Search Results (40)

Traditional approaches for monitoring aquatic organic carbon, such as satellite remote sensing and automated underwater sensors, are often constrained by limited temporal resolution, data gaps under cloudy conditions, maintenance requirements, and cost-effectiveness. To overcome these limitations, we developed and field-demonstrated a ground-based hyperspectral remote sensing system (GHRSS) for continuous, high-frequency monitoring of dissolved organic carbon (DOC) and particulate organic carbon (POC). The system is based on the above-water method and integrates three miniature hyperspectral spectrometers to measure water-surface radiance, sky radiance, and downwelling irradiance for deriving hyperspectral remote sensing reflectance ($R_{rs}$). The spectrometers cover 400–900 nm with a spectral resolution of 1 nm and support a minimum sampling interval of 10 s. The GHRSS also integrates solar power supply, 4G communication, and a microcomputer, enabling autonomous long-term deployment and wireless data transmission. Based on the GHRSS, retrieval models for DOC and POC were developed and validated using 90 paired in situ measurements collected from the Cao’e River. Empirical and machine learning methods were applied to retrieve DOC and POC from the measured $R_{rs}$ data. The empirical models showed limited retrieval performance, whereas partial least squares regression (PLSR) and support vector regression (SVR) substantially improved model accuracy. Among all models, SVR achieved the best performance on the independent test set, with $R^2=0.979$, RMSE = 0.031 mg/L, and MAE = 0.024 mg/L for DOC and $R^2=0.960$, RMSE = 0.152 mg/L, and MAE = 0.066 mg/L for POC. Using the optimal SVR models, minute-scale time series of DOC and POC were reconstructed from the GHRSS observations. The results revealed pronounced sub-daily variability in both parameters, with DOC varying relatively smoothly, whereas POC exhibited stronger short-term fluctuations and more rapid responses to hydrodynamic changes. These findings demonstrate that the GHRSS, combined with machine learning models, provides an effective and practical approach for continuous, high-frequency monitoring of riverine organic carbon dynamics. Full article

Accurate modeling of irradiance scintillation is important for evaluating underwater wireless optical communication (UWOC) systems operating in oceanic turbulence. Existing studies have mainly focused on weak oceanic turbulence conditions, while irradiance scintillation modeling under arbitrary oceanic turbulence strength remains insufficiently developed. In this work, the Gaussian beam is adopted as the representative model of practical laser beams, whereas the plane-wave and spherical-wave cases are introduced as limiting cases to support the derivation and theoretical completeness of the Gaussian-beam formulation. A unified theoretical framework is developed based on the general oceanic turbulence optical power spectrum (OTOPS). Building upon previously reported weak-turbulence results, the scintillation index (SI) under saturated strong turbulence is first derived using asymptotic theory. Then, within the extended Rytov approximation, an effective-scale treatment is introduced to characterize the contributions of large- and small-scale eddies to irradiance fluctuations. By connecting the weak- and saturated-turbulence limits through asymptotic matching, a closed-form SI expression valid over a wide range of oceanic turbulence strengths is obtained. Numerical results show that the proposed model agrees well with the corresponding boundary cases and reproduces the characteristic “bump” behavior of oceanic turbulence, while highlighting the influence of ocean-specific cutoff spatial frequencies on the predicted scintillation peaks. These results provide a physically consistent analytical framework for UWOC channel modeling and performance evaluation under arbitrary oceanic turbulence strength. Full article

This work presents a novel one-step plasma–solution synthesis of Prussian Blue (PB) and copper hexacyanoferrate (Cu-PBA) nanoparticles via underwater pulsed DC discharge. For the first time, the direct plasma-assisted formation of these coordination polymers is reported. The obtained materials were examined by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy (SEM). These analyses confirmed that the desired phases had formed, along with small amounts of oxide byproducts (α-Fe₂O₃, CuO) arising from the erosion of the electrodes. Photocatalytic activity was evaluated through the degradation of organic dyes (Reactive Red 6C, Rhodamine B, and Methylene Blue) under UV-light irradiation. Both catalysts achieved complete dye degradation within 90 min of UV irradiation (after an initial 30 min dark adsorption step, total experiment time 120 min). Notably, selective performance was observed: PB exhibited higher activity toward the cationic dye Methylene Blue, while Cu-PBA was more effective for the anionic dye Reactive Red 6C. This selectivity is attributed to the specific oxide impurities forming heterojunctions that facilitate charge separation and generate distinct reactive oxygen species. The plasma–liquid method offers a rapid and environmentally benign route to functional PBA-based composites, with potentially scalable characteristics pending further engineering optimization. These findings highlight the potential of utilizing synthesis-induced impurities to tailor photocatalytic selectivity for water purification applications. Full article

