Temporal Gravity Signals in Reprocessed GOCE Gravitational Gradients

Betty Heller,Thomas Gruber,Roland Pail,Frank Siegismund,Roger Haagmans

doi:10.3390/rs12213483

Abstract

The reprocessing of the satellite gravitational gradiometry (SGG) data from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission in 2018/2019 considerably reduced the low-frequency noise in the data, leading to reduced noise amplitudes in derived gravity field models at large spatial scales, at which temporal variations of the Earth’s gravity field have their highest amplitudes. This is the motivation to test the reprocessed GOCE SGG data for their ability to resolve time-variable gravity signals. For the gravity field processing, we apply and compare a spherical harmonics (SH) approach and a mass concentration (mascon) approach. Although their global signal-to-noise ratio is <1, SH GOCE SGG-only models resolve the strong regional signals of glacier melting in Greenland and Antarctica, and the 2011 moment magnitude 9.0 earthquake in Japan, providing an estimation of gravity variations independent of Gravity Recovery and Climate Experiment (GRACE) data. The benefit of combined GRACE/GOCE SGG models is evaluated based on the ice mass trend signals in Greenland and Antarctica. While no signal contribution from GOCE SGG data additional to the GRACE models could be observed, we show that the incorporation of GOCE SGG data numerically stabilizes the related normal equation systems.

Highlights

The satellite mission Gravity field and steady-state Ocean Circulation Explorer (GOCE [1]) collected data on the Earth’s gravity field from October 2009 to October 2013 [2], with the objective of determining the static global geoid on cm-level at a resolution of 100 km half-wavelength ([1,3])
The subsequent questions we address in our study both pursue the goals to verify the conclusions given in previous studies that are based on GOCE satellite gravitational gradiometry (SGG) data prior to the reprocessing in 2018/2019, as well as to investigate the new possibilities due to the reduced noise contained in the reprocessed gradient data: (1) Which time-variable signals can be resolved by gravity field models solely based on GOCE SGG data? Are the improvements in the northern polar area due to the recent reprocessing good enough to detect ice mass variations in Greenland in GOCE SGG-only models?
Regarding the second research question, we find in Section 3.3.1 by using the mascon approach that if the Gravity Recovery and Climate Experiment (GRACE) part in GRACE/GOCE SGG combination models is spectrally limited to d/o 45 and the GOCE part is overweighted by a factor of wscriptsizeGOCE = 100, GOCE SGG data add high-frequency time-variable signal contents in the regions of Greenland and West Antarctica

Summary

Introduction

The satellite mission Gravity field and steady-state Ocean Circulation Explorer (GOCE [1]) collected data on the Earth’s gravity field from October 2009 to October 2013 [2], with the objective of determining the static global geoid on cm-level at a resolution of 100 km half-wavelength ([1,3]). The main measurement principles of the GOCE mission are satellite gravitational gradiometry (SGG) and high-low satellite-to-satellite tracking (SST-hl). In this contribution, we exclusively focus on the SGG data, from which static gravity field models up to spherical harmonic (SH) degree and order (d/o) 280–300 can be derived [4]. The main purpose of the Gravity Recovery and Climate Experiment (GRACE) satellite mission, in contrast, was the determination of temporal variations of the Earth’s gravity field at a temporal resolution of one month and a spatial resolution of 400 km to 40,000 km [5].

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