Underwater Particles Research Articles

Breakthrough Underwater Physical Environment Limitations on Optical Information Representations: An Overview and Suggestions

Underwater optics have seen a notable surge of interest in recent years, emerging as a critical medium for conveying information crucial to underwater resource exploration, autonomous underwater vehicle navigation, etc. The intricate dynamics of underwater optical transmission, influenced by factors such as the absorption by the water and scattering by multiple particles, present considerable challenges. One of the most critical issues is that the optical information representation methods fail to take into account the impact of the underwater physical environment. We conducted a comprehensive review and analysis of recent advancements in underwater optical transmission laws and models. We summarized and analyzed relevant research on the effects of underwater particles and turbulence on light and analyzed the polarization effects in various environments. Then, the roles of various types of underwater optical propagation models were analyzed. Although optical models in complex environments are still mostly based on Monte Carlo methods, many underwater optical propagation mechanisms have been revealed and can promote the impacts of optical information expression. We delved into the cutting-edge research findings across three key domains: the enhancement of underwater optical image quality, the 3D reconstruction from monocular images, and the underwater wireless optical communication, examining the pivotal role played by light transmission laws and models in these areas. Drawing upon our extensive experience in underwater optics, including underwater optical sensor development and experiments, we identified and underscored future directions in this field. We advocate for the necessity of further advancements in the comprehension of underwater optical laws and physical models, emphasizing the importance of their expanded application in underwater optical information representations. Deeper exploration into these areas is not only warranted but essential for pushing the boundaries of current underwater optical technologies and unlocking new potential for their application in underwater optical sensor developments, underwater exploration, environmental monitoring, and beyond.

Window-based transformer generative adversarial network for autonomous underwater image enhancement

The estimation of high-quality underwater images is an important step towards the development of computer vision systems in marine environments. This fundamental step contains numerous computer vision and robotics applications including marine exploration, robotics manipulation, navigation, object detection, tracking, and sea life monitoring. However, this pre-processing step becomes more challenging in the presence of back-scattering of underwater particles and attenuation issues, which lead to the formation of hazy underwater images. Vision transformers have recently demonstrated outstanding performance in many computer vision applications. Window-based Transformers (WT) show promising enhancement performance by computing self-attention within non-overlapping local windows. WT has been identified as an essential component in improving representation capabilities; however, it has received less attention in improving the performance of Underwater Image Enhancement (UIE). Therefore, we propose a novel end-to-end Underwater window-based Transformer Generative Adversarial Network (UwTGAN). Our proposed algorithm consists of two main components, including a transformer generator that generates a restored underwater image and a transformer discriminator that classifies the generated underwater image. Both components are equipped with Window-based Self-Attention Blocks (WSABs), which maximize efficiency by limiting self-attention computation to non-overlapping local windows and provide relatively low computational costs. WSAB-based transformer generators and discriminators are trained end-to-end. We formulated an efficient loss function to ensure that the variables are closely integrated. Extensive experimental evaluations are performed on four independent underwater image datasets. Our results demonstrate that the proposed UwTGAN algorithm has outperformed several state-of-the-art UIE methods in terms of both quantitative and qualitative metrics by a significant margin.

A Depth‐Averaged Description of Submarine Avalanche Flows and Induced Surface Waves

AbstractThis paper develops a depth‐averaged theory to investigate submarine landslides and resulting water waves. The problems here consist of a pure fluid regime and a mixture regime of grains and fluid. Both regimes separate from one another by an interface, which is a material surface for grains. While the downslope velocities of the both phases are assumed to be identical in the mixture regime, the velocity shear causes a rearrangement of grains, which induces a vertical relative motion between the phases. The established theory consists of five coupled conservation equations, which describe the evolution of the pure fluid thickness, the mixture thickness, the solids volume fraction, and depth‐averaged velocities. To handle nonconservative products emerging in the equations, a new coordinate system is introduced to rewrite the equation system in an equivalent form, so that numerical solutions are insensitive to the choice of discretization of nonconservative products, which enables us to accurately characterize the dynamic behaviors of particles in the collapse experiments of underwater particles and describe free‐surface wave profiles. It is shown that the computed results are in good agreement with the experiments reported in previous literatures.

Polarization Reconstruction Algorithm of Target Based on the Analysis of Noise in Complex Underwater Environment

How to effectively eliminate interference such as scattering, absorption, and attenuation is a hot topic of underwater photoelectric detection at present. Around the hot issues, this paper carries out studying the method of polarization-imaging recovery in a dynamic complex underwater environment from the theory of underwater radiation transfer, and numerical simulation of imaging interference characteristics to the simulation of underwater environment experiment. First, by conducting the analysis and simulation of scattering characteristics of underwater suspension particles and bubble by using the theory of radiation transfer, and taking advantage of quantitative description on changing tendency of radiation intensity and polarization properties of light waves in turbid water under the condition of scattering interference. Second, by constructing an underwater target polarization reconstruction model on the basis of the Mueller matrix analysis, and taking target polarization characteristic into reconstruction model on the basis of classical Schechner’s model, automatically estimating polarization information of target by the method of covariance. Finally, by building a polarization imaging system in the simulated complex underwater environment that contains bubble and suspended particles, obtaining reconstructed results with different underwater environments and different materials of target. According to experiment results, and compared with other traditional methods, using the proposed method in this paper can get higher resolution and higher contrast of target in the reconstructed result.

