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Marine Sensors: Recent Advances and Challenges

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 56618

Special Issue Editors


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Guest Editor
1. CMEMS-University of Minho, 4804-533 Guimarães, Portugal
2. Department of Industrial Electronics, University of Minho, 4804-533 Guimarães, Portugal
Interests: sensors; actuators; electronics
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Guest Editor
INESC TEC, R. Dr. Roberto Frias, 4200-465 Porto, Portugal
Interests: underwater acoustic communications; underwater transducers; deep-sea sensing
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The ocean has a huge impact on our way of life, and there is a need to monitor and protect its biodiversity. Additionally, the ocean industrial potential for health, minerals, and oil has promoted the need for constant and real-time monitoring. Because of all of these concerns, it is important to develop efficient and smart marine sensors to improve our knowledge of the sea environment and to support marine sustainable development. Taking advantage of the most recent progress in sensing techniques, the purpose of this Special Issue is to provide an opportunity for the engineering and biological marine community to exchange knowledge and information on the latest advances and challenges in marine sensors and their applications to monitor sea environment. We hope to bring together researchers who are interested in the general field of sensors, especially in their applications in the sea.

In this Special Issue, we invite contributions (original research papers, review articles, and brief communications) that focus on the latest advances and challenges in marine sensors and related fields applied to marine sustainable development.

Prof. Luís Miguel Valente Gonçalves
Dr. Marcos Silva Martins
Prof. Rui Alberto Madeira Macedo Lima
Prof. Graça Minas
Guest Editors

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Keywords

  • marine sensing technologies
  • marine instrumentation
  • marine data communication
  • sensor networks
  • sea monitoring
  • sea modelling
  • remote sensing
  • sea pollution
  • energy harvesting
  • submersible power
  • submersible devices and equipment
  • submersible lab-on-chip devices
  • physical oceanography
  • biological oceanography
  • sustainable development

Published Papers (16 papers)

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Editorial

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2 pages, 193 KiB  
Editorial
Marine Sensors: Recent Advances and Challenges
by Luís Gonçalves, Marcos Silva Martins, Rui A. Lima and Graça Minas
Sensors 2023, 23(4), 2203; https://doi.org/10.3390/s23042203 - 15 Feb 2023
Cited by 1 | Viewed by 1106
Abstract
The ocean has a huge impact on our way of life; therefore, there is a need to monitor and protect its biodiversity [...] Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)

Research

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20 pages, 4132 KiB  
Article
Underwater Energy Harvesting to Extend Operation Time of Submersible Sensors
by Carlos L. Faria, Marcos S. Martins, Tiago Matos, Rui Lima, João M. Miranda and Luís M. Gonçalves
Sensors 2022, 22(4), 1341; https://doi.org/10.3390/s22041341 - 10 Feb 2022
Cited by 12 | Viewed by 4348
Abstract
A linear electromagnetic energy harvesting device for underwater applications, fabricated with a simple manufacturing process, was developed to operate with movement frequencies from 0.1 to 0.4 Hz. The generator has two coils, and the effect of the combination of the two coils was [...] Read more.
A linear electromagnetic energy harvesting device for underwater applications, fabricated with a simple manufacturing process, was developed to operate with movement frequencies from 0.1 to 0.4 Hz. The generator has two coils, and the effect of the combination of the two coils was investigated. The experimental study has shown that the energy capture system was able to supply energy to several ocean sensors, producing 7.77 mJ per second with wave movements at 0.4 Hz. This study shows that this energy is enough to restore the energy used by the battery or the capacitor and continue supplying energy to the sensors used in the experimental work. For an ocean wave frequency of 0.4 Hz, the generator can supply power to 8 sensors or 48 sensors, depending on the energy consumed and its optimization. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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19 pages, 20377 KiB  
Article
Autonomous System for Lake Ice Monitoring
by Ilya Aslamov, Georgiy Kirillin, Mikhail Makarov, Konstantin Kucher, Ruslan Gnatovsky and Nikolay Granin
Sensors 2021, 21(24), 8505; https://doi.org/10.3390/s21248505 - 20 Dec 2021
Cited by 4 | Viewed by 3191
Abstract
Continuous monitoring of ice cover belongs to the key tasks of modern climate research, providing up-to-date information on climate change in cold regions. While a strong advance in ice monitoring worldwide has been provided by the recent development of remote sensing methods, quantification [...] Read more.
