星光成像的大气影响研究(Ⅱ):大气湍流

Atmospheric Effects of Star Imaging(Ⅱ):Atmospheric Turbulence

工作于近地空间的星敏感器,其观测过程将不可避免受到天空背景辐射、大气湍流以及大气折射的影响。本文是星光成像的大气影响系列文章之二,建立了湍流大气星光传输模型,研究了恒星成像的大气湍流影响。基于ERA5数据和光学湍流预报方法得到大气湍流参数廓线,计算了典型地区不同时刻及观测条件下星光的闪烁指数,对比星光闪烁的理论值,验证了数值计算的可靠性。研究了湍流大气中星光传输的闪烁效应及星像质心的抖动特性,得到了典型观测高度及观测天顶角情况下的恒星抖动量。研究表明:恒星抖动的到达角和到达角起伏与星光的闪烁指数呈正相关关系,提升星敏感器的观测高度、减小星敏感器的观测天顶角,能一定程度上减轻星光成像的大气湍流影响。

The rapid development of aerospace technology,such as GPS satellite navigation system,represented by high precision and sensitivity,is gradually gaining wide attention from researchers and replacing traditional radio navigation systems,playing an important role in military defense,space exploration,engineering surveying,air-to-air combat and other fields.However,due to the limitations of traditional electromagnetic theory,satellite navigation technology has relatively weak anti-electronic deception and electromagnetic jamming capabilities.In order to enhance the autonomy and reliability of the navigation system,a passive and strong counter-jamming navigation method,which is named as starlight navigation,has been proposed.In the 1950 s,the advent of star sensors greatly improved the accuracy of starlight navigation.Star sensors are high-precision attitude-sensitive measuring instruments that measure the star vector component in the star sensor coordinate system by conducting the stellar observation,and determine the three-axis attitude of the carrier relative to the inertial coordinate system using known precise star positions.The high accuracy,strong counter-jamming ability,and independence from other systems of star sensor navigation technology have a wide range of applications and important military value on various airborne,shipborne,and vehicle-mounted platforms in near-earth space.However,as the development of observation platforms and the decrease in the observation height of star sensors in the atmosphere,a star sensor operating in the terrestrial space will inevitably be affected by sky background radiation,atmospheric turbulence,and atmospheric refraction during the observation.This three-part paper aims to extensively reveal these atmospheric effects on stellar observation.In Part II,we develop a starlight atmospheric propagation model to investigate the effects of atmospheric turbulence on star imaging.Based on the profile of atmospheric turbulence obtained by the ERA5 data of typical regions and optical turbulence prediction method,we employ von Karman spectrum of refractive index fluctuation and the so-called subharmoniccompensation-based fast-Fourier-transform algorithm to generate the corresponding random phase screens and calculate the spatial distribution,number,and strength of phase screens in accordance with the rule of equivalent Rytov-index interval phase screen.After that,we calculate the scintillation index of starlight for different moments and different observation conditions in typical regions by eliminating the apertureaveraging effect at the receiver.Further,we verify the reliability of the numerical calculation by comparing the theoretical counterpart of stellar scintillation.We investigate the scintillation effects and the jitter characteristics of starlight transmission in atmospheric turbulence and obtain the jitter displacements in the far field under typical observation height and zenith angle according to the far-field imaging theory.We show that the arrival angle and arrival angle fluctuation of stellar jitter are positively correlated with the scintillation index of starlight,and the effects of atmospheric turbulence on star imaging can be mitigated to a certain extent by increasing the observation altitude and reducing the observation zenith angle of the star sensor.This research provides a comprehensive analysis of atmospheric turbulence effects on star imaging and offers suggestions for improving stellar observation in terrestrial space.Moreover,these findings are of great significance for the practical application of star sensor navigation technology in various fields.