Development of a laser heterodyne spectroradiometer for high-resolution measurements of CO₂, CH₄, H₂O and O₂ in the atmospheric column

Abstract

We have developed a portable near-infrared laser heterodyne radiometer (LHR) for quasi-simultaneous measurements of atmospheric carbon dioxide (CO2), methane (CH4), water vapor (H2O) and oxygen (O2) column absorption by using three distributed-feedback diode lasers as the local oscillators of the heterodyne detection. The developed system shows good performance in terms of its high spectral resolution of 0.066 cm−1 and a low solar power detection noise which was about 2 times the theoretical quantum limit. Its measurement precision of the column-averaged mole fraction for CO2 and CH4 is within 1.1%, based on the standard deviation from the mean value of the retrieved results for a clean sky. The column abundance information of the O2 is used to correct for the variations and uncertainties of atmosphere pressure, the solar altitude angle, and the prior profiles of pressure and temperature. Comparison measurements of daily column-averaged atmospheric mole fractions of CO2, CH4 and H2O, between our developed LHR and a greenhouse gas observing satellite, show a good agreement, which proves the reliability of our developed system.

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

“…In 2014, Rodin A et al used a 1.65 μm optical fiber LHR to achieve absorption measurements of CH 4 and CO 2 with a signal-to-noise ratio (SNR) of 120 with an exposure time of 10 min [15]. The groups of Gao X and Kan R also reported the study of optical fiber LHR [16,17]. However, the above studies generally focus on the measurement of carbon-containing GHGs, and there are few studies on the content and characteristics of water vapor concentration.…”

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

“…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 …”

Statistical Characterization of Temperature and Pressure Vertical Profiles for the Analysis of Laser Heterodyne Radiometry Data

“…One of the most commonly used methods for the retrieval of mixing ratios from LHR data is the optimal estimation method (OEM) developed by C. D. Rodgers, to which vertical profiles can be fed from sources such as European Centre for Medium-Range Weather Forecasts (ECMWF) or National Centers for Environmental Prediction (NCEP) [3][4][5][6]. Weidmann et al demonstrated the application of this method to LHR data using pressure, temperature, and volume mixing ratios extracted from ECMWF [7].…”