Nearshore Environments Research Articles

Spatial patterns and environmental drivers of demersal fish assemblages in the Swartkops and Sundays estuarine to marine seascapes, South Africa

Estuaries are often observed as the boundary between the ocean and the river, separating coastal environments, rather than being seen as a continuum. Owing to insufficient research on demersal fish communities across nearshore marine to estuarine habitats, particularly in South Africa, this study employed a spatial seascape approach, with seasonal sampling of soft-bottom benthic habitats in two permanently open estuaries and the adjacent marine nearshore environment of Algoa Bay on the south coast of South Africa. A total of 790 fish representing 29 species were collected in the marine nearshore, and 6 414 fish (28 species) were caught in the estuarine zone. Two discrete demersal fish assemblages were identified as representing the marine nearshore and estuarine environments. The marine nearshore fish assemblages were dominated by marine species (e.g. Argyrosomus inodorus and Cynoglossus zanzibarensis) that were not recorded in the estuarine environment, whereas marine estuarine-opportunist species (e.g. Pomadasys olivaceus and Galeichthys feliceps) were more abundant in the marine nearshore than in the estuarine environment. The estuaries were dominated by benthic marine estuarine-dependent and marine and estuarine species (e.g. Rhabdosargus holubi, Solea turbynei, Heteromycteris capensis, Psammogobius knysnaensis and Glossogobius callidus). Differences observed in abundance and species richness along the estuarine to marine continuum were primarily related to the salinity gradient. These findings are significant as altered freshwater flows and consequent changes in salinity and productivity can have an impact on the nursery use of both estuaries and the marine nearshore by fish species.

STIRUnet: SwinTransformer and inverted residual convolution embedding in unet for Sea–Land segmentation

Extraction of coastline from optical remote sensing images is of paramount importance for coastal zone management, erosion monitoring, and intelligent ocean construction. However, nearshore marine environment complexity presents a challenge when capturing small-scale and detailed information regarding coastlines. Furthermore, the presence of numerous tidal flats, suspended sediments, and coastal biological communities exacerbates the reduction in segmentation accuracy, which is particularly noticeable in medium–high-resolution remote sensing image segmentation tasks. Most previous related studies, based primarily on convolutional neural networks (CNNs) or traditional feature extraction methods, faced challenges in detailed pixel-level refinement and lacked comprehensive understanding of the studied images. Therefore, we proposed a new U-shaped deep learning model (STIRUnet) that combines the excellent global modeling ability of SwinTransformer with an improved CNN using an inverted residual module. The proposed method has the capability of global supervised feature learning and layer-by-layer feature extraction, and we conducted sea–land segmentation experiments using GF-HNCD and BSD remote sensing image datasets to validate the performance of the proposed model. The results indicate the following: 1) suspended sediments and coastal biological communities are major contributors to coastline blurring, and 2) the recovery of minute features (e.g., narrow watercourses and microscale artificial structures) effectively enhances edge details and leads to more realistic segmentation outcomes. The findings of this study are highly important in relation of accurate extraction of sea–land information in complex marine environments, and they offer novel insights regarding mixed-pixel identification.

Predator-Prey Interactions in Marine Ichthyofaunal Communities of the Nearshore Environment of South Bimini Island

Predator-Prey Interactions in Marine Ichthyofaunal Communities of the Nearshore Environment of South Bimini Island

Biostratigraphic analysis of a Late Pleistocene to Holocene section from Punta Pescador, eastern Venezuela

