Leendert L. Dorst

• PhD, MSc
• Deputy Hydrographer at Ministry of Defense, Netherlands

To fulfill its task of publishing accurate and up-to-date nautical charts, the Hydrographic Service of the Royal Netherlands Navy employs two survey vessels worldwide: HNLMS Snellius and Luymes. In 2013, these vessels have been fitted with new Trimble DGNSS receivers in combination with the Fugro Marinestar SBAS service. The advantages are clear: a...

The creation of vertical reference surfaces at sea, related to a reference ellipsoid, is a necessary step to enable the use of GPS (Global Positioning System) for referencing depth measurements at sea. Several projects exist for specific parts of the oceans, resulting in surfaces that partly overlap. As an example, we will present the French BATHYE...

We discuss two cases of international cooperation between hydrographic offices. The first case is the unified approach to populate the CATZOC indicator for bathymetric quality in nautical charts, in the presence of sand wave fields. The second case is the North Sea wide formulation of resurvey policies. The two cases can only be successful if it is...

Water level reduction with global navigation satellite systems in bathymetric surveying requires knowledge of the ellipsoidal heights of lowest astronomical tide (LAT). The traditional approach uses tidal water levels of an ocean tide model, which are subtracted from mean sea level (MSL). This approach has two major drawbacks: the modeled water lev...

Bathymetric resurveying in shallow seas is a costly process with limited resources, yet necessary for adequate nautical charts and therefore crucial for safe navigation. An important factor in an efficient resurvey policy is the type and size of sea floor dynamics. We propose four indicators, which we use in a procedure to recommend changes to the...

Over the past few years, the baseline of the Netherlands in the North Sea has undergone several large-scale changes. We present two of these changes: the construction of the Maasvlakte 2 extension to the Port of Rotterdam and the construction of the Zandmotor sand nourishment project. Both projects are man-made at a scale that influences natural pr...

Despite the best efforts of Hydrographic Offices (HOs) around the world, the ENCs that are on the market today do not always depict the real world as accurately as would be desired. This situation arises because gathering detailed hydrographic data is slow and consequently, ENCs (and paper charts) are compiled from multiple data sources, some moder...

Sedimentary coasts and shallow-sea beds may be dynamic. The large-scaled spatial variation in these dynamics and the smaller-scaled behaviour of individual marine bedforms are largely unknown. Sea-bed dynamics are relevant for the safety of shipping, and therefore for monitoring strategies, and for offshore engineering projects and archaeological i...

The optimization of the bathymetric resurvey policy of the Netherlands Hydrographic Service requires insight into sea floor dynamics in the Southern North Sea. To study the spatial variations in sea floor dynamics, the bathymetric archives of the Netherlands Hydrographic Service are analyzed using deformation analysis, a statistical and innovative...

In hydrography, we are used to working underwater where no positions are available from satellite navigation systems. In other professional fields, experience has shown that position updates from satellites may not always be available, or are potentially incorrect: examples are unintentional jamming of the extremely weak GNSS signals and signal ref...

The creation of reference surfaces has primarily been a national activity in the North Sea countries. A national approach prevents the creation of consistent common references, which are desperately needed for international data distribution in the coastal zone, GNSS-based bathymetric surveying, and the development of hydrodynamic models, on the sc...

Maritime delimitation usually starts with the calculation of an equidistance line, which is often corrected for special circumstances. The correction process aims to produce a line that is “equitable”, a concept open to various interpretations. While the equidistance line is calculated by a technical expert, an equitable line is the result of a neg...

The Hydrographic Service of the Royal Netherlands Navy (NLHO) is responsible for charting the Dutch sea areas in Europe and the Caribbean. Products of the NLHO include official Elec-tronic Navigational Charts (ENC's), Paper Charts and other Nautical Publications. To meet quality requirements for both military and civilian purposes, the Royal Nether...

Safe nautical charts require a carefully designed bathymetric survey policy, especially in shallow sandy seas that potentially have dynamic sea floor patterns. Bathymetric resurveying at sea is a costly process with limited resources, though. A pattern on the sea floor known as tidal sand waves is clearly present in bathymetric surveys, endangering...

The analysis of series of offshore bathymetric surveys provides insight into the morphodynamics of the sea floor. This knowledge helps to improve resurvey policies for the maintenance of port approaches and nautical charting, and to validate morphodynamic models. We propose a method for such an analysis that is based on statistical testing theory,...

The baseline of the Netherlands in the North Sea is changing in time. The effects of these changes are illustrated by two examples, one of the juridical situation in the Eems-Dollard boundary region with Germany and one of a case against fishermen in the Zeeland region near the Scheldt estuary. We conclude that it is necessary to provide maritime l...

The Dutch part of the North Sea is mapped by two authorities. Both authorities predict the behavior of the sea floor by analyzing time series of bathymetric data. The Hydrographic Service determines parameters for sand wave dynamics from an area, based on deformation analysis. The North Sea Directorate uses a multivariate state space modelling appr...

The publication of up-to-date nautical charts of shallow seas requires periodic resurveys. Information on the behaviour of the sea floor improves the planning of resurvey frequencies, which could be provided by an analysis of a series of archived sea floor surveys. We present a method to extract those dynamics using deformation analysis. It models...

In Membach, Belgian Ardennas, a superconducting gravimeter has been placed inside a hill. The Royal Observatory of Belgium (ROB) owns this instrument, that measures temporal variations in gravity. Scientists use the signal of such an instrument for geodynamical investigations, especially Earth tides. The ROB uses a standard procedure to pre-proces...