Sea Environment Research Articles

Processing Strategy for Deep Imaging Beneath Complex Shallow Structures Under Shallow Water: a Case Study in the Enping Sag

Abstract As offshore exploration targets deeper parts of shallow-water areas in the eastern South China Sea, an increasing number of hydrocarbon discoveries have been made in recent years, and the difficulty of such exploration has increased. One such challenge lies in mid-depth imaging beneath complex shallow geological structures. When a seismic wave penetrates through groups of densely distributed fractures and/or volcanic rocks, only a fraction of the energy reaches the target depth. As the ray path becomes complex, the middle to deep imaging quality becomes significantly poorer. In this study we applied three techniques: 3D joint source and receiver deghosting and zero-phasing, dynamic resolution time-lag full waveform inversion (DR-TLFWI), and least square Q-compensated Kirchhoff pre-stack depth migration (LSQPSDM), to improve the related seismic data and ultimately improve the imaging quality beneath complex shallow geological structures in the shallow-water environment of the eastern South China Sea, providing better subsurface understanding for the exploration of this area.

Experimental investigation on seakeeping performance of variable-structure SWATH in heading regular waves

The variable-structure unmanned surface vehicle (VS-USV) have high maneuverability, strong survival, and multitasking characteristics in complex sea environment. In this study, a variable-structure small waterplane area twin hull (VS-SWATH) is proposed, which combines the advantages of straight strut SWATH and inclined strut SWATH. In order to study the seakeeping performance of the VS-SWATH with rotatable strut and hydrofoils at medium to low speeds, a series of seakeeping towing model tests was conducted. A variable-structure device was installed on the test model to change the strut rotation angle, and a detachable hydrofoil adjustment device was designed for the test model enabling the exchange of wingless and winged models. The test equipment includes a seaworthiness instrument system and a data acquisition system to measure values such as pitch, heave, vertical acceleration, and monitor the fluid around the ship. The test results show that the VS-SWATH can avoid resonance by changing the strut rotation angle. Hydrofoils mainly reduce heave and pitch at longer wavelengths, but their improvement in seakeeping performance is relatively limited in short waves.

A Monocular Ranging Method for Ship Targets Based on Unmanned Surface Vessels in a Shaking Environment

Aiming to address errors in the estimation of the position and attitude of an unmanned vessel, especially during vibration, where the rapid loss of feature point information hinders continuous attitude estimation and global trajectory mapping, this paper improves the monocular ORB-SLAM framework based on the characteristics of the marine environment. In general, we extract the location area of the artificial sea target in the video, build a virtual feature set for it, and filter the background features. When shaking occurs, GNSS information is combined and the target feature set is used to complete the map reconstruction task. Specifically, firstly, the sea target area of interest is detected by YOLOv5, and the feature extraction and matching method is optimized in the front-end tracking stage to adapt to the sea environment. In the key frame selection and local map optimization stage, the characteristics of the feature set are improved to further improve the positioning accuracy, to provide more accurate position and attitude information about the unmanned platform. We use GNSS information to provide the scale and world coordinates for the map. Finally, the target distance is measured by the beam ranging method. In this paper, marine unmanned platform data, GNSS, and AIS position data are autonomously collected, and experiments are carried out using the proposed marine ranging system. Experimental results show that the maximum measurement error of this method is 9.2%, and the average error is 4.7%.

Modified REL-Based Piecewise Path Loss Modeling Approach for Shore-to-Ship Communication at 5.6 GHz

