Bathymetry Research Articles

Development of a compact pulsed time-of-flight LiDAR platform for underwater measurements

The mapping and inspection of underwater topography and infrastructure require precise and robust instrumentation which cannot be completely fulfilled by sonar or camera-based systems. At Fraunhofer IPM we have therefore built a versatile platform that implements all necessary building blocks for various laser scanner configurations targeted at subsea applications. Based on this platform, we present two scanner prototypes: One compact and lightweight multi-wavelength airborne laser scanner for deployment with unmanned aerial vehicles. It is intended for easy and fast shallow water bathymetric and topographic mapping. The second scanner is embedded in a pressure resistant housing and designed for submerged deployment on stationary or moving platforms to facilitate numerous inspection tasks. Initial tests of the scanners have been performed in an excavation pond and on a dedicated underwater measurement range. The resulting point clouds indicate promising performance in terms of resolution, accuracy, and speed. Further work will focus on extensive field tests and software optimization for increased usability.

The invasive mollusk Rapana venosa (Mollusca: Neogastropoda: Muricidae) in the mid-southern Black Sea: Distribution, growth, and stock structure

The rapa whelk, Rapana venosa (Valenciennes, 1846), known also as the veined rapa whelk or the Asian rapa whelk, settled in the Black Sea in 1940 and within the past 30 years has become an important economic contribution to local fishers along the coastline. This study examines the annual change in biomass, population structure, and interaction of the species with the ecosystem of rapa whelk in the mid-southern Black Sea. The samples were collected monthly in 2011 and 2012 by hydraulic dredge at different sites. Stock biomass was estimated at five different subregions and along four depth contours. In 2012 the biomass of rapa whelk increased significantly in in all subregions compared with the previous year sampling. Food availability is the main factor for species distribution, and in parallel, striped Venus clams, Chamelea gallina (Linnaeus, 1758), the main food source for rapa whelks, was significantly concentrated in the study area. The von Bertalanffy growth parameters (VBGP) were expressed as Lt = 121.78(1 − e−0.246(t + 0.33)). As a fisheries management point, our results highlight the overpopulation of rapa whelk in the region.

Chart features, data quality, and scale in cartographic sounding selection from composite bathymetric data

ABSTRACT Cartographic sounding selection is a constraint-based bathymetric generalization process for identifying navigationally relevant soundings for nautical chart display. Electronic Navigational Charts (ENCs) are the premier maritime navigation medium and are produced according to international standards and distributed around the world. Cartographic generalization for ENCs is a major bottleneck in the chart creation and update process, where high volumes of data collected from constantly changing seafloor topographies require tedious examination. Moreover, these data are provided by multiple sources from various collection platforms at different levels of quality, further complicating the generalization process. Therefore, in this work, a comprehensive sounding selection algorithm is presented that focuses on safe navigation, leveraging both the Digital Surface Model (DSM) of multi-source bathymetry and the cartographic portrayal of the ENC. A taxonomy and hierarchy of soundings found on ENCs are defined and methods to identify these soundings are employed. Furthermore, the significant impact of depth contour generalization on sounding selection distribution is explored. Incorporating additional ENC bathymetric features (rocks, wrecks, and obstructions) affecting sounding distribution, calculating metrics from current chart products, and introducing procedures to correct cartographic constraint violations ensures a shoal-bias and mariner-readable output. This results in a selection that is near navigationally ready and complementary to the specific waterways of the area, contributing to the complete automation of the ENC creation and update process for safer maritime navigation.

Utility of remotely operated underwater vehicle in flood inundation mapping for dam failure: A case study of Lake Tuscaloosa Dam

