath signals,and the time delay value is estimated at the multipath signal,causing a fixed error in the time delay estimate.The results of this thesis show that the hydroacoustic channel response and ship attitude affect the signal waveform structure and time delay estimation value during ultrashort baseline positioning,which are the main error factors,while the environmental noise,sound speed error,GPS error,transducer distortion error and other factors affect the absolute coordinates of the target and distortion of the transmitted signal,which have less impact on the positioning system and are secondary factors. |
