Time-Invariant Sea-Floor Depths Using the Ellipsoid As Zero-Reference Surface

摘要

A GPS survey combined with acoustic soundings can determine highly accurate sea-floor depths. Using the ellipsoid as the zero-reference surface then allows navigators, while underway, to determine both keel and overhead obstruction clearance independent of the stage of the tide and the draft of the ship and freeboard. For safe sailing, two most important requirements are to be able to determine clearances between the sea floor and the keel of the ship, and between the mainmast and overhead structures, such as cables and bridges. For these clearances, the mariner has to know correctly and accurately the following: 1. Location of the sea floor or ocean depth, 2. Height of the overhead structure, 3. Locations of the ship's keel and mainmast.