Modified Restoration Technique for Improved Visual Perception of Shallow Underwater Imagery

Images captured underwater often suffer from quality degradation such as low contrast, non-uniform illumi-nation, etc. due to the attenuation and backscattering of light by suspended underwater particles. To over-come this, restoration-cum-enhancement techniques are necessary. Here we present the modified under-water light attenuation prior (MULAP) model using supervised linear regression model to restore the degraded image. The image formation model (IFM)-based restoration depends on dual factors: back-ground light and transmission map.Initially, datasets are collected on the close-range point-of-interest. Then, experimental analyses are carried out for those images using the IFM-based methods. For the above techniques, both subjective analysis and objective analysis are done by considering dual metrics such as universal quality index and visual information fidelity factor. Finally, the proposed MULAP shows over-whelming qualitative and quantitative results among other state-of-the-art techniques.

Analysis of the polarization characteristics of scattered light of underwater suspended particles based on Mie theory

Aiming at the problem of underwater polarized laser scattering caused by underwater suspended particles, the equivalent spherical particle Mie scattering theory simulation method is used to study the polarization characteristics of underwater scattered light. The relationship between underwater suspended particle characteristics and optical characteristics is analyzed, and the effects of particle size, polarization characteristics of incident light, and angle of incidence on the degree of polarization of forward and backward scattering light are studied. The results show that: When the incident light is natural light, the degree of polarization of scattered light is very low at the forward-scattering angle, which increases with the increase of the scattering angle, but changes frequently with the increase of the particle size. When the incident light is linearly polarized, the degree of linear polarization of the scattered light is related to the azimuth Angle. The degree of circular polarization is largely unaffected by particle size.

Buckling-induced reconfigurability in underwater acoustic scatterers

In this work, we explore switchable acoustic scattering from underwater particles via instability-induced internal pattern transformation in the 50 kHz–80 kHz frequency range. Our wavelength scale aqueous scatterer is designed based on modeling using the finite element method for a square lattice of air-filled voids within a shape memory polymer and is directly 3D printed. The structure undergoes a buckling transformation when subjected to an external deformation while simultaneously being heated. Through computational and experimental results, we demonstrate that the deformation state change leads to programmable acoustic transparency, or opacity, for the scattering particle. Underwater propagation experiments resolved in the near field illustrate that the switchable acoustic characteristics are frozen in the structure with rapid cooling after compression, and the initial acoustic state can be automatically recovered through reheating.

Enhancement of Underwater Images using Color Balancing and Multi-Scale Fusion Technique

The method proposed in this paper is efficient and does not need any external hardware nor does it need information regarding the conditions and structure of the scene which is to be enhanced after being captured in underwater as it is a degraded image due to presence of scattering and absorption intensity due to underwater particles and light. Two images, which are obtained after white balancing and color compensation of the degraded input image, are combined and the weight maps of the two images help in enhancement of edges and color contrast of the final output image. The creation of weight maps lead to the low frequency component of the recombined image having artifacts in it. Multiscale fusion technique has also been adopted in this paper. On making a comparative analysis, it was observed that the proposedmethod leads to enhancement of underwater images and videos in such a way that the dark regions exposition is improved, global contrast is better and edges are sharper.

An Improved Accurate Solver for the Time-Dependent RTE in Underwater Optical Wireless Communications

Underwater optical wireless communication (UOWC) has been widely advocated as a viable way to satisfy these high-speed links constraints in the marine medium through the use of the visible spectrum. Nevertheless, UOWC faces several limitations, such as the path-loss due to the absorption and scattering phenomena, caused by underwater particles. Thus, quantifying this path-loss is of paramount importance in the design of futuristic UOWC systems. To this end, several approaches have been used in this regard, namely the Beer–Lambert’s law, Monte Carlo simulation, as well as radiative transfer equation (RTE). This last mentioned evaluates the optical path-loss of the light wave in an underwater channel in terms of the absorption and scattering coefficients as well as the scattering phase function (SPF). In this paper, an improved numerical solver to evaluate the time-dependent RTE for UOWC is proposed. The proposed numerical algorithm was improved based on the previously proposed ones, by making use of an improved finite difference scheme, a modified scattering angular discretization, as well as an enhancement of the quadrature method by involving a more accurate seven-point quadrature scheme in order to calculate the weight coefficients corresponding to the RTE integral term. Importantly, we applied the RTE solver to three different volume scattering functions, namely the single-term Henyey–Greenstein (HG) phase function, the two-term HG phase function, and the Fournier–Forand phase function, over both Harbor-I and Harbor-II water types. Based on the normalized received power evaluated through the proposed algorithm, the bit error rate performance of the UOWC system is investigated in terms of system and channel parameters. The enhanced algorithm gives a tightly close performance to its Monte Carlo counterpart by adjusting the numerical cumulative distribution function computation method as well as optimizing the number of scattering angles.

Real-time underwater image enhancement: An improved approach for imaging with AUV-150

An RGB YCbCr Processing method (RYPro) is proposed for underwater images commonly suffering from low contrast and poor color quality. The degradation in image quality may be attributed to absorption and backscattering of light by suspended underwater particles. Moreover, as the depth increases, different colors are absorbed by the surrounding medium depending on the wavelengths. In particular, blue/green color is dominant in the underwater ambience which is known as color cast. For further processing of the image, enhancement remains an essential preprocessing operation. Color equalization is a widely adopted approach for underwater image enhancement. Traditional methods normally involve blind color equalization for enhancing the image under test. In the present work, processing sequence of the proposed method includes noise removal using linear and non-linear filters followed by adaptive contrast correction in the RGB and YCbCr color planes. Performance of the proposed method is evaluated and compared with three golden methods, namely, Gray World (GW), White Patch (WP), Adobe Photoshop Equalization (APE) and a recently developed method entitled “Unsupervised Color Correction Method (UCM)”. In view of its simplicity and computational ease, the proposed method is recommended for real-time applications. Suitability of the proposed method is validated by real-time implementation during the testing of the Autonomous Underwater Vehicle (AUV-150) developed indigenously by CSIR-CMERI.