The need for reliable and uninterrupted communication systems in the marine environment has become critically important with increasing maritime activities, environmental monitoring, and the spread of autonomous systems. However, the complex structure of electromagnetic wave propagation in a sea environment limits the accuracy of the existing propagation models. Thus, the Modified Round Earth Loss (REL) model was first developed in this study to estimate the path loss more accurately in shore-to-ship communication. Subsequently, a piecewise modeling approach based on the principle of two-segment data modeling was proposed. In the Modified REL model, unlike the traditional REL model, the paths and gains of the direct and reflected waves were not considered equal in the calculations. Moreover, unlike in the classical approach, the receiver height was not taken as a fixed value; the estimated best receiver height value for each measurement was included in the calculations as a representation of the effect of roughness in the sea environment. Thus, the model is better adapted to various environmental conditions. In addition, the proposed piecewise model divides the propagation medium into two regions using a break point calculated by Fresnel zone theory. The Modified REL model was used for the first region and the log-distance model was used for the second region. This method allows for more accurate modeling of signal behaviors, especially at different distances. Experimental measurements and performance evaluations conducted using four different shore-to-ship communication scenarios show that the Modified REL model shows an average improvement of up to 3% in Root Mean Square Error (RMSE) values compared to the classical REL model. Additionally, the proposed piecewise model improves the fitting error of the Modified REL model, which models the data as a single whole, by an average of 22.25%. These findings emphasize the necessity of propagation models that are sensitive and adaptable to environmental changes for maritime communication.

Winch Traction Dynamics for a Carrier-Based Aircraft Under Trajectory Control on a Small Deck in Complex Sea Conditions

When the winch traction system of a carrier-based aircraft works under complex sea conditions, the rope and the tire forces are greatly changed compared with under simple sea conditions, and it poses a potential threat to the safety and stability of the aircraft’s traction system. The accurate calculation of the rope and tire forces of a carrier-based aircraft’s winch traction under complex sea conditions is an arduous problem. A novel method of dynamic analysis of the aircraft-winch-ship whole system under complex sea conditions is proposed. A multiple-frequency excitation is adopted to describe the complex sea conditions and the influences of pitching amplitude, and the rolling frequency on the traction dynamics of a carrier-based aircraft along the setting trajectory under complex sea conditions are studied. The advantages and disadvantages of a winch traction system with trajectory control and without trajectory control in complex sea conditions are analyzed. For realizing the trajectory control of the aircraft, the vector difference between the center of mass for the carrier-based aircraft and the position on the predetermined Bessel curve is calculated, so as to obtain the azimuth vector in the aircraft coordinate system. This research is innovative in the modeling of the whole system and the trajectory control of a carrier-based aircraft’s winch traction system under the complicated sea condition of the multi-frequency excitation. ADAMS (Automatic Dynamic Analysis of Mechanical System) is used to verify the correctness of the theoretical calculation for the winch traction. The results show that the complex sea environment has a certain influence on the winch traction safety of the aircraft; in the range of 10–15 s for the traction, the rope force amplitude of complex sea conditions under the multi-frequency excitation is 29.5% larger than that of the single-frequency amplitude, while the vertical force amplitude of the tire is 201.1% larger than that of the single-frequency amplitude. This research has important guiding significance for the selection of rope and tire models for a carrier-borne aircraft’s winch traction in complex sea conditions.

Beach wrack as a potential microplastic hot spot in the South-Eastern Baltic Sea environment

Beach wrack is considered as a major source of nutrients to the sandy coast ecosystems in the South-East Baltic Sea, and it serves as the natural beach sediment storage and habitat formation material. However, it also could be a hot spot for microplastic and other types of marine litter accumulation. We carried out the recovery rate experiments to determine the most reliable method for a rapid and cost-effective application to extract microplastics from the beach wrack. The aeration of media in a saturated solution of sodium chloride revealed to be statistically significant and reliable, therefore was selected as a most suitable to extract the microplastics from the beach wrack. This study shows that the concentration of microplastics is significantly different between the four analyzed compartments in the coastal zone. The microplastic concentration in a beach wrack, with a mean value of 0.47 ± 0.17 items/cm3, contained 4.7 times more microplastics than observed in the surface sand samples. This study estimated that on average over 450 million microplastic items could be found during the castaway event in the South-East Baltic Sea coast.

