Research On Signal Demodulation System Of Laser Flowmater At Deep Sea

The deep sea is an unknown new field for human beings.The submarine hydrothermal vent is a window for the exchange of internal and external matter between the Earth and an important factor in the circulation of the Earth's heat flux and chemical elements.Submarine hydrothermal flow rate measurement can provide an effective means for mass flux analysis of hydrothermal output,and has important application value in many fields such as geology,ocean and ecology.The laser Doppler velocity measurement technology is suitable for the flow rate measurement of submarine hydrothermal vents due to its non-contact measurement and high precision.As a key component of laser Doppler deep-sea hydrothermal flow velocity detection,the signal demodulation system has an important influence on the final signal velocity accuracy and anti-noise performance.Due to the limitation of the volume and weight of the equipment by the deep sea detection,the signal demodulation system needs to solve the narrow space of the pressure tank,the difficulty in extracting the peak of the seafloor hydrothermal signal,and the weak signal of the deep sea hydrothermal vent is extremely weak.In view of the above problems,this paper proposes a new Doppler signal processing platform,improves the Doppler signal processing scheme,and realizes the flow velocity measurement under the simulated "black chimney" environment.Firstly,this dissertation proposes a Doppler signal processing platform based on the SoC.The Zynq ARM+FPGA SoC chip XC7Z020 from Xilinx is selected as the main chip of the system.Bandpass sampling is selected as the signal sampling method according to the requirements.The implementation plan was planned and designed.The platform is small in size and can be implemented in a narrow pressure-resistant cabin space in deep sea applications.It does not require the interconnection of FPGA and ARM core microcontrollers on the PCB,and reduces heat generation without affecting temperature sensitivity.Laser light path for deep sea laser flow meters.Secondly,this paper analyzes the difficulties caused by the flow characteristics of seabed hydrothermal fluid to signal measurement,and improves the conventional Doppler signal processing scheme.In the signal processing process,the spectral peak clustering processing method is added to the spectrum peak in the signal spectrum.The clustering of 2 clusters solves the problem of spectral peak dispersion caused by turbulence,and uses the symmetrical zero-area method to obtain spectral peaks in the specific design of the signal processing scheme,which improves the demodulation of the system at low SNR.Sensitivity,also superimposed the appropriate window function before the Fourier transform,to avoid causing spectrum leakage.Finally,based on the above scheme,this paper realizes the signal demodulation system suitable for deep sea laser Doppler velocimeter,and successfully calibrates the dial speed,verifies the measurement accuracy of the system,and carries out system integration test and pool experiment.This equipment is ready for the final deep sea launch.