基于HITRAN数据库的深海甲烷辐射光谱仿真研究

研发能够精确、实时、原位获取热液甲烷数据的深海甲烷传感器对深海研究具有非常重要的意义。前期研制的两款深海甲烷光学成像干涉系统，均利用甲烷辐射光谱开展甲烷状态参数探测和反演。首先，以分子光谱辐射理论为基础，建立了分子辐射光谱与浓度、温度、压强的理论关系式，结合深海高压环境特点，建立了基于Lorentz线型的深海分子辐射模型，该模型为利用光谱法定量反演分子浓度、温度、压强等状态参数提供理论依据，同时为深海分子光谱仿真提供有力工具。接着，借助HITRAN分子光谱数据库提供的分子基本谱线参数，挑选出甲烷成像干涉系统的光源谱线。对比CH₄分子与CO₂, H₂S, H₂O等分子的特征吸收谱线，在5 990～6 150 cm-1波段范围内，CH₄谱线强度比CO₂, H₂S, H₂O等三种干扰分子的谱线强度约高2～3个数量级，且此波段内甲烷六条有效谱线分布均匀，谱线间距皆约为2～3 nm，非常适合采用光谱法进行分子状态参数探测，因此选择谱线干扰较弱、谱线分布均匀、谱线间距适中的甲烷六条谱线(1 640.37, 1 642.91, 1 645.56, 1 648.23, 1 650.96和1 653.72 nm)作为甲烷成像干涉探测系统的目标光源谱线。最后，基于深海分子辐射模型和HITRAN数据库的甲烷分子基本谱线参数，人工合成了甲烷任意浓度，任意温度和任意压强的辐射光谱数据，并分析了甲烷辐射光谱随浓度、温度和压强的变化特征。对于单一中心谱线，甲烷分子辐亮度随着浓度的升高而线性增大，随着温度的升高而非线性增大，随着压强的升高而非线性减小。对于全波段谱线，甲烷辐射光谱的全线宽随着浓度、温度的升高而变宽，随着压强的升高而变窄。建立的深海甲烷辐射光谱理论和仿真分析结果，可以为基于光谱法的海洋原位甲烷传感器的研制和数据反演提供数据支撑和理论依据。

Simulation of Emission Spectrum of Abyssal Methane Based on HITRAN Database

The development of a deep-sea methane sensor that can accurately, in real-time and in-situ, obtain hydrothermal methane data is of great significance for deep-sea research. Previously, two kinds of optical imaging interference systems that use methane radiation spectrum to detect and retrieve methane state parameters have been proposed. Firstly, based on the molecular spectral radiation theory, the theoretical relationship between molecular radiation spectrum and concentration, temperature and pressure is established. Then, combined with the characteristics of a high-pressure deep-sea-environment, the deep-sea molecular radiation model based on the Lorentz spectra line is established. The model provides a theoretical basis for the inversion of state parameters such as molecular concentration, temperature and pressure by spectral legal quantity. At the same time, it provides a powerful tool for deep-sea molecular spectrum simulation. Then, with the help of the molecular basic spectral line parameters provided by the HITRAN molecular spectral database, the light source spectral line of the methane imaging interference system is selected. Comparing the characteristic absorption spectra of CH₄ molecule with CO₂, H₂S, H₂O and other molecules in the 5 990~6 150 cm-1 band, the intensity of the CH₄ spectral line is about 2~3 orders of magnitude higher than that of interfering molecules, and the six effective spectral lines of methane are evenly distributed in this band, with a spectral line spacing of about 2~3 nm, which is very suitable for temperature and other state parameters detection by the spectral method. Therefore, six methane spectral lines (1 640.37, 1 642.91, 1 645.56, 1 648.23, 1 650.96 and 1 653.72 nm) with weak spectral line interference, uniform spectral line distribution and moderate spectral line spacing are selected as the target light source spectral lines of methane imaging interference detection system. Finally, based on the deep-sea molecular radiation model and the basic spectral line parameters of methane in the HITRAN database, the radiation spectrum data of methane with arbitrary concentration, temperature and pressure are synthesized, and the variation characteristics of methane radiation spectrum with concentration, temperature and pressure are analyzed. For a single central spectral line, the radiance of methane molecules increases linearly with the increase of concentration, increases nonlinearly with the increase of temperature, and decreases nonlinearly with the increase of pressure. For the full band spectral line, the full width of the methane radiation spectrum widens with the increase of concentration and temperature and narrows with the increase of pressure. The theory and simulation results of the deep-sea methane radiation spectrum established in this paper can provide data support and a theoretical basis for developing and data inversion of marine in-situ methane sensors based on the spectral method.