AbstractA remotely operated underwater vehicle (ROV) is a tethered underwater mobile device that can conduct a bathymetric survey cost‐efficiently. Assessment of the utility of ROV‐based bathymetric surveys in flood inundation mapping remains limited. This study aims to examine the utility of ROV‐based bathymetric surveys in high‐resolution flood inundation mapping for a hypothetical case study of the Lake Tuscaloosa Dam breach in the state of Alabama, USA. This study conducted the sensitivity test of flood inundation mapping to the river channel depth (ROV‐based vs. digital elevation model [DEM]‐based) and initial flow condition (e.g., wet vs. dry), via six different simulations of the parallelized diffusion hydrodynamic model (pDHM). This study found that the ROV‐based pDHM runs had higher maximum water depths over the flood‐inundated areas, ranging from +73% to +166% of the simulated depths of the DEM‐based pDHM runs. However, the impact of initial streamflow condition on the maximum depths was limited. This study also found that the pDHM runs with a dry initial flow condition delayed the time to reach the maximum depth after the dam breach by 2 h relative to the pDHM runs with a wet initial streamflow condition. This study suggests that ROV‐based bathymetry surveys improve flood inundation mapping by emphasizing the influence of river channel depth, initial streamflow conditions, and bathymetry, thereby bolstering community resilience to a potential human‐made hazard such as dam failure.

Improved BINN-Based Underwater Topography Scanning Coverage Path Planning for AUV in Internet of Underwater Things

Deep understanding the special nature of underwater topography plays an important role for Internet of Underwater Things (IoUT). Nowadays, underwater topography scanning with Autonomous Underwater Vehicle (AUV) has been becoming the chief methodology of knowing Seabed topography and geomorphology. How to design topography scanning trajectory can be mathematically described as a full Coverage Path Planning (CPP) problem. In this paper, facing the complete coverage path planning problem of mobile AUV, a new strategy based on Bio-Inspired Neural Network (BINN) algorithm with improved activity value of each neuron is discussed in detail. The original activity value function in BINN is instead of a piecewise linear function to reduce computational complexity. In addition, to overcome traditional dead-zone problem, an A* path planning based dead-zone escape method along the shorter path as early as possible to the recently uncovered area is described in deep. Extensive simulation results and practical experiments verify the performance of proposed Improved Bio-Inspired Neural Network (IBINN in short) based algorithm.

Alongshore variability in berm and sandbar migration patterns on a highly dynamic beach

Sediment exchange between the shoreface and the foreshore is investigated through the analysis of sandbar and berm migration cycles at La Misión beach in Baja California, Mexico. In general, nearshore sandbars migrate onshore during low-energy wave conditions merging with the shoreline to become intertidal sandbars that later contribute to berm rebuilding. However, significant alongshore differences were observed in the sandbar welding and berm rebuilding process, which can be attributed to alongshore wave skewness and near-surfzone flow variations. The analysis of topographic and bathymetric surveys collected monthly over a 5-year period revealed larger shoreline retreat and longer recovery times in the southern beach compared to the north. This was related to the inability of sandbars to weld to the intertidal beach during spring and summer, occurring only during extended periods of low-energy waves. In the southern beach, the berm formation process exhibited less dependence on incoming wave energy, persisting during mild-energy winters, and reforming in the presence of sandbars. Hydrodynamic measurements indicated that the southern part of the beach experienced relatively more intense net offshore flows (up to −0.2 ms−1) due to undertow, and possibly related to the presence of persistent rip currents. In contrast, the berm in the northern beach followed a seasonal erosion and rebuilding process associated with sandbar migrations driven by variations in incoming wave energy and cross-shore sediment transport. This was characterized by larger near-bed wave velocity skewness compared to the south. Net flows in the north were predominantly onshore, reaching up to 0.1 ms−1 during lower-energy periods with oblique wave incidence. This study reveals the presence of considerably distinct sandbar and berm migration cycles along a relatively short beach of 2.2 km long. It also highlights how such variability can be related to the morphodynamic feedback with sandbars affecting hydrodynamics, particularly near-bed wave skewness and near-surfzone flow variations, which in turn influence sediment transport and morphological evolution.

