In recent years, the environmental effects of both active and legacy mining activity have motivated many research groups worldwide through the use of a variety of methods that have been conducted among diverse environments. In this study, we measured radionuclide concentrations at two coastline locations of the Northern Aegean Sea: Stratoni and Ierissos. We deployed KATERINA II, an in situ gamma ray spectrometer. Our results indicate that the activity concentration for ²³⁸U progenies (²¹⁴Bi), ²³²Th progenies (²⁰⁸Tl and ²²⁸Ac) and ⁴⁰K vary by up to (33 ± 4) Bq kg⁻¹, (19 ± 3) Bq kg⁻¹, and (420 ± 30) Bq kg⁻¹, respectively. The activity concentration of the ¹³⁷Cs in Stratoni and Ierissos beach sands were (8.1 ± 2.2) and (3.9 ± 1.2) Bq kg⁻¹, respectively. Lab-based measurements were also collected prior to the in situ data collection for the determination of radionuclide and metal concentrations. The lab-based data were found to be (800 ± 40) μg g⁻¹ and (12 ± 1) μg g⁻¹, for As, (1200 ± 60) μg g⁻¹ and (33.3 ± 0.3) μg g⁻¹ for Pb, (100 ± 6) μg g⁻¹ and (6.0± 0.3) μg g⁻¹ for Cu and (2000 ± 60) μg g⁻¹ and (8.0 ± 0.4) μg g⁻¹ for Zn, respectively. We used the R language and environment for statistical computing to produce radiological maps of the subject beach sands. We used the Enrichment Factor (EF) to estimate assessment indices for the target area and compared them to internationally recommended values. The in situ maps will be discussed since the beach area of the load-out pier area of Stratoni was undergoing the first phase of active remediation. We conclude that the temporal aspect of this dataset can be of significant reference value against future comparative studies after the remediation of the Stratoni beach with potentially denser spatial and temporal data coverage. Full article

In this study, a thermal spring located in the Gulf of Gera (Lesvos Island) is investigated in terms of radiotracers, water flow velocities and acoustic back-scattering properties by in situ observations. Water flow characteristics were deduced using in situ deployments of three marine sensors: an Acoustic Doppler Velocimeter (ADV), a High-Frequency Acoustic Doppler Current Profiler (ADCP), and a medium-resolution underwater gamma-ray detection system. The flow velocity combined with the activity concentration of natural radionuclides in the thermal spring provided information on the characteristics of the thermal spring in the specific gulf. The proposed methodology estimated the water supply, the residence time in the effective area of the in situ systems, and the residence time in the gulf. Eventually, the estimation of the characteristics of the discharged water source resulted from the synthetic evaluation of oceanographic measurements alongside appropriate models. Full article

Sedimentation can cause numerous problems in rivers, estuaries, harbors, and coastal areas. It is therefore important to trace and model the movement of sediments. The natural physical, chemical, and biological components of the aquatic sediment generally relate to these features in its terrestrial catchment area. It consequently contains the naturally occurring radionuclides of thorium, uranium, and potassium, which can be used as tracers. To achieve this aim, a delta underwater gamma system (DUGS) was developed to map the radionuclides in aquatic sediments. Though the system has been tested for radiometric accuracy, the low concentrations of natural radionuclides in aquatic sediments and the attenuation by the water and detector enclosure necessitated an evaluation to determine the detection efficiency of the detector along with optimal operational parameters. These included spectra accumulation time and underwater speed. The DUGS was consequently used to determine and optimize these parameters for mobile measurement of aquatic sediments. The acquired gamma spectra were also analyzed using full spectrum and energy window analysis to determine the optimal method for extracting the activity concentrations of the nuclides in the sediments. Full article

