Earth Orientation and Temporal Variations of the Gravity Field

TL;DR

This paper investigates the temporal variations of Earth's gravity field using space geodetic data, linking these variations to Earth Orientation Parameters and refining estimates of tidal and secular effects.

Contribution

It introduces a new computation of degree 2 gravity field coefficients using multiple satellite data and recent orbit standards, enhancing understanding of Earth's geophysical variations.

Findings

Refined estimates of the 18.6-year tidal term.

Detection of secular drift in the C20 coefficient.

Improved correlation between gravity variations and EOP changes.

Abstract

The high accuracy now reached in the VLBI Earth Orientation Parameters (EOP) determination requires looking further at the various geophysical contributions to variations in EOP. The determination of the Earth gravity field from space geodetic techniques now allows us to obtain the temporal variations of the low degree coefficients of the geopotential, combining the treatment of different satellites (e.g. Lageos1, Lageos2, Starlette ...). We present a new computation of the degree 2 coefficients of the variable Earth gravity field. This study is based upon the using of (i) new orbit standards, (ii) the GRACE mean gravity field and (iii) Lageos1 data from 1985 until 2004 (merged with Lageos2 data from 1993). These temporal variations of the Earth gravity field can be related to the Earth Orientation Parameters through the inertia tensor. This paper shows these relations and discusses how such geodetic data can contribute to the understanding of the variations in EOP. This paper also studies if these refined 20-yr of Lageos data can give us refined value of the 18.6-yr tidal term, as well as of the secular drift of the C20 geopotential coefficient.