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Aliasing of ocean tides in satellite gravimetry: a two-step mechanism
https://orcid.org/0000-0002-6165-4425
https://orcid.org/0000-0003-1796-0131
Abstract 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 $$M_2$$, $$N_2$$, $$S_2$$, $$K_2$$, $$O_1$$, $$P_1$$, $$Q_1$$ and $$K_1$$ in CHAMP, GOCE, GRACE and GRACE Follow-On missions is analysed. The primary alias periods of individual constituents change from a few to hundreds of days depending on the orbital geometry. The long-term $$S_2$$ aliasing may cause bias in gravity fields derived by GOCE data if the $$S_2$$ tide is not well-represented by the ocean tide model applied in the data processing. Comparing the primary aliasing properties of CHAMP with that of GRACE indicates that tuning orbit inclination can improve aliasing properties, i.e. shorter aliasing periods and less couplings with annual/semi-annual signals. The strict definition of secondary alias periods is compromised in case of GRACE and GRACE Follow-On due to non-constant recovery periods, which results in irregular sampling and blurs the sharp spectral lines that are described by the two-step mechanism. The two-step aliasing mechanism can also be used in understanding aliasing of other periodic signals observed by satellite gravimetry.
Aliasing of ocean tides in satellite gravimetry: a two-step mechanism
https://orcid.org/0000-0002-6165-4425
https://orcid.org/0000-0003-1796-0131
Abstract 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 $$M_2$$, $$N_2$$, $$S_2$$, $$K_2$$, $$O_1$$, $$P_1$$, $$Q_1$$ and $$K_1$$ in CHAMP, GOCE, GRACE and GRACE Follow-On missions is analysed. The primary alias periods of individual constituents change from a few to hundreds of days depending on the orbital geometry. The long-term $$S_2$$ aliasing may cause bias in gravity fields derived by GOCE data if the $$S_2$$ tide is not well-represented by the ocean tide model applied in the data processing. Comparing the primary aliasing properties of CHAMP with that of GRACE indicates that tuning orbit inclination can improve aliasing properties, i.e. shorter aliasing periods and less couplings with annual/semi-annual signals. The strict definition of secondary alias periods is compromised in case of GRACE and GRACE Follow-On due to non-constant recovery periods, which results in irregular sampling and blurs the sharp spectral lines that are described by the two-step mechanism. The two-step aliasing mechanism can also be used in understanding aliasing of other periodic signals observed by satellite gravimetry.
Aliasing of ocean tides in satellite gravimetry: a two-step mechanism
https://orcid.org/0000-0002-6165-4425
https://orcid.org/0000-0003-1796-0131
Abstract 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 $$M_2$$, $$N_2$$, $$S_2$$, $$K_2$$, $$O_1$$, $$P_1$$, $$Q_1$$ and $$K_1$$ in CHAMP, GOCE, GRACE and GRACE Follow-On missions is analysed. The primary alias periods of individual constituents change from a few to hundreds of days depending on the orbital geometry. The long-term $$S_2$$ aliasing may cause bias in gravity fields derived by GOCE data if the $$S_2$$ tide is not well-represented by the ocean tide model applied in the data processing. Comparing the primary aliasing properties of CHAMP with that of GRACE indicates that tuning orbit inclination can improve aliasing properties, i.e. shorter aliasing periods and less couplings with annual/semi-annual signals. The strict definition of secondary alias periods is compromised in case of GRACE and GRACE Follow-On due to non-constant recovery periods, which results in irregular sampling and blurs the sharp spectral lines that are described by the two-step mechanism. The two-step aliasing mechanism can also be used in understanding aliasing of other periodic signals observed by satellite gravimetry.
Aliasing of ocean tides in satellite gravimetry: a two-step mechanism
Liu, Wei (author) / Sneeuw, Nico (author)
Journal of Geodesy ; 95
2021
Article (Journal)
Electronic Resource
English
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