星载GNSS反射信号时-空性能仿真分析

针对星载全球导航卫星系统(GNSS)反射信号时-空性能问题，该文从1阶统计量角度定义了平均空间覆盖次数、全球覆盖面积百分比和平均回访时间3个衡量星载GNSS反射信号时-空性能的指标，并通过建立GNSS和低轨卫星轨道仿真研究了低轨卫星轨道高度、倾角、升交点赤经以及天线波束对星载GNSS反射信号时-空性能的影响。结果表明:单颗卫星无法满足全球探测的任务需求，当轨道高度为1300 km，倾角为98.7°，天线波束为40°时，平均覆盖次数、平均覆盖面积百分比和平均回访时间分别为1.6, 36.5%和8 h；通过单一轨道的卫星组网可有效提高星载GNSS反射信号的时-空性能，当卫星数目为4，高度为635 km，倾角为98.7°，波束宽度为40°时，星载GNSS反射信号的时-空性能指标高于单颗ASCAT卫星24 h覆盖地球65%的指标；当卫星数目增加至8颗时，星载GNSS反射信号可在平均4.5 h内观测地球88.9%的区域。

Spatiotemporal Performance of Spaceborne Global NavigationSatellites System Reflectometry

The mean of spatial coverage number, the percentage of global coverage, and the mean of revisiting time are defined based on first-order statistics to evaluate spatiotemporal performance of spaceborne Global Navigation Satellites System (GNSS) reflectometry, in addition develops the GNSS and LEO orbits to simulate the influence of LEO orbit height, inclination and right ascension of ascending node on spatiotemporal performance. The results show that the mean of spatial coverage number, the percentage of global coverage, and the mean of revisiting time are respectively 1.6, 36.5, and 8 h with the orbit height of 1300 km, inclination of 98.7°, and the beam width of 40° so that the requirement of global observation could not be met. When the number of satellites in same orbital plane is 4 and the orbit height, inclination, and the beam width are respectively 1300 km, 98.7°, 40°, the spatiotemporal performance is higher than the 65% of single ASCAT. For the case of 8 satellites, spaceborne GNSS reflectometry could observe the area of 88.9% of the earth in 4.5 h.