Analysis of the Bottom Topography of the Reservoir Due to Sediment Trapping (According to the Krasnodar Reservoir, Russia)

Morphometric descriptions of reservoirs are usually limited to the type, shape, altitude position, bed size and volume of water in them. The article presents the results of the analysis of the bottom topography of the Krasnodar reservoir and the transformations of this for 2005-2021. The analysis was carried out based on the materials of bathymetric surveys for the usable volume of the reservoir on an area of 224 km2 with the creation of digital elevation models. The topography of the reservoir bottom is represented by flat sections of flooded accumulative plain with prevailing slopes of about 0.2–0.4°, dissected by riverbeds of lower-order tributaries. The transformation of the topography is caused by gradual silting. The total volume of sediments for this area in 2005-2021 amounted to 127 million m3 with an average siltation layer of 0.4 m. To describe the morphological properties of the bottom topography, we used geomorphometry techniques with the calculation of the BPI index (Bathymetric Position Index) and the classification of mesoscale topography forms based on it. For the riverbed, there are topography forms related to three types of surfaces: flat (Lower Bank Shelves), concave (Depressions, Deep Depressions) and convex (Reef Crests, Back Reefs, Mid-Slope Ridges). The constructed maps reflect the differentiated morphology of the bed surface, the evolution of topography forms and the change in roughness under conditions of continuous transformation of the basin and allow judging the prevailing morphogenetic processes. Morphologically, the coastal zone and the shallow part of the riverbed are the most difficult to construct. Here, along with long-shore reef crests of different genesis, deep depressions and simple depressions in the form of underwater channels on the deltas of extension can form on the accumulative shoal.

STRUCTURE AND ORIGIN OF THE BOTTOM RELIEF OF LAKE CHUKHLOMSKOE (KOSTROMA REGION)<a href="#FN1"><sup>1</sup></a>

The article discusses the first results of studying the structure of the bottom topography and bottom sediments of Chukhlomskoe Lake (Kostroma Region, Chukhlomsky District). We analyzed the lake bottom topography based on the results of our bathymetric survey and discovered two hollows with maximum depths diverging from the lake’s center towards the city of Chukhloma. The maximum depth inside the hollows (and for the entire lake) reaches 5.4 m, and the average lake depth is 2.2 m. There are two steps seen in the bottom topography; 2.0–2.4 m and 1.5–1.8 m. The bottom sediment structure of Chukhlomskoe Lake was revealed by drilling from the ice with two boreholes (with lengths of 9.45 and 7.45 m, located in the area of background depths and inside the hollow, respectively). Five radiocarbon AMS dates were obtained for the core from the hollow’s bottom. The sedimentary sequences of the pre-Holocene part of both cores show high similarity in structure and depths of the marker horizons identified by a set of lithological analyses. The structure and thickness of Holocene sediments differ significantly. In the area of background depths, the Holocene organo-mineralogenic silt is 3.8 m, and inside the hollow, the thickness of this layer is only 1.45 m. Moreover, hiatuses in sedimentation were documented in the structure of the Holocene sediment inside the hollow. The age of hiatuses, based on the sedimentary model, was estimated as 10.6–5.3 and 4.9–0.06 thousand years ago. A probable mechanism for the origin of hollows is localized erosion caused by wind currents in a highly shallow lake. An additional erosion factor can be the degassing of bottom sediments, which leads to the loosening of the bottom layer of sediments, which makes them susceptible to erosion. The cutoff of sediment erosion inside the hollow coincided in time with the construction of a dam on the Veksa River and a rise in the lake level by 1.0–1.5 m in the 1960s.

Scattering of moving atmospheric pressure induced tsunamis by bathymetry and coastline

Tsunamis can be generated by a moving atmospheric pressure disturbance. The 2022 Tonga volcanic eruption and tsunami demonstrated the global relevance of such a tsunami generation mechanism. The generated locked and free waves are often scattered by bathymetric variations and coastlines, generating more free waves and resulting in a complex wave field. The physical processes involved can be described by the forced linear shallow water equations. Analytical solutions are sought after for simplified bathymetric variations and coastline configurations. In this paper, a moving atmospheric pressure front, which is uniform in the direction normal to its propagation direction, is considered. The water wave motion is assumed to start from the quiescent condition, so that the incident locked and free waves are related. However, since the wave scattering processes are linear, the solutions obtained in this paper can be used for analyzing scattering of the incident locked and free waves with uncorrelated amplitudes. For one-dimensional horizontal (1DH) problems, the water depth is either a constant or has a sudden change (i.e., a step) with or without a vertically walled coastline and the atmospheric pressure front always moves in the direction normal to the depth contours. In the case where a coastline is considered, the atmospheric pressure front can either move from the land to the sea or from the sea to the land. In the 2DH (two-dimensional horizontal) example, the wave field generated by a moving atmospheric pressure front, sweeping over the a circular island surrounded by a circular shelf, is investigated and discussed. For all the cases considered, analytical solutions in the integral form are obtained using the Fourier transform method. For the 1DH cases, analytical solutions are also presented in the form of infinite series, summing over infinite number of scattered and reflected waves from the bathymetric variations and coastlines. The new solutions reveal both the complexity of the wave scattering process and the significant differences between locked and free waves.

