Research On ADCP Environment Adaptability Doppler Frequency Estimation Technology And DSP Implementation

Acoustic Doppler velocity profiler(ADCP)is a common instrument used in modern hydrologic surveys.It is mainly used to measure the currents velocity of rivers and oceans.The ADCP system takes advantage of the acoustic Doppler effect and calculates the corresponding velocity by estimating the Doppler shift of the echo.The quality of the echo signal has been influenced by the complex measurement environment,which seriously affects the accuracy of the flow estimation.Therefore,in view of the ADCP measurement environment,this thesis studies the Doppler frequency estimation technology with environmental adaptability,and proposes corresponding improvement methods.The specific work is as follows:1.This thesis analyzes and discusses the basic theories and methods of ADCP Doppler flow measurement principle,transducer formation,flow stratification principle and so on.It analyses the commonly used method of Doppler frequency estimation of complex autocorrelation method,and three kinds of flow measurement methods,such as broadband measurement.2.On the basis of the broadband flow measurement and the Doppler frequency estimation of the complex autocorrelation method,a Doppler frequency estimation method based on the linear phase characteristic of complex autocorrelation peaks is proposed.By analyzing the phase characteristics of the complex autocorrelation peaks of the phase coded modulation signals,the least square solution of the phase between the peaks is derived.At the same time,a phase ambiguity method based on frequency offset prediction is proposed for phase ambiguity problem of phase least square solution.In this method,by the means of the characteristic of the frequency domain resolution of frequency spectrum analysis superior to the frequency length corresponding to the phase fuzzy interval,the Doppler frequency is pre-estimated by the FFT transform,and the phase ambiguity problem is solved.The effectiveness of the proposed method is verified by simulation analysis.3.In this thesis,the influence of environmental factors such as scatterer distribution on signal quality such as SNR is analyzed.A Doppler frequency measurement method based on the variable length pulse signal is proposed.The spatial resolution of the shallow water layer and the Doppler frequency estimation precision of the deep water layer are ensured by alternately transmitting the long and short pulse signals.Besides the weighted average Doppler frequency estimation method of piecewise signal is proposed.The Doppler frequency of the segmented signal is smoothed by different weighting methods,which makes the standard deviation of the Doppler frequency estimation lower by more than 20%,and effectively improves the accuracy of the Doppler frequency estimation.Simulation analysis verified the feasibility of the two methods mentioned above.4.The algorithm software is developed on the hardware platform of TMS320C6678 based core DSP processor and MCU MSP430F5359 coprocessor.Aiming at the large amount of computation of environmental adaptability frequency estimation,a multithread parallel computing method is designed,which improves the efficiency and speed of data processing.At the same time,the system has been debugged and verified.