Mitigation of ionospheric signatures in Swarm GPS gravity field estimation using weighting strategies
<p>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 <span class="inline-formula">480</span> km...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-02-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/37/111/2019/angeo-37-111-2019.pdf |
| Summary: | <p>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 <span class="inline-formula">480</span> km
for Swarm A and Swarm C and <span class="inline-formula">530</span> 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 <span class="inline-formula">2017</span>, 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.</p>
<p>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.</p> |
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| ISSN: | 0992-7689 1432-0576 |