Analysis of Key Parameters of Passive Tropospheric Wind Field Detection Based on Oxygen A- band Absorption Line

Real- time and high- precision wind field data play an important role in improving the accuracy of weather forecasts,ensuring the safety of spacecraft take- off and landing,tracking atmospheric pollutants, and radio sound detection. In the visible light and near-infrared bands,there are three absorption bands formed by the absorption of oxygen molecules,namely the oxygen. band,the oxygen B band and the oxygen A band. The absorption intensity of the A band is greater than that of the. band and the B band, and without interference from other gases,it is an ideal atmospheric detection source for tropospheric wind speed. The Doppler asymmetric spatial heterodyne wind measurement technology is a technology based on the Fourier transform of the interferogram to realize the Doppler frequency shift detection of the wind,the tropospheric wind velocity can be retrieved by detecting the Doppler shift of the oxygen A- band absorption line. This paper explores the technical feasibility of using Doppler asymmetric spatial heterodyne to detect the tropospheric atmospheric wind field based on the oxygen A- band absorption line. Based on the ideal instrument model and the 1976 American standard profile,the solar zenith angle is taken as 40 degrees,without considering the influence of clouds,rain, aerosol,and surface reflection. Through the analysis of the integral limb radiation characteristics of the absorption spectrum line observed in the single instantaneous field of view at the entrance pupil of the instrument,the paper simulates the forward simulation interference curve of a single space altitude layer,establishes a mathematical model of the instrument response function from the atmospheric absorption spectral line entrance pupil limb radiation to the interference curve,and two harmonics with the same spatial frequency as the interference curve are used for phase demodulation and wind speed inversion of line-of-sight wind. This method does not require Fourier transform,and can directly process the interferogram data to obtain the phase difference of the interferogram before and after the wind speed is applied,so as to solve the wind speed. At the same time,the algorithm only needs to perform a multiplication calculation, and can quickly realize the wind speed inversion. Based on the absorption line wind measurement theory,the measurement accuracy of tropospheric wind field detection using Doppler asymmetric spatial heterodyne is mainly affected by the interferometer optical parameters, filtering parameters,system noise,instrument stability and etalon off- axis effect. Through the simulation analysis of the influence of various instrument parameters on the results of line- of-sight wind speed retrieval,the optimal value range of the optical system parameters is determined. The results show that for the oxygen absorption line with the center wavelength at 769 nm,when the interferometer asymmetry value is 6.5 similar to 6.7 mm,the spectral resolution value is 0.49 similar to 0.51 cm(-1),the value of the etalon spacing is 0.8 similar to 1.4 mm,the fineness coefficient is 30 similar to 100,the off-axis angle of the etalon is less than 0.2 degrees,and the transmission peak deviation of the etalon is less than 0.018 cm(-1), the signal-to-noise ratio of the interferogram is greater than 40 times,the wind speed retrieval accuracy is better than 8 m/s. The research results can provide a theoretical reference for passive tropospheric wind field detection and related instrument design.