Mitigation of ionospheric signatures in Swarm GPS gravity field estimation using weighting strategies
Mitigation of ionospheric signatures in Swarm GPS gravity field estimation using weighting strategies
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DOI：
10.5194/angeo-37-111-2019
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发表时间：
2019-02-12
影响因子：
1.9
通讯作者：
Jaggi, Adrian
中科院分区：
文献类型：
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作者：
Schreiter, Lucas;Arnold, Daniel;Jaggi, Adrian
尽管欧空局由三颗卫星组成的近地轨道(LEO)任务群主要是一次磁场任务，但它也可以作为一次重力任务。它位于近极轨道上，A群和C群的初始高度为480公里，B群的初始高度为530公里，配备了大地测量型双频全球定位系统(GPS)接收器，适合于重力场计算。当然，仅适用于全球定位系统的重力场无法与由超精密重力恢复和气候实验(GRACE)K波段测量得出的重力场相竞争。但由于各种原因，如2017年10月GRACE任务的结束，前几个月电池老化导致的数据差距，以及GRACE与最近发射的GRACE后续任务之间的差距，群重力场对于保持连续的时间序列和弥合两个专门的重力任务之间的差距变得重要。通过比较由星群运动位置得到的重力场和GRACE重力场，观测到了星群结果的系统误差，特别是在地磁赤道附近。这些误差已经在运动学位置上表现为几厘米的尖峰，从那里它们传播到重力场解。我们通过使用高斯滤波器和Savitzky-Golay滤波器的组合以及总电子含量(TEC)指数(ROTI)来分析GPS载波相位观测值及其时间导数的无几何线性组合来研究这些系统误差。在此基础上，我们提出了不同的加权方案，并研究了它们对重力场解的影响，以评估不同缓解策略的成功。我们将展示基于导数的加权方法和基于旋转的加权方法的组合，能够将受严重影响的月份的大地水准面RMS从21.6 mm减少到12.0 mm，并且与基于导数的筛选相比，可以保留近10%的动态位置。
Even though ESA's three-satellite low-earth orbit (LEO) mission Swarm is primarily a magnetic field mission, it can also serve as a gravity field mission. Located in a near-polar orbit with initial altitudes of 480 km for Swarm A and Swarm C and 530 km for Swarm B and equipped with geodetic-type dual frequency Global Positioning System (GPS) receivers, it is suitable for gravity field computation. Of course, the Swarm GPS-only gravity fields cannot compete with the gravity fields derived from the ultra-precise Gravity Recovery And Climate Experiment (GRACE) K-band measurements. But for various reasons like the end of the GRACE mission in October 2017, data gaps in the previous months due to battery aging, and the gap between GRACE and the recently launched GRACE Follow-On mission, Swarm gravity fields became important to maintain a continuous time series and to bridge the gap between the two dedicated gravity missions. By comparing the gravity fields derived from Swarm kinematic positions to the GRACE gravity fields, systematic errors have been observed in the Swarm results, especially around the geomagnetic equator. These errors are already visible in the kinematic positions as spikes up to a few centimeters, from where they propagate into the gravity field solutions.We investigate these systematic errors by analyzing the geometry-free linear combination of the GPS carrier-phase observations and its time derivatives using a combination of a Gaussian filter and a Savitzky-Golay filter and the Rate of Total Electron Content (TEC) Index (ROTI). Based on this, we present different weighting schemes and investigate their impact on the gravity field solutions in order to assess the success of different mitigation strategies. We will show that a combination of a derivative-based weighting approach with a ROTI-based weighting approach is capable of reducing the geoid rms from 21.6 to 12.0 mm for a heavily affected month and that almost 10% more kinematic positions can be preserved compared to a derivative-based screening.