Continuous monitoring of ice cover belongs to the key tasks of modern climate research, providing up-to-date information on climate change in cold regions. While a strong advance in ice monitoring worldwide has been provided by the recent development of remote sensing methods, quantification of seasonal ice cover is impossible without on-site autonomous measurements of the mass and heat budget. In the present study, we propose an autonomous monitoring system for continuous in situ measuring of vertical temperature distribution in the near-ice air, the ice strata and the under-ice water layer for several months with simultaneous records of solar radiation incoming at the lake surface and passing through the snow and ice covers as well as snow and ice thicknesses. The use of modern miniature analog and digital sensors made it possible to make a compact, energy efficient measurement system with high precision and spatial resolution and characterized by easy deployment and transportation. In particular, the high resolution of the ice thickness probe of 0.05 mm allows to resolve the fine-scale processes occurring in low-flow environments, such as freshwater lakes. Several systems were tested in numerous studies in Lake Baikal and demonstrated a high reliability in deriving the ice heat balance components during ice-covered periods. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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13 pages, 3320 KiB  
Article
Optoacoustic Sensing of Surfactant Crude Oil in Thermal Relaxation and Nonlinear Regimes
by Pavel Subochev, Alexey Kurnikov, Ekaterina Sergeeva, Mikhail Kirillin, Ivan Kapustin, Roman Belyaev, Alexey Ermoshkin and Alexander Molkov
Sensors 2021, 21(18), 6142; https://doi.org/10.3390/s21186142 - 13 Sep 2021
Cited by 1 | Viewed by 1479
Abstract
We propose a laser optoacoustic method for the complex characterization of crude oil pollution of the water surface by the thickness of the layer, the speed of sound, the coefficient of optical absorption, and the temperature dependence of the Grüneisen parameter. Using a [...] Read more.
We propose a laser optoacoustic method for the complex characterization of crude oil pollution of the water surface by the thickness of the layer, the speed of sound, the coefficient of optical absorption, and the temperature dependence of the Grüneisen parameter. Using a 532 nm pulsed laser and a 1–100 MHz ultra-wideband ultrasonic antenna, we have demonstrated the capability of accurate (>95%) optoacoustic thickness measurements in the 5 to 500-micron range, covering 88% of slicks observed during 2010 oil spill in the Gulf of Mexico. In the thermal relaxation regime of optoacoustic measurements, the value of optical absorption coefficient (30 mm−1) agreed with the data of independent spectrophotometric measurements, while the sound speed (1430 m/s) agreed with the tabular data. When operating in a nonlinear regime, the effect of local deformation of the surface of the oil film induced by heating laser radiation was revealed. The dose-time parameters of laser radiation ensuring the transition from the thermal relaxation regime of optoacoustic generation to nonlinear one were experimentally investigated. The developed OA method has potential for quantitative characterization of not only the volume, but also the degree and even the type of oil pollution of the water surface. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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15 pages, 3221 KiB  
Article
PtOEP–PDMS-Based Optical Oxygen Sensor
by Camila M. Penso, João L. Rocha, Marcos S. Martins, Paulo J. Sousa, Vânia C. Pinto, Graça Minas, Maria M. Silva and Luís M. Goncalves
Sensors 2021, 21(16), 5645; https://doi.org/10.3390/s21165645 - 21 Aug 2021
Cited by 6 | Viewed by 4512
Abstract
The advanced and widespread use of microfluidic devices, which are usually fabricated in polydimethylsiloxane (PDMS), requires the integration of many sensors, always compatible with microfluidic fabrication processes. Moreover, current limitations of the existing optical and electrochemical oxygen sensors regarding long-term stability due to [...] Read more.
