Underwater Channel Research Articles

Submarine landslide susceptibility assessment along the southern convergent margin of the Colombian Caribbean

Submarine landslides are a mixture of rock, sediment, and fluids moving downslope due to a slope's initial event of mechanical failure. Submarine landslides play a critical role in shaping the morphology of the seafloor and the transport of sediments from the continental shelf to the continental rise in the southern margin of the Colombian Caribbean. Two fundamental considerations can be highlighted: first, mass transport complexes produced by submarine landslides encompass significant portions of the stratigraphic record; second, these mass movements could affect underwater infrastructure. The mapping of the Southern Caribbean seafloor using 3D seismic surveys and multibeam bathymetry data in an area encompassing 59,471 km2 allowed the identification of 220 submarine landslides with areas ranging between 0.1 and 209 km2. Distinctive characteristics were found for submarine landslides associated with canyon walls, channel-levee systems, tectonically controlled ridges, and the continental shelf break. The analysis of the relationship between submarine landslides and seafloor morphological features made it possible to estimate a mass movement susceptibility map that suggests the following considerations: first, structural ridges and adjacent intraslope subbasins related to the South Caribbean Deformed Belt are more likely to be submarine landslide hazards; second, the continental shelf break and channelized systems produce a moderate submarine landslide hazard potential; and third, deep marine systems with a slope less than 5° show the lowest submarine landslide hazard potential. This work contributes to the understanding of submarine landslides in the study area through the presentation of conceptual diagrams that provide additional visual elements facilitating the level of abstraction necessary for visualizing bathymetric data. Likewise, the mass movement susceptibility map presented herein gives insights for future studies that seek to evaluate geohazards in the southern Colombian Caribbean margin.

Genesis, evolution and reservoir identification of a Neogene submarine channel in the southwestern Qiongdongnan Basin, South China Sea

Genesis, evolution and reservoir identification of a Neogene submarine channel in the southwestern Qiongdongnan Basin, South China Sea

Analysis of Optical Wireless Communication Links in Turbulent Underwater Channels With Wide Range of Water Parameters

In this study, the performance of underwater optical wireless communication links is investigated by taking into account turbulence, absorption and scattering effects. Weak turbulent channel is modeled using log-normal distribution while moderate and strong turbulence channels are modeled using gamma-gamma distribution. Rytov variance of Gaussian beam is derived analytically for oceanic turbulence optical power spectrum. Subsequently, scintillation index is calculated using the computed Rytov variance. Moreover, the closed-form expression of bit-error-rate (BER) for underwater wireless optical communication (UWOC) systems using intensity-modulated/direct detection (IM/DD) implementation and on-off-keying (OOK) modulation scheme is obtained. Results show that the performance of wireless optical communication link between two platforms in underwater medium is degraded significantly due to turbulence, absorption and scattering. In fact, as the turbulence level increases, its effect becomes quantitatively comparable to those of absorption and scattering effects. The variation of both scintillation index and BER performance are presented for various underwater medium and communication system parameters, such as chlorophyll concentration, average temperature, average salinity concentration, temperature and dissipation rates, wavelength, link length and receiver aperture size. Optical network and internet of underwater things (IoUT) applications, which are growing day by day and requiring high data rates, will benefit from the results of this study.

An Improved Time Delay Measurement Method for the Long-Distance Underwater Environment.

With the development of underwater navigation and underwater communication, it remains difficult to obtain time delay measurements after propagating long distance. This paper proposes an improved high-accuracy time delay measuring method for long distance underwater channel propagation. First, by sending an encoded signal, the signal acquisition is carried out at the receiving end. Then, to improve signal to noise ratio (SNR), bandpass filtering is carried out on the receiving end. Next, considering the random changes in the underwater sound propagation channel, a strategy is proposed to select the optimal time window for cross-correlation. Then, new regulations are proposed to calculate the cross-correlation results. To verify the effectiveness of the algorithm, we compared it with other algorithms under low SNR conditions using Bellhop simulation data. Finally, the accurate time delay is obtained. With underwater experiments over different distances, the method proposed by the paper achieves high accuracy. The error is about 10-3 s. The proposed method makes a contribution to underwater navigation and communication.

