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A natural reference area for the quality control of multibeam echosounder bathymetry and backscatter measurements: The Kwinte area on the Belgian part of the North Sea
No full textThe Kwinte area in the Belgian part of the North Sea serves as a site for monitoring the quality of shallow water multibeam echosounder bathymetric and backscatter data. Time series acquired over two decades confirm its bathymetric and sedimentary stability. Included in the Belgian Marine Spatial Plan and freely accessible, the Kwinte area allows for verification of bathymetric data compliance to IHO hydrographic quality standards. The availability of reference backscatter angular responses obtained with a calibrated singlebeam echosounder facilitates cross-calibration of backscatter data, thereby enabling a comparison of backscatter data from diverse array of multibeam echosounders deployed on various vessels
Underwater laser scanning: Evaluating the performance of ULi in laboratory environments and presenting first insights from real-world applications
No full textWith the global expansion of underwater infrastructure elements, which all require regular inspection, maintenance and repair operations, precise and high-resolution monitoring solutions become crucial. Subsequently, technologies which are able to detect deformations in the range of millimetres, indicating damage at an early stage, are required. Since underwater laser scanning systems are supposed to achieve a much higher accuracy and measurement speed than acoustic techniques, they deliver an enormous potential. However, since water presents physical difficulties to optical systems in terms of turbidity and reachable distance, up to date, only sparse information regarding the performance of an underwater laser scanner and only view estimates about to the actual usability of such a system for corresponding monitoring purposes, are available. For that purpose, the underwater lidar system ULi was tested in two laboratory and one real-world environment. It can be concluded, that (1) man-made and organic structures down to a size of 2.36 mm can be detected at a close-range of ≤ 0.56 m in static laboratory environments, (2) a Böhler star with an arc length of 2.95 mm can be fully resolved at a mid-range of ≤ 8.03 m in static laboratory environments and that (3) the operation of ULi is not suitable for water bodies with a turbidity level of ≥ 6 NTU or a Secchi depth of ≤ 1.10 m
Epilogue: The interplay of agency and instruction in written corrective feedback: Reflections and future directions
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New horizons for hydrography
Full text linkCompared to the complexity required to measure other physical quantities, the continuous monitoring globally of water levels, current directions, and velocities, as well as the measurement of underwater topography, do not appear ambitious tasks for modern technologies. The challenges lie in the sheer size of the area to be measured, which makes up about 70% of the Earth’s total surface, in its constant variability due to natural processes, the inaccessibility of the seabed, and the still inadequate mathematical modelling of global geophysical processes at the oceanic scale. Since most of the world’s population lives on, from and with the oceans, a demand-oriented provision of hydrographic information is of fundamental importance. Hydrography is called upon to serve this need for information in support of informed decision-making. Starting from the present status and the discernible trends in technical development, this article aims to provide a glimpse into the expected future development up to the end of the current decade
Definition of the words “Hydrographer” and “Hydrography”
Full text linkThis manuscript is a reprint of the original paper previously published in 1934 in the Hydrographic Review, a predecessor journal of The International Hydrographic Review (IHR, https://ihr.iho.int/): Nares, J. D. (1934). Definition of the words “Hydrographer” and “Hydrography”. Hydrographic Review, 11 (1), 8-11. https://journals.lib.unb.ca/index.php/ihr/article/view/2815
Water level measurements using reflected GNSS signals
Full text linkGNSS Interferometric Reflectometry (GNSS-IR) is a method that can be used to measure water levels. The frequency of the interference pattern created by direct and reflected GNSS signals is used to estimate the height of the GNSS antenna above the reflecting surface. In principle each rising and setting satellite arc that reflects off the water can be used, yielding ~350 water level measurements per day at sites that track the four major constellations and have a good view of the water. Two examples of the GNSS-IR method are presented, one at a coastal site in Australia and the other from the Ems river in Germany. Each site has collocated traditional tide gauge instrumentation. Open source GNSS-IR software is used to analyze the GNSS data from each site. Correlations between GNSS-IR with the traditional gauge are shown to be better than 0.99