Tides in Complex Coastal Regions: Early Case Studies From Wide-Swath SWOT Measurements

Studying ocean tides with satellite altimetry has traditionally been difficult in coastal regions. The 1 day repeat of the Cal/Val phase of SWOT provides a unique dataset that can be exploited for tidal analysis. In this work, KaRIn data from the SWOT Cal/Val phase are analyzed in two coastal regions to present a first look at the possibilities for tidal analysis from SWOT. The areas are: (a) Bristol Channel and (b) Great South Bay. When benchmarked against in situ measurements in these regions, substantial improvements over tide models, which typically report errors exceeding tens of centimeters and degrees, are seen. Specifically, the SWOT ocean-tide estimates exhibit amplitude discrepancies ranging from 1.75 to 3 cm and phase lag discrepancies between 1.75 degrees and 2.75 degrees when compared with in situ tide gauge data. These findings underscore the value of SWOT for tidal research in complex coastal regions. Estimating ocean tides in the coastal region has challenged tide modelers for decades. The recently launched SWOT satellite provides the opportunity to derive estimations of ocean tides at unprecedented spatial scales thanks to the innovative wide-swath measurement principle, particularly in complex coastal regions. The mission's Calibration and Validation (Cal/Val) phase is particularly interesting for tidal research, as the tide-favorable orbit allows for the derivation of the major tidal constituents with a relatively short time series of SWOT data. This manuscript evaluates the largest tidal constituent, the principal lunar M2 ${\mathrm{M}}_{2}$ tide, derived from SWOT's Cal/Val phase within two complex coastal regions. Results within the Bristol Channel and the Great South Bay demonstrate unprecedented spatial variability in the amplitude and phase lag of the M2 ${\mathrm{M}}_{2}$ tide. Additionally, with respect to in situ measurements, SWOT-derived estimates resulted in reduced errors compared with global tide models in these complex coastal regions. The initial insights demonstrated several strengths and opportunities for using SWOT to improve tide models and new avenues of research with satellite measurements of ocean tides, particularly within fjords and estuaries. SWOT KaRIn data from the Cal/Val phase is used to derive M2 ${\mathrm{M}}_{2}$ tide in two complex coastal regions Results demonstrate the spatial variability of amplitude and phase lag of coastal tides SWOT KaRIn measurements are useful for studying tidal flats and ocean tides in river mouths and estuaries