Improving the Coastal Mean Dynamic Topography by Geodetic Combination of Tide Gauge and Satellite Altimetry

Andersen, Ole; Nielsen, Karina; Knudsen, Per; Hughes, Chris W.; Bingham, Rory; Fenoglio-Marc, Luciana; Gravelle, Médéric; Kern, Michael; Polo, S. Padilla

doi:10.1080/01490419.2018.1530320

Cited by 32 publications

(21 citation statements)

References 38 publications

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“…On other coastlines, however, different dynamics apply. Tide gauge data, satellite altimetry, and ocean model simulations agree on the general features of the global coastal mean dynamic topography (Woodworth et al 2012;Andersen et al 2018), which shows smooth variations on eastern boundaries (except at the Strait of Gibraltar where the Mediterranean inflow allows for a step, Hughes et al 2015), but larger and sharper steps in places along western boundaries, with different models in particular showing significant differences in the latter case. The sharp steps appear to be associated with western boundary currents, the Gulf Stream in particular being a clear example (Higginson et al 2015), but the steps are smaller than those across the western boundary currents and occur equatorward of the main open-ocean step as if displaced in the direction of CTW propagation.…”

Section: The Low Frequency Limitsupporting

confidence: 52%

Sea Level and the Role of Coastal Trapped Waves in Mediating the Influence of the Open Ocean on the Coast

et al. 2019

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The fact that ocean currents must flow parallel to the coast leads to the dynamics of coastal sea level being quite different from the dynamics in the open ocean. The coastal influence of open-ocean dynamics (dynamics associated with forcing which occurs in deep water, beyond the continental slope) therefore involves a handover between the predominantly geostrophic dynamics of the interior ocean and the ageostrophic dynamics which must occur at the coast. An understanding of how this handover occurs can be obtained by considering the combined role of coastal trapped waves and bottom friction. We here review understanding of coastal trapped waves, which propagate cyclonically around ocean basins along the continental shelf and slope, at speeds which are fast compared to those of baroclinic planetary waves and currents in the open ocean (excluding the large-scale barotropic mode). We show that this results in coastal sea-level signals on western boundaries which, compared to the nearby open-ocean signals, are spatially smoothed, reduced in amplitude, and displaced along the coast in the direction of propagation of coastal trapped waves. The open-ocean influence on eastern boundaries is limited to signals propagating polewards from the equatorial waveguide (although a large-scale diffusive influence may also play a role). This body of work is based on linearised equations, but we also discuss the nonlinear case. We suggest that a proper consideration of nonlinear terms may be very important on western boundaries, as the competition between advection by western boundary currents and a counter-propagating influence of coastal trapped waves has the potential to lead to sharp gradients in coastal sea level where the two effects come into balance.

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Section: The Low Frequency Limitsupporting

confidence: 52%

Sea Level and the Role of Coastal Trapped Waves in Mediating the Influence of the Open Ocean on the Coast

et al. 2019

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“…Abulaitijiang et al 2015;Passaro et al 2016;Bonnefond et al 2018). As a result, the coastal geodetic MDTs derived from these data approximately agree at several centimetres level with the ocean models and tide gauge-derived MDT data (Ophaug et al 2015;Idžanović et al 2017;Andersen et al 2018). This shows that recent altimetry data may serve as an additional source for coastal gravity field and MDT modelling and validation.…”

Section: Introductionsupporting

confidence: 65%

Coastal gravity field refinement by combining airborne and ground-based data

Abulaitijiang

Featherstone

et al. 2019

J Geod

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Gravity field modelling in coastal region faces challenges due to the degradation of the quality of altimeter data and poor coverage of gravimetric measurements. Airborne gravimetry can provide seamless measurements both onshore and offshore with uniform accuracies, which may alleviate the coastal zone problem. We study the role of airborne data for gravity field recovery in a coastal region, and the possibility to validate coastal gravity field model against recent altimetry data (CryoSat-2, Jason-1, and SARAL/Altika). Moreover, we combine airborne and ground-based gravity data for regional refinement, and quantify and validate the contribution introduced by airborne data. Numerical experiments in the Gippsland Basin over the southeastern coast of Australia show that the effects introduced by airborne gravity data appear as small-scale patterns on the centimetre scale in terms of quasi-geoid heights. Numerical results demonstrate that the combination of airborne data improves the coastal gravity field, and the recent altimetry data can be potentially used to validate the high-frequency signals introduced by airborne data. The validation against recent altimetry data demonstrates that the combination of airborne measurements improves the coastal quasigeoid, by ~5 mm, compared with a model computed from terrestrial and altimetry-derived gravity anomalies alone. These results show that the recently released altimetry data with relatively denser spatial resolutions and higher accuracies than older altimeter data may be beneficial for gravity field model assessment in coastal areas.

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“…Santamaría-Gómez et al (2011) showed that this combination (of a power-law and white noise model) represents the best approximation of the noise content for 275 GNSS station position time series. This combination was also implemented in studies concerned with VLM SAT-TG estimation (WM16; Kleinherenbrink et al, 2018;Ballu et al, 2019). In particular, the spectral index κ can contribute to detecting the intrusion of low-frequency signals in the differenced time series.…”

Section: Statistical Analysis: Trend and Uncertainty Estimationmentioning

confidence: 99%

The zone of influence: matching sea level variability from coastal altimetry and tide gauges for vertical land motion estimation

Oelsmann¹,

Passaro²,

Dettmering³

et al. 2021

Ocean Sci.

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Abstract. Vertical land motion (VLM) at the coast is a substantial contributor to relative sea level change. In this work, we present a refined method for its determination, which is based on the combination of absolute satellite altimetry (SAT) sea level measurements and relative sea level changes recorded by tide gauges (TGs). These measurements complement VLM estimates from the GNSS (Global Navigation Satellite System) by increasing their spatial coverage. Trend estimates from the SAT and TG combination are particularly sensitive to the quality and resolution of applied altimetry data as well as to the coupling procedure of altimetry and TGs. Hence, a multi-mission, dedicated coastal along-track altimetry dataset is coupled with high-frequency TG measurements at 58 stations. To improve the coupling procedure, a so-called “zone of influence” (ZOI) is defined, which confines coherent zones of sea level variability on the basis of relative levels of comparability between TG and altimetry observations. Selecting 20 % of the most representative absolute sea level observations in a 300 km radius around the TGs results in the best VLM estimates in terms of accuracy and uncertainty. At this threshold, VLMSAT-TG estimates have median formal uncertainties of 0.58 mm yr−1. Validation against GNSS VLM estimates yields a root mean square (rmsΔVLM) of VLMSAT-TG and VLMGNSS differences of 1.28 mm yr−1, demonstrating the level of accuracy of our approach. Compared to a reference 250 km radius selection, the 300 km zone of influence improves trend accuracies by 15 % and uncertainties by 35 %. With increasing record lengths, the spatial scales of the coherency in coastal sea level trends increase. Therefore, the relevance of the ZOI for improving VLMSAT-TG accuracy decreases. Further individual zone of influence adaptations offer the prospect of bringing the accuracy of the estimates below 1 mm yr−1.

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Improving the Coastal Mean Dynamic Topography by Geodetic Combination of Tide Gauge and Satellite Altimetry

Cited by 32 publications

References 38 publications

Sea Level and the Role of Coastal Trapped Waves in Mediating the Influence of the Open Ocean on the Coast

Sea Level and the Role of Coastal Trapped Waves in Mediating the Influence of the Open Ocean on the Coast

Coastal gravity field refinement by combining airborne and ground-based data

The zone of influence: matching sea level variability from coastal altimetry and tide gauges for vertical land motion estimation

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