Real-time imaging of CO in vehicle exhaust was demonstrated using a gas correlation spectrometry based mid-infrared camera for the first time. The novel gas-correlation imaging technique is used to eliminate the spectral interferences from background radiation and other major combustion products, and reduce the influences of the optical jitter and temperature variations, thereby identifying and quantifying the gas. We take several spectral factors into account for the instrument design, concentration calibration and data evaluation, including atmospheric transmission, radiation interference, as well as the spectral response of infrared camera, filter and gas cell. A calibration method based on the molecular spectroscopy and radiative transfer equation is developed to identify the numerical relationship between the CO concentration × length and the measured image intensity. Two-dimensional CO distribution of vehicle exhaust with a time resolution of 50 Hz and detection limit of 20 ppm × meter is achieved when the distance between optical equipment and engine nozzle is 3 m. The gas correlation spectrometry based mid-infrared camera shows a great potential as a future technique to monitor vehicle pollution emissions quantitatively and visually.

The Fengyun-4A/B (FY-4A/B) geostationary satellite carries the Geostationary Interferometric Infrared Sounder (GIIRS). The instrument parameters of the GIIRS on FY-4A and FY-4B are not exactly the same, which is crucial for the atmospheric temperature and humidity measurements. The objective of this paper is to discuss the influence of spectral range on the retrieval for the FY-4A/B GIIRS. Firstly, we performed channel selection to choose the appropriate channels for retrieval. Then, the multiple cycling utilization of the physical retrieval method is proposed and conducted for improving the accuracy, and the retrieval results of FY-4A/B GIIRS are compared. Finally, perturbation analysis is performed to discuss the sensitivity of the retrieval to temperature perturbations due to the difference in spectral range between the two GIIRS. The results show the retrieval method can realize the improvement of the average accuracy by more than 0.9 K for temperature and 3.0% for humidity. As the spectral range widens, the retrieval accuracy of FY-4B GIIRS is superior to that of FY-4A GIIRS from 130 hPa to 400 hPa. Furthermore, perturbation analysis also shows the extension of the spectral range is beneficial to the retrieval. This study could offer the usefulness of current GIIRS instruments with observed on-orbit bias, and a reference for the parameter design of the subsequent instruments.

The O₂(a¹Δ_g) emission near 1.27 μm has relatively bright signal and extended altitude coverage and provides an important means to remotely sense the compositional structures and dynamical features of the upper atmosphere globally. In this paper, we report the simulation and application of O₂(a¹Δ_g) dayglow near 1.27 μm for wind observations from limb-viewing satellites. A line by line radiative transfer model of the ${\text{O}}_2(a{}^1\Delta {}_g^{},{\upsilon }^{\prime }=0)\to {\text{O}}_2(X{}^3\Sigma {}_g^{},{\upsilon }^{″}=0)$ band is developed by taking both multiple scattering radiative transfer and nonlocal thermal equilibrium (non-LTE) models into account. The emission line O₁₉P₁₈ (7772.030 cm⁻¹) with weak self-absorption, bright radiation intensity, and large spectral separation range is proved to be suitable for limb-viewing wind detection, due to its advantages of significantly lower cost, risk, and platform requirements. In order to ascertain the wind precision of O₁₉P₁₈, observations by a DASH-type (the Doppler asymmetric spatial heterodyne) instrument are simulated. The simulated results indicate a wind measurement precision of 1-2 m/s over an altitude range of 40 to 70 km in general, and possibly to 2-4 m/s due to a strong dependence on the spectral interference of the scattered sunlight background.

The O₂(a¹Δ_g) emission near 1.27 μm provides an important means to remotely sense the thermal characteristics, dynamical features, and compositional structures of the upper atmosphere because of its photochemistry and spectroscopic properties. In this work, an emission–absorption transfer model for limb measurements was developed to calculate the radiation and scattering spectral brightness by means of a line-by-line approach. The nonlocal thermal equilibrium (non-LTE) model was taken into account for accurate calculation of the O₂(a¹Δ_g) emission by incorporating the latest rate constants and spectral parameters. The spherical adding and doubling methods were used in the multiple scattering model. Representative emission and absorption line shapes of the ${\mathrm{O}}_2(a^1{\Delta }_g,{\upsilon }^{\prime }=0)\to {\mathrm{O}}_2(X\mathsf{\Sigma }_g^3,{\upsilon }^{″}=0)$ band and their spectral behavior varying with altitude were examined. The effects of solar zenith angle, surface albedo, and aerosol loading on the line shapes were also studied. This paper emphasizes the advantage of using infrared atmospheric band for remote sensing of the atmosphere from 20 up to 120 km, a significant region where the strongest coupling between the lower and upper atmosphere occurs.

A molecular Faraday optical filter (MFOF) working in the mid-infrared region is realized for the first time. NO molecule was used as the working material of the MFOF for potential applications in atmospheric remote sensing and combustion diagnosis. We develop a complete theory to describe the performance of MFOF by taking both Zeeman absorption and Faraday rotation into account. We also record the Faraday rotation transmission (FRT) signal using a quantum cascade laser over the range of 1,820 cm⁻¹ to 1,922 cm⁻¹ and calibrate it by using a 101.6 mm long solid germanium etalon with a free spectral range of 0.012 cm⁻¹. Good agreement between the simulation results and experimental data is achieved. The NO-MFOF’s transmission characteristics as a function of magnetic field and pressure are studied in detail. Both Comb-like FRT spectrum and single branch transmission spectrum are obtained by changing the magnetic field. The diversity of FRT spectrum expands the range of potential applications in infrared optical remote sensing. This filtering method can also be extended to the lines of other paramagnetic molecules.

The Doppler asymmetric spatial heterodyne spectroscopy is one of the primary techniques for measuring the upper atmospheric wind profile. In this work, the detailed derivation of the analytical expression of phase uncertainty was presented, including two significant parameters, fringe contrast and signal-to-noise ratio. The effectiveness of the re-parameterized analytical expression was proved using the numerical simulations and laboratory experiments, and both results are in good agreement with them from the analytical expression. Therefore, the re-parameterized analytical expression could be used to optimize the interferometer design and evaluating the instrument performance.