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摘要:
为分析地气光辐射对空间目标成像特性的影响，以地球同步轨道(GEO)卫星搭载的可见光成像器为探测平台，利用卫星工具包(STK)设计高椭圆轨道(HEO)及近地轨道(LEO)目标运动场景，根据空间目标、地球、太阳、探测平台之间的位置关系，采用微元法建立空间目标与地气光背景等效星等模型，推导出空间目标信噪比(SNR)计算公式。分析了距离、角度参数变化对不同轨道空间目标、地气光背景等效星等及空间目标信噪比的影响。仿真结果表明：当探测平台距离空间目标较远时，地气光背景等效星等低于空间目标等效星等，地气光辐射比空间目标信号强。当地气光辐射进入和离开空间目标探测视场时，空间目标信噪比最大，该时间段是进行空间目标探测的最佳“观测窗口”。仿真得出的空间目标信噪比值为空间目标探测识别提供了理论计算依据。
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关键词:
- 地气光辐射 /
- 空间目标 /
- 等效星等 /
- 信噪比(SNR) /
- 卫星工具包(STK)
Abstract:To analyze the influence of earth-atmosphere radiation on imaging characteristics of space object, first, the visible light imager mounted on Geosynchronous Orbit (GEO) satellite was treated as an observation platform, and the motion scenes of Highly Elliptical Orbit (HEO) and Low Earth Orbit (LEO) objects were designed by the Satellite Tool Kit (STK). Then, the equivalent magnitude model of space object and earth-atmosphere background, and the calculation formulation for the Signal-to-Noise Ratio (SNR) of space object were derived by adopting infinitesimal method, according to the relative relationship among the space object, the sun, the earth and the observation platform. The effects of the distance and angle variables on the equivalent magnitude of different orbital objects and earth-atmosphere, as well as the SNR were analyzed. The simulation results indicate that the equivalent magnitude of earth-atmosphere background is lower than space object while the object is far away from the observation platform, which means that the earth-atmosphere radiation is stronger than the target signal. The observation window between the time when the earth-atmosphere radiation enters and leaves the target detecting field of view is the best time for target detection since the SNR is the largest. Moreover, the value of SNR obtained by simulation provides a theoretical calculation basis for the detection and recognition of space object.
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图 2 空间目标与地气光辐射观测示意图
Figure 2. Schematic diagram of space object and earth-atmosphere radiation observation
图 4 空间目标等效星等及相关参数变化
Figure 4. Variation of space target equivalent magnitude and related parameter
图 5 地气光背景等效星等及相关参数变化
Figure 5. Variation of earth-atmosphere background equivalent magnitude and related parameter
图 7 不同观测时段空间目标及地气光背景特性变化
Figure 7. Characteristic variation of target and earth-atmosphere background in different observation periods
图 8 两种模型得到的空间目标等效星等变化
Figure 8. Equivalent magnitude variation of space objects with two models
表 1 探测系统参数
Table 1. Parameters of observation system
参数 数值 光学系统孔径/m 0.4 透过率τ 0.56 可见光谱段λ1~λ2/μm 0.3~0.9 探测器IFOV/arcsec 1.76 暗电流噪声nd 18e- 读出噪声nr 6e- 探测器对信号光的量子效率Q 0.66 曝光时间t/s 0.5 注：arcsec指弧秒，角度单位；e-表示热电子，用以表征暗电流噪声大小。 
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表 2 地气光辐射进入HEO轨道目标探测视场时间段
Table 2. Period when earth-atmosphere radiation enters the HEO orbit target detection field of view
地气光进入HEO轨道目标探测视场 开始时间(世界时) 结束时间(世界时) 持续时间/s 第1次 01:49:06 02:18:38 1 773 合计持续时间 1 773
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表 3 地气光辐射进入LEO轨道目标探测视场时间段
Table 3. Period when earth-atmosphere radiation enters the LEO orbit target detection field of view
地气光进入LEO轨道目标探测视场 开始时间(世界时) 结束时间(世界时) 持续时间/s 第1次 02:06:38 02:32:31 1 554 第2次 03:41:56 04:12:46 1 851 第3次 05:19:42 05:50:05 1 824 第4次 06:59:37 07:24:23 1 487 合计持续时间 6 716
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表 4 距离和角度参数变化
Table 4. Variation of distance and angle parameters
轨道 参数 极小值 变化规律 探测相角α 单调递减 Rtd/m 3.54×107 先减后增 Rst/m 1.489 8×1011 先减后增 LEO 光照角β 8.586 5 先减后增 出射角θ 21.427 4 先减后增 Red/m 3.607 6×107 先减后增 Rse/m 1.4901×1011 先减后增 探测相角α 单调递减 Rtd/m 2.782 5×107 单调递增 Rst/m 1.489 7×1011 单调递增 HEO 光照角β 23.523 5 先减后增 出射角θ 28.585 7 先减后增 Red/m 3.637 0×107 先减后增 Rse/m 1.490 0×1011 先减后增
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表 5 两种模型空间目标等效星等数据对比
Table 5. Comparison of space target equivalent magnitude between two models
类别 HEO轨道目标等效星等均值 LEO轨道目标等效星等均值 普森公式 11.698 3 11.589 4 本文模型 11.580 5 11.513 6 差值 0.117 8 0.075 8
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