Reseach On The Key Technology Of Acoustic Doppler Current Velocity Measurement

Acoustic Doppler Current Profiler(ADCP) is the improved sonar based on traditional method of flow measurement. As a new-style flow velocity measurement instrument, ADCP has been widely used in more and more projects related with rivers and oceans due to its high measurement accuracy, wide measurement scope and so on. So there is great theoretical and practical meaning to research acoustic Doppler measurement technology. In this thesis, we design and realize the acoustic Doppler current measurement system, and based on this system, detailed analysis and comparison among three Doppler technologies are given. Besides, we propose a method to solve velocity ambiguity occurred in current measurement. The main works are as follows:First of all, the whole flow chart of Doppler flow velocity measurement is proposed and explained, and the research and simulation about transmitting signal's sound field and directional pattern are given and analyzed. And the transformation formulas about current velocity from instrumental coordinate system to geodetic coordinate system are given.Secondly, based on the acoustic Doppler current measurement system, we compare the flow measurement characteristics and performances about three Doppler measurement technologies, and they are pulse to pulse incoherent Doppler technology, pulse to pulse coherent Doppler technology and broad-band Doppler technology. The broad-band Doppler technology combines the advantages of pulse to pulse incoherent technology and pulse to pulse coherent technology, demonstrating high measurement accuracy and scope.Then a method used to solve velocity ambiguity is proposed. Every transducer transmits N sets of signals with different code lengths to get measured velocities using complex autocorrelation method. The measured velocities are combined with the repeated phases to get N sets of possible velocities. And finally accurate velocity can be obtained by comparing the velocities in the sets. The scheme is simple and of high accuracy.Finally, we make a performance analysis about possible errors caused by calculating formula, ship swaying, sound speed and beam width. And some recommendations are given to improve measurement performance.