Upper Atmospheric Wind Research Articles

Ground-based airglow imaging interferometer. Part 2: forward model and inverse method.

The ground-based airglow imaging interferometer (GBAII) observes the nighttime airglow of the O₂(0-1) 867.7 nm line, peaked at 94 km altitude, to measure the upper atmospheric wind and temperature field. Its forward model, a code package in interactive data language (IDL), is developed to simulate the expected imaging interference fringes. It includes eight modules to simulate the light source, the atmospheric radiation transmission, the wide-angle Michelson interferometer, the interference filter, the optical system decay function, the responsivity, the imaging CCD, and the noises. The inverse method is also developed for obtaining the rest phase calibration, temperature, and wind. By means of both theoretical tools, we carry out a comparison of theoretical results with a field observation case. The apparent quantities J(1-p) from the forward model has the deviation of 1.5%-2.5% compared with that from the observation image. The temperature falls mainly in the range of 167-196 K with the precision of 2 K. The zonal and meridional winds are mainly in the region of 5.1 to 46.5 m/s and 12.5 to 48.3 m/s respectively, with errors of 13.2 to 21.5 m/s. The consistent trends between the observation results and standard models (MSISE90 and HWM93) suggest that the forward model and inverse method are suitable for GBAII.

Modulation transfer function of a modified spatially modulated imaging interferometer

The modulation transfer function (MTF) is one of the main criteria for judging the image quality of an imaging system. Together with the well-known optical transfer function, the MTF can be regarded as an objective basis reflecting the comprehensive performance of an imaging interferometer. In order to improve the imaging quality of a modified spatially modulated imaging interferometer (MSMII) with large optical path difference, the boundary conditions of an incident ray, at full field of view, along the x and y directions, respectively, are first calculated by the method of prism expansion, and then the exact expression of the pupil function of the MSMII is given. The two-dimensional MTF of the MSMII is obtained by the Fourier transform. Compared with previous studies, this work gives the two-dimensional MTF for the MSMII, and analyzes the effects of various parameters on the MTF. The optimal values of the incident angle i together with the acute angels and are chosen as and , respectively. If so, a high MTF is obtained, i.e. the imaging quality of the MSMII can satisfy the need of detecting upper atmospheric wind fields.

The estimation of upper atmospheric wind model updates from infrasound data

In our recent paper, the sensitivity of infrasound to the upper atmosphere is investigated using impulsive signals from the Tungurahua volcano in Ecuador. We reported on the coherent variability of thermospheric travel times, with periods equal to those of the tidal harmonics. Moreover, it was shown that the error in predicted thermospheric travel time is in accord with typical uncertainties in the upper atmospheric wind speed models. Given the observed response of the infrasound celerities to upper atmospheric tidal variability, it was suggested that infrasound observations may be used to reduce uncertainty in the knowledge of the atmospheric specifications in the upper atmosphere. In this paper, we discuss the estimation of upper atmospheric wind model updates from the infrasound data described in the aforementioned paper. The parameterization of the model space by empirical orthogonal functions is described; it is found that the wind model in the upper mesosphere and lower thermosphere can be described by a four‐parameter model. Due to the small dimensionality of the model space, a grid search method can be used to solve the inverse problem. A Bayesian method is used to assess the uncertainty in the inverse solution given the a priori uncertainty in the data and model spaces and the nonlinearity of the inverse problem at hand. We believe that this is the first study in which such methods are applied to real infrasound data, allowing for a rigorous analysis of this inverse problem. It is found that the complexity of the a posteriori model distribution increases for a larger dimensional model space and larger uncertainties in the data. A case study is presented in which the nonlinear propagation from source to receiver is simulated using an updated wind model and nonlinear ray theory. As nonlinear propagation effects further constrain the propagation path, this is a way to check the physical self‐consistency of the travel time inversion approach. We obtain excellent agreement between the simulated and observed waveforms.

Modulation depth of static four-phase-divided wind imaging interferometer

The static four-phase-divided imaging interferometry is a new technology of passive detection for the upper atmospheric wind field. It is featured with real-time detection, no moving parts, stability, and so on. In this paper, its basic theory is discussed, and its characteristics are briefly introduced. Furthermore, its key technical parameter, modulation depth, is analyzed. The relationships of modulation depth with the incident angle and temperature of the working environment are derived by using computer simulation. It is shown that the modulation depth decreases with the increase of the temperature and incident angle. The study provides a theoretical basis to increase the modulation depth of the interferometer, and it is of significance for the development of the upper atmosphere detection technique and theory.

