Upper Atmospheric Wind Field Research Articles

Thermal imaging drift monitoring of Doppler asymmetric spatial heterodyne spectroscopy for wind measurement based on segmented edge fitting

Doppler asymmetric spatial heterodyne spectroscopy is recently developed for spaceborne measurement of middle and upper atmospheric wind field, which relies on the accurate inverse of interferogram phase to calculate the Doppler shift of airglow emission lines. The change of temperature leads the optical and mechanical components to thermally deformed, causing the imaging plane to thermally drift relative to the detector, changing the distribution of interferogram phase on pixels, and directly introducing phase errors to affect the wind speed inversion. In order to reduce the influence of imaging thermal drift on phase inversion, the segmented fitting method is used in this paper to detect the sub-pixel edges of notch patterns and monitor imaging thermal drift accordingly. In the thermal stability test of a near-infrared Doppler asymmetric spatial heterodyne interferometer prototype, the thermal imaging drifts and ambient temperature show a high consistency in the trend of high-frequency oscillation, and the correlation coefficient can reach 0.86 after removing the baseline. After phase correct by using the thermal imaging shift, the high-frequency oscillation of interferogram phase shift is also greatly suppressed. In order to further verify the accuracy of the algorithm, the influence of the data signal-to-noise ratio and the data distribution characteristic parameter errors used in the fitting on the edge detection are simulated. The results show that the edge detection accuracy is restricted mainly by the data signal-to-noise ratio and the accuracy of the fringe frequency parameters. When the error of the fringe frequency parameter used for fitting is less than 0.5%, the error of other data distribution characteristic parameters is less than 5%, and the data signal-to-noise ratio is enhanced more than 35 times, the algorithm in this paper can achieve a detection accuracy higher than 0.05 pixels.

An Ionospheric Climate Index Based on GNSS

AbstractThe ionospheric total electron content (TEC) is a significant parameter for scientific studies of the ionosphere and space weather. Ground‐based Global Navigation Satellite System (GNSS) station network provides an opportunity for modeling the ionospheric TEC with high accuracy. Based on global ionospheric TEC maps, by using data from the International GNSS Service (IGS) stations for 21 years (from 1998 to 2018), we establish an ionospheric climate index (ICI) for representing the general state of the ionosphere. In addition, we build a multiple linear regression model for fitting ICI using the SSN, F10.7, Ap, and Dst indices and upper atmospheric wind field. We quantitatively analyze the contribution of these factors to ICI time series. ICI during the past six solar cycles, namely, from 1958 to 2018, are presented, which are assigned as the adjectives (cold, cool, mild, warm, hot, and sizzling) for ionospheric climatology studies. This new index is a very promising representative of day‐to‐day variations of middle‐ and low‐latitude ionosphere.

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.

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.

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.