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Articles

1980: Vol. LVII, No. 1

Theoretical Offshore Tide Range Derived from a Simple Defant Tidal Model Compared with Observed Offshore Tides

Submitted
August 6, 2015
Published
2015-07-10

Abstract

A simple Defant model, based on the M2 constituent, is presently used by the National Ocean Survey to estimate the offshore range of the tide, with observations at coastal tide stations of the actual tide supplying the necessary boundary condition for the model. The calculated values provide preliminary tide correctors for soundings obtained in offshore hydrographic surveys. Using offshore tide data from Deep Sea Tide Gage (DSTG) deployments and Offshore Telemetering Tide System (OTTS) buoys, the quantitative effects of the continental slope and shelf on the incoming semi-diurnal tide are discussed, and anomalies in the predicted tide curve due to Hurricane Belle are shown. Comparison of the observed tide range with the theoretical tide range reveals the need to modify the initial Defant model, which is accomplished by decomposing the range into its major harmonic constituents, resulting in an improved calculated offshore range.