Bathymetric Surveying Using Autonomous Surface Vehicle for Shallow-water Area with Exposed and Partially Exposed Rocks

Bathymetric Surveying Using Autonomous Surface Vehicle for Shallow-water Area with Exposed and Partially Exposed Rocks

Application of Filtering Techniques to Smooth a Surface of Hybrid Digital Bathymetric Model

The aim of the research is to identify the optimal method for smoothing the surface of a hybrid digital bathymetric model (HDBM). The initiation of this research is justified by the fact that a model created from diverse types of data may have different surface textures and outliers. This diversity may cause problems in subsequent data processing stages, such as generating depth contours. As part of the adopted research methodology, fifteen filters were analysed. Filtering techniques were examined for filter type, the number of iterations, weights, and window size. The result is the adopted research methodology, which enabled the selection of the optimal filtering method. The research undertaken in this work is an extension of the methodology for developing an HDBM. An important aspect of the research is the approach to elaborating on such kinds of models in shallow and ultra-shallow waters adjacent to the land, as well as the use of data obtained by modern measurement platforms, such as unmanned surface vehicles (USV) and unmanned aerial vehicles (UAV). The studies fit into the general context of works related to the development of this type of model and undoubtedly provide a solid reference for further development or improvement of similar methods.

A Case-Based Reasoning Method for Generalizing Depth Contours considering Both Navigational Safety Assurance and Line Shape Preservation

To address the problem that the parameters are relatively fixed in the existing automatic methods of depth contour generalization, a case-based reasoning method for generalizing depth contours is proposed considering navigational safety and line shape. First, the structured description of depth contours before and after cartography generalization is made to form case samples. Then, driven by the training samples, the machine learning of BP neural network model is constructed, to obtain the simplification degree taking into consideration the preservation of contour shapes. Finally, the generalization parameters are flexibly adjusted based on the simplification degree obtained through the case-based reasoning, so that depth contours can be adaptively generalized for various complex situations. The experimental results demonstrate that: (1) The case-based reasoning method can make the generalization of depth contours comply with the principle of navigational safety; (2) The case-based reasoning method has a stronger applicability maintaining the shape of depth contour, and is more suitable for the automatic generalization of depth contours, compared with the rolling circle method and the triangulation method. Generally, the case-based reasoning method has the potential to improve cartographic quality meeting the requirements of IHO specification, supporting the automatic production of ENC and nautical chart product.

Recent intensification of riverbed mining in the Mekong Delta revealed by extensive bathymetric surveying

Large-scale sand extraction has had significant and compounding impacts on the riverine environment of the Vietnamese Mekong Delta (VMD). Yet, effective and targeted implementation of regulations and sustainable management remains hindered by scant data availability, limiting a comprehensive understanding of the delta's sand mining scale and extent. This study assessed recent intensifying patterns of sand mining activities in the VMD mainly based on extensive bathymetric surveys carried out across 800 km2 of the VMD river channel from 2017 to 2022. Our results revealed severe riverbed deepening across the VMD, with the upper reaches of the Hau (Bassac) River experiencing an average incision of 1.4 m from 2017 to 2022, resulting in sediment losses of 127 Mm3. Similarly, the upper reaches of the Tien (Mekong) River and the Co Chien branch showed incisions of 1.3 m and 0.7 m from 2017 to 2020, accompanied by sediment losses of 139 Mm3 and 87 Mm3, respectively. The observed spatial and temporal variability in incisions, along with widespread sand mining pockmarks along the riverbed profiles, provide strong evidence of the significant contribution of sand mining to changes in riverbed morphology. The progressive lowering of riverbed elevation provides further evidence of the recent intensification of sand mining activities. Additionally, field surveys highlighted the proximity of perceived sites of bank collapse to pitted riverbeds, providing reliable indications of sand mining-induced erosion. Ultimately, we intend for this evidence-based assessment of sand mining activities in the VMD to contribute to informed quantitative assessments of sediment budgets and effective implementation of regulatory frameworks for sustainable sand mining in the future.

