Study on the Backscattered Singals of Laser Radar
|School||Harbin Institute of Technology|
|Keywords||laser radar Doppler three-dimensional wind field coherent detection signal-to-noise ratio(SNR)|
Laser radar is a kind of radar which takes laser beam as the carrier. It measures not only the distance, but also the velocity, which achieves accurate tracking. By calculating the Doppler frequency shift of the scattered signals, the system can get the information of the velocity of the target. As the frequency of the laser is 2-4 magnitudes higher than that of the typical millimeter-wave, the Doppler shift is directly proportional to the frequency of the carrier, so the sensitivity of laser radar or lidar is better than the typical radar. The Doppler Lidar makes the measurement of the three-dimensional global wind fields into reality.In this dissertation, based on the thorough research of the development and the principle of the Doppler Lidar, a lidar system has been constructed, which contains a CW laser of 1.5μm, acousto-optic modulators, a heterodyne detector and other equipments. The dissertation analyzes the structure of each section of the system and all principal devices, including a transmitter, air channel, a receiver and the unit of signal process. The space channel is an important section so the dissertation focuses on this part, proposes the theory of slicing of the atmosphere and constructs the channel model. Based on the models of the space channel and the whole system, the simulation in the time domain has been achieved. Both the waveforms of the time domain and frequency domain have been drafted. From the two waveforms, a high signal-to-noise ratio(SNR) has also been got. The dissertation analyzes the effect to SNR of each parameter. The simulation verifies the correctness of the theory and the system, which lays a good basis for the further work of setting up the real system.Finally, based on the theory analysis and the simulation, the key devices have been chosen, and tested for whether they are practical. The real system is founded by the structure of the theory and we carry out field testing. The Doppler lidar system gets the scattered signal from the space channel successfully. The result of the test demonstrates that the velocity of the air can be calculated below 1km in the distance, the accuracy of the velocity is 0.5m/s, and the accuracy of the distance is around 17m. The research of the theory and testing indicates that the Doppler Lidar system is correct and the prototype is practical. It can probe the atmosphere in the clean air conditions with high resolution and high accuracy.