In this paper, we present one-pot methods for synthesizing β- and g-C₃N₄ composites with titanium and copper oxides using underwater plasma and solution combustion techniques. The resulting structures were characterized using a range of complementary analytical methods. Analysis revealed that solution combustion produces composites containing mixed-phase titanium dioxide and Cu₄O₃, whereas plasma incorporation results in the integration of Cu and Ti ions, forming a composite based on copper oxide and copper titanate. These composites were successfully evaluated for the photocatalytic degradation of a mixture of three dyes under both UV and visible light irradiation. Composites synthesized via solution combustion exhibited remarkable photocatalytic activity toward all three dyes. The rates of photodecomposition of dyes in the presence of composites are 1.5–2.5 times higher compared to pure C₃N₄. Furthermore, all composite materials demonstrated high stability in photocatalytic performance after six cycles. Full article

In the marine environment, numerous factors endanger the preservation of underwater rock surfaces as well as submerged archeological artifacts, including physical, chemical, and biological processes. Limestone and marble are common materials used in artifacts due to their availability and long-term durability. However, such surfaces provide a suitable substrate for the settlement of micro- and macro-organisms, causing so-called biofouling, which significantly contributes to stone deterioration. Previous studies have demonstrated the applicability of antifouling coatings containing ionic liquids (ILs) on marble surfaces and assessed their durability for up to 15 days under submerged environments. To further corroborate these results, additional physical studies (colorimetric, contact angles, capillarity water absorption measurements, and UV aging) were carried out on treated limestone. Washout tests were also performed on both lithotypes to verify the coatings’ stability under medium-term underwater exposures. The results of these investigations are reported here. Our data confirm that the application of IL-based coatings had no effect on the intrinsic properties of the limestone surfaces, as previously reported for marble, including resistance to daily UV irradiation. In addition, laboratory tests demonstrated good coating durability against seawater erosive action for up to 6 months. Full article

Oily wastewater poses severe ecological and health threats, but conventional separation technologies have limitations like low efficiency or high energy consumption. Herein, two superwettable carbon fiber (CF)-based membranes were fabricated for efficient oil–water separation. Using CF (low cost, excellent mechanical stability) as the substrate, Cu-TiO₂@CF (superhydrophilic/underwater superoleophobic, renewable) was prepared via a deep ultraviolet (DUV)-assisted sol–gel method, and OTMS/Cu-TiO₂@CF (superhydrophobic/superoleophilic) was obtained by modifying Cu-TiO₂@CF with octadecyltrimethoxysilane (OTMS) via hydrothermal synthesis. Characterization showed Cu-TiO₂ coatings uniformly covered CF, with strong substrate bonding. Both membranes exhibited outstanding performance: Cu-TiO₂@CF achieved water fluxes of up to 79,839.6 L·m⁻²·h⁻¹ and >97.3% separation efficiency for four oil–water mixtures; OTMS/Cu-TiO₂@CF had a maximum oil flux of 86,593.4 L·m⁻²·h⁻¹ and >98.1% efficiency. Cu-TiO₂@CF regenerated via 10 min UV irradiation (restoring underwater oil contact angle to 153°), while OTMS/Cu-TiO₂@CF achieved recovery through the process of UV irradiation followed by OTMS re-modification. Both membranes maintained stable performance over 100 cycles, demonstrating considerable potential for engineering applications. Full article

This paper is a result of the search for design assumptions for a sensor to detect oil dispersed in the sea waters (oil-in-water emulsions). Our approach is based on analyzing changes in the underwater solar radiance (L) field caused by the presence of oil droplets in the water column. This method would enable the sensor to respond to the presence of oil contaminants dispersed in the surrounding environment, even if they are not located directly at the measurement point. This study draws on both literature sources and the results of current numerical modeling of the spread of solar light in the water column to account for both downward and upward irradiance (Es). The core principle of the analysis involves simulating the paths of a large number of virtual solar photons in a seawater model defined by spatially distributed Inherent Optical Properties (IOPs). The IOPs data were taken from the literature and pertain to the waters of the southern Baltic Sea. The optical properties of the oil used in the model correspond to crude oil extracted from the Baltic shelf. The obtained results were compared with previously published spectral analyses of an analogous polluted sea model, considering vertical downward radiance, vertical upward radiance, and downward and upward irradiance. It was found that the optimal wavelength ratio of 555/412, identified for these quantities, is also applicable to scalar irradiance. The findings indicate that the most effective way to determine this index is by measuring it using a sensor with its window oriented in the direction of upward-traveling light. Full article