Research on Marine Environmental Noise Based on Acoustic Bait Domestication Technology

Acoustic domestication type of marine pastures are generally established in shallow waters with water depth not exceeding 200 m. In order to study the effect of acoustic domestication, this paper aims to investigate the environmental noise in the shallow waters of the sea. Unlike the stable deep sea environment, the environmental noise in the shallow sea is extremely complex, which has a direct impact on the effect of acoustic domestication. In this paper, in order to study the marine environmental noise, a hydroacoustic signal processing system is established, which is divided into two parts: the hardware part and the software part; the hardware part is mainly for signal sampling, and the software part is for signal processing. The hardware part of the hydroacoustic signal processing system includes three parts: acoustic-electric conversion, intermediate processing and signal recording. The study of ship noise showed that the fishing boat is about 5m long, with a power of 60hp, and passes about 10m away from the hydrophone, and it is more than 10dB higher than that without a ship, when there is a ship passing, in which the 400Hz is 17.82dB higher. Measurements of ocean ambient noise at different depths show that the noise decreases with depth, but when close to the seabed, the noise decreases with depth due to the reflection effect of the seabed on the sound and the biological noise of the seabed.

Fluorescent analyses of sediments and near-seabed water in the area of the WW2 shipwreck “Stuttgart”

Motorship wrecks on the seabed pose a serious threat to the marine environment due to oil leaking from their fuel tanks. Such substances can penetrate the sediments and enter the water. There is a need to analyse bottom water and seabed sediment samples for the content of toxic petroleum substances. Tests were undertaken on samples collected near ​​the site of the World War II shipwreck of the s/s “Stuttgart”. The wreck is located in the Baltic Sea, in the Gulf of Gdańsk. To answer whether toxic hydrocarbons from wrecks enter the sea environment, a fluorometric analysis was carried out based on measurements of excitation-emission ultraviolet spectra for sediments and near-seabed water. The results of these analyses indicate the presence of oil substances in the sediments and the bottom water at some sampling points close to the wreck site. Studies have shown that the applied method of the so-called fluorometric indicator allows for determining the sites of water pollution with oil substances hidden in sediments.

A Graphic Review of Studies on Ocean and Mediterranean Sea Environment Quality

With so many studies today on the water quality of the sea, one can hardly comprehend the multitude of topics that arise all over the world. This study provides a few graphic syntheses related to the most frequent words (including their clustering and links), trend topics, the spatial distribution of the researched areas, and the thematic evolution of the research directions over the decades. The most frequent authors’ keywords have a 50% similitude between the ocean studies and the studies related to the Mediterranean Sea; these keywords are part of a causal chain that dominates the marine studies on water quality: nutrients → eutrophication → phytoplankton → chlorophyll → seagrass. The most frequent words in the titles and abstracts of the selected papers from the Web of Science are “concentration” and “species”; in the Mediterranean studies, “chlorophyll” and “temperature” are the most frequent. In close connection with water quality, Zostera marina (eelgrass) and Crassotrea virginica (eastern oyster) prevail at the global scale, while Posidonia oceanica (Neptune grass) is relevant in the Mediterranean space. Some of the most studied water bodies are the South China Sea, San Francisco Bay, Chesapeake Bay, and, in the Mediterranean Sea, the Adriatic, Ionian, Aegean, and Marmara seas. “Climate change” and “remote sensing” are trend topics that shape the current studies on water quality; the increasing sea surface temperature enhances algal blooms—these need to be monitored using satellite imagery for the sustainable evolution of human activities, including aquaculture.

Study on the Prediction of Motion Response of Offshore Platforms Based on ResCNN-LSTM

In the random sea environment, offshore platforms are influenced by factors such as wind, waves, and currents, as well as their interactions, leading to complex motion phenomena that affect the safety of offshore platform operations. Consequently, accurately predicting the motion response of offshore platforms has long been a key focus in the fields of naval architecture and ocean engineering. This paper utilizes STAR-CCM+ to simulate time-history data of offshore platform motion responses under both regular and irregular waves. Furthermore, a predictive model combining residual convolutional neural networks and long short-term memory neural networks using neural network technology is also studied. This model utilizes an autoregressive approach to predict the motion responses of offshore platforms, with its predictive accuracy validated through comprehensive evaluations. Under regular wave conditions, the coefficient of determination (R2) for the platform’s heave and pitch responses consistently exceeds 0.99. Meanwhile, under irregular wave conditions, the R2 values remain generally above 0.4. Additionally, the model exhibits commendable performance in terms of Mean Squared Error (MSE) and Mean Absolute Percentage Error (MAPE) metrics. The aim of this study is to present a novel approach to predicting offshore platform motion responses, while providing a more scientific basis for decision-making in offshore platform operations.

