Determination and Combination of Monthly Gravity Field Time Series from Kinematic Orbits of GRACE, GRACE-FO and Swarm

Grombein, Thomas; Lasser, Martin; Arnold, Daniel; Meyer, Ulrich; Jäggi, Adrian

doi:10.1007/1345_2022_163

Cited by 3 publications

(1 citation statement)

References 38 publications

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“…Time-variable gravity field has been directly determined using observations from SLR (Bonin et al 2018;Löcher and Kusche 2021;Sośnica et al 2015) and the GPS-based orbit of low-orbiting satellites, such as the Swarm mission (Dahle et al 2020). Combinations of data from Swarm and GRACE have also been performed (Grombein et al 2022), by setting the scale factor based on differences in the sampling rate of the observed data when stochastically combining other gravity solutions. Combination of data from different analysis centers is also successfully performing (Gauer et al 2023;Jäggi et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Impact of the combination and replacement of SLR-based low-degree gravity field coefficients in GRACE solutions

Gałdyn,

Sośnica

2024

Prog Earth Planet Sci

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GRACE and GRACE Follow-On (FO) missions provide time-variable gravity field models of unprecedented quality that allow for the hydrological, oceanic, and ice mass change studies on a global scale. However, the very low-degree coefficients derived from GRACE and GRACE-FO are of inferior quality due to thermal effects acting on satellites and malfunctioning of the onboard accelerometers. Therefore, C20 and C30 coefficients describing the Earth’s oblateness and the pear shape of the Earth, respectively, are being replaced by values derived from satellite laser ranging (SLR) in the standard GRACE solutions. This study assesses the impact of the replacement of low-degree gravity field coefficients in GRACE/GRACE-FO solutions by SLR data on the trend and seasonal signals of ice mass changes in Greenland and Antarctica. We found that the replacement of the low-degree gravity field coefficients changes the estimates of trends by 4, 8, and 22 Gt/year in Greenland, West, and East Antarctica, respectively, depending on the source of SLR coefficients and period for which the coefficients are replaced. In SLR and GRACE solutions, all coefficients of the same order and the same parity of degrees are strongly correlated. Therefore, replacing only two selected coefficients may lead to a biased solution. Thus, we propose to combine GRACE with SLR solutions up to a degree and order 10 × 10 to properly consider the sensitivity of each of the techniques to gravity field coefficients, instead of replacing two coefficients from SLR in GRACE solutions. The combined solution reduces the residual trend of post-glacial rebound from 1.2 to 0.9 Gt/year and from − 57.8 to − 57.0 Gt/year in Scandinavia and South Canada, respectively, when compared to GRACE/GRACE-FO solutions with the replacement of coefficients. The SLR-GRACE combination reduces the noise in the GRACE/GRACE-FO solutions by 8%, from 38 to 35 Gt, in the Fennoscandia region. In the periods when GRACE is at the end of its mission and observations are disrupted, the weights adjust the contribution from SLR and GRACE based on relative ratio of variances from each techniques. Thus, the combined solutions are more consistent with independent geophysical models of glacial isostatic adjustment, and the combinations are affected by smaller noise than the standard GRACE solutions and properly account for different sensitivities of SLR and GRACE techniques to low-degree time-variable gravity field coefficients.

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Section: Introductionmentioning

confidence: 99%

Impact of the combination and replacement of SLR-based low-degree gravity field coefficients in GRACE solutions

Gałdyn,

Sośnica

2024

Prog Earth Planet Sci

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Reprocessed precise science orbits and gravity field recovery for the entire GOCE mission

Arnold

Grombein

Schreiter

et al. 2023

J Geod

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ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) orbited the Earth between 2009 and 2013 for the determination of the static part of Earth’s gravity field. The GPS-derived precise science orbits (PSOs) were operationally generated by the Astronomical Institute of the University of Bern (AIUB). Due to a significantly improved understanding of remaining artifacts after the end of the GOCE mission (especially in the GOCE gradiometry data), ESA initiated a reprocessing of the entire GOCE Level 1b data in 2018. In this framework, AIUB was commissioned to recompute the GOCE reduced-dynamic and kinematic PSOs. In this paper, we report on the employed precise orbit determination methods, with a focus on measures undertaken to mitigate ionosphere-induced artifacts in the kinematic orbits and thereof derived gravity field models. With respect to the PSOs computed during the operational phase of GOCE, the reprocessed PSOs show in average a 8–9% better consistency with GPS data, 31% smaller 3-dimensional reduced-dynamic orbit overlaps, an 8% better 3-dimensional consistency between reduced-dynamic and kinematic orbits, and a 3–7% reduction of satellite laser ranging residuals. In the second part of the paper, we present results from GPS-based gravity field determinations that highlight the strong benefit of the GOCE reprocessed kinematic PSOs. Due to the applied data weighting strategy, a substantially improved quality of gravity field coefficients between degree 10 and 40 is achieved, corresponding to a remarkable reduction of ionosphere-induced artifacts along the geomagnetic equator. For a static gravity field solution covering the entire mission period, geoid height differences with respect to a superior inter-satellite ranging solution are markedly reduced (43% in terms of global RMS, compared to previous GOCE GPS-based gravity fields). Furthermore, we demonstrate that the reprocessed GOCE PSOs allow to recover long-wavelength time-variable gravity field signals (up to degree 10), comparable to information derived from GPS data of dedicated satellite missions. To this end, it is essential to take into account the GOCE common-mode accelerometer data in the gravity field recovery.

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Exploring Thermospheric Disturbance Patterns Through Space‐Borne Accelerometer Measurement Errors: A Weighted Accelerometer 1B Dataset of GRACE C

Tzamali,

Pagiatakis

2024

Geophysical Research Letters

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Satellite measurements are essential for understanding Earth's complex system, yet they often lack a reliable a‐priori covariance matrix. This study presents a new methodology to enhance the reliability of satellite measurements by deriving experimental covariance matrices from the original observation. We focus on the accelerometer measurements (1A dataset) from the GRACE (Gravity Recovery and Climate Experiment) C satellite. Using autocorrelation analysis, we create a block‐diagonal covariance matrix for the 1A dataset. We then apply a low‐pass Gaussian filter that integrates this covariance matrix into the least squares estimation, resulting in a refined 1B dataset that minimizes spikes and spurious accelerations while preserving measurement error. Our variance analysis uncovers disturbances linked to geomagnetic storms and the satellite's transitions through Earth's shadow and terminator, with fluctuations notably peaking during the equinoxes.

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Determination and Combination of Monthly Gravity Field Time Series from Kinematic Orbits of GRACE, GRACE-FO and Swarm

Cited by 3 publications

References 38 publications

Impact of the combination and replacement of SLR-based low-degree gravity field coefficients in GRACE solutions

Impact of the combination and replacement of SLR-based low-degree gravity field coefficients in GRACE solutions

Reprocessed precise science orbits and gravity field recovery for the entire GOCE mission

Exploring Thermospheric Disturbance Patterns Through Space‐Borne Accelerometer Measurement Errors: A Weighted Accelerometer 1B Dataset of GRACE C

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