As an environmentally friendly and clean energy technology, solar-driven interfacial evaporation technology has attracted wide attention. However, organic pollutants can easily pollute distilled water during the evaporation of wastewater. In this work, we report a strategy of N-TiO₂/C solar absorption with a low bandgap (2.33 eV), excellent light absorption ability, and high photothermal conversion efficiency (48.2%). Black N-TiO₂/C was prepared by the sol-gel method in the presence of hexamethylenetetramine as a source of nitrogen and carbon. The simultaneous N doping and C with superior photothermal effect rapidly increased the surface temperature of the material, reduced the recombination rate of electrons and holes, and improved the photocatalytic activity, showing great potential for solar thermal energy conversion. The prepared solar absorbent and polyurethane (PU) were mixed evenly to form a porous N-TiO₂/C/PU (NTCP) foam for purifying water. The evaporator produced clean water at a rate of 1.73 kg m⁻² h⁻¹ under the simulated sunlight of 1 sun irradiation. Meanwhile, the evaporator simultaneously photodegraded methylene blue (MB) and rhodamine B (RhB) underwater at a removal rate > 90%. The bifunctional solar water evaporation device combining photocatalytic and photothermal effects holds great potential for water purification. Full article

Hyperspectral payloads with high spatial and spectral resolution, combined with a wide field of view, are crucial for tackling the complexity of coastal and estuarine water ecosystems, enabling effective monitoring of water quality and ecological conditions. This study introduces a modular spectrometer design utilizing multiple sub-modules in an extended slit configuration. The system delivers a spectral resolution of 5 nm (400–1000 nm) and 10 nm (1000–2500 nm), a spatial resolution of 20 m, and a swath width of 80 km. Smile and keystone distortions are maintained below 1/5 of a pixel. Using Modran to simulate solar irradiance, the SNR of different targets under typical background conditions is calculated. Compared to conventional designs, the proposed modular approach provides compactness and high fidelity, effectively addressing size and optical aberration challenges. The simulation results confirm the system’s robustness, setting a benchmark for next-generation coast observation missions, particularly in coastal monitoring, underwater exploration, and dynamic environmental change tracking. Full article

Ultraviolet (UV) radiation effects on Earth’s ecosystems on a global scale can be assessed on a basis of satellite estimates of hyperspectral irradiance on the surface and in ocean waters and the spectral biological weighting functions. The satellite UV surface irradiance algorithms combine satellite retrievals of extraterrestrial solar irradiance, cloud/surface reflectivity, aerosol optical depth, and total column ozone with radiative transfer computations. The assessment of in-water irradiance requires additional information on inherent optical properties (IOPs) of ocean water. Our Ozone Monitoring Instrument (OMI) surface hyperspectral irradiance algorithm is updated by implementing a new absorbing aerosol correction based on OMI daily retrievals of UV aerosol absorption optical depth (AAOD). To provide insight into the temporal and spatial variability of absorbing aerosols, we consider a monthly global AAOD climatology derived from the OMI UV aerosol algorithm. Hyperspectral underwater irradiance is computed using Hydrolight radiative transfer calculations along with a Case I water model of IOPs extended into UV. Both planar and scalar irradiances are computed on the Earth’s surface and propagated underwater. The output surface products include the UV index. The output underwater products include the hyperspectral diffuse attenuation coefficients of the planar and scalar irradiances. Effects of the seasonal variability of AAOD on the UV index and the deoxyribonucleic acid (DNA) damage dose rates are considered. The reduction in the UV index and DNA damage dose rate due to the presence of absorbing aerosols can be as large as 30–40%. Full article

In this paper, InSe nanosheets were synthesized by a ball milling method, and photoelectrochemical-type photodetectors (PEC PDs) based on the ball milling InSe (M-InSe) were fabricated using simulated seawater as the electrolyte. M-InSe nanosheets show good absorption in the visible region of 450–600 nm. The M-InSe PEC PDs display a good self-powered photoresponse under 525 nm irradiation, including a high responsivity of 0.8 mA/W, fast response time of 28/300 ms, and good stability. Furthermore, the InSe PEC PDs successfully demonstrated prototype application in wireless underwater optical communication and optical imaging. These results demonstrate that M-InSe holds good application prospects in underwater optoelectronic devices. Full article