A biostratigraphic study was undertaken on a shallow borehole drilled to 90 meters in the easternmost Orinoco Delta, Venezuela. Twenty-eight samples were analyzed for palynomorphs and foraminifera. Palynomorphs were recovered in all except one sample consisting of 178 entities. Foraminifera assemblages of low diversity were recovered in 17 of the 28 samples. The analysis provides some insight into the vegetation, climate, and depositional history allowing comparisons with other Late Pleistocene to Holocene studies in the northern South America region. The Late Pleistocene to Early Holocene transition is marked by an unconformity, where the vegetation changes from a diverse flora of Mauritia flexuosa, grasses (Poaceae), ferns, and mangroves (Rhizophora, Avicennia) to one dominated by Rhizophora around 10,000 years BP. This transition also contains reworked palynomorphs and abundant black wood (inertinite), indicative of erosion and oxidation. The absence of foraminifera suggests an exposed continental shelf and lowering of sea level. The Early Holocene mangrove flora is replaced by vegetation dominated by Mauritia flexuosa, with Symphonia globuliflora, grasses, and ferns. The palynological signature for the upper 42 m of the section compares favorably with a previous study of the Holocene in the Orinoco Delta. Radiocarbon dating indicates there is an unconformity or condensed section at the vegetation change, representing as much as 5500 ± years. Foraminifera indicate an open shelf environment immediately above this horizon followed by a significant shallowing to nearshore transitional environments near the top of the section. Local climate and/or human influence may have been a factor in the abundance of Mauritia flexuosa as suggested by other studies.

Scattering-Point-Guided Oriented RepPoints for Ship Detection

Ship detection finds extensive applications in fisheries management, maritime rescue, and surveillance. However, detecting nearshore targets in SAR images is challenging due to land scattering interference and non-axisymmetric ship shapes. Existing SAR ship detection models struggle to adapt to oriented ship detection in complex nearshore environments. To address this, we propose an oriented-reppoints target detection scheme guided by scattering points in SAR images. Our method deeply integrates SAR image target scattering characteristics and designs an adaptive sample selection scheme guided by target scattering points. This incorporates scattering position features into the sample quality measurement scheme, providing the network with a higher-quality set of proposed reppoints. We also introduce a novel supervised guidance paradigm that uses target scattering points to guide the initialization of reppoints, mitigating the influence of land scattering interference on the initial reppoints quality. This achieves adaptive feature learning, enhancing the quality of the initial reppoints set and the performance of object detection. Our method has been extensively tested on the SSDD and HRSID datasets, where we achieved mAP scores of 89.8% and 80.8%, respectively. These scores represent significant improvements over the baseline methods, demonstrating the effectiveness and robustness of our approach. Additionally, our method exhibits strong anti-interference capabilities in nearshore detection and has achieved state-of-the-art performance.

Serpula? alicecooperi sp. nov. – a new serpulid from the Lower Jurassic (Pliensbachian) Hasle Formation of Bornholm, Denmark

Serpulid remains are very rare in the Lower Jurassic Hasle Formation of Bornholm, Denmark. A historical specimen mentioned, but not figured by Malling & Grön wall (1909) was reexamined and attributed to Pentaditrupa quinquesculcata and here f igured for the first time. New finds of additional well-preserved serpulid tubes are described as Serpula? alicecooperi sp. nov, which show adaptations for a lifestyle on fine-grained sediment in a nearshore environment.

Predicting excess attenuation: An investigation of turbulence in a littoral environment

This work presents an effort to effectively represent turbulence in a numerical model of atmospheric sound propagation in a near-shore environment. Model results are compared with a set of atmospheric transmission loss measurements made in a pitch-catch configuration with a stationary source 500 m from shore. High resolution temperature profiling and scanning Doppler LIDAR wind profiling measurements in the source-to-receiver direction are concurrent with the acoustic transmission loss measurements at the shoreline. These meteorological measurements inform the input parameters used in the parabolic equation. The numerical predictions are compared to the measured transmission loss values to evaluate model performance with a variety of different approaches to implement turbulence parameters.