Method of Time Estimation for the Bathymetric Surveys Conducted with a Multi-Beam Echosounder System

Exact and complete preparation of a hydrographic survey project allows for the avoidance or reduction of additional costs and unexpected delays and, at the same time, increases the efficiency of the survey. One of the essential requirements at the survey planning stage is a calculation of time necessary for performing bathymetric measurements with a multi-beam echosounder. Based on these calculations, many decisions related to the costs and methodology are made. The article presents the method of time estimation for the hydrographic surveys and takes into account many variables that directly affect the final duration of the project. The paper demonstrates the influence of water depth, multi-beam echosounder swath angle, and other planning parameters related to the scheme of survey lines on the total time of stay at sea. The main findings are based on the author’s over twenty years of experience aboard the Polish Navy hydrographic ship Arctowski and include thorough analysis of specialist literature, publications, manuals, and international standards.

Predicting lake bathymetry from the topography of the surrounding terrain using deep learning

AbstractLake morphometric features like surface area, volume, mean, and maximum depth are important predictors of many physical, biological, and ecological processes. Lake bathymetric maps that present the lake basin contours are thus an integral part of limnological investigations. Accurate but cumbersome traditional bathymetric surveys measure the depth using a lead line or echosounder. Recently, airborne bathymetric mapping using imagery or laser scanning has been attempted in shallow freshwater and coastal habitats. However, these methods depend on the ability of light to penetrate the water column, which can be problematic in eutrophic lakes and shallow lakes. To alleviate these issues, we developed and tested a deep learning model (based on the U‐net) using data from 153 lakes in Denmark to predict bathymetry using the topography of the surrounding terrain. The deep learning model performed much better (pixel‐wise mean absolute error: validation set = 1.75 and test set = 2.15 m) than baseline interpolation approaches (validation set = 3.12 m). In addition, the deep learning model generated more realistic bathymetry maps that did not suffer from interpolation artifacts. We find that the model performance improves slightly with increasing model size (number of trainable parameters) and the extent of the surrounding terrain. In addition, our pretraining procedure improved performance and reduced the time for model convergence. Because the model only relies on digital elevation data which are widely available, it can be fine‐tuned and used to predict lake bathymetry in other geographical regions.

Bathymetries of proglacial lakes: a new data set from the northern Tien Shan, Kazakhstan

Between 2009 and 2020, 74 bathymetric surveys of 57 glacial lakes were conducted in the northern Tien Shan using the ecosounding technique. The surveys provided data on lake depths and other parameters characterising the three-dimensional lake geometry, and bathymetrically derived lake volumes. The sample included 21 glacier-connected lakes, 27 lakes formed on the young moraines without glacier-connected with glacier tongue, eight lakes formed on the older moraines and one rock-dammed lake. The lakes’ volumes ranged between 0.029x105 and 53.89x105 m3 with the largest value of mean depth was 23 m. There is a statistically significant correlation between lake depth and width, length and area, best approximated by the power, linear, and polynomial models, with coefficients of determination ranging between 0.50 and 0.78 for the glacier-connected lakes. The power equations underestimated both depths and volumes of larger lakes but the second-order polynomial model provided a closer approximation in the study region. The obtained data were combined with the bathymetrically derived depth and volume data published in the literature extending the global data set of bathymetries of lakes with natural dams. The area-depth scaling equations derived from the combined data set showed a considerable improvement in correlation between area and depth in comparison with the earlier studies. The measured bathymetries of the glacier-connected lakes were compared with bathymetries of the same lakes simulated using GlabTOP2 model and published simulated ice thickness data. There is generally a good agreement between the measured and simulated bathymetries although GlabTOP2 tends to overestimate lake depths. The data from the bathymetric surveys and GlabTOP2 model are used by the practitioners to reduce and avoid risks associated with glacier lake outburst floods and are important instruments of the regional strategy of adaptation to climate change.