Mobile microrobots are of great scientific significance. However, external actuation and control methods are still challenging to conduct. We present a single carbon nanocoil (CNC) microrobot induced by an NIR laser beam, capable of light-driven locomotion and photothermal actuation. This research demonstrates that CNC-based microrobots roll away from the focal spot when the laser beam is focused near the CNC. The maximum translational distance of a CNC microrobot increases with an increase in laser power, and the direction of motion is guided by controlling the focusing position of NIR. CNC-based microrobots can load and transport multiple cells under NIR light irradiation, resulting from the temperature gradient generated by photothermal conversion, which causes thermophoresis. The hydrophobic surface and unique helical structure of CNCs are beneficial to the underwater drag reduction in CNC microrobots’ motion and the adhesion of cells on CNC microrobots. Therefore, CNC microrobots, as cell vectors driven by a laser beam, may find applications in a wide range of biomedical applications. In addition, the rotation of a CNC powered by a laser beam provides promising prospects for the future of nanomechanical devices using a carbon nanocoil as a micro/nanomotor. Full article

Underwater spectral detection plays an important role in the study of the underwater environment, ecology, oceanography, and environmental monitoring. A kind of underwater spectral radiometer that can observe the distribution of underwater spectral radiation bidirectionally has been developed. The flat-field concave holographic grating is used as the only optical component, the optical design parameters are optimized, and the system is miniaturized. The mechanism of stray light generation in the spectrometer is studied, and a method of suppressing stray light is proposed and simulated. The level of stray light in the system is suppressed to the order of 10⁻⁴, the signal-to-noise ratio of the system is improved, and the ability to detect weak light is enhanced. The wavelength calibration experiment was completed, and the experimental results show that the wavelength resolution of the underwater spectral radiometer is better than 3 nm. Finally, the quantitative relationship between spectral irradiance and digital output is obtained through radiation in the calibration of the system. Full article

Optical wireless power transmission (OWPT) attracts attention because it enables wireless power transfer over longer distances than current wireless power transfer methods, irradiating laser light to a light-receiving element. In this study, an OWPT system was investigated under water and deep seawater using visible lasers with low optical absorption loss in water. Three laser beams (450 nm, 532 nm, and 635 nm) were transmitted through 30 cm, 60 cm, and 90 cm long tanks filled with tap water and deep seawater and were irradiated to 1.0 × 1.0 cm² GaInP solar cells. The light reaching rate (η_op) of laser light and the system efficiency (η_sys) of the system (excluding the laser efficiency) were investigated. GaInP solar cells showed photo-electric conversion efficiencies of 30.6%, 40.3%, and 39.3% for 450 nm, 532 nm, and 635 nm irradiations, respectively. As a result, a 532 nm laser through a 90 cm water tank in tap water showed a 78.4% η_op and a 30.8% η_sys. Under deep seawater, a 532 nm laser through a 90 cm tank exhibited a 58.3% η_op and a 23.5% η_sys. A 532 nm green laser showed a higher efficiency than the other 450 nm and 635 nm lasers in this underwater system using GaInP solar cells. Full article

The development of sustainable alternatives to chemical and mechanical biofilm removal for submerged technical devices used in freshwater and marine environments represents a major technical challenge. In this context, the antibiotic impact of blue light with its low absorption underwater provides a potentially useful alternative. However, former technical limitations led to hours of treatment. Here, we applied high-power blue laser irradiation (1500 W) with a wavelength of 448 nm to demonstrate its strong antibiotic and algicidal effect on different bacteria and algae in seconds. High-power blue light treatment (139 W/cm²) for only 8.9 s led to the efficient deactivation of all tested organisms. Analyses of the underlying biological mechanisms revealed the absorption of the blue light by endogenous chromophores (flavins, tetrapyrroles) with the generation of reactive oxygen species (ROS). In agreement, Escherichia coli transcriptome analyses demonstrated a stress response at the level of DNA damage repair, respiration, and protein biosynthesis. Spectroscopic measurements of the irradiated algae indicated the irreversible damage of chlorophyll by photooxidation with the formation of singlet oxygen. In conclusion, high-power blue laser radiation provides a strong sustainable tool for the removal of biofouling in a very short time for applications in aquatic systems. Full article