Inverse Histogram-Based Clustering Approach to Seafloor Segmentation from Bathymetric Lidar Data

A current hindrance to the scientific use of available bathymetric lidar point clouds is the frequent lack of accurate and thorough segmentation of seafloor points. Furthermore, scientific end-users typically lack access to waveforms, trajectories, and other upstream data, and also do not have the time or expertise to perform extensive manual point cloud editing. To address these needs, this study seeks to develop and test a novel clustering approach to seafloor segmentation that solely uses georeferenced point clouds. The proposed approach does not make any assumptions regarding the statistical distribution of points in the input point cloud. Instead, the approach organizes the point cloud into an inverse histogram and finds a gap that best separates the seafloor using the proposed peak-detection method. The proposed approach is evaluated with datasets acquired in Florida with a Riegl VQ-880-G bathymetric LiDAR system. The parameters are optimized through a sensitivity analysis with a point-wise comparison between the extracted seafloor and ground truth. With optimized parameters, the proposed approach achieved F1-scores of 98.14–98.77%, which outperforms three popular existing methods. Further, we compared seafloor points with Reson 8125 MBES hydrographic survey data. The results indicate that seafloor points were detected successfully with vertical errors of −0.190 ± 0.132 m and −0.185 ± 0.119 m (μ ± σ) for two test datasets.

Opening an Arctic Escape Route: The Bellot Strait Expedition

During the second half of the 1950s, Canadian and American vessels surged into the North American Arctic to establish military installations and to chart northern waters. This article narrates the expeditions by the eastern and western units of the Bellot Strait hydrographic survey group in 1957, explaining how these “modern explorers” grappled with unpredictable ice conditions, weather, and extreme isolation to chart a usable Northwest Passage for deep-draft ships. The story also serves as a reminder of the enduring history of US Coast Guard and Navy operations in Canada’s Arctic waters in collaboration with their Canadian counterparts. Au cours de la deuxième moitié des années 1950, des navires canadiens et américains ont envahi l’Arctique nord-américain pour y établir des installations militaires et cartographier les eaux du Nord. Le présent article traite des expéditions des unités est et ouest du groupe de levés hydrographiques du détroit de Bellot en 1957 et explique comment ces « explorateurs modernes » ont été confrontés à des états de glace imprévisibles, à des conditions météorologiques et à un isolement extrême en traçant un passage du Nord-Ouest utilisable pour les navires à forts tirants d’eau. Le récit nous rappelle également l’histoire durable des opérations de la Garde côtière et de la Marine américaines dans les eaux arctiques du Canada en collaboration avec leurs homologues canadiens.

Structural Analysis and Optimization of Hybrid Unmanned Amphibian Aerial Vehicle

Hybrid Unmanned Amphibian Aerial Vehicle (HUAAV) is a hybrid unmanned system consisting of a multi-rotor and a hovercraft. Water quality management, hydrographic survey, bathymetric survey and related application areas still employs time consuming and erroneous traditional methods of using boats to access the test sites. The application of unmanned systems will significantly increase the efficiency of this process by getting access to remote locations of both air and water. This paper deals with the design optimization and finite element structural analysis to validate the structural capability of the hybrid amphibian aerial vehicle for operational conditions. The Reserve Factors (RF) for all the components in the amphibian aerial vehicle are calculated and then optimized.

Satellite-Derived Bathymetry Using Landsat-8 Imagery for Safaga Coastal Zone, Egypt

Satellite-Derived Bathymetry (SDB) modeling is used to derive bathymetric data needed for enriching several applications including nautical charting. The nautical charts of Safaga port, Egypt, contains significant gaps as they are based on 50-years old hydrographic survey data and it needs an update. We applied the SDB algorithm (log-ratio approach) using multispectral Landsat-8 OLI images for extracting bathymetry to update the nautical charts of SAFAGA port. The results are verified against the old nautical chart of SAFAGA with a coefficient of determination (R2) varies between 0.42 to 0.71 in areas where hydrographic data are old, unavailable or costly to obtain.

