Analysis on Error Distribution of Earth’s FCN Parameters with
Tetra-Frequency Spectrum Method
Xiange Lei
Heping Sun
Chinese Academy of Sciences, Institute of Geodesy and Geophysics,
Xudong Street 340, Wuhan 430077, Hubei Province, China.
E-mail: leixe@whigg.ac.cn
The rotation of the Earth’s liquid core creates the nearly diurnal free wobble (NDFW)
and appears the Earth’s free core nutation (FCN) in inertial space. The tidal factors of
diurnal waves occupy some nonlinear change as the effect of NDFW phenomena,
which is often called the NDFW resonance of diurnal tides. The Earth’s FCN
parameters provide some valuable information on the Earth’s core structure. By
introducing the stacking method, Neuberg, Zürn and Hinderer (1987) began to
retrieve the FCN parameters from the gravity tide data recorded by six gravimetric
stations in middle Europe. The stacking method resolved the FCN parameters and the
intensity of NDFW resonance (A*) by applying the least square technique with five
diurnal tidal waves. The later researchers mainly followed the stacking method and
gained the similar observational results. In fact the resolved FCN parameters did not
followed the gauss distribution, the stacking method could not provide the accurate
description of the FCN parameters error. We develop a new kind method to resolve
the FCN parameters, which can realize the resolution of FCN parameters by the
calculation of the Observational Amplitude-Frequency Parameter (OAFP) and the
Observational Phase-Frequency Parameter (OPFP) and the structure of
Amplitude-Frequency Spectrum (AFS) and the Phase-Frequency Spectrum (PFS). As
the whole process of the resolution only requires four diurnal waves nearby FCN
frequency, this new resolution method was also called as Tetra-Frequency Spectrum
Method (TFSM).We resolved the FCN parameters from the gravity tide data recorded
by SGs at Moxa station with Tetra -Frequency Spectrum Method, and it could provide
the detail description of the FCN parameters error distribution and improve the
resolution quality.
Acknowledgements: Three months of academic visit at GFZ on Nov. 2006 invited by
Dr. Neumeyer and Prof. Rothacher, and the published SG tidal factors at Moxa station.
This work was supported jointly by the National Natural Science Foundation of China
(Grant No. 40974046 and No. 40730316), the Knowledge Innovation Project of
Chinese Academy of Sciences (Grant No.KZCX2-YW-133), Natural Science
Foundation of Hubei Province in China. (Grant No.2008CDB389).
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