Bulk analysis of underwater sound spectra from vibratory pile driving of cylindrical steel piles in coastal waters

Vibratory pile driving is a common means of pile installation in both near-shore and offshore environments. Spectral knowledge of the noise produced by this activity is crucial in modeling and assessing the impacts to aquatic species. With the goal of providing generic representative spectra to better inform propagation modeling and related impacts, approximately 80 near-pile measurements of vibratory pile driving of cylindrical steel piles from more than 19 hydroacoustic reports were analyzed. Included pile diameters range from 24–48 inches and all measurements were of activities in U.S. coastal waters. Results include representative spectra based on the mean and median spectra binned by pile size and the presence of noise mitigation systems, an examination of the variation in the data, marine mammal hearing group weighted spectra, broadband sound pressure levels, and comparisons with general knowledge of vibratory pile driving spectra characteristics in previous literature. Finally, data availability and larger efforts aimed at a comprehensive underwater pile driving acoustic spectral database are discussed.

Jake Seller Draw impact structure, Bighorn Basin, Wyoming, USA: The deepest known buried impact structure on Earth and its possible relation to the Wyoming crater field

We provide evidence demonstrating the impact origin of a structure, here named the Jake Seller Draw impact structure, which is buried below the Jake Seller Draw drainage basin, in the Bighorn Basin of Wyoming, western United States. The 4.3-km-diameter structure was first recognized as a seismic disturbance at a depth of ∼6.5 km in two- and three-dimensional seismic profiles. Microstructural analysis of drill cuttings situated in the center and outside of Jake Seller Draw revealed the presence of multiple sets of planar deformation features and planar fractures in nine quartz grains, thereby confirming the hypervelocity impact origin of the structure. The seismic data show that Jake Seller Draw is a complex impact structure containing a 1-km-wide central uplift. The geologic and seismic data suggest that Jake Seller Draw is the most deeply buried impact structure known on Earth to date. The stratigraphic framework suggests that the crater was formed in a nearshore environment at the Pennsylvanian−Permian boundary, ∼280 m.y. ago. This age coincides with the age of the Wyoming crater field 300 km southeast of Jake Seller Draw and may suggest a common origin.

Anthropogenic structure emplacement and sediment transport at King Herod's harbour, Israel: ED-μXRF (Itrax) data and foraminifer Pararotalia calcariformata as proxies of coastal development over millennia

The construction of harbours along high energy nearshore environments, which commonly include the emplacement of hard structures both as central features (e.g., piers, jetties) as well as protective measures (e.g., wave breakers, coastal armouring), can alter coastlines in a multitude of ways. These include reconfiguring the coast's morphology, introducing or redistributing exogenous and endogenous materials, and changing localized environmental substrate and structural conditions; and, as a result, impact the associated ecological communities. With growing coastal populations and associated coastal development, concerns over the long-term consequences of such projects are of global interest. Caesarea Maritima, a large-scale, artificially constructed ancient harbour built between 21 and 10 BCE, provides a rare opportunity to address these impacts and investigate its fingerprint on the landscape over 2000 years. To approach this, representative sediment samples were isolated and analyzed from two sediment cores (C1, C2), an excavated trench (W), and a sample of ancient harbour construction material (aeolianite sandstone and hydraulic concrete; COF). Geochemical (Itrax μXRF, magnetic susceptibility) and foraminifera analyses were conducted and results from both methods were statistically grouped into significantly similar clusters. Results demonstrated the increased presence of aeolianite-associated elemental contributions only after the construction of Caesarea as well as in particularly high concentrations following previously proposed tsunami events, during which shallower and deeper materials would have been transported and redeposited. The foraminifera data shows the appearance and eventual abundance dominance of Pararotalia calcariformata as an indicator of coastal hardening. Results suggest that they are an especially well-suited species to demonstrate changing environmental conditions existing today. In previous studies, this species was mistakenly presented as a recent Lessepsian arrival from the Red Sea, when in fact it has had a long history as an epiphyte living on hardgrounds in the Mediterranean and co-existencing with humans and their harbour-building habits. Specimens of P. calcariformata, therefore, are useful indicators for the timing of harbour construction at Caesarea and may be used as rapid and cost-effective biostratigraphic indicators on sandy nearshore coastline in future geoarchaeological studies. This has implications for future studies along the Israeli coast, including both paleoenvironmental and modern ecological assessments.

