Onshore Real-time Correction System For Acoustic Doppler Current Profiler

The onshore correction system of acoustic doppler current profiler is a device that uses simulated echo to verify and calibrate the flow and depth measurement performance of ADCP,which can not only improve the calibration efficiency of ADCP,but also greatly save the cost of underwater calibration of ADCP.In this paper,the concept of real-time calibration is proposed according to the actual debugging and calibration requirements,and the design and implementation of ADCP onshore real-time calibration system is completed.At the same time,the real-time calibration system was used to carry out a validation calibration test on the flow measurement performance of the laboratory ADCP prototype,and the expected results were obtained,which laid a foundation for the subsequent research work.The main contents of this paper are as follows:1.The development status of ADCP calibration technology at home and abroad is introduced,and the relevant principles and methods of acoustic Doppler flow measurement are studied.2.According to the principle of the generation of echo,echo model was established based on the broadband flow in a way that the echo simulation,and through the actual water echo contrast and analysis of the statistical features of radial velocity estimation results confirmed the simulation echo in two ways flow approximate to actual water echo effect validation,can meet the requirements of the docking calibration.3.Realized the design of the upper computer application program of the land real-time calibration system and the FPGA circuit construction and hardware development of the echo transmitting module of the lower computer.The application of the host computer mainly completes the function of producing,saving and transmitting the echo simulation signal,and controls the working state of the calibration system.The echo transmitting module of the lower computer mainly performs the functions of receiving and saving the echo data and digital to analog conversion,and controls the transmitting of the echo signal.4.Based on the designed calibration system,two real-time calibration schemes are proposed :(1)online real-time calibration mode;(2)Offline real-time calibration mode.The calibration processes of the two calibration modes are respectively applicable to different calibration scenarios: the online real-time calibration mode has the user editable function,that is,the environmental parameters and echo data can be updated in real time through the upper computer files directly,and it is suitable for the calibration scenes with long time and complex parameter changes;The offline real-time calibration mode does not need to be connected to the upper computer,and the calibration module can work independently.Waveform and environmental data are solidified in the onboard memory,which simplifies the calibration steps and improves the calibration efficiency.It is suitable for fast calibration scenes.The two calibration modes also expand the application range of the calibration system.5.The output echo of the calibration system is compared with the original simulation echo of the upper computer from the perspective of time domain,frequency domain and Doppler frequency offset to verify the correctness of the echo signal output by the lower computer of the calibration system.Finally,the performance of radial stratified velocity estimation,depth estimation and bottom velocity estimation of laboratory ADCP prototype device was fully calibrated by the onshore real-time calibration system.The calibration results were consistent with the set values,and the real-time performance was good.The validation test further confirmed the flexibility and practicability of the onshore real-time docking calibration system,and also provided an efficient and convenient means for the subsequent RESEARCH,development,debugging and precision calibration of ADCP.