Reconciling bathymetric and stratigraphic expressions of submarine channel geometry

Modern submarine channels form distinctive morphological features on the seafloor and play a critical role in shaping the marine sedimentary record. Recent studies have captured the extremely diverse range of cross-sectional geometries in submarine channels from bathymetric data, which typically display aspect ratios markedly different to the stratigraphic record of ancient submarine channels. Here, we compare and reconcile the relationship between the geomorphic expression of submarine channels as observed on the seafloor and the geometry of their stratigraphic bodies as mapped in seismic-reflection data, using the Niger Delta slope an exemplar. For the same channels, our data allows us to contrast the distribution of widths, depths, and aspect ratios from bathymetric data and at two hierarchical scales in the underlying stratigraphy – the channel element and channel system scale. Channel characteristics are also contextualised with respect to two key variables, the underlying structural template and the relative timescale for which the studied systems have been active. Analysis of the seafloor bankfull geometries highlights substantial variability with widths ranging from ∼300 m to ∼4 km and aspect ratios from ∼10:1–100:1. In contrast, the geometry of stratigraphic channel element bodies remains remarkably consistent across the three channels with widths ∼480–620 m and aspect ratios of ∼9:1. At channel system scale stratigraphic width is comparable to that seen in the bathymetric data, but with aspect ratios of 6–23:1. Our results therefore highlight a marked disparity in the cross-sectional geometries on the present-day seafloor and for their associated channels in the stratigraphic record. We demonstrate that a large part of the disparity between modern and ancient submarine channel geometries may be explained by post-abandonment modification of the seabed channels where there is reduced Holocene activity and we argue this effect likely plays a role in the differences seen in global data sets. These results have significant implications for the use of bankfull process analogues when applied to bathymetric data to estimate submarine channel flow characteristics.

Seismic reservoir characterization of the syn-rift lower Miocene Rudeis Formation in the July oilfield, Gulf of Suez basin, Egypt: Implication for reservoir quality assessment

The Lower Miocene Rudeis Formation is among the most potential oil-bearing sedimentary sequences in the Gulf of Suez (GOS), representing the main producer of Egyptian oil. This study concerns primarily with revealing the reservoir characteristics and facies distribution, as well as the implication of the predominant diagenetic factors on the quality of the Lower Miocene syn-rift Rudeis reservoir in the July oilfield. Therefore, this study integrates 2D seismic, and wireline logs, as well as conventional and special core analyses to determine the reservoir characteristics and facies distribution. The interpreted data elucidate four different seismic facies in the Rudeis Formation with a net pay thickness ranging from 29 to 233 m in the studied wells of 16.3% average porosity, 62.9% average oil saturation, and 9.3% average shale volume. Four seismic facies (SF1-SF4) were interpreted and correlated with the Rudeis clastic deep-water turbiditic succession. The 3D static property models revealed that the best reservoir facies in terms of low shale content and water saturation, as well as high porosity, coincide with the submarine channels and fans containing coarse-grained, clean sandstones. From the core analysis, the Lower part of the Rudeis sequence is subdivided into five reservoir rock types (RRTs). The RRT1 is characterized by the best reservoir quality; it is composed of quartz arenites, sublithic arenites, and subfeldspathic arenites. In contrast, the RRT5 represents the lowest reservoir quality; it consists of very coarse siltstone, laminated glauconitic siltstone, and highly compacted dolomitic and calcareous quartz arenites. The poor reservoir characteristics of the RRT5 are attributed to tight compaction, cementation, and early dolomitization phase, whereas the highest quality of the RRT1 is related to fracturing and dissolution processes. The RRT1 rocks are mostly associated with the submarine channel and fan facies, whereas the poor quality RRT5 sediments were accumulated as hemipelagic/background. This integrated workflow study can be applied to further case studies in the Middle East, Africa, and the other analogues all over the world.

