Regional Evaluation of Minor Tidal Constituents for Improved Estimation of Ocean Tides

Michael G Hart-Davis,Florian Seitz,Denise Dettmering,Roman Sulzbach,Christian Schwatke,Maik Thomas

doi:10.3390/rs13163310

Michael G Hart-Davis, Florian Seitz + Show 4 more

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https://doi.org/10.3390/rs13163310

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Abstract

Satellite altimetry observations have provided a significant contribution to the understanding of global sea surface processes, particularly allowing for advances in the accuracy of ocean tide estimations. Currently, almost three decades of satellite altimetry are available which can be used to improve the understanding of ocean tides by allowing for the estimation of an increased number of minor tidal constituents. As ocean tide models continue to improve, especially in the coastal region, these minor tides become increasingly important. Generally, admittance theory is used by most global ocean tide models to infer several minor tides from the major tides when creating the tidal correction for satellite altimetry. In this paper, regional studies are conducted to compare the use of admittance theory to direct estimations of minor tides from the EOT20 model to identify which minor tides should be directly estimated and which should be inferred. The results of these two approaches are compared to two global tide models (TiME and FES2014) and in situ tide gauge observations. The analysis showed that of the eight tidal constituents studied, half should be inferred (2N2, ϵ2, MSF and T2), while the remaining four tides (J1, L2, μ2 and ν2) should be directly estimated to optimise the ocean tidal correction. Furthermore, for certain minor tides, the other two tide models produced better results than the EOT model, suggesting that improvements can be made to the tidal correction made by EOT when incorporating tides from the two other tide models. Following on from this, a new approach of merging tidal constituents from different tide models to produce the ocean tidal correction for satellite altimetry that benefits from the strengths of the respective models is presented. This analysis showed that the tidal correction created based on the recommendations of the tide gauge analysis provided the highest reduction of sea-level variance. Additionally, the combination of the EOT20 model with the minor tides of the TiME and FES2014 model did not significantly increase the sea-level variance. As several additional minor tidal constituents are available from the TiME model, this opens the door for further investigations into including these minor tides and optimising the tidal correction for improved studies of the sea surface from satellite altimetry and in other applications, such as gravity field modelling.

Highlights

Investigations of global sea level from satellite altimetry have been done for almost three decades following the launch of the ERS-1 and TOPEX/Poseidon altimeters in the early 1990s
Three regional studies were conducted to assess the accuracy and importance of minor tidal constituents. For each of these regions, the empirical ocean tide (EOT)-R, FES2014, and TiME tide models, as well as tides inferred from the EOT20 model (EOT-I), were compared to tide gauges obtained from the TICON dataset [26]
TICON is a global tide gauge dataset derived from the Global Extreme Sea Level Analysis (GESLA) project which provides tidal constants for individual tide gauges that have been estimated through least-squares-based harmonic analysis

Summary

Introduction

Investigations of global sea level from satellite altimetry have been done for almost three decades following the launch of the ERS-1 and TOPEX/Poseidon altimeters in the early 1990s. Several additional altimeter missions have followed, allowing for the continued assessment of sea level trends both in the open ocean and in the coastal 4.0/). Errors resulting from ocean tide signals continue to affect the studying of sea surface processes using along-track altimetry. In the years that have followed, several empirical ocean tide models have been developed based on the increased availability of altimeter observations, which has resulted in the increased accuracy of tidal estimations in the open ocean and coastal regions [5,7]. Recent advances in coastal altimetry, such as the ALES retracker for improved retrieval of coastal signals [8], has been influential in advancing the accuracy of tidal estimations in the coastal region [9,10]

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