Nautical Charts with SEP Models: Historic Evolution and Perspectives for the Brazilian Hydrography

Abstract

Advances in high-precision GNSS techniques have allowed the reduction of vertical uncertainties in bathymetric surveys, with a better determination of the heave, the dynamic draft and the reduction of co-tidal errors. However, it is necessary to determine a separation model (SEP) between the Chart Datum and the reference ellipsoid. This article will present a historical evolution on the development of SEP models in the world across seven countries: the United States, Canada, Netherlands, Saudi Arabia, Colombia, England and Brazil. Research from foreign countries shows uncertainties in SEP models ranging from 6.6 cm to 22.6 cm in relation to the ITRF. In the case of Brazil, a pioneering study for the SEP of Guanabara Bay is described, where an average difference of 2.5 cm was found with a standard deviation of 5.1 cm between the surface generated with the traditional reduction method and by GPS-tide. For national coverage, the Alt-Bat project is presented, which provides the use of the geoid as a vertical reference for hydrodynamic models. As for the prospects, there is a virtuous cycle for port development: investment in environmental data, provides greater accuracy of SEP models and less uncertainty of surveys, providing greater draft, possibility of increased cargo flow in ports and more resources for investment. SEP models are fundamental for the gathering of information from different vertical references, providing safe navigation and management of coastal process.