Determining the dynamic draught for precise hydrographic surveying

Abstract

In hydrographic surveying, high precision is needed for engineering applications such as the construction of tube tunnels placed to seabed and the navigational safety of ships for the under keel clearance (UKC) in shallow canals or waterways. Minimum measurement standards for hydrographic surveying are created by the International Hydrographic Organization (IHO) for safety of navigation. As well as IHO, the Swedish Maritime Administration (SMA), Land Information New Zealand (LINZ), and the United States Army Corps of Engineers (USACE) standards are used in surveys. At 40-m depth, the depth error budget must be less than 40cm, according to IHO standards. Allowable maximum error is only 22cm in SMA hydrographic survey standards. These standards can be achieved by minimizing the error sources. One of the errors in hydrographic surveying is the determination of the transducer draught. Usually a static draught is used in hydrographic surveying. In this paper, the dynamic draught of a survey vessel is determined using the RTK GNSS method for different speeds. Differences between the static and dynamic draught values are analyzed for precise hydrographic surveying. It is determined that the dynamic draught of the vessel should be used for achieving the international standards in precise surveying projects.