Metabolic adaptations of Shewanella eurypsychrophilus YLB-09 for survival in the high-pressure environment of the deep sea.

Elucidation of the adaptation mechanisms and survival strategies of deep-sea microorganisms to extreme environments could provide a theoretical basis for the industrial development of extreme enzymes. There is currently a lack of understanding of the metabolic adaptation mechanisms of deep-sea microorganisms to high-pressure environments. The objective of this study was to investigate the metabolic regulatory mechanisms enabling a strain of the deep-sea bacterium Shewanella eurypsychrophilus to thrive under high-pressure conditions. To achieve this, we used nuclear magnetic resonance-based metabolomic and RNA sequencing-based transcriptomic analyses of S. eurypsychrophilus strain YLB-09, which was previously isolated by our research group and shown to be capable of tolerating high pressure levels and low temperatures. We found that high-pressure conditions had pronounced impacts on the metabolic pattern of YLB-09, as evidenced by alterations in energy, amino acid, and glycerolipid metabolism, among other processes. YLB-09 adapted to the high-pressure conditions of the deep sea by switching from aerobic intracellular energy metabolism to trimethylamine N-oxide respiration, altering the amino acid profile, and regulating the composition and the fluidity of cell membrane. The findings of our study demonstrate the capacity of microorganisms to alter their metabolism in response to elevated pressure, thereby establishing a foundation for a more profound understanding of the survival mechanisms of life in high-pressure environments.

A new type of submarine chimneys built of halite

In contrast to the subaquatic sulphide and carbonate chimneys, which are known from Mid Ocean Ridges and abyssal submarine volcanoes, chimneys built of salts have not been described yet. Here we present such halite chimneys as a new form of cold-water smokers in hypersaline environments. The here described structures rise up from the bottom of the Dead Sea and result from the submarine discharge of saturated halite-dissolution brines into the salt lake, which is at halite saturation and holds remarkable chloride excess. At the interface with the lake brine, halite precipitates instantaneously, forming chimneys up to several meters in height. The brines leading to the formation of these chimneys vary in composition, while their generation processes are similar. Fresh groundwater from surrounding aquifers enters the saline lake sediments and considerably leaches halite in the adjacencies of the lake. Simultaneously, it mixes with ancient brines before it emerges from the lake floor. The distinct differences in composition between the Dead Sea and the emerging chimney brines lead to the instantaneous crystallisation of halite and few other mineral phases. The chimney structure result from the buoyancy flow of the chimney brines, which are less dense then the ambient Dead Sea.The chimneys indicate intense cavitation of massive halite bodies in the subsurface of the Dead Sea environment, a process that leads to increasing formation of hazardous sinkholes. Since chimneys are proven in shallow water but may be expected in deeper parts too, they are comfortably mappable by echo-sounding or aerial imaging. They thus provide in the Dead Sea as in any likewise setting a potent predictive tool to locate dangerous subsurface cavitation and hence areas that are at risk of collapse in the near future.

The Relationship of the Change in Hydrogeochemical Features and Lithium Values of Kızılırmak Basin (Nevsehir-Central Anatolia) Water with Tectonic Fields

In this study, in particular, the relationship between high lithium values and geological environments was examined. To determine this, the geology, structural geology, hydrogeology, and hydrogeochemistry of the area in the north of the Gülşehir-Yeşilöz sub-basin of the Kızılırmak Basin were investigated. For hydrogeological studies, 19 water samples were collected in May and September. Tectonically, this area has a horst-graben structure. The relationships between the water analysis values of the study area and the tectonic areas were investigated. In particular, the lithium content of the waters in the study area was investigated. Hydrogeochemical properties and seasonal changes in water resources were studied in detail, and their relationship with tectonic areas was evaluated. Water analyses were carried out during wet and dry periods to determine temporal hydrogeochemical changes. According to the analysis, the waters in the area are of Ca-HCO3 and Ca-Mg-HCO3 facies. In addition, there are water samples with high lithium content in the study area. IDW and Kernel diagrams of these were prepared. It was found that these high values were influenced by the rocks formed in the ancient sea and saline lake environments. The region with the highest lithium value is in the formations that represent the former salt lake environment. High lithium (Li) values are generally higher in the region within the Kızılırmak graben. Lithium values in this area were determined as 241.3 µg/L, 154.5 µg/L, 155.2 µg/L, 156.8 µg/L, and 155.6 µg/L.

