A mosaic imaging study of the northern and southern hemispheres of the nearside of the Moon based on the Sanya Incoherent Scatter Radar
-
摘要: 当使用地基雷达并应用距离多普勒算法对月球正面进行成像时，不可避免会遇到“南北模糊”问题. 这是由于距离多普勒成像算法对旋转的天体进行成像时，位于视赤道共轭的两点的回波在距离多普勒图像中是重叠在一起无法分辨的. 针对该问题并基于三亚非相干散射雷达我们提出了一种解决方案，即月球正面南北半球拼接成像技术. 该技术通过将波束指向调整到特定位置，对月球正面南北半球分开照射的方法进行两次独立的实验，最后将正面南北半球图像拼接的方法得到完整的月球成像图. 实验结果证明该技术可以得到较为理想的图像，但仍然存在一些不足需要改进.Abstract: When ground-based radar and range-Doppler algorithm are used to image the nearside of the Moon, it is inevitable to encounter the problem of "north-south ambiguity". This is because when the range-Doppler imaging algorithm is used to image a rotating celestial body, the echoes of the two points conjugated at the apparent equator are superposed together and cannot be resolved in the range-Doppler image. We propose a solution to this problem based on the Sanya Incoherent Scatter Radar, namely the mosaic imaging technology of the northern and southern hemispheres of the near side of the Moon. In this technology, two independent experiments were carried out to separately illuminate the northern and southern hemispheres of the nearside of the Moon by adjusting the beam direction to a specific position. Finally, a complete Moon nearside map was obtained by combining the images of the northern and southern hemispheres. The results of experiments show that this technique can successfully get the Moon images, but there are still some defects that need to be improved.
-
图 1 距离多普勒算法几何示意图. X轴为距离轴指向雷达，Z轴沿着视自转轴方向，Y轴为方位轴满足右手定则. 距离环为X轴上距离分辨率单元在月面的投影，距离环上所有点到雷达的距离相等，多普勒条带为Y轴上多普勒分辨率单元在月面的投影，多普勒条带上所有点相对于雷达的多普勒频移相等
Figure 1. Schematic diagram of range-Doppler algorithm geometry. The X-axis is the range axis pointing to the radar, the Z-axis is along the apparent rotation axis, and the Y-axis is the azimuth axis, which satisfies the right-hand rule. The range ring is the projection of the X-axis range resolution unit on the lunar surface, and the ranges from all points on the range ring to the radar are equal. The Doppler band is the projection of the Y-axis Doppler resolution unit on the lunar surface. The Doppler frequency shifts of all points on the Doppler band are equal
图 2 三亚非相干散射雷达归一化天线方向图. 横轴代表天顶角，单位为度；纵轴代表归一化辐射能量，单位为dB. 波束主瓣指向天顶方向，3 dB波束宽度用红色横线上的黑点和文字标出，10 dB波束宽度用黄色横线上的黑点和文字标出，第一零点波束宽度用横轴上的黑点和文字标出
Figure 2. Normalized antenna pattern of Sanya incoherent scatter radar. The horizontal axis represents the zenith angle, in degrees; the vertical axis represents normalized radiation energy, in dB. The main lobe of the beam points to the zenith direction, the 3 dB beam width is noted by the black dots on the red horizontal line, the 10 dB beam width is noted by the black dots on the yellow horizontal line, and the first zero beam width is noted by the black dots on the horizontal axis
图 3 不同波束宽度定义下进行观测时观测半球与视赤道另一侧半球照射能量对比分析图. 上半图蓝色线表示照射到观测半球的能量占主瓣总能量的比重，红色线表示照射到视赤道另一侧半球的能量占主瓣总能量的比重. 下半图绿色线表示的是上半图蓝色线与红色线的比值. 三条黑色竖虚线从左到右分别表示3 dB波束宽度、10 dB波束宽度以及第一零点波束宽度
