摘要
大气二氧化碳作为最重要的温室气体之一,它的变化和分布备受关注,差分吸收激光雷达(DIAL)系统是探测大气二氧化碳浓度的重要手段,对于研究温室气体的源和汇具有重要意义。主要研究正弦调制连续波差分吸收激光雷达在水平路径上探测CO2平均浓度,利用HITRAN数据库中CO2及H2O的吸收光谱,综合考虑CO2的吸收截面及H2O的干扰,选择差分吸收激光雷达的工作波长On-line:1 572.335 nm, Off-line:1 572.180 nm;声光调制器取代电光调制器对连续波激光强度进行正弦波调制,两路调制信号频率有细微差别,其中On-line调制频率为101.833 kHz, Off-line调制频率为99.733 kHz;On-line光源激光器通过光谱调制技术将激光频率锁定在气体池吸收峰1 572.335 nm处,并采用在相位调制器上施加直流偏置反馈电压来消除相位调制器的残余幅度调制(RAM),使波长锁定精度大幅提高,激光频率锁定系统实现On-line光源激光器在12小时输出波长均方根误差为0.05 pm;在CPU中实现快速傅立叶变换获取回波光信号和发射监视端激光强度的功率谱,并选择窗函数和频谱校正算法来提高计算精度;通过调制连续波激光强度的正弦波相位鉴别获取路径的长度;系统光路为光纤光路,使其结构紧凑;对系统进行外场实验和对比实验;获取上海市区1.3 km路径上二氧化碳平均浓度,实验数据显示系统观测精度为4 ppm(百万分之一),且探测到的CO2日变化趋势与二氧化碳点探测器LI-7500A探测到的日变化趋势相吻合。
As one of the most important greenhouse gases,CO2 has attracted much attention for its change and distribution.The differential absorption laser radar(DIAL)system is an effective means to detect the concentration of CO2,which is of great significance for studying the source and sink of greenhouse gas.This paper mainly studies the detection of CO2 average concentration by sinusoidal modulated continuous wave(cw)DIAL on the horizontal path.Using the absorption spectrum of CO2 and H 2O in HITRAN database,considering the absorption cross section of CO2 and the interference of H 2O,the detection wavelength of DIAL is selected as:On-line is 1572.335 nm and Off-line is 1572.180 nm;Acousto-optic modulator replaces electro-optic modulator to transmit cw laser and the frequency of the two modulation signals is slightly different.The On-line modulation frequency is 101.833 kHz,and the Off-line modulation frequency is 99.733 kHz.On-line is locked at the frequency of absorption peak of the gas pool at 1572.335 nm by spectral modulation technology,and the residual amplitude modulation(RAM)of the phase modulator is eliminated by applying DC bias feedback voltage on the phase modulator in the research process.The system achieves a continuous output wavelength RMS error of 0.05 pm at 12 hours.Fast Fourier transform(FFT)is used to acquire the power spectrum of the echo signal and the laser intensity at the monitor in the CPU.The ranging of the target is possible by utilizing the phase difference between the monitored and the received signals;The optical circuit is fiber based,and this makes the system compact and reliable.The field experiment and comparative experiment were carried out to obtain the average concentration of CO2 on the 1.3 km path in Shanghai.The experimental data showed that the system observation accuracy was 4 ppm(ppm is parts per million),and the detected daily variation trend coincides with the in situ CO2 sensors(LI7500A).
作者
洪光烈
梁新栋
刘豪
章桦萍
舒嵘
HONG Guang-lie;LIANG Xin-dong;LIU Hao;ZHANG Hua-ping;SHU Rong(Key Laboratory of Space Active Optoelectronic Technology,Shanghai Institute of Technical Physics,Chinese Academy of Sciences,Shanghai 200083,China;University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《光谱学与光谱分析》
SCIE
EI
CAS
CSCD
北大核心
2020年第12期3653-3658,共6页
Spectroscopy and Spectral Analysis
基金
国家重点研发计划项目(2017YFB0504000)资助。
