3:30 PM - 3:45 PM
[SGD01-06] Bathymetric accuracy verification and prototyping of vertical chart datum model for establishment of ellipsoidally referenced survey procedure
★Invited Papers
Keywords:Ellipsoidally referenced survey (ERS), Bathymetric accuracy verification, Vertical chart datum model, Hydrographic survey, Multibeam echosounder (MBES)
In hydrographic surveys to obtain bathymetric depth referenced to the vertical chart datum, the following survey operations are performed in principle: bathymetric surveying to measures the depth from the instantaneous sea surface at the time of bathymetry, and tidal observation to measure the height of the sea surface that changes from time to time due to tides and other factors. Especially in shallow waters, where high bathymetric accuracy is required, it is essential to continuously perform the tide observations during bathymetric surveying.
However, the tide observations associated with bathymetric surveying can prevent rapid and efficient operations of hydrographic surveys. For example, in the case of temporary tide observations, there are risk factors such as equipment malfunction of the pressure sensor, selection error of the installation site, etc. Even in permanent tide stations, there are risk factors such as some distortions of observation data due to clogging of wells, etc. If tide level data is missing for a period of time, in the worst case, there is even a possibility of redoing the bathymetric surveying. In addition, it is difficult to ensure the accuracy of bathymetric data by hydrographic surveys under conditions where tide observations cannot be performed promptly, such as emergency hydrographic surveys after a huge tsunami.
As a new method of hydrographic surveys to solve these problems, ellipsoidally referenced surveys (ERS) have recently been proposed, which, in principle, do not require tide observations during bathymetric surveying. Unlike traditional hydrographic surveys, which require tidal reduction, ERS is a method of converting the ellipsoid height of the seafloor, measured directly from the bathymetry without tidal reduction obtained by the echosounder and the ship's ellipsoid height by GNSS positioning, into the bathymetry referenced to vertical chart datum using an ellipsoid-based vertical chart datum model. Although tide observations are necessary to determine the vertical chart datum model, continuous tide observations during bathymetric surveying is no longer necessary, so the practical application of ERS is expected to speed up and improve the efficiency of hydrographic surveys.
In this study, the vertical chart datum modeling method and validity of ERS depths were verified in the Japan Sea (west of Yamaguchi Prefecture) and the Tokyo Bay in order to establish a bathymetric data processing procedure in ERS. As a result of the verification, the depths obtained by ERS were sufficiently appropriate for hydrographic survey, and then basic bathymetric data processing procedure in ERS has been established. This means that, technically, it is possible to derive bathymetric depths by ERS processing as provided that vertical chart datum model in a surveying area is available.
However, the tide observations associated with bathymetric surveying can prevent rapid and efficient operations of hydrographic surveys. For example, in the case of temporary tide observations, there are risk factors such as equipment malfunction of the pressure sensor, selection error of the installation site, etc. Even in permanent tide stations, there are risk factors such as some distortions of observation data due to clogging of wells, etc. If tide level data is missing for a period of time, in the worst case, there is even a possibility of redoing the bathymetric surveying. In addition, it is difficult to ensure the accuracy of bathymetric data by hydrographic surveys under conditions where tide observations cannot be performed promptly, such as emergency hydrographic surveys after a huge tsunami.
As a new method of hydrographic surveys to solve these problems, ellipsoidally referenced surveys (ERS) have recently been proposed, which, in principle, do not require tide observations during bathymetric surveying. Unlike traditional hydrographic surveys, which require tidal reduction, ERS is a method of converting the ellipsoid height of the seafloor, measured directly from the bathymetry without tidal reduction obtained by the echosounder and the ship's ellipsoid height by GNSS positioning, into the bathymetry referenced to vertical chart datum using an ellipsoid-based vertical chart datum model. Although tide observations are necessary to determine the vertical chart datum model, continuous tide observations during bathymetric surveying is no longer necessary, so the practical application of ERS is expected to speed up and improve the efficiency of hydrographic surveys.
In this study, the vertical chart datum modeling method and validity of ERS depths were verified in the Japan Sea (west of Yamaguchi Prefecture) and the Tokyo Bay in order to establish a bathymetric data processing procedure in ERS. As a result of the verification, the depths obtained by ERS were sufficiently appropriate for hydrographic survey, and then basic bathymetric data processing procedure in ERS has been established. This means that, technically, it is possible to derive bathymetric depths by ERS processing as provided that vertical chart datum model in a surveying area is available.