A Novel Method on Hydrographic Survey Technology Selection Based on the Decision Tree Supervised Learning

Hydrographic survey or seabed mapping plays an important role in achieving better maritime safety, especially in coastal waters. Due to advances in survey technologies, it becomes important to choose well-suited technology for a specific area. Moreover, various technologies have various ranges of equipment and manufacturers, as well as characteristics. Therefore, in this paper, a novel method of a hydrographic survey, i.e., identifying the appropriate technology, has been developed. The method is based on a reduced elimination matrix, decision tree supervised learning, and multicriteria decision methods. The available technologies were: remotely operated underwater vehicle (ROV), unmanned aerial vehicle (UAV), light detection and ranging (LIDAR), autonomous underwater vehicle (AUV), satellite-derived bathymetry (SDB), and multibeam echosounder (MBES), and they are applied as a case study of Kaštela Bay. Results show, considering the specifics of the survey area, that UAV is the best-suited technology to be used for a hydrographic survey. However, some other technologies, such as SDB come close and can be considered an alternative for hydrographic surveys.

Morphotectonic analysis along the northern margin of Samos Island, related to the seismic activity of October 2020, Aegean Sea, Greece

<p>On October 30<sup>th</sup> 2020 a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea. This seismic event was another destructive active deformation in the long seismic history of Samos since the ancient times. Preliminary reports focused the seismic epicenter at about 10 km north of Karlovassi, situated at the western part of the Samos E-W trending coastline. The earthquake mechanism corresponds to an E-W normal fault dipping to the north. The activated fault was assumed to be running along the northern margin of Samos Island, which bounds from the south the Samos basin.</p><p>Immediately after the seismic activity and during the aftershock period in December 2020 an hydrographic survey off the northern coastal margin of Samos Island was conducted with R/V NAUTILOS of the Hellenic Navy Hydrographic Service, using the multibeam SeaBat 7160 RESON. The result of the hydrographic survey was a detailed bathymetric map with 15m grid interval and 50m isobaths.  The main morphological aspects of Samos Basin are a 14 km long, 6 km wide and 690 m deep elongated E-W basin developed north of Samos Island.</p><p>The southern margin of the basin is abrupt with morphological slopes of more than 10<sup>o</sup>, following the major E-W normal fault surface, running along the coastal zone, with an overall throw of more than 500m. In contrast, the northern margin of the basin shows a gradual slope increase towards the south from 1<sup>o</sup> to 5<sup>o</sup>. Numerous small canyons trending N-S transversal to the main direction of the Samos coastline are observed along the southern margin, between 600 and 100 m water depth.  These canyons have a length around 2,7 km and width between 100-300 m. Two large submarine landslides with a canyon width of 1,3 km and 0,8 Km, are located north of Karlovasi. The creation of the canyons is probably due to the uplift of Northern Samos Island and their 500 m vertical height difference corresponds to the average fault throw that has controlled the steep slopes of the margin. The orientation of the fault scarp changes at the western Samos coastline from E-W to ENE-WSW facing the neighboring Ikaria Basin, which is developed to the west of Samos Basin. The division line between the Ikaria and Samos basins runs N-S from the northern slopes and coast of the Kerketeas mountain (1443m). The aftershocks of the 30<sup>th</sup> October main shock are limited east of the N-S division line with only a minor activity 15 km to the west within the eastern margin of the Ikaria Basin.</p>

Research on the hydrographic survey cycle for updating navigational charts

Due to the vast ocean area and limited human and material resources, hydrographic survey must be carried out in a selective and well-planned way. Therefore, scientific planning of hydrographic surveys to ensure the effectiveness of navigational charts has become an urgent issue to be addressed by the hydrographic office of each coastal state. In this study, a reasonable calculation model of hydrographic survey cycle is established, which can be used to make the plan of navigational chart updating. The paper takes 493 navigational charts of Chinese coastal ports and fairways as the research object, analyses the fundamental factors affecting the hydrographic survey cycle and gives them weights, proposes to use the BP neural network to construct the relationship between the cycle and the impact factors, and finally establishes a calculation model of the hydrographic survey cycle. It has been verified that the calculation cycle of the model is effective, and it can provide reference for hydrographic survey planning and chart updating, as well as suggestions for navigation safety.