Abstract
Guaranteeing safety of navigation within the Netherlands Continental Shelf (NCS), while efficiently using its ocean mapping resources, is a key task of Netherlands Hydrographic Service (NLHS) and Rijkswaterstaat (RWS). Resurvey frequencies depend on seafloor dynamics and the aim of this research is to model the seafloor dynamics to predict changes in seafloor depth that would require resurveying. Characterisation of the seafloor dynamics is based on available time series of bathymetry data obtained from the acoustic remote sensing method of both single-beam echosounding (SBES) and multibeam echosounding (MBES). This time series is used to define a library of mathematical models describing the seafloor dynamics in relation to spatial and temporal changes in depth. An adaptive, functional model selection procedure is developed using a nodal analysis (0D) approach, based on statistical hypothesis testing using a combination of the Overall Model Test (OMT) statistic and Generalised Likelihood Ratio Test (GLRT). This approach ensures that each model has an equal chance of being selected, when more than one hypothesis is plausible for areas that exhibit varying seafloor dynamics. This ensures a more flexible and rigorous decision on the choice of the nominal model assumption. The addition of piecewise linear models to the library offers another characterisation of the trends in the nodal time series. This has led to an optimised model selection procedure and parameterisation of each nodal time series, which is used for the spatial and temporal predictions of the changes in the depths and associated uncertainties. The model selection results show that the models can detect the changes in the seafloor depths with spatial consistency and similarity, particularly in the shoaling areas where tidal sandwaves are present. The predicted changes in depths and uncertainties are translated into a probability risk-alert map by evaluating the probabilities of an indicator variable exceeding a certain decision threshold. This research can further support the decision-making process when optimising resurvey frequencies.
Highlights
The bathymetric surveying necessary for accurate nautical charts and adequate maintenance dredging is a joint responsibility of the Netherlands Hydrographic Service (NLHS) and Rijkswaterstaat (RWS)
The main objectives of this research are (a) the definition of additional functional models which can be used to describe the complex behaviour of the changing seafloor depths especially where sandwave features are present (b) designing a more rigorous approach to select the nominal model to be used in the testing procedure and (c) designing the statistical hypothesis testing procedure to allow for reliable prediction and evaluation of probabilities for risk-alert levels
The majority of area NF has a time series length per grid node of 10 available epochs which spans 24 years from 1989 to 2013. The edges of this sub-area show a decrease in the length of the time series because of the size of the buffer areas used to subdivide the whole area into smaller sub-areas in a preprocessing step
Summary
The bathymetric surveying necessary for accurate nautical charts and adequate maintenance dredging is a joint responsibility of the Netherlands Hydrographic Service (NLHS) and Rijkswaterstaat (RWS). The fundamental knowledge of seabed dynamics in relation to the changes in depths is an important factor to consider for safety of navigation, maintenance of channels and for optimising the resurvey policy where the overall aim is to provide timely and accurate predictions of the changes in seafloor depths as a resurvey decision-making tool. This can ensure more cost-effective and efficient use of the mapping resources given the extensive use of the NCS and the nature of the oceanographic and seafloor properties which make it a complex marine environment
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