Late Holocene pteropod distribution across the base of the south-eastern Mediterranean margin: the importance of the > 63 µm fraction

Abstract. Euthecosomata pteropods were analysed in core sediments collected in the framework of the 2016 EUROFLEETS2 SEMSEEP cruise, offshore of Israel, in the eastern Mediterranean Sea. The investigated cores were retrieved in a deep-sea coral area at 690 m depth, an actively methane-seeping pockmark area at 1038 m depth, and a deep-sea channel area at 1310 m water depth. We identified and documented the pteropod species belonging to the families Heliconoididae, Limacinidae, Creseidae, Cavoliniidae, Cliidae, and Hyalocylidae and to some heteropods. Our study highlights the importance of investigating pteropods in the size fractions > 63 µm instead of the > 125 µm only. In particular, neglecting the small size fraction may result in a remarkable (up to 50 %–60 %) underestimation of the relative abundance of the epipelagic species Creseis acicula and Creseis conica and the mesopelagic species Heliconoides inflatus. This may significantly affect palaeoenvironmental reconstructions. The observed presence of tropical species supports the suggestion that the eastern Mediterranean is a refugium for these species. This study provides a basic benchmark for the late Holocene evolution of pteropod and heteropod distribution over 5800–5300 cal BP across the base of the south-eastern Levantine margin.

Lateral and temporal variations of a multi-phase coarse-grained submarine slope channel system, Upper Cretaceous Cerro Toro Formation, southern Chile

ABSTRACTUnderstanding variations in the sedimentary processes and resulting stratigraphic architecture in submarine channel systems is essential for characterizing sediment bypass and sedimentary facies distribution on submarine slopes. In the Santonian to Campanian Cerro Toro Formation, southern Chile, a coarse-grained slope system, informally known as the Lago Sofia Member, developed in a structurally controlled environment, with complex and poorly established relationships with the surrounding mud-rich heterolithic deposits.A detailed architectural analysis of the most continuous and best-exposed channel system in the Lago Sofia Member, the Paine C channel system, provides insights on lateral facies transitions from channel axis to margin, stacked in a multi-phase sequence of events marked by abrupt changes in facies, facies associations, and architecture.The Paine C channel system is incised into siltstones and claystones interbedded with thin-bedded very fine sandstones, interpreted to be either channel-related overbank or unrelated background deposits. The coarse-grained deposits are divided into a lower conglomeratic unit and an upper sand-rich unit. The lower conglomeratic unit can be further subdivided into three phases: 1) highly depositional and/or aggradational, dominated by thick and laterally continuous beds of clast- to matrix-supported conglomerate, herein named transitional event deposits; 2) an intermediate phase, including deposits similar to those dominant in phase 1 but also containing abundant clast-supported conglomerates and lenticular sandstones; and 3) a bypass-dominated phase, which records an architectural change into a highly amalgamated ca. 45-m-thick package composed purely of lenticular clast-supported conglomerates with local lenticular sandstones. Between the conglomeratic phases, a meter-scale package composed of interbedded thin- to medium-bedded sandstone and mudstone deposits is interpreted to drape the entire channel, indicating periods of weaker gravity flows running down the channel, with no evidence of bedload transport.The upper sand-rich unit is divided into lower amalgamated and upper non-amalgamated phases, and represents a rapid architectural change interpreted to record an overall waning of the system. The sandstone unit laps out onto a mass-transport complex which is interpreted to have been triggered initially at the same time as major architectural change from conglomerates to sandstones.While mindful of the fact that each system is a complete analogue only for itself, we propose a new depositional model for coarse-grained submarine channel systems, in which particular characteristics can provide significant insights into architectural heterogeneity and facies transitions in channelized systems, allowing substantial improvement in subsurface facies prediction for fluid reservoirs.