Advanced marine observation infrastructures are the most significant scientific tool for the study of marine ecosystem trends and shifts. Ocean monitoring technologies, though highly demanding and expensive, are essential for the monitoring and long-term study of oceanic systems. The POSEIDON system for monitoring and forecasting the marine environment is an augmented research infrastructure, unique in the Eastern Mediterranean basin, contributing to the European Ocean Observing System implementation, focusing—among others—on biogeochemical observations and deep-sea ecosystem and geological processes. The technological evolution of the POSEIDON system through a science-coupled strategy supported by engineers and scientists, resulted in a state-of-the-art ocean observing system. There has been a continuous expansion of the infrastructure with new scientific platforms and supporting facilities. Innovative sensing technologies were introduced in the operational data acquisition and new methodologies and tools were developed to improve the system operations and efficiency. As a part of the scientific community of ocean observatories, POSEIDON contributes actively to the improving of the ocean observing. International access to engineering and field demonstrating services, data products and technology testing facilities has been offered to scientists and industry partners. POSEIDON is a widely recognizable international technology testing/demonstrating node specializing in marine technology providing high-level services. Full article

Effective testing of new sensing technologies requires realistic yet deterministic test ranges. The advancements in customizable, adaptive unmanned surface vessels (USV) have contributed to the increasing presence of USVs completing maritime site characterizations of test ranges using commercial off-the-shelf (COTS) sensors such as the Tritech Starfish 990F side-scan sonar. This paper aims to present recommendations for the electromechanical integration of a COTS sonar system onto a capable USV through passive techniques such that underwater objects within the littoral zone of Sand Island, Hawaii, are characterized. Results demonstrated a 49% improvement in the sonar images. Therefore, designers are recommended to fully isolate the sensing system from the USV, physically separate the sonar and USV components, and to establish a baseline performance for the system prior to operation. Full article

Affected by the Taiwan Strait Warm Current, the evaporation intensity around the Taiwan Strait is significantly higher than in other southern and eastern coastal areas of China. To explore a new and effective method for maritime communication across the Taiwan Strait, we present a preliminary investigation of wireless microwave transmission in an evaporation duct. From 9 to 14 o’clock, the percentage of the evaporation duct height exceeding 10 m reached over 90% in 2020. With the favorable channel in this period, a “straight-through propagation channel” emerged, with a serviceable ratio of 99.00% at a 300 km transmission range. The high-quality transmission with BPSK modulation occurred 98.90% of the year from 12 to 13 o’clock, with 89.89% of the signal-to-noise ratio (SNR) exceeding 90 dB. Based on the effective use of the evaporation duct, the proposed method can provide favorable support for maritime applications across the Taiwan Strait. Full article

To minimize the major decline in direction of arrival (DOA) estimation performance for an acoustic vector sensor array (AVSA) with the coexistence of axial deviation and non-uniform noise, a two-step iterative minimization (TSIM) method is proposed in this paper. Initially, the axial deviation measurement model of an AVSA is formulated by incorporating the disturbance parameter into the signal model, and then a novel AVSA manifold matrix is defined to estimate the sparse signal power and noise power mutually. After that, to mitigate a joint optimization problem to achieve the sparse signal power, the noise power and the axial deviation matrix, two auxiliary cost functions, are presented based on the covariance matrix fitting (CMF) criterion and the weighted least squares (WLS), respectively. Furthermore, their analytical expressions are also derived. In addition, to further enhance their prediction accuracy, the estimated axial deviation matrix is modified based on its specific structural properties. The simulation results demonstrate the superiority and robustness of the proposed technique over several conventional algorithms. Full article

The lack of techniques for monitoring ship emissions all day and in all weather conditions to obtain real-time emission factor values is the main problem in understanding the characteristics of ship emissions, and there is still no perfect solution. In this study, a real-time measurement-modeling system was designed and implemented. The system was divided into three parts: (1) a portable exhaust monitoring device, which could be mounted on a drone, aircraft, patrol boat, dock, and bridge crane, as well as on the shore, to conduct all-weather and real-time online monitoring of ship emissions; (2) a monitoring information platform for ship emissions, based on a Spring + Spring MVC + MyBatis (SSM) framework and Vue front-end technology; and (3) a cloud server that received real-time ship emission measurement data and stored it after verification and analysis to calculate the pollutant gas and particulate matter emission factors. Following development, this system was used to monitor the emissions of ocean-going and inland river ships. Analysis of the acquired data showed that the system could effectively measure the emission factors of ship exhausts full-time in a variety of weather scenarios. This system can improve the efficiency of maritime law enforcement and provide technical support for promoting the construction of ship emission control areas. It can also help researchers obtain ship emission data, as well as an improved understanding of the emission characteristics of ships. Full article