Characterizing Seiches Oscillations in a Macro-Tidal Estuary

Seiches oscillations may account for an important proportion of sea level variations in nearshore environments, inducing overflow and surges while impacting the safety of marine areas. However, complementary investigations are still required to characterize seiches in coastal basins, including especially estuaries. The present study exhibited seiches characteristics in the intertidal zone of the upper Elorn estuary (western Brittany, France), within the city of Landerneau, which is regularly subjected to river overflow and inundation. This investigation relied on five-year measurements of the free-surface elevation. As recorded time series were highly discontinuous around low tide, an original data analysis technique was implemented to exhibit seiches characteristics during the different tidal cycles. Measurements revealed important seiches oscillations with heights liable to exceed 0.6 m and periods of around 45–70 min. Seiches showed furthermore a fortnightly variability with pronounced heights and an increased number of oscillations during neap tides. These variations appeared, however, to be disturbed by the additional effects of meteorological conditions, including especially the influence of wind. The number of oscillations around high tide was thus found to increase in strong wind conditions. These effects were particularly noticeable at low atmospheric pressure, suggesting a sensitivity of seiches to wind meteorological patterns during cyclonic events.

Optimized 3D reconstruction in nearshore underwater environments: A cost-effective pre-processing strategy for Neural Radiance Fields implementation

Nearshore oceans, teeming with diverse benthic ecosystems, continue to be a focal point for marine research. While 2D visual representations have been the mainstay in this area, the intricate, multi-dimensional nature of the seafloor ecosystems underscores the need for 3D modeling to capture their full essence. This study unveils a novel approach tailored for static image processing and 3D modeling through Neural Radiance Fields (NeRF), with a particular emphasis on the refined instantNGP variant. A meticulously crafted pipeline is employed, centered on neutralizing the visual impediments brought about by the interplay of light and seawater in underwater imaging. This refined pre-processing strategy ensures that images are primed for a seamless transition to NeRF-based 3D reconstruction, all the while conserving computational resources. The refined image processing techniques rectify underwater color discrepancies, notably the prevalent blue-green hue resulting from unique lighting conditions. Moreover, the system's ability to identify and excise seawater boundaries guarantees that the 3D models remain singularly focused on the richness of the seafloor ecosystems. Remarkably, achieving this does not demand vast datasets or exorbitant computational prowess, positioning it as an ideal fit for processing images from nearshore regions. As a more resource-friendly and efficient counterpart to existing methodologies, this study furnishes marine ecologists with a powerful instrument for RGB-centric 3D renderings of nearshore terrains. Nonetheless, for broader applicability in diverse marine settings, fusing this approach with neural networks could prove invaluable.

20th Century Warming in the Western Florida Keys Was Dominated by Increasing Winter Temperatures

AbstractLong‐lived Atlantic coral species like Orbicella faveolata are important archives of oceanographic change in shallow, marine environments like the Florida Keys. Not only can coral‐based records extend for multiple centuries beyond the limits of the instrumental record, but they can also provide a more accurate representation of in situ conditions than gridded interpolated sea‐surface temperature (SST) products for nearshore reef environments. We use the coral Sr/Ca paleothermometer to produce a 150‐year (1830–1980 C.E.) monthly SST reconstruction from an O. faveolata colony collected in the Marquesas Keys, FL, USA. An important feature of our record is a significant 20th‐century warming trend in winter SSTs. We hypothesize that the winter warming trend was driven partially by a decrease in upwelling associated cyclonic eddies spinning off the Florida Current. A long‐term weakening of winter Florida Current transport over the 20th century could be responsible for decreased cyclonic eddy formation in the Florida Straits. Another feature of the record is pronounced multidecadal fluctuations of mean annual warming and cooling in the record, which correspond to Atlantic Multidecadal Variability (AMV), with the AMV lagging behind western Florida Keys temperatures by 5–11 years. Strong coherence between coral‐based SST reconstructions in the western Florida Keys with broader scale Atlantic oceanographic trends over the past century suggests a common driver of regional SST variability.