Figure 3. Comparison and analysis diagram of the energy illuminated on the observed hemisphere and the hemisphere on the other side of the apparent equator using different beam width definitions. The blue line in the upper half of the figure indicates the ratio of the energy illuminated on the observed hemisphere to the total energy of the main lobe, and the red line indicates the ratio of the energy illuminated to the hemisphere on the other side of the apparent equator to the total energy of the main lobe. The green line in the lower half of the figure represents the ratio of the blue line to the red line in the upper half of the figure. The three black vertical dotted lines from left to right represent the 3 dB beam width, 10 dB beam width and the first zero beam width respectively
图 4 月球南北半球拼接成像图. 图像数据来自2021年3月16日三亚当地时14:30～15:00的实验. 坐标系为月球投影坐标，即经纬度坐标，经度范围100°W～100°E，步长0.05°，纬度范围90°S～90°N，步长0.05°. 红字标出了一些月球标志性地质单元名称. 黄色框标出的条带斑纹状区域是由于线性插值处理产生的额外的无效区域，不属于成像范围
Figure 4. Mosaic image of the northern and southern hemispheres of the nearside of the moon. The data comes from the experiment of 14:30～15:00 local time in Sanya on March 16, 2021. The coordinate system is the lunar projection coordinates, that is, the latitude and longitude coordinates, the longitude range is 100°W～100°E, the step length is 0.05°, the latitude range is 90°S～90°N, and the step length is 0.05°. The red words mark the names of some lunar geological units. The striped areas marked by the yellow frames are invalid area caused by the linear interpolation process, which does not belong to the mapping region
图 5 回波功率中已校正的三个影响因素. （a）归一化的天线方向图函数在月球正面观测半球的投影分布，该图是借助星历计算得到的2021年3月16日三亚当地时14:46:19、雷达波束仰角77.54°、方位角170.84°情况下天线方向图在月面的投影，用于校正当地时14:45:19～14:47:19这2 min积累得到的图像；（b）散射单元面积在距离多普勒二维坐标下的分布图，是根据距离多普勒二维分辨率单元在月面投影面积来计算的理论数值；（c）归一化极化回波功率随入射角变化曲线，其中蓝色线是2021年3月16日三亚当地时14:30～15:00的观测数据平均得到的变化曲线，红色点为Hagfors（1970）文献中总结的68 cm波长雷达探测数据，黑色线为文献数据拟合曲线，校正使用的是拟合曲线
Figure 5. Three influence factors corrected in the echo power. (a) The distribution of the normalized antenna pattern on the observed hemisphere of the nearside of the moon. It is calculated with the help of ephemeris at 14:46:19 local time in Sanya on March 16, 2021, with the radar beam elevation angle of 77.54° and azimuth angle of 170.84°. It is used to correct the images accumulated during the 2 minutes from 14:45:19 to 14:47:19 local time; (b) The area of the scattering unit in the range-Doppler domain. It is a theoretical map calculated by the projection area of the two-dimensional range-Doppler resolution unit on the lunar surface; (c) The curves of normalized polarized echo power with the angle of incidence, in which the blue curve is the average curve of the observation data from 14:30 to 15:00 local time in Sanya on March 16, 2021. The red points are the 68 cm-wavelength radar detection summarized in the Hagfors (1970) literature, and the black curve is the fitting curve of red points. The fitting curve was used for calibration
表 1 雷达指标以及实验参数
Table 1. Radar index and experiment parameters
参数名称 数值或说明 极化方式 发射右旋圆极化，接收左旋圆极化 天线增益 43 dB（法线方向） 天线孔径 ~778 m2 扫描范围 天顶角南北方向±48°，东西方向±25° 发射波形 线性调频 脉宽 2 ms 波形带宽 0.3 MHz 发射峰值功率 2 MW 发射频率 430 MHz 脉冲重复周期 60 ms 相干积累时间 2 min 距离向分辨率 ~500 m 方位向分辨率 ~2 km 
下载: 导出CSV
-
