Research On Current Velocity Measurement Technology Of Acoustic Doppler Current Profiler

Acoustic Doppler current profile(ADCP)is a new type of current measuring instrument which uses the principle of acoustic scattering to measure current velocity.It has been widely used in oceanographic research and marine application development.It can realize high-precision and long-distance flow measurement,and is an important foundation for hydrological monitoring,ocean observation,national defense construction and waterway navigation.Therefore,the research on Doppler Current Profiler is of great significance.This paper mainly focuses on the transmitting signal and receiving processing algorithm of Doppler flow measurement.On the basis of previous studies,the structure of the classical wideband Doppler current velocity measurement coding signal is improved,and an optimization algorithm is proposed to solve the problem of inevitable accuracy degradation after under sampling Doppler current velocity measurement,which effectively improves the accuracy of Doppler current velocity measurement and the environmental adaptability of the algorithm.The specific work is as follows:(1)Aiming at the phase ambiguity problem caused by classical pulse pair algorithm,an orthogonal coded unwrapping signal is proposed.The correlation and ambiguity functions of LFM signal,m sequence and Barker code are compared.The results show that the measurement accuracy and stability of coded signal are better than LFM signal.On this basis,a better coding method is selected to design the orthogonal coded unwrapping signal and the processing method of the receiver.The signal is composed of two pseudo-random coded signals with the same pulse delay and different pulse interval.Simulation results show that compared with the traditional wideband coded signal,the proposed signal can achieve 8 dB gain,realize phase unwrapping and improve the current measurement accuracy.(2)Aiming at the limitation of narrow-band complex autocorrelation algorithm and wide-band pulse pair algorithm in band-pass sampling,the optimization algorithm is proposed.Combining RVCI-M algorithm with complex autocorrelation method,a velocity measurement algorithm based on RVCI-M and complex autocorrelation method is proposed.The simulation results show that the current velocity measurement performance of the algorithm is better than that of the classical algorithm at different under sampling frequencies,and the real-time performance is higher.Based on the analysis of the spectrum characteristics of wideband coded echo,a phase wrapping algorithm based on local spectral peak search is proposed to solve the problem of wideband velocity ambiguity.The simulation results show that the algorithm is effective in velocity ambiguity.(3)The environment adaptability of the algorithm is verified.The ocean noise model is established by using the statistical power spectrum of ocean noise.The echo model with variable environmental parameters is established by combining the ocean noise model with the echo scattering model.By changing the number of scattering particles,water velocity,background noise,Doppler frequency offset and other environmental parameters,the environmental adaptability of the proposed narrowband velocity measurement algorithm and wideband phase unwrapping algorithm is tested and analyzed.Simulation results show that,compared with the classical flow measurement algorithm,the proposed algorithm has better adaptability to the environment.