Benthic foraminiferal assemblages in the coastal zone of the yellow river delta: Environmental significance and characteristics of microbial diversity

Unicellular eukaryotes known as benthic foraminifera have sophisticated survival mechanisms and ecological environmental indicators. Ten surface samples from the Yellow River Delta's coastal region were taken for this study to analyze the distribution of foraminifera in relation to environmental factors and to examine their microbial diversity. We looked at the physicochemical aspects of the environment at each sampling site (such as pH, TN, TOC, EC, δ13C, δ15N, PAHs, etc.), and we employed 16S rRNA high-throughput sequencing analysis to look into the interactions between microbial communities and foraminiferal species. The findings demonstrated that the Yellow River Delta's advantage benthic foraminiferal species were Quinqueloculina complanata, Ammonia beccarii, and Ammonia aomoriensis, and that TOC and TN were significant determinants of the distribution of benthic foraminiferal communities. PAH enrichment in the coastal zone effects on microbial communities and benthic foraminifera are not yet readily apparent. Sediment organic carbon and nitrogen isotope analysis revealed that marine plankton may be the dominant source of organic matter in the coastal zone sediments in the research area, which was made up of both land-based and marine organic matter. It implies that foraminifera have some environmental indicators, especially when combined with the distributional traits of the benthic foraminiferal assemblages and their considerable association with environmental parameters. The findings revealed that Q. complanata was found in the Yellow River water-affected estuarine coastal zone, A. aomoriensis was significantly influenced by sediment organic matter content and reflected the estuarine and nearshore environments and the combination of Ammonia beccarii-Ammonia aomoriensis-Elphidium excavatum assemblage indicated a semi-open intertidal shallow marine environment. Additionally, benthic foraminifera showed a responsive association with microorganisms, indicating that microbial diversity may be one of the driving forces behind benthic foraminifera's ability to adjust to environmental changes. The findings of this study will open up new avenues for research into the environmental importance of coastal zone ecosystems and for understanding how benthic foraminiferal communities survive.

A 3D BEM-Coupled Mode Model for the Performance Analysis of Wave Energy Converter Parks in Nearshore-Coastal Regions

Estimation on the production capacity of wave energy converter arrays (WECs) of the type of simple floaters deployed in nearshore locations highly depends on the evaluation of their performance. The latter also depends on various factors, including the dimensions and inertial characteristics of the devices, their relevant positioning, and the power take-off (PTO) system characteristics. Studying the system operation, based on the prevailing sea conditions in the region considered for deployment, can ensure that such WEC farms are sized and designed in an effective way. Furthermore, the wavelength and propagation direction of incoming wave fields can be significantly impacted by wave-seabed interactions in coastal areas, which can alter the WECs’ response pattern and ultimately the array’s power output. In this work, a 3D BEM hydrodynamic model is proposed aiming to assess the energy-capturing capacity of WEC arrays, accounting for the hydrodynamic interactions between various identical floating devices, as well as the local seabed topography. The model is supplemented by a Coupled Mode System (CMS) to calculate the incident wave field propagating over variable bathymetry, in order to simulate realistic nearshore environments. Finally, a case study is performed for an indicative geographical area, north of the coast of the island of Ikaria, located in the Eastern Aegean Sea region, where the wave potential is high, using long-term data. The latter study highlights the applicability of the proposed method and suggests its usage as a tool to support optimal WEC park design.

Characterizing 226Ra and its daughters in coastal zone groundwater of a typical human-activity affected bay: occurrence, safety, and source evaluation.