Conventional sediment classification methods based on Multibeam Echo System (MBES) data have low accuracy since the correlation between features and sediment has not been fully considered. Moreover, their poor resistance to the residual error of MBES backscatter strength (BS) processing also degrades their performances. Toward these problems, we propose a seabed sediment classification method using spatial statistical features extracted from angular response curve (ARC), topography, and geomorphology. First, to reduce interference of noise and residual error of beam pattern correction, we propose a robust method combining the Generic Seafloor Acoustic Backscatter (GSAB) model and Huber loss function to estimate the parameters of ARC which is strongly correlated with seabed sediments. Second, a feature set is constructed by AR features composed of GSAB parameters, BS mosaic and its derivatives, and seabed topography and its derivatives to characterize seabed sediments. After that, feature selection and probability map acquisition are employed based on the random forest algorithm (RF). Finally, a denoising and final sediment map generation method is proposed and applied to probability maps to obtain the sediment map with reasonable sediment distribution and clear boundaries between classes. We implement experiments and achieve the classification accuracy of 93.3%, which verifies the validity of our method. Full article

The growing need for interoperability among the different oceanic monitoring systems to deliver services able to answer the requirements of stakeholders and end-users led to the development of a low-cost machine-to-machine communication system able to guarantee data reliability over marine paths. In this framework, an experimental evaluation of the performance of long-range (LoRa) technology in a fully operational marine scenario has been proposed. In-situ tests were carried out exploiting the availability of (i) a passenger vessel and (ii) a research vessel operating in the Ligurian basin (North-Western Mediterranean Sea) both hosting end-nodes, and (iii) gateways positioned on mountains and hills in the inland areas. Packet loss ratio, packet reception rate, received signal strength indicator, signal to noise, and expected signal power ratio were chosen as metrics in line of sight and not the line of sight conditions. The reliability of Long Range Wide Area Network (LoRaWAN) transmission over the sea has been demonstrated up to more than 110 km in a free space scenario and for more than 20 km in a coastal urban environment. Full article

Ocean in-situ sensors are crucial for measuring oceanic parameters directly from the sea in a spatial and temporal basis. Real-time operation is used in many applications related to decision support tools and early warning services in case of accidents, incidents and/or disasters. The design of the proposed system is described as a rapid-response detection system, which aims to measure natural and artificial radioactive contaminants or other crucial ocean parameters, to replace the traditional method of sampling. The development of an interactive cellular system is undertaken using a commercial router that is programmed according to sensor specifications. A radioactivity sensor is integrated in a communication box enabling self-powered operation with a solar panel. The proposed system operates in (near) real-time mode and provides gamma-ray spectra by integrating the sensor and the appropriate electronic modules in it. Additionally, an on-site experiment was conducted to test the operability of the system in a real environment close to the sea, for monitoring fallout due to rainfall and snowfall events. The main intense radionuclides that were observed by different energy lines, were radon progenies (²¹⁴Bi, ²¹⁴Pb). The continuous operation of the whole system was controlled by operating the system during the winter period. Full article

Marine in situ gamma-ray spectrometry was utilized for a rainfall study at the W1M3A observing system in Ligurian Sea, Mediterranean Sea, Italy. From 7 June to 10 October 2016, underwater total gamma-ray counting rate (TCR) and the activity concentration of radon daughters ²¹⁴Pb, ²¹⁴Bi and potassium ⁴⁰K were continuously monitored along with ambient noise and meteorological parameters. TCR was proven as a good rainfall indicator as radon daughters’ fallout resulted in increased levels of marine radioactivity during and 2–3 h after the rainfall events. Cloud origin significantly affects TCR and radon progenies variations, as aerial mass trajectories, which extend upon terrestrial areas, result in higher increments. TCR and radon progenies concentrations revealed an increasing non-linear trend with rainfall height and intensity. ⁴⁰K was proven to be an additional radio-tracer as its dilution was associated with rainfall height. ⁴⁰K variations combined with ²¹⁴Bi measurements can be used to investigate the mixing of rain- and seawater. In comparison with measurements in the atmosphere, the application of marine in situ gamma-ray spectrometry for precipitation investigation provided important advantages: allows quantitative measurement of the radionuclides; ⁴⁰K can be used, along with radon daughters, as a radio-tracer; the mixing of rain- and seawater can be associated with meteorological parameters. Full article