The advanced and widespread use of microfluidic devices, which are usually fabricated in polydimethylsiloxane (PDMS), requires the integration of many sensors, always compatible with microfluidic fabrication processes. Moreover, current limitations of the existing optical and electrochemical oxygen sensors regarding long-term stability due to sensor degradation, biofouling, fabrication processes and cost have led to the development of new approaches. Thus, this manuscript reports the development, fabrication and characterization of a low-cost and highly sensitive dissolved oxygen optical sensor based on a membrane of PDMS doped with platinum octaethylporphyrin (PtOEP) film, fabricated using standard microfluidic materials and processes. The excellent mechanical and chemical properties (high permeability to oxygen, anti-biofouling characteristics) of PDMS result in membranes with superior sensitivity compared with other matrix materials. The wide use of PtOEP in sensing applications, due to its advantage of being easily synthesized using microtechnologies, its strong phosphorescence at room temperature with a quantum yield close to 50%, its excellent Strokes Shift as well as its relatively long lifetime (75 µs), provide the suitable conditions for the development of a miniaturized luminescence optical oxygen sensor allowing long-term applications. The influence of the PDMS film thickness (0.1–2.5 mm) and the PtOEP concentration (363, 545, 727 ppm) in luminescent properties are presented. This enables to achieve low detection levels in a gas media range from 0.5% up to 20%, and in liquid media from 0.5 mg/L up to 3.3 mg/L at 1 atm, 25 °C. As a result, we propose a simple and cost-effective system based on a LED membrane photodiode system to detect low oxygen concentrations for in situ applications. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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19 pages, 4968 KiB  
Article
Underwater Holographic Sensor for Plankton Studies In Situ including Accompanying Measurements
by Victor Dyomin, Alexandra Davydova, Igor Polovtsev, Alexey Olshukov, Nikolay Kirillov and Sergey Davydov
Sensors 2021, 21(14), 4863; https://doi.org/10.3390/s21144863 - 17 Jul 2021
Cited by 12 | Viewed by 2724
Abstract
The paper presents an underwater holographic sensor to study marine particles—a miniDHC digital holographic camera, which may be used as part of a hydrobiological probe for accompanying (background) measurements. The results of field measurements of plankton are given and interpreted, their verification is [...] Read more.
The paper presents an underwater holographic sensor to study marine particles—a miniDHC digital holographic camera, which may be used as part of a hydrobiological probe for accompanying (background) measurements. The results of field measurements of plankton are given and interpreted, their verification is performed. Errors of measurements and classification of plankton particles are estimated. MiniDHC allows measurement of the following set of background data, which is confirmed by field tests: plankton concentration, average size and size dispersion of individuals, particle size distribution, including on major taxa, as well as water turbidity and suspension statistics. Version of constructing measuring systems based on modern carriers of operational oceanography for the purpose of ecological diagnostics of the world ocean using autochthonous plankton are discussed. The results of field measurements of plankton using miniDHC as part of a hydrobiological probe are presented and interpreted, and their verification is carried out. The results of comparing the data on the concentration of individual taxa obtained using miniDHC with the data obtained by the traditional method using plankton catching with a net showed a difference of no more than 23%. The article also contains recommendations for expanding the potential of miniDHC, its purpose indicators, and improving metrological characteristics. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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6 pages, 529 KiB  
Communication
The Potential of Satellite Imagery for Surveying Whales
by Caroline Höschle, Hannah C. Cubaynes, Penny J. Clarke, Grant Humphries and Alex Borowicz
Sensors 2021, 21(3), 963; https://doi.org/10.3390/s21030963 - 01 Feb 2021
Cited by 23 | Viewed by 5619
Abstract
The emergence of very high-resolution (VHR) satellite imagery (less than 1 m spatial resolution) is creating new opportunities within the fields of ecology and conservation biology. The advancement of sub-meter resolution imagery has provided greater confidence in the detection and identification of features [...] Read more.
