星光掩星探测技术的轨道模拟结果分析

Analysis of Simulation Results of Orbit Observation of Stellar Occultation Technology

星光掩星技术是利用恒星光谱进行地球及其他行星大气痕量成分密度、温度、气溶胶等测量的有效手段。该探测原理主要是根据不同的大气成分在恒星光谱的不同位置上表现出不同的吸收特征,具体表现在:紫外波段可进行臭氧、氧气、氢气等的测量,可见光谱段可探测二氧化氮、三氧化氮、氧气等,红外可探测水蒸气、气溶胶、甲烷、二氧化碳、氧气等。星光掩星的实现过程为:当LEO卫星和恒星分别位于地球的两侧时,恒星发射的光经过地球大气的吸收、散射等作用,被另一侧的LEO所接收,即构成掩星观测。根据光谱流量得到恒星的视星等范围,给出恒星在天球坐标系中的分布和不同的光谱型,以及利用各光谱型可探测的大气成分,再利用恒星和LEO卫星在地固坐标系中的相对位置,进行恒星-LEO星光掩星轨道观测模拟,基本流程为:首先读取LEO卫星的轨道位置以及目标恒星的位置,设置24 h的模拟时间,其次判断是否处于掩星状态,当掩星开始时,计算并输出掩星发生的经纬度、速度等,直至模拟时间结束。其中涉及恒星从天球坐标系转换到地固系的过程, LEO卫星轨道、掩星切点经纬度等的计算。根据模拟流程,计算并分析掩星事件的日观测量、全球分布、持续时间以及漂移速度等,得到以下结果:(1)目标恒星在全天区都有一定数量的分布且具有不同的光谱型,可进行臭氧、二氧化氮等成分的探测;(2)在对星光掩星进行24 h的轨道模拟过程中,日观测量为5 563次,其中包括2 737次上升掩星, 2 826次下降掩星;(3)从全球分布来看,掩星事件主要分布在低纬度,两极最少,其他纬度数量相当,且经度方向分布均匀;(4)根据方位角的分布,正常掩星占比为78.25%,持续时间平均为1.5 min,切点水平漂移在18~600 km;(5)21.75%的侧面掩星事件,其较正常掩星来说,持续时间长,切点的水平漂移速度大,方位角变化也大。该结果为卫星轨道设计和探测载荷设计提供理论指导。

Stellar occultation is an effective means of measuring the trace components density, temperature, aerosol, etc. on the Earth and other planets using stellar spectra. Thedetection principle mainly shows different absorption characteristics in different positions of the stellar spectrum according to different atmosphericcomponents, and the specific performance is as follows: the ultraviolet band can measure ozone, oxygen, hydrogen, etc., the visible spectrum can detect nitrogen dioxide, nitrogen trioxide, oxygen, etc., and infrared can detect water vapor, aerosol, methane, carbon dioxide, oxygen and so on. The realization process of the stellar occultation is: when the LEO satellite and the stellars are located on both sides of the earth, the light emitted by the stellar passes through the absorption and scattering of the earth’s atmosphere, and is received by the LEO on the other side, which constitutes an occultation observation. According to the spectral flow, the magnitude range of stellars is obtained, and the distribution of stars in the celestial coordinate system and different spectral types are given, as well as the atmospheric components detectable by each spectral type. The stellar-LEO occultation orbit observation simulation is carried out using the relative positions of the stellars and LEO satellite in the ground-solid coordinate system. The basic process is: firstly, reading the orbital position of the LEO satellite and the position of the target stellar, setting the simulation time of 24 hours, and then judging whether it is in the occultation state. When the occultation starts, parameters of occulation, such as the latitude and longitude are calculated and output until the end of the simulation time, which involves the process of the stellar transformation from the celestial coordinate system to the ground-solid system and calculation of LEO satellite orbit, occultation point latitude and longitude, etc. Through calculation and analysis of the daily measurement, global distribution, duration, and drift velocity of the occultation event according to the simulation process, the following results are obtained:(1)The target stellars have a certain number of distributions in the whole sky zone.(2)During the 24-hour orbital simulation of the stellar occultation, the daily observation is 5 563 times, including 2 737 rising occultations and 2 826 descending occultations.(3)From the perspective of global distribution, occultation events are mainly distributed at low latitudes, with the least two poles, the other latitudes are equal, the longitude direction is evenly distributed.(4)According to the azimuthal distribution, the normal occultation ratio is 78.25%, the average duration is 1.5 minutes, and horizontal drift of the tangent point is between 18 and 600 km.(5)The side occultation is 21.75%, longer than the normal occultation, the horizontal drift speed of the tangent point is large, and the azimuth angle is also large. The above results provide theoretical guidance for satellite orbit design and detection of load design.