Study On Detection And Processing Of Optical Heterodyne Detection Signal For Ship Wake

In recent years, optical detection of ship wakes has become a hot research topic. According to the motion characteristics of bubbles and turbulence in ship wakes area, the existence and the characteristics of wake are determined by detecting the change of the Doppler frequency shift of moving bubbles and turbulence, in order to get the distance, azimuth and other data of the target ship indirectly. In this paper, the heterodyne detection method of the ship wake laser Doppler shift is studied, and a heterodyne optical signal detection and process system is designed for the Doppler frequency shift of the ship wakes.1. Based on the principles of laser heterodyne detection and wake bubble heterodyne laser Doppler shift signal characteristics, the main characteristics of the optical signal and the electric signal of the detector are analyzed, and compared with the common signal process method.2. The experimental system of Doppler frequency shift heterodyne detection of wake bubbles is set up, and the characteristics of the heterodyne signal of the Doppler shift of different simulated wake are studied. The characteristics of Doppler frequency shift heterodyne signal of the bubble group under different bubble number density and different velocity distribution are obtained.3. According to the characteristics of Doppler frequency shift optical heterodyne signal, the sampling rate and sampling precision of the signal acquisition circuit are determined, and then the appropriate operational amplifier chip and analog digital conversion chip. CPLD is chosen as the control signal acquisition circuit chip. The corresponding signal conditioning circuits, analog to digital conversion circuit and CPLD operating circuit are designed. The hardware description language Verilog is used to realize the control of analog digital conversion circuit, data read and data cache, and the DMA interface for high-speed data transmission to the signal processor.4. The digital signal processor DSP is used as the main chip of signal processing, and the signal processing circuit of DSP is designed. Based on the fast Fourier transform algorithm to analysis discrete digital signal spectrum analysis, the Fast Fourier transform is implemented by DSP, which can obtain the real-time shift spectrum of wake bubble.