Carbon dioxide detection technology based on the laser occultation absorption spectrum
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摘要: 本文分析了固定波长激光掩星差分吸收技术的优点和不足，介绍了可调谐激光直接吸收光谱技术测量原理。分析了最优波长透过率与信噪比的关系以及测量误差与背景光干扰的关系。根据高灵敏度探测器的工作波长范围，选择了6310.915 cm−1、6310.893 cm−1、6310.890 cm−1、6310.8834 cm−1作为吸收的工作波长，同时选择6310.15 cm−1作为参考波长，并对各波长的探测能力进行了仿真分析。通过仿真结果可知，在1 km垂直分辨率下，在5~35 km内CO2浓度探测误差优于0.9%，7~42 km范围内的探测误差优于0.4%。该技术降低了系统成本和复杂度，有利于星载产品的设计和实现。Abstract: The advantages and disadvantages of fixed-wavelength laser occultation differential absorption technology are analyzed, and the measurement principle of tunable laser direct absorption spectroscopy technology is introduced. The relationship between optimal wavelength transmittance and signal-to-noise ratio and the relationship between measurement error and background light interference are analyzed. According to the working wavelength range of the high-sensitivity detector, 6310.915 cm−1, 6310.893 cm−1, 6310.890 cm−1 and 6310.8834 cm−1 are selected as the absorption working wavelengths, and 6310.15 cm−1 is selected as the reference wavelength, and the detection ability of each wavelength is simulated and analyzed. Simulation results show that the detection error of a CO2 concentration is better than 0.9% in the range of 5~35 km and better than 0.4% in the range of 7~42 km with a vertical resolution of 1 km. This technology reduces the cost and complexity of the system, and is beneficial to the design and implementation of space-borne products.
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Key words:
- laser occultation /
- carbon dioxide /
- direct absorption spectrum
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图 1 直接吸收光谱激光掩星探测原理
Figure 1. Detection principle of laser occultation direct absorption spectroscopy
图 3 （a）背景光谱与（b）CO2光谱对比（波数ν范围5882 cm−1~7143 cm−1，高度5 km）
Figure 3. Comparison of (a) background spectrum and (b) CO2 spectrum (The range of wave number ν is 5882 cm−1~7143 cm−1 and the height is 5 km.)
图 4 背景光谱干扰误差
Figure 4. Error caused by background spectral interference
(λon is 6310.915 cm−1 @ 5~10 km, 6310.893 cm−1 @ 11~18 km, 6310.890 cm−1 @ 19~26 km, 6310.8834 cm−1 @ 27~39 km, and λoff is 6310.15 cm−1)
表 1 系统仿真参数
Table 1. System simulation parameters
System parameter Value Unit Orbit altitude of laser transmitter 500 km Orbit altitude of laser receiver 600 km repetition rate 40 Hz Laser power 1 W Laser wavenumber 6309.8834~6311.8834 cm−1 Absorption wavenumber 6310.915@5~10 km, 6310.893@11~18 km,
6310.890@19~26 km, 6310.8834 @27~39 kmcm−1 Reference wavenumber 6310.15 cm−1 Laser line width 10 MHz Laser beam divergence 0.3 mrad Telescope diameter 0.3 m System optical efficiency 0.5 1 Detector responsivity (InGaAs-APD,
C30662, 1584.6 nm)10.3 A/W Nominal gain 10 1 Noise factor 5.5 1 Dark current 45 nA Spectral noise current 0.7 pA/rt (Hz) Bandwidth 3000 Hz 
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