The emergence of very high-resolution (VHR) satellite imagery (less than 1 m spatial resolution) is creating new opportunities within the fields of ecology and conservation biology. The advancement of sub-meter resolution imagery has provided greater confidence in the detection and identification of features on the ground, broadening the realm of possible research questions. To date, VHR imagery studies have largely focused on terrestrial environments; however, there has been incremental progress in the last two decades for using this technology to detect cetaceans. With advances in computational power and sensor resolution, the feasibility of broad-scale VHR ocean surveys using VHR satellite imagery with automated detection and classification processes has increased. Initial attempts at automated surveys are showing promising results, but further development is necessary to ensure reliability. Here we discuss the future directions in which VHR satellite imagery might be used to address urgent questions in whale conservation. We highlight the current challenges to automated detection and to extending the use of this technology to all oceans and various whale species. To achieve basin-scale marine surveys, currently not feasible with any traditional surveying methods (including boat-based and aerial surveys), future research requires a collaborative effort between biology, computation science, and engineering to overcome the present challenges to this platform’s use. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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18 pages, 7907 KiB  
Article
Vicarious Radiometric Calibration of Ocean Color Bands for FY-3D/MERSI-II at Lake Qinghai, China
by Shengli Chen, Xiaobing Zheng, Xin Li, Wei Wei, Shenda Du and Fuxiang Guo
Sensors 2021, 21(1), 139; https://doi.org/10.3390/s21010139 - 28 Dec 2020
Cited by 9 | Viewed by 2096
Abstract
To calibrate the low signal response of the ocean color (OC) bands and test the stability of the Fengyun-3D (FY-3D)/Medium Resolution Spectral Imager II (MERSI-II), an absolute radiometric calibration field test of FY-3D/MERSI-II at the Lake Qinghai Radiometric Calibration Site (RCS) was carried [...] Read more.
To calibrate the low signal response of the ocean color (OC) bands and test the stability of the Fengyun-3D (FY-3D)/Medium Resolution Spectral Imager II (MERSI-II), an absolute radiometric calibration field test of FY-3D/MERSI-II at the Lake Qinghai Radiometric Calibration Site (RCS) was carried out in August 2018. The lake surface and atmospheric parameters were mainly measured by advanced observation instruments, and the MODerate spectral resolution atmospheric TRANsmittance algorithm and computer model (MODTRAN4.0) was used to simulate the multiple scattering radiance value at the altitude of the sensor. The results showed that the relative deviations between bands 9 and 12 are within 5.0%, while the relative deviations of bands 8, and 13 are 17.1%, and 12.0%, respectively. The precision of the calibration method was verified by calibrating the Aqua/Moderate-resolution Imaging Spectroradiometer (MODIS) and National Polar-orbiting Partnership (NPP)/Visible Infrared Imaging Radiometer (VIIRS), and the deviation of the calibration results was evaluated with the results of the Dunhuang RCS calibration and lunar calibration. The results showed that the relative deviations of NPP/VIIRS were within 7.0%, and the relative deviations of Aqua/MODIS were within 4.1% from 400 nm to 600 nm. The comparisons of three on-orbit calibration methods indicated that band 8 exhibited a large attenuation after launch and the calibration results had good consistency at the other bands except for band 13. The uncertainty value of the whole calibration system was approximately 6.3%, and the uncertainty brought by the field surface measurement reached 5.4%, which might be the main reason for the relatively large deviation of band 13. This study verifies the feasibility of the vicarious calibration method at the Lake Qinghai RCS and provides the basis and reference for the subsequent on-orbit calibration of FY-3D/MERSI-II. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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18 pages, 7803 KiB  
Article
Analysis of the Antenna Array Orientation Performance of the Interferometric Microwave Radiometer (IMR) Onboard the Chinese Ocean Salinity Satellite
by Yan Li, Mingsen Lin, Xiaobin Yin and Wu Zhou
Sensors 2020, 20(18), 5396; https://doi.org/10.3390/s20185396 - 21 Sep 2020
Cited by 8 | Viewed by 2131
Abstract
The Chinese Ocean Salinity Satellite is designed to monitor global sea-surface salinity (SSS). One of the main payloads onboard the Chinese Ocean Salinity Satellite, named the Interferometric Microwave Radiometer (IMR), is a two-dimensional interferometric radiometer system with an L-band, Y-shaped antenna array. The [...] Read more.