Due to their extremely toxic properties, 226Ra and it daughters (222Rn, 210Pb, and 210Po) in drinking groundwater require monitoring. Recent studies have reported exceptionally high levels of natural 210Po (up to 10,000Bq/m3), 226Ra, and 222Rn isotopes in groundwater. This study aims to provide background data on 226Ra and its daughter radionuclides in the typical agricultural-industrial Dongshan Bay (DSB) before the construction of Zhangzhou Nuclear Power Plant (Zhangzhou NPP). The measurement results indicate that no abnormally high activities of 210Po and 210Pb were detected in the investigated wells. Strong positive correlations between 210Pb and 210Po, as well as between 222Rn and 210Pb activities, suggest that the origins of 210Pb and 210Po in groundwater are strongly influenced by the decay of the parent radionuclides 222Rn and 210Pb, respectively. In the DSB coastal zone groundwater, significant deficiencies of 210Po relative to 210Pb and 210Pb relative to 222Rn were observed, providing further evidence that 210Po and 210Pb are also effectively scavenged due to their geochemical properties (specifically particle affinity) within the groundwater-aquifer system. A systematic comparison among all relevant water bodies in the DSB revealed that the activity concentrations of 210Pb and 210Po in groundwater were the highest, except for rainwater. Based on the evaluation of 210Pb sources, the results imply that submarine groundwater discharge (SGD) is an important pathway for transferring radionuclides (such as 210Pb) from land to the nearshore marine environment, even though the study area has a lower 210Pb background groundwater. By considering all the 210Pb's sources in the DSB, we found low 210Pb background groundwater discharge still needs to be taken into account for small-scale bays. This is because SGD was calculated to be one of the most important 210Pb sources in the bay during observation season. Regardless of whether the system is in a normal state or a nuclear accident emergency state, greater attention should be paid to the groundwater discharge of radionuclides into the ocean.

Giant mobile coralliths from the Florida Keys, USA

Coralliths are spherical, free-living (motile), scleractinian colonies inhabiting present day and ancient coral reefs. They form by the coral rolling on the seabed which can occur through biological and/or physical processes. While diving and snorkeling in nearshore environments in the upper Florida Keys, we observed hundreds of coralliths of varying sizes and species. This included colonies of Porites astreoides, Siderastrea radians, and Solenastrea bournoni. The largest coralliths we observed were all S. bournoni and ranged between 0.5 and 1.4 m in diameter. The exceptionally large colonies identified (>1 m) may be the largest and oldest spherical coralliths described to date. Relatively frequent movement of a corallith is key to their formation as all colony surfaces must be exposed to sunlight and currents periodically to maintain their spherical shape. Intuitively, the larger a corallith grows, the stronger the current energy must be to initiate movement. Considering the shallow depth of the corallith habitat and the high frequency of tropical storms and hurricanes impacting south Florida, we hypothesized that the forces generated by shoaling, breaking storm waves would be sufficient to cause the formation of these giant coralliths. Calculations based on hydrodynamic forces and field observations after the passage of a storm support the efficacy of storm-generated waves and surge to move and roll these giant coralliths. The tropical storm/hurricane return time where we found these large colonies in the Florida Keys is one in every seven years. This return time is apparently frequent enough to maintain their spherical morphology and assist in the formation of these giant coralliths.

The nearshore aquatic environment of eastern Lake Erie: A thirty-year perspective from a monitoring station

