Detection of CO2 Average Concentration in Atmospheric Path by CW Modulated Differential Absorption Lidar
HONG Guang-lie1, LIANG Xin-dong1, 2, LIU Hao1*, ZHANG Hua-ping1, 2, SHU Rong1, 2
1. Key Laboratory of Space Active Optoelectronic Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
Abstract：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 H2O in HITRAN database, considering the absorption cross section of CO2 and the interference of H2O, the detection wavelength of DIAL is selected as: On-line is 1 572.335 nm and Off-line is 1 572.180 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 1 572.335 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).
Key words：Integral path differential absorption lidar IPDA; CO2 column-averaged mixing ratios; Acoustic-optic intensity modulation; Laser frequency locking; Phased laser rangefinders
洪光烈，梁新栋，刘 豪，章桦萍，舒 嵘. 连续波差分吸收激光雷达探测路径大气CO2平均浓度[J]. 光谱学与光谱分析, 2020, 40(12): 3653-3658.
HONG Guang-lie, LIANG Xin-dong, LIU Hao, ZHANG Hua-ping, SHU Rong. Detection of CO2 Average Concentration in Atmospheric Path by CW Modulated Differential Absorption Lidar. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(12): 3653-3658.
