There exists no single EM induction source that is sensitive to the whole mantle.We need to integrate several natural sources in order to bridge across the scales.On the global scale, the most promising methodology is to combine magnetospheric and ocean tidal signals to image mantle under both continents and oceans

Alexander Grayver,

Kuvshinov, Alexey

Olsen, Nils

Sabaka, Terence J.

Toffner-Clausen, Lars

NASA Technical Reports Server

Swarm satellites in EM induction studies
Alexander Grayver, Alexey Kuvshinov Institute of Geophysics, ETH Zurich, Switzerland
Nils Olsen, Lars Tøffner-Clausen DTU Space, Denmark
Terence Sabaka Geodesy and Geophysics Laboratory, NASA, USA
Motivation
Presented at EMIW, August, 2018
• There exists no single EM induction source that is sensitive 
to the whole mantle. 
• We need to integrate several natural sources in order to 
bridge across the scales. 
• On the global scale, the most promising methodology is to 
combine magnetospheric and ocean tidal signals to image 
mantle under both continents and oceans. 
SWARM Data
Figure: Individual and joint inversions for a synthetic conductivity profile.
Magnetospheric source:
• Four years of SWARM data enable us to 
reliably estimate C1-response up to the period 
of six months. 
• The responses become biased if too simplistic 
source assumption is assumed. Therefore, we 
include spherical harmonic terms up to degree 
n = 2 when estimating magnetospheric source. 
Figure: C1-responses estimated using different 
lengths of Swarm time series.
Figure: Spherical harmonic spectra for tidal magnetic 
signals at the ground level. 
Principal semi-diurnal lunar M2 tide:
• M2 magnetic field is co-estimated from the 
four years of SWARM data. 
• The noise level is significantly lower compared 
to CHAMP data (Sabaka et al. 2015). 
• The spectrum for the SWARM signal has 
systematically higher level than spectra based 
on synthetic and CM5 data for n < 15.
Figure: Simulated and extracted tidal magnetic 
signals at 430 km altitude.
Inversion results
• We inverted magnetospheric responses and tidal magnetic 
signals detected by SWARM and CHAMP (Grayver et al. 
2017).
• Full 3D forward operator was used to account for the 
ocean-induced effect.
• The global conductivity model has been derived in the 
whole mantle depth range, thereby improving resolution of 
individual inversions.
• Retrieved conductivity profiles are compatible with a 
pyrolytic composition and a moderate mantle water 
content.
Figure: Comparison of the recovered models with 
the lab-based conductivity profiles.
Figure: Conductivity profiles retrieved from 
individual and joint inversion of satellite data
References:
Grayver, AV, Munch, FD, Kuvshinov, AV, Khan, A, Sabaka, TJ, 
Tøffner-Clausen, L. 2017, Geophysical research letters, 44(12).
Sabaka, TJ, Olsen, N, Tyler, RH, & Kuvshinov, A. 2015, Geophysical
Journal International, 200(3).
https://ntrs.nasa.gov/search.jsp?R=20180006090 2019-08-31T15:08:23+00:00Z


Swarm Satellites in EM Induction Studies

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