Research On The Technology Of Acoustic Doppler Velocity Measurement For Underwater Vehicles

Underwater vehicles are important instruments for human oceanology,which will be widely used either in military or civilian fields.Underwater navigating and positioning technology with high precision makes the voyage of underwater vehicles without accident,and acoustic Doppler velocity log is necessary for underwater navigating and positioning systems.This paper studies the key technologies(including the processing method of broadband and narrowband acoustic Doppler velocity log,the technology of narrowband phased-array antenna),the technology of installation eccentricity error separation and calibration of misalignment angle of acoustic array,the detecting method for acoustic Doppler velocity log based on phased coupling array.Resolving power increases when using the broadband technique,which has been widely used in acoustic Doppler current profiler,compared with the narrowband technique.But fewer attentions have been paid on bottom echo in the past.Performance of underwater navigating and positioning in underwater vehicles relies on the velocities relative to bottom.This paper studies performance of the broadband technique with pulse-to-pulse coherent Doppler sonar signal processing techniques,transmitting m sequence signal.And the performance comparision of broadband versus narrowband is made using the method of Monte Carlo.The result proves the validaty of broadband technique when processing the bottom echo.Unlike conventional transducer,phased array antenna needn't sound compensation and has advantages in volume,weight,etc,which is suitable for applications in underwater vehicles.But there are errors among channels,such as phase shift errors,gain errors,etc,and may bring higher level of side lobe and decrease accuracy of the log.The paper analyzes the sound field and the influences caused by these errors to beam patterns after phased and velocities.We design a 300 kHz phased array antenna and its processing units with considering the conclusions drew from the simulation.Some experiments in pool,lake are carried out.When we install the acoustic Doppler velocity log on vehicles,it is difficult to make the reference frames of array and vehicles coincide with each other,because of the structures of vehicles and man-made errors,which may bring out installation eccentricity error and misalignment angle error and then decrease the precision of navigation and position.For the problem of installation eccentricity error,this paper gives an attatched velocity remending method when installation position offseting swing center,realizing the seperaiton between ture and attatched velocity.For the problem of misalignment angle error,a dead reckoning calibrating method is put forward.We establish the observation equation between dead reckoning and vehicle trajectory,realizing the calibration of misalignment angle error on any trajectory and velocity based on the least square algorithm,which simplified the experimental requirement and improving the calibrating efficiency.The simulation and experiment results show the validity of this method.It is necessary to make a thoroughly detect on velocity log after underwater vehicles assembling on land,especially for phased array antenna,which is composed of many elements arranged in a certain pattern that emit acoustic energy with different phase.There are demerits in traditional detecting method,such as disassembling the velocity log or simulating the echo with few transducers.Focusing on the problem,this paper puts forward a detecting method for acoustic Doppler velocity log based on phased coupling array antenna.It can simulate echo signal of phased array acoustic velocity log at different oceanic environments with phased coupling array antenna,realizing the acoustic signal transfered between two phased array antennas.We analyze the phased coupling array mechanism,establish the mathematic model and simulate different coupling errors that influencing on the performance of phased coupling array.Finally,a phased coupling array system is fulfilled.The simulation and experiment results show the validity of this technology.