The Chinese Ocean Salinity Satellite is designed to monitor global sea-surface salinity (SSS). One of the main payloads onboard the Chinese Ocean Salinity Satellite, named the Interferometric Microwave Radiometer (IMR), is a two-dimensional interferometric radiometer system with an L-band, Y-shaped antenna array. The comparison of two different array orientations is analyzed by an end-to-end simulation based on the configuration of the IMR. Simulation results of the different array orientations are presented and analyzed, including the brightness temperature (TB) images, the distribution of the incidence angles in the field of view, the TB radiometric resolutions, the spatial resolutions, the number of measurements in the Earth grid and the expected SSS accuracy. From the simulations we conclude that one of the array orientations has better performance for SSS inversion than the other one. The advantages mainly result in wider swath and better SSS accuracy at the edge of the swath, which then improve the accuracy of the monthly SSS after averaging. The differences of the Sun’s effects for two different array orientations are also presented. The analysis in this paper provides the guidance and reference for the in-orbit design of the array orientation for the IMR. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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13 pages, 6732 KiB  
Article
Study on the Classification Performance of Underwater Sonar Image Classification Based on Convolutional Neural Networks for Detecting a Submerged Human Body
by Huu-Thu Nguyen, Eon-Ho Lee and Sejin Lee
Sensors 2020, 20(1), 94; https://doi.org/10.3390/s20010094 - 23 Dec 2019
Cited by 41 | Viewed by 6854
Abstract
Auto-detecting a submerged human body underwater is very challenging with the absolute necessity to a diver or a submersible. For the vision sensor, the water turbidity and limited light condition make it difficult to take clear images. For this reason, sonar sensors are [...] Read more.
Auto-detecting a submerged human body underwater is very challenging with the absolute necessity to a diver or a submersible. For the vision sensor, the water turbidity and limited light condition make it difficult to take clear images. For this reason, sonar sensors are mainly utilized in water. However, even though a sonar sensor can give a plausible underwater image within this limitation, the sonar image’s quality varies greatly depending on the background of the target. The readability of the sonar image is very different according to the target distance from the underwater floor or the incidence angle of the sonar sensor to the floor. The target background must be very considerable because it causes scattered and polarization noise in the sonar image. To successfully classify the sonar image with these noises, we adopted a Convolutional Neural Network (CNN) such as AlexNet and GoogleNet. In preparing the training data for this model, the data augmentation on scattering and polarization were implemented to improve the classification accuracy from the original sonar image. It could be practical to classify sonar images undersea even by training sonar images only from the simple testbed experiments. Experimental validation was performed using three different datasets of underwater sonar images from a submerged body of a dummy, resulting in a final average classification accuracy of 91.6% using GoogleNet. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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18 pages, 7854 KiB  
Article
A Bioinspired Twin Inverted Multiscale Matched Filtering Method for Detecting an Underwater Moving Target in a Reverberant Environment
by Xueli Sheng, Chaoping Dong, Longxiang Guo and Li Li
Sensors 2019, 19(23), 5305; https://doi.org/10.3390/s19235305 - 02 Dec 2019
Cited by 3 | Viewed by 3260
Abstract
To this day, biological sonar systems still have great performance advantages over artificial sonar systems, especially for detection in environments with clutter, strong reverberation, and a low signal to noise ratio (SNR). Therefore, mammal sonar systems, for instance, bats and toothed whales, have [...] Read more.