A comprehensive propulsion system analysis: an integrated approach utilising engine simulation and free-running model experiments

Regulations concerning the environmental impact and energy efficiency of ships are becoming increasingly stringent. To meet these demanding criteria, new technologies are actively being developed to achieve emission reductions while maintaining efficient fuel energy conversion into propulsion power. However, the propulsion system behaviour in a dynamic environment of the actual sea is highly nonlinear and complex, and a profound understanding of the mutual interactions is still lacking. This paper proposes an integrated approach for comprehensive propulsion system analysis. The key feature of this technique is the utilisation of an intelligent propeller drive controlled by a marine diesel engine simulator (MDES) to drive the free-running model of a ship, providing real-like behaviour of the engine model in real-time in response to actual measured values. The core of the MDES consists of a continuous cycle-mean value dynamic engine model supplemented with a detailed combustion cycle evaluation. The developed fast calculation algorithm of crank-angle resolved thermodynamic equations of the gas state in the engine cylinder enables the complete engine model to be integrated into the real-time environment of a physical model ship. Thus, the propulsion system's performance can be analysed under conditions that closely mimic those of the actual sea environment.

Mitigating the impact of accidental ammonia release during bunkering operation

Abstract Ammonia is a carbon free energy carrier that is gaining popularity as the next generation marine fuel. However, the adoption of ammonia by ships will not be feasible without solving the challenges during its bunkering operation, of which the utmost is the harmful effect from ammonia’s toxicity. A potential release of ammonia during bunkering operation will cause harmful impacts of various levels depending on its initial physical states, rate of release, total released inventory, local geometries, terrain and weather conditions. Without any mitigation measures in place, the released ammonia will undergo a complicated dispersion, dilution and uplifting pathway, affecting potential sensitive receptors in the surrounding. The knowledge and experience learnt from chemical, fertilizer and refrigeration use of ammonia provide valuable references for ammonia handling at sea and port. Mitigation for released ammonia can follow a two-pronged strategy: 1) the preventive strategy to reduce the likelihood of accidental release and 2) the protective strategy to reduce the release severity. This translates into mitigation technologies developed for pre-release scenarios and post-release scenarios. The pre-release mitigation considers inherent safer engineering design and good management, while the post-release mitigation focuses on early vapor detection and warning, containment, suppression, counter measures and emergency response. Nevertheless, there is a lack of understanding and use cases on how to extend the findings to ammonia bunkering operation, where the contact between ammonia and the sea environment, in particular sea water surface and column, is inevitable. The review provides a consolidated view on the applicability of land-based post-release mitigations such as physical containment, use of barriers, foams, dilutions and other chemical approaches to mitigation the consequences of accidental ammonia release from future ammonia bunkering operation.

New carnivorous sponges (Porifera: Cladorhizidae) from Western Australia, collected by a Remotely Operated Vehicle (ROV).

The last two decades have reinvigorated systematic research on predatory sponges, mainly fuelled by advances in technology that have facilitated collection in deep-water habitats. This research presents six new species of carnivorous sponges from the family Cladorhizidae Dendy, 1922 from the western continental margin of Australia. The new species are Abyssocladia johnhooperi nov. sp., Abyssocladia aurora nov. sp., Abyssocladia janusi nov. sp., Axoniderma challengeri nov. sp., Cladorhiza vanessaekins nov. sp. and Nullarbora ningalooa nov. sp.. This material was collected by ROV during expeditions FK200308 to the Ningaloo Canyons expedition off the mid-west coast near Ningaloo, and FK200126 to the Southwest Australian canyons expedition, in Western Australia. These and other expeditions by the Schmidt Ocean Institute in 2020-21 formed a campaign around Australia's deep sea and mesophotic environments, which has vastly increased our understanding of biodiversity in these habitats.