Submarine groundwater discharge (SGD) is an important pathway of nutrients into coastal areas. During the last decades, interest of researchers in SGDs has grown continuously. However, methods applied for SGD research usually focus on the aquifer or on the mixing processes on larger scales. The distribution of discharged water within the water column is not well investigated. Small remotely operated vehicles (ROV) equipped with environmental sensors can be used to investigate the spatial distribution of environmental parameters in the water column. Herein, a low-cost multi-sensor platform designed to investigate the spatial distribution of water quality properties is presented. The platform is based on an off-the-shelf underwater vehicle carrying various environmental sensors and a short-baseline localisation system. This contribution presents the results of SGD investigations in the area of Woodman Point (Western Australia). Various potential SGD plumes were detected using a skiff equipped with a recreational echo sounder. It was demonstrated that this inexpensive equipment could be used to detect and investigate SGDs in coastal areas. In addition, the low-cost multi-sensor platform was deployed to investigate the spatial distribution of environmental parameters including temperature (T), electric conductivity (EC), dissolved oxygen (DO), oxidation-reduction potential (ORP), pH, and dissolved organic matter fluorescence (FDOM). Three ROV surveys were conducted from different skiff locations. Analyses of the spatial distribution of the environmental parameters allowed the identification of nine potential SGD plumes. At the same locations, plumes were identified during the sonar surveys. In addition, fuzzy logic was used for the fusion of salinity, DO, and FDOM readings in order to enhance SGD detection capability of the designed multi-sensor system. The fuzzy logic approach identified 293 data points as potential within a SGD plume. Average minimum-distance between these points and the identified SGD plumes was 0.5 m and 0.42 m smaller than the minimum-distance average of the remaining data points of survey one and three respectively. It was shown that low-cost ROVs, equipped with environmental sensors, could be an important tool for the investigation of the spatio-temporal behaviour of SGD sites. This method allows continuous mapping of environmental parameters with a high spatial and temporal resolution. However, to obtain deeper insights into the influence of SGDs on the nearshore areas, this method should be combined with other well-established methods for SGD investigation, such as pore water sampling, remote sensing, or groundwater monitoring. Full article

In a nuclear emergency, the application of in situ spectrometers for monitoring environmental radioactivity is significantly important, as information on the type and activity of radionuclides released from the accident can be obtained quickly. However, in emergency environmental radiological monitoring, a balance between energy resolution and detecting efficiency must be considered in selecting an appropriate detector. In this study, in situ gamma spectrometry was conducted with the LaBr₃ detector to determine the radioactivity of seawater at the discharging outlet of a coastal nuclear power plant in southeast China. The results show that the LaBr₃ scintillator has excellent energy resolution and detection efficiency, making it a promising detector for emergency monitoring. Full article

The integration of the radioactivity spectrometer KATERINA II in a fixed station (buoy) of the POSEIDON network at the North Aegean Sea within the framework of MARRE Project is presented. The acquisition period lasted from 20 November 2019 till 22 February 2020. An intense increment of the activity concentration of radon progenies (up to an order of magnitude) was recorded during rainfall. More specifically, the ²¹⁴Bi activity concentration varied from 0.09 to 0.53 Bq L⁻¹ without rainfall and the ²¹⁴Pb activity concentration varied from 0.14 to 0.81 Bq L⁻¹. The ²¹⁴Bi activity concentration during rainfall ranged from 0.4 to 5.4 Bq L⁻¹ and of ²¹⁴Pb from 0.3 to 5.3 Bq L⁻¹. The minimum detectable activity of the KATERINA II detection system for measuring low level activities of ¹³⁷Cs is optimized applying background subtraction and the full spectrum analysis technique. Full article