星基反演TEC与地基GNSS TEC数据融合可行性分析

Feasibility of the Data Fusion Between Space-Borne and Ground-Based TEC Products

  • 摘要: 卫星测高、DORIS(Doppler Orbitography and Radio-positioning Integrated by Satellite)和无线电掩星等星基观测技术具有不受地表形态限制的全球观测范围,能够作为地基全球导航卫星系统(Global Navigation Satellite System,GNSS)电离层反演在海洋区域的补充观测。然而星基观测电离层高度范围仅限于低轨卫星轨道面以下,无法覆盖整个电离层高度范围,因此不能直接用于与地基GNSS反演的电离层总电子含量(total electron content,TEC)格网融合。针对DORIS观测反演的相对斜向总电子含量(slant total electron content,STEC),以全球电离层TEC格网(global ionosphere maps total electron content,GIM TEC)为基准,采用整体偏移方法将两者归算至统一观测尺度上;而卫星测高和GNSS掩星电离层产品则选取国际GNSS服务(International GNSS Service,IGS)组织提供的全球电离层TEC格网中均方根(root mean square,RMS)误差小于2 TECU的区域作为基准,采用2014年1月份低轨卫星观测值反演的TEC和GIM TEC数据进行对比,统计Jason-2和COSMIC(Constellation Observing System for Meteorology,Ionosphere and Climate)卫星反演的TEC与GIM TEC之间基于比例因子的函数关系,并将不同的观测手段归算到统一的观测尺度上,对比归算前后的TEC产品差异。并根据反演产品附近的全球定位系统(Global Positioning System,GPS)电离层穿刺点数量进行分类,验证星基电离层反演精度的有效性。对比结果显示,卫星测高、DORIS和掩星3种星基技术归算后的TEC产品与GIM TEC的匹配度在地基观测密集区域均能达到较好的符合度,而在地基观测不足区域符合度存在明显差异。考虑星基观测精度不受地域限制的特性,可认为该海洋区域的差异是由于星基观测在海洋区域观测精度比地基GNSS观测精度更高,星基观测反演的电离层TEC产品可作为海洋地区地基电离层TEC观测的有效补充。

     

    Abstract: The space-borne observations like satellite altimetry (SA), Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) and radio occultation (RO) techniques are average distributed around world without any limitation on the Earth surface landforms, hence could be used as complemented observations for the ground-based Global Navigation Satellite System (GNSS) ionosphere total electron content (TEC) retrieval. However, all the three space-borne observations are limited below the low earth orbit(LEO) satellite orbits which could not reflect the whole ionosphere TEC values. In this research, the DORIS relate slant total electron content(STEC) were leveled up/down to consist with global ionosphere maps (GIM) mean STEC, and for SA and RO TEC products, sample regions where the GIM TEC root mean square(RMS) below 2 TECU were selected as reference, and the scaling factors between the space-borne TEC products and GIM TEC were calculated with data in January, 2014. The retrieved TEC products were transferred to unified ionosphere datum as GIM TEC products, and comparison results were satisfied to validate the effectiveness of the space-borne ionosphere retrieval techniques. And also, the differences between the space-borne TEC and GIM TEC were summarized and compared with the ionospheric pierce point (IPP) number. The results show that the adjusted space-borne retrieved TEC products have good agreement with GIM TEC on IPP density distributed areas and less coincident on areas where IPP are sparely distributed. As the accuracy of the space-borne ionosphere retrieval technique basically has no spatial variance, it could be concluded that the adjusted TEC retrieved from the three space-borne techniques could effectively improve the GIM TEC products on ocean area where ground GNSS observation are not enough.

     

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