Fachbeiträge

Sämtliche Fachbeiträge aus den Hydrographischen Nachrichten seit der Ausgabe HN 100 sind online verfügbar.
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Satellite-derived bathymetry in practice
Current examples for cable route surveys and coastal monitoring

Multibeam bathymetry surveying is a well-established method but limited to water depths accessible by vessels or small boats. Airborne LiDAR bathymetry (ALB) systems can cover this gap by surveying both the coastal topography and the shallower water regions. ALB surveys are mostly suitable for larger pro-jects where accurate measurements are requested, as they require on-site mobilisation and a noticea-ble amount of costs. Satellite-derived bathymetry (SDB) can be seen as an option for an easy to imple-ment, cost-effective and globally available solution to provide full coverage with moderate density and accuracy which may be suitable for certain projects in coastal regions or as a precursor survey before commissioning a targeted survey. This paper describes methods providing information to fill data gaps for cable landing sites and for coastal zone monitoring. They are based on the new SDB online software eoLytics SDB by ¬EOMAP. Results obtained compare well against acoustic survey data. The procedure was found to be highly useful for the described purposes.

SDB – satellite-derived bathymetry | LiDAR | cable route survey | coastal zone monitoring | eoLytics SDB

Ausgabe: HN 116, Seite 40–47
DOI: 10.23784/HN116-06
Autor/en: Marina Niederjasper

Drohnengestützte Erfassung von maritimen Infrastrukturen

Das Institut für den Schutz maritimer Infrastrukturen des Deutschen Zentrums für Luft- und Raumfahrt e. V. in Bremerhaven befasst sich mit der Entwicklung von automatisierten Technologien und echtzeit-nahen Verarbeitungsmethoden zur Erstellung neuartiger Lagebilder für den maritimen Bereich. Über- und Unter-Wasser-Drohnen (UAV, AUV, ROV) werden mit neuartigen optischen Kamera- und Sonar-systemen eingesetzt, um dreidimensionale Lagebilddaten aufzunehmen. Spektrale Informationen und dreidimensionale Punktwolken werden zu Lagedarstellungen kombiniert, die die Lösung von Sicher-heitsfragestellungen vereinfachen und beschleunigen (Suche von Lecks, Schäden an Anlagen, Erfas-sung von Fahrzeugen und Personen auf dem Hafengelände). Die Technologie leistet einen wichtigen Beitrag zum Überblick über die maritimen Infrastrukturen. Durch die gute Verfügbarkeit und die Leis-tungsfähigkeit der Systeme sowie Möglichkeiten zum automatisierten Betrieb lässt sich der zeitliche Aufwand der Modellierung auf ein Minimum reduzieren.

Drohnen | 3D-Modellierung | Photogrammetrie | Visualisierung | Punktwolke | AUV | Multikopter

Ausgabe: HN 116, Seite 36–39
DOI: 10.23784/HN116-05
Autor/en: David Heuskin, Frank Lehmann

Bathymetry from multispectral aerial images via convolutional neural networks

Recently, optical approaches were applied more often to derive the depth of waterbodies. In shallow areas, the depth can be deduced mainly by modelling the signal attenuation in different bands. In this approach, it is examined how well a convolutional neural network (CNN) is able to estimate water depths from multispectral aerial images. To train on the actually observed slanted water distances, the net is trained with the original images rather than the orthophoto. The trained CNN is showing a stand-ard deviation of 3 to 4 decimetres. It is able to recognise trends for varying depths and ground covers. Problems mainly occurred when facing sunglint or shaded areas.

CNN – convolutional neural network | multispectral aerial images | orthophoto | LiDAR

Ausgabe: HN 116, Seite 32–35
DOI: 10.23784/HN116-04
Autor/en: Hannes Nübel

Fusing ROV-based photogrammetric underwater imagery with multibeam soundings for reconstructing wrecks in turbid waters

Observation and monitoring of wrecks are an integral part of the duties of hydrographic offices such as BSH. A common practice consists of first surveying wrecks using vessel-based multibeam echo sound-ing systems and subsequently having divers visually inspect them. In order to provide an objective pro-cedure and set a baseline for monitoring wrecks, unmanned underwater vehicles equipped with imag-ing systems can be used to inspect wrecks and other obstructions in more details. This paper presents a workflow for combining multibeam soundings and photogrammetric point clouds generated by a ROV-based camera system. Structure from motion and image enhancement are used to obtain a colour-coded point cloud, which is then fused and scaled with the multibeam soundings, resulting in data den-sification on wrecks. Finally, the feasibility of integrating this fused data to common hydrographic prac-tice is demonstrated.

ROV | underwater photogrammetry | multibeam echo sounder | point cloud fusion

Ausgabe: HN 116, Seite 23–31
DOI: 10.23784/HN116-03
Autor/en: Robin Rofallski, Patrick Westfeld, Jean-Guy Nistad, Annett Büttner, Thomas Luhmann

Coastal cliff monitoring using UAS photogrammetry and TLS

Climate change and the imminent sea-level rise mean that coastal protection is becoming increasingly important, and measures must be taken to ensure that life and important infrastructure in coastal areas are protected. An essential prerequisite for the implementation of appropriate coastal protection measures is the monitoring of endangered areas through appropriate sensor technology for the docu-mentation and quantification of damages caused. In this contribution, a practical application is intro-duced using low-cost UAS (unmanned aerial system) to perform aerial flights for the monitoring of a coastal cliff at the Baltic Sea in Germany, since cliffs are exposed to and unprotected from autumn and winter storms. In comparison to UAS-based photogrammetric monitoring with terrestrial laser scanning (TLS), the photogrammetric method showed the same accuracy, but better coverage of the investigated area and a more efficient workflow.

3D | comparison | erosion | dense image matching | DSM | landslide

Ausgabe: HN 116, Seite 16–22
DOI: 10.23784/HN116-02
Autor/en: Thomas P. Kersten, Maren Lindstaedt, Klaus Mechelke

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