Feasibility analysis of an achromatic quarter wave plate in a static polarizing wind imaging interferometer

A modified static polarizing wind imaging interferometer (SPWII) for measuring the upper atmospheric wind and temperature is presented. The atmospheric temperature and wind velocity can be derived by observing multiple emission lines. The principle of the SPWII is described. The effects of the dispersion of the quarter wave plates on the derived results are analyzed. Using a simulated annealing algorithm, some multilayer achromatic quarter wave plates (AQWPs) are designed to suppress the errors introduced by the dispersion. Two alternative AQWPs (six- and ten-layer) are obtained. The transmission loss of the interferometer and the measurement errors of atmospheric temperature and wind velocity introduced through dispersion can, through the use of achromatic QWPs, be reduced to below 0.2%, 0.15 K and 0.03 m s−1, respectively.

Data Processing of the Middle and Upper Atmospheric Wind Retrieval Based on the Fabry‐Perot Interferometer

Abstract:Since the Doppler shifts of airglow orauroralemission lines due to neutral winds are extremely small, it is essential to determine the center position and radius of fringes with the uppermost accuracy. In this paper, a new method is presented for the center position and radius determination of incomplete interference fringes of Fabry‐Perot Interferometer (FPI). Due to the data noise comes from FPI instrument and space environment, the data pre‐processing was firstly carried out including mean filtering and wiener weightingadaptive filtering. Then, according to the Gauss distribution of fringe intensity, interference fringe peak coordinates were derived from both radius obtained using Gaussian fitting and fringe center coordinates. Subsequently, based on the peak coordinates, new center position and radius were estimated by using circular coordinate fitting with the least square method. Finally, the center coordinate and radius were determined by using the iterative operation between Gaussian fitting and circular coordinate fitting. The new method was applied to Fabry‐Perot interferometer data processing for wind velocity estimation of the middle and upper atmosphere. The retrieval results are 96.9537 m/s (actual wind velocity ∼100 m/s) and 7.5282 m/s (actual wind velocity ∼10 m/s), lower by 2.977 m/s and 2.465 m/s, respectively. Compared with theoretical values, both of them are less than 3 m/s, which suggests a tentatively reliable and practicable method of circle center and radius determination for wind retrieval of the middle and upper atmosphere.

Principle of temperature, velocity and pressure of upper atmospheric wind measurement for the Voigt profile

Using the accurate expression of the Fourier transform of the pure Voigt spectral line profile, we present the principle of the passive optical method to measure temperature, velocity, and pressure of atmospheric wind for the Voigt profile. Through discussion, from the Gaussian, Lorentzian and Voigt profiles, we find that velocity will not be affected, pressure can be derived for Lorentzian and Voigt profiles, and temperature will be affected greatly. By simulation and comparison, we find that temperature derived from the Voigt profile is greater than that from the Gaussian profile, and it is less than that from the Lorentzian profile. This discussion will be significant in accurate upper atmospheric wind measurement.

Design and analysis of a modified Sagnac interferometer for upper atmospheric wind measurement

In this paper, for upper atmospheric wind measurement, according to the requirement of the optical path difference, we present a stable, high throughput and wide field-of-view modified Sagnac interferometer for upper atmospheric wind measurement. We analyze the main performances of the modified Sagnac interferometer, and results show that the modified Sagnac interferometer is more suitable for upper atmospheric wind measurement than the Michelson interferometer. Finally, we point out the measurement pattern with the modified Sagnac interferometer.

Optical throughput of the Sagnac interferometer with a modified large optical path difference

The basic principle of Sagnac interferometer with modified large optical path difference is expounded on in this paper. According to the Fresnel formula, electromagnetic field energy, and energy flux, the transmittance and reflectance of each interface of a Sagnac interferometer are calculated, respectively, and then the exact expressions of the optical throughput changing with the incident angle, the angle of the incident plane, and paper plane (the bottom plane of Sagnac interferometer) and Sagnac interferometer acute angles are given. Furthermore, we analyze the effects of various parameters on the optical throughput by computer simulation, and some important conclusions are obtained. This work is of great scientific significance to the static, real-time simultaneous detection of upper atmospheric wind field.