To this day, biological sonar systems still have great performance advantages over artificial sonar systems, especially for detection in environments with clutter, strong reverberation, and a low signal to noise ratio (SNR). Therefore, mammal sonar systems, for instance, bats and toothed whales, have many characteristics worth learning from. This paper proposes a bioinspired twin inverted multiscale matched filtering method to detect underwater moving targets. This method can be mainly divided into three parts. Firstly, a hyperbolic frequency modulation (HFM) continuous wave (CW) multiharmonic detection signal was adopted after analyzing signals from bats and dolphins. This signal combines the advantages of CW and HFM signals and has excellent time measurement and speed measurement performance when detecting a moving target. Secondly, the twin inverted waveform was introduced to suppress strong linear reverberation and highlight moving targets. The pulse interval was determined by assessing the reverberation reduction time. Thirdly, when processing echoes, a multiscale matched filtering method was proposed to make use of multiharmonic information and improve detection performance. Finally, a channel pool experiment was carried out to test the performance of the proposed method. The experimental result demonstrates that the proposed method has better performance when detecting a moving target in a reverberant environment compared to the conventional matched filtering method. Related results can be applied to small underwater platforms or sensor network platforms for target detection and coastal defense applications. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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15 pages, 3507 KiB  
Article
A Microfluidic Prototype System towards Microalgae Cell Separation, Treatment and Viability Characterization
by Yanjuan Wang, Junsheng Wang, Chen Zhou, Gege Ding, Mengmeng Chen, Jiang Zou, Ge Wang, Yuejun Kang and Xinxiang Pan
Sensors 2019, 19(22), 4940; https://doi.org/10.3390/s19224940 - 13 Nov 2019
Cited by 12 | Viewed by 3323
Abstract
There are a huge number, and abundant types, of microalgae in the ocean; and most of them have various values in many fields, such as food, medicine, energy, feed, etc. Therefore, how to identify and separation of microalgae cells quickly and effectively is [...] Read more.
There are a huge number, and abundant types, of microalgae in the ocean; and most of them have various values in many fields, such as food, medicine, energy, feed, etc. Therefore, how to identify and separation of microalgae cells quickly and effectively is a prerequisite for the microalgae research and utilization. Herein, we propose a microfluidic system that comprised microalgae cell separation, treatment and viability characterization. Specifically, the microfluidic separation function is based on the principle of deterministic lateral displacement (DLD), which can separate various microalgae species rapidly by their different sizes. Moreover, a concentration gradient generator is designed in this system to automatically produce gradient concentrations of chemical reagents to optimize the chemical treatment of samples. Finally, a single photon counter was used to evaluate the viability of treated microalgae based on laser-induced fluorescence from the intracellular chlorophyll of microalgae. To the best of our knowledge, this is the first laboratory prototype system combining DLD separation, concentration gradient generator and chlorophyll fluorescence detection technology for fast analysis and treatment of microalgae using marine samples. This study may inspire other novel applications of micro-analytical devices for utilization of microalgae resources, marine ecological environment protection and ship ballast water management. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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21 pages, 6413 KiB  
Article
Development of a Cost-Effective Optical Sensor for Continuous Monitoring of Turbidity and Suspended Particulate Matter in Marine Environment
by T. Matos, C. L. Faria, M. S. Martins, Renato Henriques, P. A. Gomes and L. M. Goncalves
Sensors 2019, 19(20), 4439; https://doi.org/10.3390/s19204439 - 14 Oct 2019
Cited by 28 | Viewed by 4641
Abstract
A cost-effective optical sensor for continuous in-situ monitoring of turbidity and suspended particulate matter concentration (SPM), with a production cost in raw materials less than 20 €, is presented for marine or fluvial applications. The sensor uses an infrared LED and three photodetectors [...] Read more.