Optimal Adaptive Waveform Design Utilizing an End-to-End Learning-Based Pre-Equalization Neural Network in an UVLC System

Visible light communication (VLC) has emerged as a promising communication method in the special field of 6G, such as intersatellite communication (ISC) and underwater wireless optical communication (UWOC). Green light-emitting diode (LED)-based underwater visible light communication (VLC) is considered a potential candidate for UWOC of mobile autonomous underwater vehicle (AUV) and remotely operated underwater vehicle, particularly in coastal and harbor environments. However, due to bandwidth limitations and variable underwater channels, implementing high-speed underwater VLC remains a challenge. In this paper, a neural network-based auto equalization model (NNAEM) using end-to-end learning is proposed to achieve a high-speed underwater VLC link with a bandwidth-limited green LED. The entire NNAEM includes a neural network-based channel model, a pre-equalization neural network, and a post-equalization neural network. Based on the data-driven channel model, our auto equalization (AE) method can dynamically pre-equalize the discrete multitone (DMT) modulated signal in different bandwidth-limited cases and various nonlinearity cases. An underwater VLC link with a data rate of 3.451 Gbps and a transmission distance of 1.2 m is experimentally demonstrated by employing the proposed NNAEM under the hard decision-forward error correction (HD-FEC) threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> . The data rate improvement is up to 30.4% compared to other advanced digital signal processing (DSP) methods. The scenario adaptation and robustness of the NNAEM are also verified in the experiments, which demonstrate that the NNAEM can serve an important role in underwater high-speed VLC transmission.

Quaternary Evolution of Ischia: A Review of Volcanology and Geology

Ischia shows intriguing and complex geology, which has been deeply investigated. In this paper, a reappraisal of the Quaternary geologic evolution of Ischia based on literature data is advised, concentrating on the volcanology of the island, based on field data and geochemistry, due to the happening of active fumarolic systems on the island and the marine geology and geophysics, which are intensively studied in the frame of the CARG Project. The literature studies have been incorporated with the geological interpretation of high-resolution seismic profiles, partly previously published and herein reorganized with the aim to highlight the geologic evolution of the different sectors of the island (northern Ischia, southern Ischia). The outcrop data have shown the deposits of ten explosive eruptions: among them, we focused on the S. Angelo Tephra. The laccolith model has been described in order to explain the resurgence of Ischia starting from 55 ky B.P. Geochemical information has been synthesized to reconstruct the volcano-tectonic development of Ischia during the last 55 ky B.P. Different models of block resurgence of Ischia have been discussed, based on literature studies. These aspects have supplemented the Quaternary geologic evolution of Ischia. While the northern Ischia offshore shows complex stratigraphic relationships between buried volcanic edifices, the southern Ischia offshore has been mainly commanded by erosional activities, progressive next to a dense system of submarine channels, and by the volcano-tectonic activities, which have triggered off the location of the Ischia Debris Avalanche.

A Traffic-Aware Fair MAC Protocol for Layered Data Collection Oriented Underwater Acoustic Sensor Networks

Underwater acoustic channels are characterized by long propagation delay, limited available bandwidth and high energy costs. These unique characteristics bring challenges to design media access control (MAC) protocol for underwater acoustic sensor networks (UASNs). Especially in data-collection-oriented UASNs, data generated at underwater nodes are transmitted hop-by-hop to the sink node. The traffic loads undertaken by nodes of different depths are different. However, most existing MAC protocols do not consider the traffic load imbalance in data-collection-oriented UASNs, resulting in unfairness in how the nodes transmit their own generated data. In this paper, we propose a novel traffic-aware fair MAC protocol for layered data-collection-oriented UASNs, called TF-MAC. TF-MAC accesses a medium by assigning time slots of different lengths to each layer via different traffic loads to achieve traffic fairness of nodes. To improve throughput and avoid collision in the network, an overlapping time slot division mechanism for different layers and multi-channel allocation scheme within each single layer is employed. Considering the time-varying traffic loads of the nodes, an adaptive packet length algorithm is proposed by taking advantage of the spatial-temporal uncertainty of underwater channels. A sea experiment was conducted to prove the spatial-temporal uncertainty of UASNs, which provides a feasibility basis for the proposed algorithm. Simulation results show that TF-MAC can greatly improve the network performance in terms of throughput, delay, energy consumption, and fairness in the layered data-collection-oriented UASNs.