Complete throughput analysis of the static four-phase-divided wind imaging interferometer

The static wind imaging interferometer, based on a four-phase-divided mirror, is an attractive approach to acquiring the wind velocity and temperature of the upper atmosphere. Herein the operational principle of the interferometer is presented in detail. The throughput is theoretically analyzed with consideration of the reflections and transmittances of each systemic component. The throughput expression is derived by employing the Fresnel theorem. We conducted simulations, and the results show that the energy transmittance reaches 20% on the surface with high reflectivity-coating film when the inclination angle of the input light is limited to the range of −5 to +5 deg. The results presented herein provide a theoretical basis for the static design configuration and coating for the upper atmosphere wind imaging interferometer.

Partially light-controlled imager based on liquid crystal plate and image intensifier for aurora and airglow measurement

In order to obtain information both of aurora and airglow in one image by the same detector, a PLCI based on liquid crystal plate LCP and super second-generation image intensifier SSGII is proposed in this research. The detection thresholds of the CCD for aurora and airglow are calculated. For the detectable illumination range of 10(4)-10(-2) lx, the corresponding electron count is 1.57×10(5) - 0.2 for every pixel of CCD. The structure and work principle of the PLCI are described. An LC is introduced in the front of CCD to decrease the intensities of aurora in overexposure areas by means of controlling transmittances pixel by pixel, while an image intensifier is set between the LC and CCD to increase the intensity of the weak airglow. The modulation transfer function MTF of this system is calculated as 0.391 at a Nyquist frequency of 15 lp/mm. The curve of transmittance with regard to gray level for the LC is obtained by calibration experiment. Based on the design principle, the prototype is made and used to take photos of objects under strong light greater than 2×10(5) lx. The clear details of [symbols: see text] presented in the image indicate that the PLCI can greatly improve the imaging quality. The theoretical calculations and experiment results prove that this device can extend the dynamic range and it provides a more effective method for upper atmospheric wind measurement.

A large scale portable infrasound network as upper atmospheric monitor.

Analysis of data from this summer’s large scale infrasound array deployment in the American West will be presented. The deployment consisted of an arc of arrays at a fixed range of 220 km and a northward line of arrays from 220 to 400 km. In this presentation particular attention will be given to data from the northward line. Tropospheric, stratospheric, and thermospheric arrivals were observed. The evolution with range of the arrivals’ propagation parameters and waveforms will be discussed and compared with theoretical predictions that make use of atmospheric specifications. The data input in these specifications decreases with height; the specifications above the stratosphere are based on semi‐empirical models rather than observations. Naturally, the largest deviations are found in the predictions of thermospheric arrivals at the various arrays. By reducing the misfit between predictions and observations, we work on updating upper atmospheric wind models using infrasound.

Image Data Processing of Spaceborne Fabry-Perot Interferometer Prototype

针对自主研制的星载法布里-珀罗干涉仪(Fabry-Perot Interferometer,FPI)样机, 介绍了Fabry-Perot (F-P)的测风原理和风速反演算法, 阐述了F-P测风干涉数据的自动化处理方法, 包括干涉条纹图像滤波、分割、细化和特征数据的提取.滤波包括中值滤波和背景补偿, 分割采用区域平均灰度值阈值法, 借助数学形态学计算填充和消除二值化条纹的断裂点和毛刺. 最后, 按照骨架提取思想细化成干涉条纹线条, 提取其特征数据. 应用VC++编程语言开发软件平台, 对上述F-P测风仪数据自动化处理方法进行了验证, 结果表明其可行性高、适应性强.

Design and laboratory tests of a Doppler Asymmetric Spatial Heterodyne (DASH) interferometer for upper atmospheric wind and temperature observations

We describe the design, fabrication and laboratory tests of a Doppler Asymmetric Spatial Heterodyne (DASH) interferometer for upper atmospheric wind and temperature observations of the O[1D] 630 nm emission. The monolithic interferometer has no moving parts, a large étendue, relaxed fabrication and alignment tolerances and can measure multiple emission lines simultaneously. Laboratory measurements indicate that the design resolution and étendue were achieved and that thermal drifts can be determined with sufficient precision for geophysical applications.