ESTIMATING ALONGSHORE SEDIMENT TRANSPORT FROM DREDGED ACCESS CHANNELS

Alongshore sediment transport rates are important in sediment budget studies or design of coastal structures. Underestimated transport rates give rise to severe siltation updrift from cross-shore structures and severe erosion downdrift. Overestimates may lead to over-design and thus high costs. Currently, these estimates are generally obtained from sediment transport equations, morphodynamic numerical modelling or bathymetrical changes in accumulation areas (Vandebroek et al. 2017). However, alongshore transport is difficult to estimate from regular bathymetrical surveys, since only locations with gradients in the transport will provide information via volume changes. On a straight coastline the sediment will simply pass by. Here an alternative data-based approach is proposed, studying an access channel suffering from repeated siltation. As the access channel effectively serves as a sediment trap it can be used to study alongshore sediment transport rates. The access channel is frequently dredged and even more frequently surveyed. It is therefore suitable to make estimates of sediment transport on the time-scale of weeks to months.

Effectiveness of vertical error budget model for portable multi-beam echo-sounder in shallow water bathymetric survey

With the increasing availability of portable survey equipment and platforms, hydrographic data acquisition now offers a diverse range of device options and installation methods. Tailoring the mounting and installation of hydrographic survey devices to fit the boat or platform dimensions has become common practice. The use of portable equipment is essential, given the wide selection of combined options available in the market. Consequently, sensor offsets and device performance differ for each survey conducted, necessitating the constant verification of accuracy performance.This paper examines the capabilities of portable multibeam echosounder (MBES) deployments on various types of survey boats. The investigation focuses on error budget modeling and field tests. A model is developed to estimate the propagated uncertainty resulting from different sources of measurement uncertainties. The model primarily considers vertical sources of error in MBES surveys, as they have the most significant impact on hydrographic data quality. To validate the model, field tests are conducted at two different locations using different boat and device configurations. The results demonstrate that the modeled uncertainties align with the measured standard deviations, particularly in the Pramuka area, where the standard deviation of data acquired at the widest beam angle of ±60° is 0.25m, close to the predicted value of 0.28m. However, in the Patimban area, the model overestimates the uncertainty, predicting 0.27m compared to the measured standard deviation of 0.17m.

Creating an Autonomous Hovercraft for Bathymetric Surveying in Extremely Shallow Water (

Coastal shallow water environments (<5 m) are extremely biodiverse and dynamic yet are often mapped too infrequently or at too low resolutions to capture the important processes occurring in these regions. Common forms of coastal surveying can leave gaps in data in the shallow water zone due to optical instrument capabilities and a vessel's ability to navigate in this region. One solution to these issues is an autonomous hovercraft that can fly over land and water and begin surveying at sub-meter water depths, bridging the gap between common optical and acoustic surveying methods. The craft's autonomy is tested via four autonomous flight paths, or missions, and the desired path is compared to both the observed heading and direction of motion. Although the accuracy for each track in the mission varies, most headings and directions of motion of the hovercraft are within 50 degrees of the desired direction. A single-beam echo sounder was used to map the bathymetry of the study site, showing a gently sloping beach.

A FRAMEWORK FOR COOPERATIVE DYNAMIC TASK ASSESSMENT FOR COTSBOT AUVs

ABSTRACT-This project presents a proposed framework aimed at collaborative and dynamic allocation of tasks for a specific group of self- governing underwater vehicles known as autonomous underwater vehicles (AUVs). These AUVs are utilized to manage the proliferation of Crown-Of-Thorns starfish (COTS) on the Great Barrier Reef situated in Australia. The concept of constrained task allocation is employed to reframe the supervision and regulation of COTS into a challenge where a central task involves eradicating clusters of COTS using the injection mechanism integrated into the COTSbot AUVs. The operational setting, encompassing underwater topography, COTS clusters, and shorelines, is mapped probabilistically. The COTSbot AUVs are then collaboratively deployed to target as many COTS clusters as possible within a designated mission timeframe, utilizing an inventive heuristic technique termed Heuristic Fleet Cooperation (HFC). To substantiate the efficiency and dependability of the proposed collaborative task allocation algorithm for COTS eradication in the Great Barrier Reef, comprehensive simulations and quantitative performance evaluations are conducted.