TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an Earth observation radar mission that consists of a SAR interferometer built by two almost identical satellites flying in close formation. With a typical separation between the satellites of 120 m to 500 m a global Digital Elevation Model (DEM) has been generated. The TanDEM-X 30m EDEM is a product variant of the global Digital Elevation Model (DEM) acquired in the frame of the German TanDEM-X mission between 2010 and 2014, and has a reduced pixel spacing of 1 arcseconds (arsec), which corresponds to 30m at the equator. An automated edition was developed by the Microwaves and Radar Institute at the German Aerospace Center (DLR) to have a full and clean coverage of all Earth’s landmasses from pole to pole.

The Weser estuary at the German North Sea coast serves as a fairway to the harbours of Bremerhaven and Bremen. To ensure safe shipping and navigation, the navigation channel depths are nowadays intensively monitored, and have been so in the past. These are valuable data for consulting and research purposes, and enables investigations leading to a better understanding of hydrodynamics, salt intrusion and morphological processes in the estuary, in the present as well as the past. For recent years, thanks to modern monitoring techniques and digitalization, measuring data has been compiled to consistent digital terrain models of high quality and accuracy. For time periods before the 1990ies however, measurements were scarcer and the data are available only in form of printed bathymetrical and nautical charts. The objective of the project “Historical system states of the Weser estuary (HIWEST)” was to: • digitalize depths measurements starting from 1960, • georeference the data points and • process and compile them to digital terrain models that can be used for research and consulting. The project was led and financed by the Federal Waterways Engineering and Research Institute (BAW). It was supported by the Federal Maritime and Hydrographic Agency (BSH) and by the German Water and Shipping Administration (WSV) who provided printed charts and scanned data sets. The smile consulting GmbH was contracted to process the data and compile digital terrain models. One of the main challenges of the project was georeferencing. While georeferencing and projecting in the horizontal domain was comparatively straightforward, the transformation of depths below different chart datums to the Germans mean height reference system represented a challenge. This was accomplished by an algorithm considering spatial polygons provided by BSH and further meta information on the different levelling systems. The accuracy of the data sets differs depending on the quality of the original data. Since the 1990ies, powerful measurement methods such as airborne laser scanning (ALS) and multibeam echo-sounding has led to high resolutions and high data accuracy. In past surveys, the depths were measured in single-beam echo-soundings, often along individual cross sections, and there is no information between these soundings. As a result, the older terrain models are much smoother then the newer ones and contain less detailed information. More technical details can be found in the appendix of the technical report. The following digital terrain models (DTM, in the following the German abbreviation DGM is used) of the Lower and Outer Weser estuary were made available: • DGM 1966, marking the situation before deepening the Outer Weser to SKN-12 m</li> • DGM 1972, marking the situation before deepening the Lower Weser to SKN-9 m</li> • DGM 1981, marking the situation before extensive river works in the Lower Weser</li> • DGM 1996, marking the situation before deepening the Outer Weser to SKN-14 m</li> • DGM 2002, marking the situation after deepening the Outer Weser to SKN-14 m, reference digital terrain model. The years were chosen so they would represent consistent periods not affected by constructive engineering measures such as channel deepenings, and secondly based on optimal data availability. Each data set however consists not only of data from the respective year, but data had to be added from adjacent years. To close gaps, data from recent surveys were used. The data sets span the whole estuary from the North Sea to the tidal weir in the city of Bremen and are available as 1x1 m raster data sets. How to cite the HIWEST data: <strong style="color: red;"> The data set is only to be quoted together with the Technical Report.</strong> Report: Bundesanstalt für Wasserbau (2021): Historical digital terrain models of the Weser Estuary (HIWEST). Technical Report B3955.02.04.70168-6. Bundesanstalt für Wasserbau. https://henry.baw.de/handle/20.500.11970/107521 Data set: Bundesanstalt für Wasserbau (2020): Historical digital terrain model data of the Weser Estuary (HIWEST) [Data set]. Bundesanstalt für Wasserbau. https://doi.org/10.48437/02.2020.K2.5200.0001

TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an Earth observation radar mission that consists of a SAR interferometer built by two almost identical satellites flying in close formation. With a typical separation between the satellites of 120m to 500m a global Digital Elevation Model (DEM) has been generated. The main objective of the TanDEM-X mission is to create a precise 3D map of the Earth's land surfaces that is homogeneous in quality and unprecedented in accuracy. The data acquisition was completed in 2015 and production of the global DEM was completed in September 2016. The absolute height error is with about 1m an order of magnitude below the 10m requirement. The TanDEM-X 30m DEM is a product variant of the global Digital Elevation Model (DEM) acquired in the frame of the German TanDEM-X mission between 2010 and 2015, and has a reduced pixel spacing of 1 arcsecond (30m at the equator). It covers all Earth’s landmasses from pole to pole. For more information concerning the TanDEM-X mission, the reader is referred to: https://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10378/

The chart datum for the German Bight 2015 is a surface representation of chart datum. It is a resource for reductions of depths from hydrographic survey data and for the production of nautical charts. This model was replaced by chart datum for the German Bight 2021

INSPIRE theme Elevation (bathymetry). Provision of the topography of the seabed in the North and Baltic Sea.