Verificação da aplicabilidade de dados obtidos por sistema laser batimétrico aerotransportado à cartografia náutica

Abstract

A Hydrographic Survey (HS) has as main goal to obtain data for editing and updating nautical documents, these, focused on the safety of navigation. In order to establish a standard of uncertainty parameters for nautical charts, the International Hydrographic Organization (IHO) defines minimum levels of confidence for different orders. The suggestion of these specifications was acknowledged by the Brazilian Navy, institution responsible to produce Brazilian nautical charts, as described in NORMAM-25. One such parameter is the maximum allowed Total Vertical Uncertainty, a quality indicator of the depth measurement. Depth information influences the maximum operational draft for a vessel to safely travel in a region, causing impact on port operations and limiting the commercial transactions. Accurately estimated depths enhance the operational parameters of the ports. Due to the aim of representing a dynamic environment, whether as consequence of the action of nature itself or because of anthropic activities, updating a nautical chart must be a constant concern. As a complement to the traditional survey technique conducted with a boat-coupled echosounder, there is the option of performing a HS using LiDAR (Light Detection And Ranging) technology from aircraft, through LiDAR aerial bathymetry (ALB - Airborne LASER Bathymetry), which operate with LASER pulses in the green region of the electromagnetic spectrum. Considering these points, this work analyzed the differences between the information obtained by these two techniques, with an aim to evaluate the ALB’s potential of application to update nautical charts. Data were acquired in the Archipelago de Fernando de Noronha in 2011, while the reference dataset was obtained in the same year by a multibeam echosounder campaign, which is stored in a Brazilian Navy’s oceanographic database. The evaluations allowed to estimate the dynamic of the depth discrepancies between the two systems in different depths, relief and seafloor composition in the area of interest.