A Posteriori De-aliasing of Ocean Tide Error in Future Double-Pair Satellite Gravity Missions

Liu, W.; Sneeuw, Nico; Pour, Siavash Iran; Tourian, Mohammad J.; Reubelt, T.

doi:10.1007/1345_2016_259

Cited by 3 publications

(4 citation statements)

References 9 publications

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“…Visser (2010) investigated a number of (post-)processing methods, including the temporal filtering of timeseries of gravity field solutions, the spatial smoothing of these timeseries and evaluation of solutions for different geographical regions for GRACE-type single-pair and Bender-type (Bender et al 2008) double pair missions. An a posteriori method for de-aliasing of OT errors in future double-pair missions was proposed by Liu et al (2016), also giving hints about optimal choices for orbit constellations to mitigate OT aliasing effects. Liu & Sneeuw (2021) describe OT aliasing as a two-step mechanism, with orbit sampling as the first step and gravity recovery as the second step.…”

mentioning

confidence: 99%

Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing

Abrykosov

Sulzbach

Pail

et al. 2021

Geophysical Journal International

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Summary Ocean tide (OT) background models (BM) used for a priori de-aliasing of GRACE/GRACE-FO observations feature distinct spatial uncertainties (primarily in coastal proximity and in latitudes above ± 60°), and therefore pose one of the largest contributors to the overall retrieval error. The retrieval performance can be expected to increase if this underlying spatial error distribution is stochastically modelled and incorporated into the data processing chain. In this contribution, we derive realistic error variance-covariance matrices (VCM) based on a set of five state-of-the-art OT models. The additional value of using such VCMs is assessed through numerical closed-loop simulations, where they are rigorously propagated from model to observation level. Further, different approximations of the resulting VCM of observations are assumed, i.e., full, block-diagonal, and diagonal, in order to evaluate the trade-off between computational efficiency and accuracy. It is asserted that correctly weighting the OT BM error can improve the gravity retrieval performance by up to three orders of magnitude, provided no further error contributors are considered. In comparison, the overall gain in retrieval performance is reduced to 75% once instrument noise is taken into account. Here, it is shown that simultaneously modelling the OT BM and the instrument errors is critical, as each effect induces different types of correlations between observations, and exclusively considering covariance information based on the sensor noise may degrade the solution. We further demonstrate that the additional benefit of incorporating OT error VCMs is primarily limited by the de-aliasing performance for non-tidal mass variations of atmosphere (A) and oceans (O). This emphasises the necessity of best-possible AO-de-aliasing (e.g. through optimized processing techniques and/or improved BMs) in order to optimally exploit the OT BM weighting.

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confidence: 99%

Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing

Abrykosov

Sulzbach

Pail

et al. 2021

Geophysical Journal International

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“…The secondary alias periods of eight constituents, calculated with primary alias periods as signal period and recovery period as sampling period are listed in Table 2. The secondary alias period can be demonstrated by spectral analysis of the time series of recovered fields (Liu et al 2016). The recovery period in our simulations is 11 solar days, within which the groundtrack distribution is sufficiently homogeneous to allow a gravity recovery (up to degree and order 60).…”

Section: Simulation and Analysismentioning

confidence: 89%

“…We use it here for the purpose of a more precise estimation of the main frequency. Liu et al (2016) validated the mean PSD by checking whether different areas have different alias periods. It was demonstrated that the PSD patterns are spatially similar, i.e., they do have the same main frequency, albeit with slightly variable energy.…”

Section: Simulation and Analysismentioning

confidence: 99%

Aliasing of ocean tides in satellite gravimetry: a two-step mechanism

Liu

Sneeuw

2021

J Geod

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Ocean tide aliasing is one of the largest error sources in satellite gravimetry. Despite its importance, the aliasing mechanism of ocean tides in satellite gravimetry is only partially understood. This paper explains tidal aliasing as a two-step mechanism. The primary aliasing is caused by orbit undersampling of original tidal signals. The secondary aliasing is due to undersampling of the primary aliasing signals through gravity recovery in discrete time intervals. The two-step aliasing mechanism is demonstrated through a closed-loop numerical simulation. The aliasing of the tidal constituents M

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confidence: 99%

Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing

Abrykosov

Sulzbach

Pail

et al. 2022

Preprint

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Due to its high-frequency, high-amplitude nature the ocean tide (OT) signal poses a core limitation within the GRACE/GARCE-FO data processing, as its temporal undersampling ultimately results in the typical striping pattern. To some degree this issue can be resolved by employing a-priori de-aliasing based on an OT background model. However, due to model errors and imperfections some residual effects inevitably remain within the resulting gravity product. So far, the background models have been assumed as error-free within the data processing. Since ocean tide models feature distinct, time-invariant spatial error patterns (low uncertainties in open oceans, high uncertainties in coastal and high-latitude regions), it is reasonable to assume that weighting the observations based on the underlying spatial error shall result in a more homogenous gravity solution. Thus, error co-variance matrices are derived for the spherical harmonic coefficients representing the eight principal tides based on a set of five modern-day OT models and propagated onto the level of observations. This error information is then employed within the least-squares parameter estimation for the final gravity product. The functionality of this approach is verified through closed-loop simulations and its limitations are discussed. Results are presented for single-pair-based gravity retrieval scenarios.

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A Posteriori De-aliasing of Ocean Tide Error in Future Double-Pair Satellite Gravity Missions

Cited by 3 publications

References 9 publications

Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing

Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing

Aliasing of ocean tides in satellite gravimetry: a two-step mechanism

Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing

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