60 research outputs found
Mapping of raw materials and habitats in the Danish sector of the North Sea
In the summer of 2010, the Geological Survey of Denmark and Greenland (GEUS) mapped the potential raw materials and substrate types, over large parts of the Danish economic sector of the North Sea, in cooperation with Orbicon A/S. The mapping was carried out for the Danish Nature Agency; it is part of the general mapping of raw material resources within the territories of the Danish state and forms part of the input for the implementation of the European Union’s Marine Strategy Framework Directive. The purpose was (1) to provide an overview of the distribution, volume and composition of available raw materials and (2) to identify, describe and map the distribution of the dominant marine bottom types
Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment
The transition zone between land and water is difficult to map with
conventional geophysical systems due to shallow water depth and often
challenging environmental conditions. The emerging technology of airborne
topobathymetric light detection and ranging (lidar) is capable of providing
both topographic and bathymetric elevation information, using only a single
green laser, resulting in a seamless coverage of the land–water transition
zone. However, there is no transparent and reproducible method for processing
green topobathymetric lidar data into a digital elevation model (DEM). The
general processing steps involve data filtering, water surface detection and
refraction correction. Specifically, the procedure of water surface detection
and modelling, solely using green laser lidar data, has not previously been
described in detail for tidal environments. The aim of this study was to fill
this gap of knowledge by developing a step-by-step procedure for making a
digital water surface model (DWSM) using the green laser lidar data. The
detailed description of the processing procedure augments its reliability,
makes it user-friendly and repeatable. A DEM was obtained from the processed
topobathymetric lidar data collected in spring 2014 from the Knudedyb tidal
inlet system in the Danish Wadden Sea. The vertical accuracy of the lidar
data is determined to ±8 cm at a 95 % confidence level, and the
horizontal accuracy is determined as the mean error to ±10 cm. The
lidar technique is found capable of detecting features with a size of less
than 1 m<sup>2</sup>. The derived high-resolution DEM was applied for detection and classification of geomorphometric and morphological features within the
natural environment of the study area. Initially, the bathymetric position
index (BPI) and the slope of the DEM were used to make a continuous
classification of the geomorphometry. Subsequently, stage (or elevation in
relation to tidal range) and a combination of statistical neighbourhood
analyses (moving average and standard deviation) with varying window sizes,
combined with the DEM slope, were used to classify the study area into six
specific types of morphological features (i.e. subtidal channel, intertidal
flat, intertidal creek, linear bar, swash bar and beach dune). The developed
classification method is adapted and applied to a specific case, but it can
also be implemented in other cases and environments
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