[1] Campbell B A, Campbell D B, Margot J L, et al. 2007. Focused 70-cm wavelength radar mapping of the moon[J]. IEEE Transactions on Geoence & Remote Sensing, 45(12): 4032-4042. https://doi.org/10.1109/TGRS.2007.906582 [2] Campbell B A, Carter L M, Campbell D B, et al. 2010. Earth-based 12.6-cm wavelength radar mapping of the Moon: New views of impact melt distribution and mare physical properties[J]. Icarus, 208: 565-573. https://doi.org/10.1016/j.icarus.2010.03.011 [3] 丁春雨, 封剑青, 郑磊, 等. 2015. 雷达探测技术在探月中的应用[J]. 天文研究与技术, 2015(2): 228-242.Ding C Y, Feng J Q, Zheng L, et al. 2015. A review of applications of radar-detection techniques in lunar explorations[J]. Astronomical Research and Technology, 2015(2): 228-242 (in Chinese). [4] Hagfors T. 1970. Remote probing of the moon by infrared and microwave emissions and by radar[J]. Radio Science, 5(2): 189-227. https://doi.org/10.1029/RS005i002p00189 [5] Li M, Yue X, Zhao B, et al. 2021. Simulation of the signal-to-noise ratio of Sanya incoherent scatter radar tristatic system[J]. IEEE Transactions on Geoscience and Remote Sensing, 59(4): 2982-2993. http://doi.org/10.1109/TGRS.2020.3008427 [6] Pettengill G H, Henry J C. 1962. Enhancement of radar reflectivity associated with the lunar crater Tycho[J]. Journal of Geophysical Research, 67(12): 4881-4885. https://doi.org/10.1029/JZ067i012p04881 [7] Pettengill G H, Zisk S H, Thompson T W. 1974. The mapping of lunar radar scattering characteristics[J]. Moon, 10(1): 3-16. https://doi.org/10.1007/BF00562016 [8] Stacy N J S. 1993. High-resolution synthetic aperture radar observations of the moon[D]. Ithaca, New York: Cornell University. [9] Stacy N J S. 1997. Arecibo radar mapping of the lunar poles: a search for ice deposits[J]. Science, 276(5318):1527-1530. https://doi.org/10.1126/science.276.5318.1527 [10] 孙靖, 杨嵩, 周峰, 等. 2021. 我国地基雷达观测月球的现状和研究进展[J]. 天文研究与技术, (5): 1-13. https://doi.org/10.14005/j.cnki.issn1672-7673.20210331.006.Sun J, Yang S, Zhou F, et al. 2021. The status of Earth-based radar astronomical observations of the Moon in China[J]. Astronomical Research and Technology, (5):1-13 (in Chinese). https://doi.org/10.14005/j.cnki.issn1672-7673.20210331.006. [11] Thompson T W. 1970. Map of lunar radar reflectivity at 7.5-m wavelength[J]. Icarus, 13(3): 363-370. https://doi.org/10.1016/0019-1035(70)90086-2 [12] Thompson T W. 1974. Atlas of lunar radar maps at 70-cm wavelength[J]. Moon, 10(1): 51-85. https://doi.org/10.1007/BF00562018 [13] Thompson T W. 1979. A review of earth-based radar mapping of the moon[J]. Moon & the Planets, 20(2): 179-198. https://doi.org/10.1007/BF00898069 [14] Thompson T W. 1987. High-resolution lunar radar map at 70-cm wavelength[J]. Earth Moon & Planets, 37(1): 59-70. https://doi.org/10.1007/BF00054324 [15] Vierinen J, Lehtinen M S. 2009. 32-cm wavelength radar mapping of the Moon[C]//Radar Conference, 2009. EuRAD 2009. European: IEEE Xplore. [16] Vierinen J, Tveito T, Gustavsson B, et al. 2017. Radar images of the moon at 6-meter wavelength[J]. Icarus, 297: 179-188. https://doi.org/10.1016/j.icarus.2017.06.035 [17] Zisk S H. 1972. A new, earth-based radar technique for the measurement of lunar topography[J]. The Moon, 4(3-4): 296-306. https://doi.org/10.1007/BF00561997 [18] Zisk S H, Pettengill G H, Catuna G W. 1974. High-resolution radar maps of the lunar surface at 3.8-cm wavelength[J]. Moon, 10(1): 17-50. https://doi.org/10.1007/BF00562017 [19] 郑磊, 苏彦, 郑永春, 等. 2009. 地基雷达技术及其在太阳系天体探测中的应用[J]. 天文学进展, (4): 85-94.Zheng L, Su Y, Zheng Y C, et al. 2009. Ground-based radar and its Aapplications in remote sensing of the solar system planets[J]. Progress in Astronomy, (4): 85-94 (in Chinese). -
点击查看大图
计量
- 文章访问数: 955
- HTML全文浏览量: 431
- PDF下载量: 105
- 被引次数: 0
