星光掩星技术中, 利用三维射线追踪方法模拟从地面到110 km高度红外辐射在大气中传输的路线。 其中, 设置频率为3.95×1014 Hz, 地球形状为椭球状, 模型为中性大气, 且已知在地固系中目标恒星的三维位置坐标和低轨卫星轨道数据。 再利用HITRAN数据库中高分辨率的氧分子吸收线参数, 包括吸收线强度、 低能态能量等, 以天狼星的红外光谱作为原始的接收光谱, 即去除地球大气的吸收散射等的作用, 光谱能量随着波长的增大而降低, 计算接收光谱在近红外氧气分子吸收A带(755～774 nm)的透过率。 考虑到仪器小型化, 选择氧气的特征吸收谱线760和762 nm, 计算两谱线位置的大气透过率随高度的变化, 并通过透过率计算接收光谱的信噪比, 进行仪器设计的指导。 另外, 由于大气折射作用, 必须将所得透过率进行折射修正。 通过仿真计算可知: 利用近红外波段755～774 nm, 计算了80, 100和110 km三个高度的大气透过率, 其随高度的逐渐增高而趋近于1。 相比0.2 nm光谱分辨率, 0.1 nm分辨率条件下大气透过率的变化范围更大, 为0.28～1, 在110 km透过率为0.987, 且探测的精确度可小一位。 折射引起的透过率在60 km以上等于1, 因此60 km以上可以忽略大气折射对大气透过率的影响, 无需进行折射修正。 利用760和762 nm的特征吸收线, 得到光强度信噪比均大于100, 且当分辨率为0.1 nm时, 光强度信噪比的值更小, 说明氧气对光谱的吸收作用更强。 两种分辨率条件下所得相邻两高度的光子数变化量差别不大且大于1。 最后, 根据以上结果, 可确定望远镜、 CCD、 光谱分辨率、 积分时间等参数, 用以研究和测试星光掩星的反演算法, 形成探测氧气从地面到110 km高度数密度变化的小型化仪器, 也可预先分析探测误差等。

The 3D ray tracing method is used to simulate the transmission of oxygen in the atmosphere from ground to 110 km in the stellar occultation technique. The carrier frequency is 3.53×1015 Hz, the Earth is ellipsoid, and the model is the neutral atmosphere. It is known that the three-dimensional position coordinates of target stellar and low-orbit satellite orbit data in the earth-solid system. And then the high resolution of oxygen molecular absorption line parameters in the HITRAN database are used, including the absorption line intensity, low-level energy, etc., to calculate the transmittance of oxygen molecules in the near-infrared absorption band A. In addition, taking Sirius’ infrared spectrum as the original receiving spectrum, that is, removing the absorption and scattering of the Earth’s atmosphere, the spectral energy decreases as the wavelength increases. The characteristic absorption lines of oxygen are selected at 760 and 762 nm, and the atmospheric transmittance of the line position is calculated as a function of height. The signal-to-noise ratio of the received spectrum is calculated by transmittance to guide the instrument design. In addition, due to atmospheric refraction, the resulting transmittance must be corrected for refraction. According to the simulation calculation, the atmospheric transmittance of three heights of 80, 100 and 110 km is calculated by using the near-infrared band of 755~774 nm, approaching 1 as the height increases gradually. Compared with 0.2 nm resolution, the atmospheric transmittance obtained under 0.1 nm resolution range is larger, is 0.28~1, the transmittance at 110 km is 0.987, and the accuracy of the detection can be a small one. The transmittance caused by atmospheric refraction above 60 km is equal to 1. Therefore, the influence of atmospheric refraction on atmospheric transmittance can be neglected above 60 km, so no refraction correction is required above 60 km. The signal-to-noise ratio is greater than 100 on the characteristic absorption lines at 760 and 762 nm. When the resolution is 0.1 nm, the value of the spectral intensity signal-to-noise ratio is smaller, indicating that the absorption of oxygen by the spectrum is strong. The amount of change in the number of photons obtained under the two resolution conditions is not much different and is greater than one. Finally, based on the above results, parameters such as the telescope, CCD, grating resolution, and integration time canconfirm. The inversion algorithm used to study and test the stellar occultation to form a miniaturized instrument that detects the change in the density of oxygen from the ground to the height of 110 km, and can also analyze the detection error in advance.