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Digital elevation models play a crucial role in the analysis of complex spatial challenges. Given the international dimension of many environmental applications, elevation data have been integrated in the European INSPIRE directive (Annex II, Elevation theme). As a result, many types of data are offered in various formats by mapping agencies and governmental organizations within the European Union. Notwithstanding the national effort to publish these data under open and public licenses, and in compliance with international data standards, the models are often projected in national coordinate reference systems, containing local orthometric heights. In order to use these models for cross-boundary applications, a transformation of locally projected coordinates and local elevations to international coordinates and ellipsoidal heights is required. Planimetric coordinate transformations are regularly performed using analytical conversion models, whereas altimetric transformations make use of geoidal models or simple vertical shifts. In this paper, digital elevation models from the Netherlands and the Flemish Region (Belgium) are transformed using the corresponding geoidal transformation grids and a simple vertical shift. Both data sets are independently acquired and processed within the framework of governmental mapping campaigns. The projected Dutch RD coordinates (EPSG:28992) and Belgian Lambert ’72 coordinates (EPGS:31370) are converted to ellipsoidal WGS84 coordinates (EPGS:4326) using open-source OGR tools. In order to obtain ellipsoidal heights from the elevation models, NLGEO08 and hBG18 are used for the conversion of Dutch and Belgian elevations respectively. Based on a quality assessment of both data sets in overlapping areas, it is stated that the mean difference and standard deviation of the elevations are within the accuracy levels of the used elevation models (0.07 ± 0.16 m). [ABSTRACT FROM AUTHOR]

In order to protect the Belgian coast, knowledge on natural sand dynamics is essential. Monitoring sand dynamics is commonly done through sediment budget analysis, which relies on determining the volumes of sediment added or removed from the coastal system. These volumetrics require precise and accurate 3D data of the terrain on different time stamps. Earlier research states the potential of permanent long-range terrestrial laser scanning for continuous monitoring of coastal dynamics. For this paper, this methodology has been implemented at an ultradissipative macrotidal North Sea beach in Mariakerke (Ostend, Belgium). A Riegl VZ-2000 LiDAR, mounted on a 42 m high building, scanned the intertidal and dry beach in a test zone of ca. 200 m wide on an hourly basis over a time period of one year. It appeared that the laser scanner cannot be assumed to have a fixed zenith for each hourly scan. The scanner compensator measured a variable deviation of the Z-axis of more than 3.00 mrad. This results in a deviation of ca. 900 mm near the low water line. A robust calibration procedure was developed to correct the deviations of the Z-axis. ‘Robust’ meaning (1) independent of a truth set of reference points (2) independent of the model and (3) independent of outlier elimination strategy. Several strategies for calibration of the vertical axis of the scanner have been tested and compared. A TIN model of the terrestrial scan – calibrated on an airborne LiDAR truth of the unchanging seawall and groin – combined with iterative statistical outlier elimination (mean ± 2.5 × standard deviation) resulted in the best outcome. [ABSTRACT FROM AUTHOR]