Golay编码差分吸收相干激光雷达研究

胡以华, 董骁, 赵楠翔. Golay编码差分吸收相干激光雷达研究[J]. 光电工程, 2019, 46(7): 19081-. doi: 10.12086/oee.2019.190081
引用本文: 胡以华, 董骁, 赵楠翔. Golay编码差分吸收相干激光雷达研究[J]. 光电工程, 2019, 46(7): 19081-. doi: 10.12086/oee.2019.190081
Hu Yihua, Dong Xiao, Zhao Nanxiang. Research on coherent differential absorption LiDAR based on Golay coding technology[J]. Opto-Electronic Engineering, 2019, 46(7): 19081-. doi: 10.12086/oee.2019.190081
Citation: Hu Yihua, Dong Xiao, Zhao Nanxiang. Research on coherent differential absorption LiDAR based on Golay coding technology[J]. Opto-Electronic Engineering, 2019, 46(7): 19081-. doi: 10.12086/oee.2019.190081

Golay编码差分吸收相干激光雷达研究

  • 基金项目:
    国家自然科学基金资助项目(61871389);国防科技大学重大基金资助项目(ZK18-01-02)
详细信息
    作者简介:
    通讯作者: 董骁(1990-),男,博士研究生,主要从事相干激光雷达技术方面的研究。E-mail:skl_dongxiao@163.com
  • 中图分类号: TN959.98

Research on coherent differential absorption LiDAR based on Golay coding technology

  • Fund Project: Supported by National Natural Science Foundation of China (61871389) and Major Fund Program of National University of Defense Technology (ZK18-01-02)
More Information
  • 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3 dB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3 dB耦合器分束比为0.495时,最优本振光功率为0.93 mW。脉冲编码后,系统对CO2的有效探测距离增加,且在104~1010范围内进行脉冲积累时,相较于原系统距离增长率大于15%。

  • Overview: The differential absorption LiDAR (DIAL) can obtain the spatio-temporal distribution information of atmospheric CO2, which needs high signal-to-noise ratio (SNR). To improve the detection SNR, the coherent detection and heterodyne detection are widely used and have been combined with DIAL due to the excellent noise-reducing ability. In this paper, we propose a coherent differential absorption LiDAR (CDIAL) based on Golay coding to further reduce the detection errors, and the decoding method is also analyzed. The coding gain formula of SNR due to Golay coding is deduced, which is related to the local oscillator (LO) power, the code length, the splitting ratio of the 3 dB coupler. When the LO power is lower, the thermal noise should not be neglected, and the coding gain is higher, which is mainly due to the suppression of thermal noise. The higher the local oscillator power is and the more the beam splitting ratio deviates from 50%, the lower the coding gains are, because these two factors can improve the shot noise and the relative intensity noise, and thus the influence of thermal noise decreases. In addition, there are optimal code lengths in actual heterodyne detection systems, when the code length is higher than the optimal code length, the increase of coding gain is not obvious. The influence of thermal noise on the detection system decreases when the LO power grows, and there are 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, and the maximum SNR in traditional pulse LiDARs is 73.27% of that in coded pulse LiDARs. When the splitting ratio is 0.49, the optimal LO power can be further lower. To analyze the improvement of CDIAL performance when the Golay coding is used, we calculate the detection error of CDIAL under different LO power. Two operation mode of CDIAL system are considered, including the collimated mode and the focused mode. The focused mode has better performance in short range detection duo to its relatively higher system efficiency. The detection accuracy of CO2 should be better than 4 ppm, and we define the range corresponding the error of 4 ppm as the effective range. And the effective range is longer with the coded pulses. In the pulse accumulations of 104~1010, the improvement ratios of effective detection range are higher than 15%. In addition, the Golay coding technology can both improve the SNR and the spatial resolution of LiDARs, which will be discussed in the future research.

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  • 图 1  Golay编码差分吸收相干激光雷达结构图

    Figure 1.  Schematic diagram of coherent differential absorption LiDAR based on Golay coding

    图 2  Golay码解码流程图

    Figure 2.  Decoding flow chart of Golay code

    图 3  编码增益随本振光功率的变化关系

    Figure 3.  Relationship between the coding gain and the power of LO

    图 4  编码增益随编码长度的变化关系

    Figure 4.  The change of coding gain with the code length

    图 5  EDFA等功率输出时Golay解码相对误差

    Figure 5.  Relative decoding errors of Golay code with a fixed power EDFA

    图 6  Golay编码后系统的归一化信噪比

    Figure 6.  Normalized SNR based on Golay coding

    图 7  CO2浓度探测误差随距离的变化关系

    Figure 7.  The variation of CO2 concentration error with detection range

    图 8  脉冲编码后对有效探测距离影响

    Figure 8.  The influence of Golay coding on effective detection range

    表 1  外差激光雷达参数表

    Table 1.  Heterodyne LiDAR system parameters

    Detector items Value
    ρ1, ρ2 1.0
    ε 0.495/0.505
    Bandwidth/MHz 20
    1/Ts/(Msps) 800
    PLO/mW 0.5~1
    E0/mJ 1
    tT/ns 400
    NRIN/(dBc/Hz) -120
    A/m2 0.152π/4
    Beam truncation[18] $1 / \sqrt{2}$
    Transmittance 1.0
    Beam type Gaussian
    下载: 导出CSV
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出版历程
收稿日期:  2019-03-01
修回日期:  2019-05-10
刊出日期:  2019-07-01

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