Aurora Intensity Conversion and Distribution Simulation

For the upper atmospheric wind field measurement, the conversion relations between the unit of auroral (airglow) intensity Rayleigh and illumination, luminance, height of atmosphere, the photon number are derived. The auroral volume emission rate (VER) of O(1S)557.7nm and O(1D)630.0nm with height is presented. The VER peak values are 668R and 2630R respectively. The results can provide theory for light illumination and brightness of detecting upper atmosphere.

Study of the Dynamic Modulation Transfer Function of Modified Super-Wide-Angle Sagnac Imaging Interferometer

Modulation transfer function (MTF) is an important parameter for one image system. In order to obtain the more imaging quality performance of the modified super-wide-angle Sagnac imaging interferometer (MSASII) put forward by our group, and also have a qualitative analysis of its advantages and disadvantages in the process of application. Its dynamic MTF is focused on in this paper. The dynamic MTF expression of the MSASII is calculated. According to earlier research parameters of the MSASII, the dynamic MTF curve is described and corresponding corrective measures in theoretical is given. The result is demonstrated that the imaging quality of MSASII could satisfy the need of detecting upper atmospheric wind field.

Modified super-wide-angle Sagnac imaging interferometer based on LCoS for atmospheric wind measurement

The modified super-wide-angle Sagnac imaging interferometer (MSASII) based on liquid crystals on silicon (LCoS) is proposed as a novel device for the detection of the upper atmospheric wind field. This device employs the phase-only modulation (POM) of LCoS coupled with the MSASII, and can measure phase changes in multi-band emissions without moving mirror. It can be used to replace the conventional Michelson’s interferometer with step-moving mirror device. The optical path difference (OPD) equation of MSASII-LCoS is derived, and the four compensation conditions (field, chromatics, thermal and achromaticity of thermal compensations) are discussed within the scope of wind measurement. The real parameters of LCoS and optical glasses are selected for numerical simulation and analysis. Three aurora lines (732.0, 630.0 and 557.7 nm) are considered, and their phase variations are 3.61, 2.02 and 0.15 fringes at the same incident angle of 3°, respectively. The rate of change of OPD with temperature is the magnitude of 10 −6 cm/K, and the corresponding phase variations are within 0.09 fringes. The accuracy of phase modulation can be 0.614×10 −2 rad when LCoS of 10-bits is used. The novel model MSASII-LCoS shows its advantage for atmospheric wind measurement in the aspects of the overall structure, anti-vibration, operational flexibility and detection accuracy.

Passive detection of upper atmospheric wind field based on the Lorentzian line shape profile

Taking the aurora in upper atmosphere as the detection source, we propose a new principle of passive detection of emission rate in upper atmosphere wind based on the Lorentzian line shape profile. Using this principle, we can detect not only the physical parameter of upper atmospheric wind such as velocity, temperature and pressure, but aslo the emission rate, which resolves the problem of detecting emission rate at present. The calculation formula of the distribution of the velocity, temperature, pressure and emission rate are deduced based on the Lorentzian line shape profile, and by using computer simulation, the error curve is described. This study provides a theoretical basis for further study of detection of upper atmospheric wind field. It will play a significant role and has a wide application prospect in aerospace, space exploration, and environmental protection.

A wide field wind image interferometer with chromatic and thermal compensation

The basic conditions for designing a wide field Michelson interferometer with chromatic and thermal compensation, which is used to measure the upper atmospheric wind field，is briefly described. Comparing with the current method for designing the wide field Michelson interferometer with chromatic and thermal compensation, we present a method uses four media for the compensation of the MI to eliminate the monochromatic thermal aberration. The result shows that, by using this method, the polychromatic thermal aberration is ten to hundred times smaller than the method now in use. The research has important theoretical significance and practical value both for the research and development of the wide field Michelson interferometer with chromatic and thermal compensation for detection of the upper atmospheric wind field.

Development for detecting upper atmospheric wind and temperature from satellite

中高层大气风场和温度场是重要的大气基本参数, 其全球高精度测量具有广泛的应用前景, 探测需求日趋强烈. 干涉光谱仪由于其多通道、高通量和高光谱分辨率等优点而成为本项目的首选. 目前被成功应用的干涉式测风/测温仪器主要有Fabry-Perot 干涉仪和广角Michelson 干涉仪两大类. 本文对干涉光谱仪用于中高层大气风场和温度场探测的发展状况进行了分析, 同时比较了几种干涉仪测风和测温的可行性及优缺点, 为中国开展中高层大气风场和温度场星载探测打下基础.