Abstract Dreissenid mussels arrived at the Waverly Shoal located above the inflow of the Niagara River in 1989, initiating marked changes in the water and sediment chemistry, and benthic invertebrate community composition at an Ontario Ministry of the Environment, Conservation and Parks monitoring station. Here we examine change in the nearshore of eastern Lake Erie until 2019, inferred from monitoring at this station. Dreissenid numbers peaked in 1991, exceeding 200,000 individual m-2, and remained above 20,000 individual m-2 until 2004 after which numbers progressively declined. In 1993, the population transitioned from mixed Dreissena polymorpha and D. bugensis, to D. bugensis in subsequent years. The decrease in particle size and increase in organic content of surficial sediment which began the year after mussel arrival has persisted until present time. The low concentrations of trace metals and PAHs at the station increased slightly after the physical alteration in bed sediments and has either not changed or declined. After an initial increase in Secchi depth, water clarity changed little over post invasion years, with prevailing moderate water clarity interspersed with periods of bed resuspension and high turbidity. Calcium concentration in the water column, which fell dramatically after the arrival of dreissenids, has gradually increased in recent years. Chlorophyll a and total phosphorus levels indicating oligo-mesotrophic conditions have not varied systematically over the years, other than a modest decline in chlorophyll a after dreissenid arrival. Benthic invertebrate assemblages have gone through multiple alterations, with shifting abundance of amphipods, oligochaetes, chironomids, gastropods and sphaeriids attributed to invasive species rather than the physical environment. Collectively, the data suggests the nearshore ecosystem has shifted in benthic productivity and trophic transfers mediated by the benthos and invasive species, with water and sediment quality appearing to not vary beyond the range driven by inherently fluctuating physical conditions.

Microtextures on quartz grain surfaces in the Bay of Bengal shoreline sediments, Bangladesh: Implications for sediment transport process and depositional environment

SEM and SEM-EDS studies of quartz grains in the shoreline sediments of the Bay of Bengal, Bangladesh were carried out to evaluate the mode of origin, paleoclimate, and depositional environment. A total of 38 microtexture types were identified, which were grouped into mechanical (23 features), mechanical/chemical (6 features), and chemical (9 features) origins. The morphology of quartz grains in the shorelines was dominantly sub-angular to sub-rounded in shape, which represents robust energy conditions, short residence time, low weathering, and nearby sediment provenance. The microtextures of mechanical origin such as straight and curved scratches, pits, broken edges, and crescent-shaped features were relatively abundant in the eastern site samples (Section-I) indicating high-energy, fluvial, and beach environments. The abundance of V-shaped marks and smooth surfaces of quartz grains indicate high-velocity storm conditions and/or high-energy impact events. The well-rounded outline, low relief with dish-shaped depressions, mechanically upturned plates, and arcuate steps were also observed on quartz grain surfaces. These features suggest that they were developed during an aeolian process in the beach berm environment. Etching, solution/irregular pits, and differential relief on quartz grains were somewhat elevated in the western site samples (Section-III), reflecting that these microtextures were associated with a subaqueous collision and humid climates in the fluvial and nearshore environments. Quartz grains in all sections represented microtextures of high energetic subaqueous environment as well as wind events. However, the absence of corrosion channels and high density of voids in the quartz grains revealed low degree of weathering.

An obstacle detection method for dual USVs based on SGNN-RMEN registration of dual-view point clouds

This paper proposes an unsupervised obstacle detection method for dual unmanned surface vessels (USVs) using the SGNN-RMEN framework. The method utilizes dual-view point clouds captured by two USVs to improve the detection of small obstacles under the condition of a visible shore. Firstly, a siamese graph neural network (SGNN) is designed to extract global contour features. A specialized task of global contour consistency classification is employed to ensure the interpretability of these features. Secondly, a rotation matrices estimation network (RMEN) is utilized to estimate the optimal rotation transformation for aligning point clouds based on the global contour features of the dual-view point clouds. The overlap degree between the dual-view point clouds before and after registration is used as feedback to train the model, enabling unsupervised learning. Finally, a " gridding - filtering - clustering” method is applied to annotate the size and position of obstacles based on the registration of the dual-view point clouds. Comparative experiments on two datasets demonstrate the effectiveness of the proposed method in accurately extracting contour features, achieving precise dual-view point cloud registration, and improving the detection rate of small obstacles in nearshore environments. The method also exhibits strong adaptability in unfamiliar marine environments.