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<p>Methane (CH<sub>4</sub>) is one of the most important greenhouse gases, and its impact on climate change is gradually increasing owing to increased emissions. Water vapor (H<sub>2</sub>O) is an important factor affecting meteorology, climate, and global hydrological cycles. The distribution of H<sub>2</sub>O in the lower troposphere plays a significant role in studying the enhancement of the greenhouse effect, weather forecasting, and other aspects. Based on the characteristics of the methane 1645&#xa0;nm absorption line coinciding with the H<sub>2</sub>O 822&#xa0;nm absorption line after frequency doubling, a dual-species detection differential absorption light detection and ranging (LIDAR) has been proposed. The system utilizes the principles of integrated path differential absorption (IPDA) to detect CH<sub>4</sub> column concentrations and differential absorption LIDAR (DIAL) to measure the H<sub>2</sub>O concentration profile. The laser source of the system mainly includes optical parametric oscillator (OPO), optical parametric amplifier (OPA) and second harmonic generation module (SHG). By comprehensively analyzing the frequency stability, profile detection precision, and laser source design, the optimal operating wavelengths for CH<sub>4</sub> and H<sub>2</sub>O measurements were presented: CH<sub>4</sub> online, offline1, and offline2 were 1645.552&#xa0;nm, 1645.807&#xa0;nm and 1645.844&#xa0;nm, respectively. Based on the proposed system parameters of the LIDAR, absorption line parameters, and global environmental parameters, such as surface reflectance, aerosol optical depth, and surface elevation, a simulation analysis of the global CH<sub>4</sub> column measurement performance of the LIDAR was conducted. The results show that with a telescope aperture of 1000&#xa0;mm, repetition rate of 25&#xa0;Hz, emitting energy of 20&#xa0;mJ and horizontal resolution of 50&#xa0;km, the random error of the CH<sub>4</sub> measurements can be below 7&#xa0;ppb in 94% area of land. Subsequently, a simulation analysis of the LIDAR H<sub>2</sub>O vertical profile measurements was conducted. The results show that, with a vertical resolution of 1&#xa0;km and a horizontal resolution of 100&#xa0;km, the precision of the H<sub>2</sub>O profile concentration can reach within 1 g/kg in the free troposphere with six typical atmosphere models.</p>

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Performance evaluation of spaceborne combined IPDA LIDAR and DIAL for simultaneous measurement of methane column concentrations and water vapor density profile

  • 期刊论文

  • 发表日期：

    2025年4月5日

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  • Zitong Wu,
  • Cheng Chen,
  • Chuncan Fan,
  • Xiaopeng Zhu,
  • Jiqiao Liu,
  • Weibiao Chen

摘要

Methane (CH4) is one of the most important greenhouse gases, and its impact on climate change is gradually increasing owing to increased emissions. Water vapor (H2O) is an important factor affecting meteorology, climate, and global hydrological cycles. The distribution of H2O in the lower troposphere plays a significant role in studying the enhancement of the greenhouse effect, weather forecasting, and other aspects. Based on the characteristics of the methane 1645 nm absorption line coinciding with the H2O 822 nm absorption line after frequency doubling, a dual-species detection differential absorption light detection and ranging (LIDAR) has been proposed. The system utilizes the principles of integrated path differential absorption (IPDA) to detect CH4 column concentrations and differential absorption LIDAR (DIAL) to measure the H2O concentration profile. The laser source of the system mainly includes optical parametric oscillator (OPO), optical parametric amplifier (OPA) and second harmonic generation module (SHG). By comprehensively analyzing the frequency stability, profile detection precision, and laser source design, the optimal operating wavelengths for CH4 and H2O measurements were presented: CH4 online, offline1, and offline2 were 1645.552 nm, 1645.807 nm and 1645.844 nm, respectively. Based on the proposed system parameters of the LIDAR, absorption line parameters, and global environmental parameters, such as surface reflectance, aerosol optical depth, and surface elevation, a simulation analysis of the global CH4 column measurement performance of the LIDAR was conducted. The results show that with a telescope aperture of 1000 mm, repetition rate of 25 Hz, emitting energy of 20 mJ and horizontal resolution of 50 km, the random error of the CH4 measurements can be below 7 ppb in 94% area of land. Subsequently, a simulation analysis of the LIDAR H2O vertical profile measurements was conducted. The results show that, with a vertical resolution of 1 km and a horizontal resolution of 100 km, the precision of the H2O profile concentration can reach within 1 g/kg in the free troposphere with six typical atmosphere models.