North Atlantic right whale calls monitoring: Signal processing meets deep learning

The monitoring of marine mammals, such as North Atlantic Right whales (NARW), via their acoustic signatures, can contribute to the protection of these endangered species. The monitoring via passive acoustics, however, may deteriorate, due to the propagation properties of the underwater channel, whereas these signals are susceptible to noise masking and/or mixing as they travel long distances. A day (July 30th, 2018) of NARW annotated recordings (Provided by DCLDE), including seven imbalanced call types, were explored for detection, classification, and density estimation purposes. The call types involved right whale upcall, gunshot, moan, scream, minke whale pulse train, low-frequency pulse, and low-frequency down sweep. Classifying these imbalanced call types represented a real challenge for classical signal processing approaches and conventional deep learning networks (e.g.,Convolutional Neural Networks). The remedy to these challenges involved data preprocessing (spectrogram cleaning/sifting) and the use of a state-of-the-art deep learning transform, self-supervised, that accounts for the imbalances in the dataset. The preprocessed spectrograms boosted the classification score at the deep learning network. The accuracy results for the training set exceeded 90% while the accuracy scored 81% for the testing set.

Sediment gravity flow frequency offshore central California diminished significantly following the Last Glacial Maximum

A high-resolution multibeam survey from a portion of the San Simeon Channel (offshore Morro Bay, California) captured a zone of recurring troughs and ridges adjacent to prominent submarine meander bends. Through an integrated study using surveying data, sediment core analysis, radiocarbon dating, and stable isotope measurements, we hypothesize that turbidity current event frequency was higher during the late Pleistocene than at present conditions. We speculate that the rise in sea-level following the Last Glacial Maximum sequestered sedimentation largely to the shelf during the Holocene. This work suggests that the occurrence of sediment gravity flows in this region, particularly away from any submarine channels, is appreciably lower than at times of continental shelf subaerial exposure.

Stratigraphic evolution of a spectacularly exposed turbidite channel belt from the Tachrift System (late Tortonian, north‐East Morocco)

ABSTRACTThe sedimentary architecture of channelized turbidites can be highly complex as it reflects the response of submarine channels to several interplaying factors. Although intensively investigated through seismic imaging, turbidite channel fills are not convincingly calibrated for sedimentary facies at a sub‐seismic scale. This contribution addresses the sedimentary architecture and the controls on the evolution of a ca 20 m thick channel‐levee complex of the Tachrift turbidite subunit (Upper Miocene, the Melloulou Formation), which accumulated along the southern slope of the Neogene Taza‐Guercif Basin (Rifian Corridor of north‐east Morocco). Facies and architectural analyses indicate that the studied channel‐levee complex is the result of three‐fold evolution. From base to top, it is comprised of: (i) a ca 7 m thick lower mud‐prone interval containing relatively small and vertically stacked channel fills with poorly developed muddy levees; (ii) a ca 4 m thick and &gt;1 km wide sandstone‐rich middle interval made of lateral accretion packages that become progressively less amalgamated and fine‐grained and is overlain by ca 5 m of thin‐bedded mud‐rich turbidites intercalated with hemiplegic marlstones; and (iii) an up to ca 9 m thick upper interval constituted by aggradational channel fills with well‐developed levees and variously directed lateral accretion packages. This organization suggests that, following a phase of inception (lower interval), the channel underwent extensive meandering with very minor vertical aggradation, prior to being blanketed by ‘retrogressive’ muddy lobes (middle interval) during a phase of reduced sediment input. In turn, the uppermost interval records a late phase of channel re‐establishment and aggradation that likely terminated as a result of up‐dip avulsion. It is suggested that the observed change of architectural style reflected the feedback of changing sediment input, slope equilibrium profile and channel morphodynamics.

Artificial Neural Network-Based Transmission Power Control for Underwater Wireless Optical Communication System