A cost-effective optical sensor for continuous in-situ monitoring of turbidity and suspended particulate matter concentration (SPM), with a production cost in raw materials less than 20 €, is presented for marine or fluvial applications. The sensor uses an infrared LED and three photodetectors with three different positions related to the light source—135º, 90º and 0º—resulting in three different types of light detection: backscattering, nephelometry and transmitted light, respectively. This design allows monitoring in any type of environment, offering a wide dynamic range and accuracy for low and high turbidity or SPM values. An ultraviolet emitter–receiver pair is also used to differentiate organic and inorganic matter through the differences in absorption at different wavelengths. The optical transducers are built in a watertight structure with a radial configuration where a printed circuit board with the electronic signal coupling is assembled. An in-lab calibration of the sensor was made to establish a relation between suspended particulate matter (SPM) or the turbidity (NTU) to the photodetectors’ electrical output value in Volts. Two different sizes of seashore sand were used (180 µm and 350 µm) to evaluate the particle size susceptibility. The sensor was tested in a fluvial environment to evaluate SPM change during sediment transport caused by rain, and a real test of 22 days continuous in-situ monitoring was realized to evaluate its performance in a tidal area. The monitoring results were analysed, showing the SPM change during tidal cycles as well as the influence of the external light and biofouling problems. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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18 pages, 6206 KiB  
Article
Wideband and Wide Beam Polyvinylidene Difluoride (PVDF) Acoustic Transducer for Broadband Underwater Communications
by Marcos S. Martins, Carlos L. Faria, Tiago Matos, Luís M. Goncalves, José Cabral, António Silva and Sérgio M. Jesus
Sensors 2019, 19(18), 3991; https://doi.org/10.3390/s19183991 - 16 Sep 2019
Cited by 13 | Viewed by 4471
Abstract
The advances in wireless communications are still very limited when intended to be used on Underwater Communication Systems mainly due to the adverse proprieties of the submarine channel to the acoustic and radio frequency (RF) waves propagation. This work describes the development and [...] Read more.
The advances in wireless communications are still very limited when intended to be used on Underwater Communication Systems mainly due to the adverse proprieties of the submarine channel to the acoustic and radio frequency (RF) waves propagation. This work describes the development and characterization of a polyvinylidene difluoride ultrasound transducer to be used as an emitter in underwater wireless communications. The transducer has a beam up to 10° × 70° degrees and a usable frequency band up to 1 MHz. The transducer was designed using Finite Elements Methods and compared with real measurements. Pool trials show a transmitting voltage response (TVR) of approximately 150 dB re µPa/V@1 m from 750 kHz to 1 MHz. Sea trials were carried in Ria Formosa, Faro (Portugal) over a 15 m source—receiver communication link. All the signals were successfully detected by cross-correlation using 10 chirp signals between 10 to 900 kHz. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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10 pages, 1364 KiB  
Article
Waveform Design for Improved Detection of Extended Targets in Sea Clutter
by Linke Zhang, Na Wei and Xuhao Du
Sensors 2019, 19(18), 3957; https://doi.org/10.3390/s19183957 - 13 Sep 2019
Cited by 6 | Viewed by 2813
Abstract
Adaptive waveform design for cognitive radar in the case of extended target detection under compound-Gaussian (CG) sea clutter is addressed. Based on the CG characteristics of sea clutter, the texture component is employed to characterize the clutter ensemble during each closed-loop feedback and [...] Read more.
Adaptive waveform design for cognitive radar in the case of extended target detection under compound-Gaussian (CG) sea clutter is addressed. Based on the CG characteristics of sea clutter, the texture component is employed to characterize the clutter ensemble during each closed-loop feedback and its estimation can be used for the next transmitted waveform design. The resulting waveform design problem is formulated according to the following optimization criterion: maximization of the output signal-to-interference-plus-noise ratio (SINR) for sea clutter suppression, and imposing a further constraint on sidelobes level of the waveform autocorrelation outputs for decreasing the false alarm rate. Numerical results demonstrate the effectiveness of this approach. Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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1 pages, 183 KiB  
Erratum
Erratum: Martins, M.S., et al. Wideband and Wide Beam Polyvinylidene Difluoride (PVDF) Acoustic Transducer for Broadband Underwater. Sensors 2019, 19, 3991
by Marcos S. Martins, Carlos L. Faria, Tiago Matos, Luís M. Goncalves, José Cabral, António Silva and Sérgio M. Jesus
Sensors 2019, 19(22), 4928; https://doi.org/10.3390/s19224928 - 12 Nov 2019
Cited by 1 | Viewed by 1733
Abstract
The authors wish to make the following erratum to this paper [...] Full article
(This article belongs to the Special Issue Marine Sensors: Recent Advances and Challenges)
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