The Potential of SWOT Data for Mapping Estuarine and Coastal Tides

Pascal Matte1, Silvia Innocenti2, Aqeel Albahadily3, Stefan A Talke4, David A Jay3, Vincent Fortin5, Natacha Bernier5, Yves Secretan6 and Marc Simard7, (1)Environment and Climate Change Canada, Meteorological Research Division, Quebec, QC, Canada, (2)Institut National de la Recherche Scientifique, Eau-Terre-Environnement, Québec, QC, Canada, (3)Portland State University, Portland, OR, United States, (4)California Polytechnic State University, Department of Civil and Environmental Engineering, San Luis Obispo, California, United States, (5)Environment and Climate Change Canada, Meteorological Research Division, Dorval, QC, Canada, (6)Institut National de la Recherche Scientifique, Eau Terre Environnement, Quebec, QC, Canada, (7)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, United States
Abstract:
Existing satellite altimeters typically lack sensitivity to fine-scale processes and present data accuracy issues within <5km of the coast and in estuaries. The upcoming SWOT satellite mission, with its higher spatial resolution and expected lower land contamination errors, should help alleviate this problem and provide a steady flow of water level data in the estuarine and coastal zones. However, several methodological challenges remain for accurate tidal mapping in these environments directly from SWOT data. Traditional unconstrained methods generally fail to provide accurate tide reconstructions from temporally sparse satellite altimetry records, due to ill conditioning. Another issue is the nonlinear coupling effects of tides with river flow and friction in shallow water, requiring a larger tidal spectrum to be resolved, including overtides and compound tides. Here, we propose a new data-driven empirical approach, called Constrained Harmonic Analysis (ConHA), to reconstruct tides using a combination of SWOT and in-situ data from nearby tide gauges. The method is applied to the St. Lawrence and Columbia River estuaries, two contrasting systems in terms of their size, morphology and tidal-fluvial dynamics, with a stronger diurnal tidal signature in the Columbia than in the St. Lawrence. Sensitivity analyses to record length and data acquisition frequency as well as on SWOT data samples are performed. An error estimation of the reconstructed 2D tidal estimates is also provided based on model error propagation and simulated SWOT errors. Results show that the spatial coherence in tidal amplitudes and phases is maintained throughout the domain, and that a stable accuracy should be achieved after one year of the SWOT science mission. It is expected that data assimilation models will benefit directly from enhanced empirical tide reconstructions. Applications of ConHA with SWOT data can be foreseen in any coastal areas where tides are spatially coherent as well as in remote areas, with limited field data.
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