Measurements of Atmospheric Water Vapor by a 1.316 μm Optical Fiber Laser Heterodyne Radiometer

Abstract

A passive optical fiber laser heterodyne radiometer prototype with a semiconductor laser near 1.316 μm as the local oscillator was built, parameters of the prototype have been optimized. Using the prototype, the water vapor concentration in the atmospheric column was measured with a spectral resolution of 0.009 cm−1 in late October and early November of 2020, the collection time was approximately 3 min, and the signal-to-noise ratio was better than 120. The water vapor column concentration and profiles were inversed based on the optimal estimation method. Compared with the measurement of the Fourier transform spectrometer (EM27/SUN) which was performed simultaneously, the inversion results deviated by less than 14%, and the variation trend of the water vapor concentration showed good consistency. It is demonstrated that the 1.316 μm optical fiber laser heterodyne radiometer possesses good stability and accuracy in the field measurement of atmospheric water vapor concentration.

Design of an all hollow fiber‐coupled middle infrared laser heterodyne radiometer (LHR)

“…At wavelength λ = 8 µm, n d (λ) = 1.9512, the thickness d of 43 µm can be calculated from Equation (4).…”

“…2,3 Compared with current FTS, LHR offers merits: high sensitivity, high spectral/spatial resolution, and cost-effective compact instrument size. [2][3][4][5][6][7][8] In the near-infrared (IR), LHR has developed rapidly in recent years. 9 Wilson et al, [10][11][12] Rodin et al, 13,14 and Wang et al 15 developed LHRs applying distributed feedback (DFB) lasers as local oscillators (LOs) for measuring CO 2 and CH 4 in the atmospheric column.…”

“…Ground‐based passive laser heterodyne radiometer (LHR), similar to the Fourier‐transform spectrometer (FTS), 1 uses the Sun as a signal source to carry out long‐term, long‐distance, and remote sensing of atmospheric gases 2,3 . Compared with current FTS, LHR offers merits: high sensitivity, high spectral/spatial resolution, and cost‐effective compact instrument size 2–8 …”

Atomic absorption spectroscopy detection system based on wavelength modulation and wavelet denoising

“…[5] In recent years, tunable diode laser absorption spectroscopy (TDLAS) technology has attracted widespread attention due to its advantages such as high resolution, strong selectivity, and high sensitivity. [6][7][8] Miyabe et al integrated laser ablation with TDLAS to develop multiple actinide metal isotope abundance detection systems, achieving precision in measuring metal isotope abundance. [9,10] Lebedev et al designed a crucible with a microchannel array, which effectively reduced the Doppler broadening of the spectrum and improved the discrimination of isotope absorption spectra.…”

Research on application of local oscillator power locking method to laser heterodyne radiometer

“…傅里叶变换光谱仪 EM27/SUN，测量 4000～11000 cm -1 波段光谱信息以反演大 气温室气体柱浓度，为温室气体浓度的监测提供了一种新型的便捷手段，但是 其成本较高且光谱分辨率较低 [2] 。 自 20 世纪 70 年代以来，激光外差光谱技术因其成本低、体积小、分辨率 高等优点得 到 快 速发 展 ， 已 广泛用 于臭 氧(O 3 )、水汽(H 2 O)、甲烷(CH 4 )、氨 (NH 3 )、一氧化氯(ClO)等大气温室气体柱丰度和垂直廓线的测量 [3][4][5][6][7][8][9][10][11] 。近年来， 伴随着小体积低功耗的分布反馈式半导体激光器(Distributed feedback，DFB)、 光纤器件及集成电路的发展，使近红外激光外差辐射计集成成为了可能。2012 年，E.L.Wilson 团队研制了一种用于大气柱中二氧化碳(CO 2 )的高灵敏测量的低 成本、小型化的激光外差辐射计 [12][13][14] 。最近，俄罗斯 Sergei Zenevich 等人研制 了具有 0.0013 cm -1 超高光谱分辨率的多通道激光外差光谱辐射计，用于测量大 气中 CO 2 和 CH 4 分子吸收，推进了外差辐射计集成的进一步发展 [15] 。国内安徽 光机所王晶晶等人在实验室搭建了一套可实现大气 CO 2 和 CH 4 的透过率谱测量 的全光纤近红外激光外差系统 [16] 。随后，邓昊等人搭建了一套以三个分布反馈 式半导体激光器作为外差探测的本振源的近红外激光外差辐射系统，实现了对 大气二氧化碳(CO 2 )、甲烷(CH 4 )、水汽(H 2 O)和氧气(O 2 )柱浓度的同时测量 [17] 。 最近，安光所曹振松课题组搭建了以 1.316 μm 附近的半导体激光器作为本振源 的无源光纤激光外差辐射计，并对其参数进行优化，并利用该外差辐射计实现 了大气柱中的水汽浓度测量 [18] 。外差辐射计在测量大气中气体浓度时，存在本 振光功率变化导致基线斜率的问题，为获得准确的大气透过率谱，激光器的功 率变化被提出作为参考的基线 [10] ，Weidmann 等人提出对测量数据进行多项式拟 合以确定基线，将多项式拟合系数作为参数代入反演中，从而计算出信号基线…”