Golay编码差分吸收相干激光雷达研究

Research on coherent differential absorption LiDAR based on Golay coding technology

针对差分吸收相干激光雷达在CO2浓度反演时对信号的高信噪比需求,研究了一种基于Golay脉冲编码的差分吸收相干激光雷达及其解码方法,以改善系统信噪比,降低浓度反演误差。分析了采用脉冲编码技术对传统大气后向散射信号相干探测信噪比的编码增益,研究了编码增益随本振光功率、编码长度和3dB耦合器分束比的变化规律,本振光功率越高、分束比偏离50%越多,则编码增益越低,且在实际系统中,存在最优的编码长度。当本振光逐渐增强时,热噪声对系统的影响逐渐降低,相干探测系统存在最优的本振光功率,该功率与回波无关仅与系统的噪声水平有关。脉冲编码后最优本振光功率相对于单脉冲探测时下降,但其探测信噪比仍优于单脉冲探测,当3dB耦合器分束比为0.495时,最优本振光功率为0.93mW。脉冲编码后,系统对CO2的有效探测距离增加,且在1041010范围内进行脉冲积累时,相较于原系统距离增长率大于15%。

The detection of CO2 based on coherent different absorption LiDAR (CDIAL) requires high signal-to-noise ratio (SNR). To improve the SNR and reduce the inversion error of CO2, a coherent differential absorption LiDAR based on Golay coding is proposed and the corresponding decoding method is also studied. The coding gain of SNR in traditional atmospheric backscattering signal detection is also analyzed when the pulse code technology is used. The variations of coding gain with the power of local oscillator (LO), the code length and the splitting ratio of 3 dB coupler are discussed. The higher the local oscillator power is and the more the beam splitting ratio deviates from 50%, the lower the coding gains. In addition, there are optimal code lengths in practical systems. The influence of thermal noise on the detection system decreases when the LO power grows, and there is optimal LO power which is only related to the system noise characteristics. The optimal LO power decreases with respect to single pulse detection after pulse coding, but the SNR is still higher than the traditional single pulse detection. When the splitting ratio of the 3 dB coupler is 0.495, the optimal LO power in coded system is 0.93 mW. The effective detection ranges of CO2 increase when the pulses are coded, and in the pulse accumulations of 104~1010, the improvement ratios of effective detection range are higher than 15%.