1.Institute of Optics and Electronics Chinese Academy of Sciences, Chengdu 610209, China 2.University of Chinese Academy of Sciences, Beijing 100049, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 61501429).
Received Date:30 October 2018
Accepted Date:10 January 2019
Available Online:01 March 2019
Published Online:05 March 2019
Abstract:Satellite infrared spectra based on ground-based detector are affected by complex factors such as satellite surface temperature, solar radiation, observation angle, etc, whose change cannot be detected in external field experiment. Therefore, it is impossible to analyze what are the main factors that affect the satellite infrared spectra. At the same time, due to the lack of physical information about the satellites through the external field experiment, the validity and physical significance of retrieving features from satellite infrared spectrum cannot be explained. In view of the above problem, a method to model and analyze satellite thermal infrared spectra based on ground-based detector is proposed. It is a feasible research method to accurately establish satellite thermal infrared spectrum model based on the ground detection, then to analyze the simulated infrared spectrum data. Firstly, considering the solar radiation, earth radiation, detectable range of the satellite on the detector, observation angle, atmospheric attenuation, etc., the satellite thermal infrared spectrum model can be established more accurately. Then, taking FY-3 satellite for example, the physical and orbital parameters of the satellite are set up, and the 3?14${\text{μ}}{\rm m}$ infrared irradiance of the satellite on the pupil of the detector is calculated by using the model. Meanwhile, the main factors affecting the infrared spectrum of the satellite are analyzed. Finally, the equivalent temperature and equivalent area are extracted by fitting the satellite infrared spectrum with the Planck formula. And they are compared with the physical properties of the satellite. The results show that among the various factors, with the satellite’ movement, the change of the visible state of the satellite induced by the satellite’s movement is the main factor that affects the satellite infrared spectrum. The physical meanings of the equivalent temperature and equivalent area can also be explained effectively. The equivalent temperature is close to the temperatures of the solar panels, and their temperature difference is only about 15 K. The change of equivalent area is consistent with that of the satellite projected area. Moreover, it is also found that there is a large temperature difference between the solar panels and the body, which makes their infrared spectra obviously different. Therefore, it is hopeful to obtain the areas and temperatures of the solar panels and the body respectively. This research can make up for the shortcomings of the external field experiments and promote the monitoring and recognizing of satellites by ground-based infrared detectors. Keywords:satellite infrared spectrum/ ground-based detector/ Planck formula/ feature extraction
我们将卫星简化为简单的几何结构模型, 如图3所示. 太阳帆板和卫星本体都视为规则的长方体. 其表面视为漫反射和漫发射的灰体. 对该模型建立坐标系, 以本体中心为坐标原点, z轴指向地心方向, x轴指向卫星运行方向, y轴由右手法则确定. 风云三号卫星 (FY-3) 的物性参数和轨道参数分别见表1和表2. 图 3 风云三号卫星的简化几何模型 Figure3. the crude geometric structure model of the FY-3 satellite.
部件名称
几何尺寸/mm
材料
发射率
吸收率
卫星本体
4460 × 2200 × 3790
F46聚酯薄膜
0.81
0.1
太阳帆板
40 × 7800 × 3790
背面
SR107白漆
0.87
0.17
正面
太阳电池
0.86
0.9
侧面
有机黑漆
0.88
0.93
表1风云三号卫星的物性参数 Table1.Physical parameters of the FY-3 satellite.
轨道半长轴/km
偏心率
倾角/(°)
升交点赤经/(°)
降交点地方时
周期/min
7207
0.001
98.5
150
10:00
102
表2风云三号卫星的轨道参数 Table2.Orbital parameters of the FY-3 satellite.
24.2.卫星光谱辐照度 -->
4.2.卫星光谱辐照度
地面探测器与卫星降交点同经度, 纬度为北纬26°, 入瞳直径为1.2 m. 对风云三号卫星于春分时9:50到10:05期间(卫星在探测器的探测范围内)进行了仿真计算, 利用(10)和(11)式求出倾角和斜距, 如图4(a)所示. 卫星各表面法线方向与探测器方向的夹角余弦即$\cos {\theta _{\rm{r}}}$如图4(b)所示, 风云三号卫星各时段下的表面稳定温度场如图4(c)所示. 由(13)和(17)式可计算求得卫星在探测器处的光谱辐照度, 并加入大气修正后4%的不确定度, 如图4(d)所示. 图 4 在观测期间, (a) 风云三号卫星对地面探测器的倾角和斜距, (b)卫星各面法线与探测器连线的夹角余弦, (c)风云三号卫星的模拟温度场, (d)风云三号卫星在探测器上的红外光谱辐照度和BASS系统实测的地球同步卫星红外光谱[3] Figure4. During the observation period, (a) the elevation angle and range of the FY-3 satellite to ground-based detector, (b) the angle cosine between the normal of satellite’s side and the direction of detector, (c) the simulated temperature field of the FY-3 satellite, (d) the infrared spectral irradiance of the FY-3 satellite on the detector and the infrared spectral irradiance of geosynchronous satellite measured by BASS.
24.3.提取目标特征 -->
4.3.提取目标特征
当n = 1时, 用(25)式去拟合红外光谱数据得到的是卫星整体的等效温度和等效面积, 如图5所示; n = 2时, 用(25)式去拟合红外光谱数据得到两组不同的温度和面积, 如图6所示. 图 5 在观测期间, (a)等效温度与太阳帆板温度的比较, (b)等效面积和卫星对探测器的投影面积的比较 Figure5. During the observation period, (a) the comparison of the color temperature of n = 1 and solar panel temperature, (b) the comparison of the emissivity·projected area of n = 1 and satellite’s projected area.
图 6 在观测期间, (a)较高温度和卫星帆板温度的比较, (b)较高温度对应的面积和帆板面积的比较, 整体面积和卫星对探测器投影面积的比较 Figure6. During the observation period, (a) the comparison of the higher temperature of n = 2 and solar panel temperature, (b) the comparison of the area corresponding to higher temperature and the area of solar panel, the comparison of the sum of the areas of n = 2 and the projection area of the satellite to the detector.