Several scientists have proposed using an underwater wireless optical communication system (UWOC) to deliver high-speed data services using the abundant optical spectrum. However, wireless optical signal propagation faces an antagonistic environment when using undersea channels due to various factors like scattering, absorption, turbulence, and optical link misalignment between the transmitter and the receiver. These factors will attenuate the optical signal and lead to degrading system performance. To reduce these factors impact on the communication system's performance, transmitted optical power (OTP) should be increased. Since the UWOC system is battery-powered, increasing OTP will consume more electrical power. Therefore, it is necessary to adjust OTP to a value commensurate with the underwater channel changes. So, an ANN model is proposed in this article for link adaptation, which can adjust the OTP level in tandem with the underwater channel conditions. Data for training, testing, and validation of the proposed system reliability was collected experimentally, and tap water was used as a transmission medium. Evaluation of the proposed model outcome demonstrates that reliable performance is achieved in predicting OTP needed in multiple scenarios. The MSE of the predicted OTP is(9.5×10-3,1.5×10-2, and 1.7×10-2) dBm in the training, testing, and validation stages, respectively. The regression values of the training, testing and validation sets are (0.9997,0.9990, and 0.9996). The results achieved by the proposed model prove it is reliable to be applied in UWOC systems.

Predicting turbidity current activity offshore from meltwater-fed river deltas

Quantification of the controls on turbidity current recurrence is required to better constrain land to sea fluxes of sediment, carbon and pollutants, and design resilient infrastructure that is vulnerable to such flows. This is particularly important offshore from river deltas, where sediment supply is high. Numerous mechanisms can trigger turbidity currents, even at a single river mouth. However quantitative analysis of recurrence and triggers has been limited to an individual trigger for each turbidity current due to the low number of precisely timed (via direct monitoring) flows. We are therefore yet to quantify if and how coincident processes combine to generate turbidity currents, and their relative importance. Here, we analyse the timing and causes of 113 turbidity currents directly-monitored from the source of turbidity current initiation to depositional sink in a single submarine channel. This submarine channel is located offshore from glacial-fed river-deltas at Bute Inlet, a fjord in British Columbia, Canada. Using a multivariate statistical approach, we demonstrate the statistical significance of combined river discharge and tidal controls on turbidity current occurrence during 2018, from which we derive a statistical model that calculates turbidity current probability for any given input of river discharge and water level. This new model predicts turbidity current activity with >84% success offshore other river deltas where flow timing is precisely constrained by directly monitoring, including the Squamish and Fraser River-deltas in British Columbia. We suggest that this model will be applicable for turbidity current prediction at glacial meltwater-fed fjords in many other regions worldwide.

Lateral migration and channel bend morphology around growing folds (Niger Delta continental slope)

AbstractUnderstanding the interactions of submarine channels with seafloor deformations is challenging as these channels more often involve a wide variety of responses relying on both autogenic and allogenic factors. The effect of active growing structures on channel pathways is well documented, but the evolution of lateral migration and the internal architectures along the deflected channel bends around ongoing active structures remain poorly constrained. Here, we use 3D seismic interpretation and quantitative geomorphologic methods to examine the channel bend morphology and the kinematics of lateral migration near gravity‐driven tectonic deformation. Using high‐resolution seismic reflection data acquired from the offshore Niger Delta, two‐channel levee systems (Amaku Major System and Amaku Channel Levee System) have been recognized in the seismic survey. Each system consists of three channel complexes, recording five types of deflected channel bends, defined here as: (i) avulsed bend, (ii) confined bend, (iii) chute cut‐off bend, (iv) blocked bend and (v) kinked bend. Geomorphologic parameters including bend sinuosity, bend amplitude, along‐bend length, straight‐bend length, channel depth and width, were considered within the deflected channels. Lateral migration estimators; channel lateral shift (SH), and channel lateral spacing (CS), were assessed throughout the distances of cross‐sectional channel patterns. The lateral migration estimators (SH and CS) were used to estimate the expression of internal architectures and the evolution of lateral migration around seabed deformation at the scale of the channel complex. The results show that the morphology and internal architecture of the deflected bends, although developing in the same structural context, display varied responses to structural deformation. Unlike previously published models of channel‐fold interactions asserting tectonics as the solitary driver, here we demonstrate that the channel deflections around structures are sensitive to the lateral confinement produced by sediment relief of the outer levees, and the autogenic forcing of channel mechanisms. This study provides new insights into the evolution of submarine channels in active tectonic settings, shows detailed mechanisms of channel bends at a small scale and offers a better understanding of the distribution of sediments in the deep sea.

