FY-3D卫星的北斗掩星分布特征与误差特性

利用2018年1－3月FY-3D卫星的掩星折射率数据，研究了北斗导航卫星系统的掩星分布特点、数据精度以及误差统计特征。北斗导航卫星系统同步静止轨道掩星沿卫星轨道呈弧状分布在南北两极地区，倾斜轨道掩星在东西半球低纬度地区分别形成一小一大两个空洞，中地球轨道掩星则全球均匀分布。北斗掩星折射率数据精度在探测核心区域，即12~32 km范围内，与ERA5再分析资料计算的折射率相比，平均偏差的标准差约为1.5%，在核心区外，标准差从1.5%逐渐增大到6%。静止轨道掩星的平均偏差在高层略大于倾斜轨道和中地球轨道掩星。下降掩星在20 km以上区域的标准差大于上升掩星，20 km以下区域小于上升掩星。高纬地区北斗掩星标准差最小，低纬地区最大，对流层中下层尤其明显。分析结果表明，北斗掩星的数据精度和误差特征与GPS掩星数据相似。 

Analysis of Beidou Radio Occultation Data from FY-3D Satellite

Based on the Beidou radio occultation refractivity data of FY-3D satellite from January to March in 2018, the distribution characteristics of Beidou occultation, data accuracy and statistical characteristics of errors are studied. The Beidou Geostationary Orbit (GEO) occultation is distributed arc-shaped along the satellite orbit in the northern and southern polar regions, the Inclined Geo-Synchronous Orbit (IGSO) occultation forms one large and one small cavity respectively in the low latitude areas of the eastern and western hemispheres to form two cavities, and the Middle-Earth Orbit (MEO) occultation is distributed uniformly around the world. The accuracy of the Beidou occultion refractivity is within the range of 12~32 km in the core area. Compared with the ERA5 reanalysis data, the standard deviation of the average deviation is about 1.5%. In the range of height below 12 km and above 35 km, the standard deviation gradually increases from 1.5% to 6%. The deviation of GEO occultation over 35 km is slightly larger than that of IGSO and MEO occultation, but the standard deviation is smaller than that of these two types of occultation. The standard deviation of the descending occultation above 20 km is higher than that of the ascending occultation, but the area below 20 km is less than that of the ascending occultation. The standard deviation of the Beidou occultation is the smallest in high latitudes, followed by that in low latitudes and the largest in middle latitudes, especially in the middle and lower troposphere. The accuracy and error characteristics of the Beidou radio occultation data are consistent with the GPS radio occultation data, indicating that the Earth atmosphere occultation detection does not depend on the satellite navigation system.