Output Feedback Adaptive Optimal Control of Multiple Unmanned Marine Vehicles with Unknown External Disturbance

This paper presents an optimal output-feedback tracking control problem for multiple unmanned marine vehicles (UMVs) to track a desired trajectory. To guarantee the control objective in an optimal manner, adaptive dynamic programming (ADP) with optimal compensation terms is adopted. A neural velocity observer is designed based on a neural network (NN) to estimate the unmeasured system states and the unknown system dynamics. Furthermore, a disturbance observer (DO) is proposed to go against the effect of the unknown external disturbance of the sea environment. It is proved that the proposed controller can guarantee that all signals in the closed-loop system are bounded. Simulation results are given to demonstrate the effectiveness of the proposed control algorithm.

Mechanical interactions modeling of inertial wave energy converters

Numerous technological solutions for wave energy converters (WECs), referred as inertial reaction mass (IRM) systems, incorporate a reacting mass within the floater, coupled with a power take-off (PTO) system, to shelter all electronic components from the hostile sea environment. While the overall complexity of the system increases, the current modeling procedures persist in considering only a limited number of modes of motion, neglecting relevant dynamical effects. In this context, this paper proposes a systematic procedure for defining the kinematic characteristics and overall analytical model for the dynamics of IRM WECs. The significance of the proposed procedure lies in the statement of the reaction mass-related dynamic equation, considering the floater’s parametric excitation in six degrees of freedom (DoF). Additionally, it introduces the procedure for defining the reaction forces that the inertial mass exerts on the floater, which are often neglected in the literature for the full simulation of such systems. Furthermore, the proposed analytical modeling procedure allows the definition of approximated models in more simplified nonlinear forms for dynamic analysis and ultimately in fully linear approximations. This enables the application of methodologies and techniques commonly used in the literature for linear systems. The development of the framework is kept generic, in order to introduce a versatile mathematical procedure, that can be easily adjusted, with minor modifications, to accurately capture and represent the mechanical interaction for a wide family of IRM WEC devices. Subsequently, a case study on a vertical-hinged pendulum WEC is analyzed, to showcase the effectiveness of the proposed methodology. Moreover, to test the reliability of the analytical framework, a comparison with the output of a commercial software is conducted.

The deeper the rounder: body shape variation in lice parasitizing diving hosts

Seal lice, unique among insects, show remarkable adaptability to the extreme conditions of the deep sea. Evolving with their seal and sea lion hosts, they have managed to tolerate hypoxia, high salinity, low temperature, and elevated hydrostatic pressure. Given the diving capabilities of their mammalian hosts, which can reach depths of hundreds to thousands of meters, our study examines the morphological variation among closely related seal lice species infesting hosts with different maximum diving depths. In particular, our research reveals a significant morphological difference between lice associated with regular and deep-diving hosts, where lice from deep-diving hosts tend to be rounder. This could be an adaptation to withstand the high hydrostatic pressures found in the deep ocean. The rounded shape optimizes the louse’s ability to withstand external pressure by redistributing it over a larger ventral/dorsal plane. This in turn minimizes the internal energy required to support body deformations, thereby increasing the louse’s resilience in the deep sea environment.

Valuing community awareness and willingness to pay for marine environment management: empirical analysis in coastal central region of Vietnam

Vietnam is a country with strengths in marine resources and economy. The coast provides habitats and livelihoods for millions of households but is in decline due to economic activity and climate change. This study’s purpose is to evaluate the awareness of people in the central coastal provinces of Vietnam about marine environmental values and their willingness to pay for the management and improvement of marine environmental quality. The study applied a binary random assessment model and surveyed 980 households in 4 coastal provinces to evaluate community payments. The results show that people have good awareness of tangible environmental values, associated with life and livelihood. They also highly agree with protecting marine environmental values and emphasize passing these values on to future generations. Community payment for sea environment management was estimated at 420 thousand/household/year in parametric model and 398 VND thousand/household/year in non-parametric model. Bid level, income and education are main factors affecting people’s ability to pay. The study also proposes implications for marine environmental management including strengthening community awareness and capacity, establishing financial mechanisms for community-led conservation at the local level, and integrating education marine environmental values for high school students to aim for sustainability in community awareness and behavior.