Detrital zircon U–Pb age constraints on the provenance of submarine channels in Ledong area, Yinggehai Basin, South China Sea

To better understand the provenance and its evolution of the submarine channels of Huangliu and Yinggehai Formation in the Ledong area, the Yinggehai Basin, 200 single detrital zircons from two sandstone samples were collected from submarine channels, and the U–Pb dating was carried out. The results show that the detrital zircon ages from the submarine channel of Huangliu Formation have a narrow range from 78 to 264 Ma with two major age peaks at ca. 96 and 235 Ma, accompanied by two subordinate age peaks at ca. 78 and 159 Ma. In contrast, the detrital zircon ages from the submarine channel of Yinggehai Formation have a wide range from 94 to 3076 Ma with three major age peaks at ca. 95, 235, and 449 Ma, accompanied by five subordinate age peaks at ca. 144, 177, 376, 549 and 801Ma. The characteristics of provenance evolution for submarine channels were furtherly analyzed using 3-MDS and source unmixing methods. The sediments in the submarine channel of Huangliu Formation were originated from the Changhua River, Beili River, Wanglou River, and Ningyuan River in the west of Hainan Island, and their relative contributions for the submarine channel were 65%, 3.5%, 6.4%, and 25.1%, respectively. The sediments in the submarine channel of Yinggehai Formation were provided with mixed source by the Red River, Wanglou River, and Ningyuan River, and their relative contributions for the submarine channel were 82.6%, 4.3%, and 13.1%, respectively. The transition of submarine channel provenance from near source of Huangliu Formation to distant source of the Yinggehai Formation may be due to the uplift of the Tibet Plateau during Pliocene.

Experimental demonstration of real-time optical DFT-S DMT signal transmission for a blue-LED-based UWOC system using spatial diversity reception.

Underwater wireless optical communication (UWOC) has broad prospects in underwater real-time applications. We design and experimentally demonstrate a real-time discrete Fourier transform spread discrete multi-tone (DFT-S DMT) signal transmission based on a field programmable gate array for a blue-LED-based UWOC system with a data rate of up to 30Mbps over a 15-m underwater channel. The architecture and usage of an on-chip resource as well as power consumption are analyzed and discussed. To reduce the impacts of multipath fading and received intensity fluctuation, spatial diversity reception is also introduced. Furthermore, the receiver sensitivity at a specified bit error rate (BER) threshold and the quality of the images are evaluated using three types of Reed-Solomon (RS) codes. At the BER threshold of 10-4, over 2.8-dB receiver sensitivity improvement is obtained by the DFT-S DMT scheme with the RS (64, 56) code as compared to the uncoded one at the data rate of 30 Mbps. The performance of BER, color difference, and structural similarity in the image transmission of DFT-S DMT is superior to that of the conventional hard clipping quadrature amplitude modulation DMT in a high-data-rate region because of the low peak-to-average-power ratio and ability to mitigate high-frequency fading in a band-limited UWOC system. With schemes of the RS code, DFT-S, and diversity reception, error-free transmission of images is achieved over a 15-m water channel. The proposed UWOC system has the advantages of low power consumption and portability, which foresees a bright future in underwater applications over short to moderate distances.

Investigation of an underwater clock and data transmission optical wireless link at 650 nm for robotic oriented geodesy applications

Underwater geodesy is important for marine studies and seafloor mapping. These studies typically make use of the time of flight, for example SONAR, and collect a lot of data. Furthermore, high map densities require big data collection and transportation, and therefore require high bandwidth underwater networks. In this article, we propose and demonstrate an underwater optical network based on a directly-modulated laser at 650 nm that enables the deployment of underwater robotic systems which are capable of transferring the captured data to a base station and allow the synchronization of the clocking signals. As proof of concept, we demonstrated a unipolar NRZ data transfer from an Arduino at 2 Mbps through an underwater channel measuring about 1 meter in length. A bit error rate value of about 10 − 5 for underwater data transmission was realised by the designed optical network, showcasing its potential for use in underwater data transfer during robotic geodesy surveys. Recovery of the clock signal from the signal generator at 2 kHz was also shown. Phase noise floor values below −90 dBc/Hz were attained for the underwater clock signal transmission.