Development of an empirical chart datum model for a region of the Southwest Atlantic Ocean

María Florencia De Azkue,Enrique Eduardo D’Onofrio,Luciano Banegas

doi:10.1590/2675-2824069.21-028mfda

María Florencia De Azkue, Enrique Eduardo D’Onofrio + Show 1 more

https://doi.org/10.1590/2675-2824069.21-028mfda

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Abstract

Abstract The datum for sounding reduction is a permanently fixed surface, to which the depths displayed on the nautical charts and the tide tables heights refer. The International Hydrographic Organization recommends adopting the lowest astronomical tide as a chart datum, although its calculation can be complex because it varies both spatially and temporally. The ever increasing accuracy of 3D positioning with Global Navigation Satellite Systems requires that the chart datum is referenced to the ellipsoid WGS84. The aims of this paper are to calculate the lowest astronomical tide and to develop an empirical model to determine the distance between the lowest astronomical tide and the WGS84 ellipsoid, for a region of the Southwest Atlantic Ocean between latitudes 36°S and 54°S and longitude 54°W, on a 5km x 5km grid. Harmonic constants from the Centre for Topographic studies of the Oceans and Hydrosphere are used to calculate the lowest astronomical tide. To refer it to the WGS84 ellipsoid, results from mean sea level models and along-track sea level heights provided by Archiving, Validation and Interpretation of Satellite Oceanographic data are utilized. The final product has been designed for open waters and will be useful both for the development of relevant marine activities in the area, as well as to increase the efficiency of hydrographic surveys while contributing to more precise navigation in critical areas.

Highlights

The chart datum (CD) is a permanently fixed surface, to which the depths displayed on the nautical charts and the tide tables heights refer
It was created by Collecte Localization Satellites (CLS) and distributed by Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO), with the support of Centre National d’Etudes Spatiales (CNES)
The lowest standard deviation value corresponds to the MSS CLS15 model, which is why this model was chosen to refer the CD data to the WGS84 ellipsoid

Summary

Introduction

The chart datum (CD) is a permanently fixed surface, to which the depths displayed on the nautical charts and the tide tables heights refer. The 3/1919 resolution of the International Hydrographic Organization (IHO) suggests that the lowest astronomical tides height (LAT) must be used as CD in areas with tidal ranges greater than 0.30m (IHO, 2010). The LAT is defined as the lowest astronomical tide. Submitted: 06-April-2021 Approved: 21-Jun-2021 Associate Editor: Alberto Piola level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions. Thereby a water level below LAT can only occur due to meteorological effects. A minimum period of 19 years, coincident with the Metonic cycle, is chosen because tide predictions are very similar at 19-year intervals (Pugh et al, 2014). Some works have shown that in some regions the lowest astronomical tide occurs in periods exceeding 19 years. Some works have shown that in some regions the lowest astronomical tide occurs in periods exceeding 19 years. Hansen et al (2015) detected in the Eastern

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