Abstract
In order to achieve underwater acoustic high data-rate and real time communications, it is essential to implement a system that operates both at high and wideband frequencies using digital modulations. Therefore, to reduce the time and cost of developing acoustic communications an emulator of a physical layer model was implemented, allowing to test in real time the performance of digital modulations. The model was composed of an emitter transducer, a hydrophone and the subaquatic medium and was integrated in a Field Programmable Gate Array (FPGA) in order to emulate the physical layer in the acoustic modem testing. The emitter transducer and the hydrophone models were designed to meet real prototype characteristics. The system prototype was implemented in order to compare the experimental trials results with those obtained in emulator, emulating the transmission of acoustic signals, using different types of digital modulations. The system was tested using Binary Phase-Shift Keying (BPSK), Binary Frequency Shift keying (BFSK) and Binary Amplitude Shift Keying (BASK) modulations with a 1 MHz carrier frequency resulting in a data rate of 125 kbps. It was verified that the implemented model represents a suitable approximation to the real subaquatic communication channel, allowing the evaluation of digital acoustic communications.

Abstract
Biofouling in marine optical sensors poses a significant challenge as it can compromise data accuracy and instrument functionality. This study investigates the effectiveness of local chlorine generation by seawater electrolysis in mitigating biological fouling and extending the operational lifespan of optical oceanographic instruments. Eight similar turbidity probes integrated with a local chlorine generation system, along with a turbidity probe constructed from ABS and another from PLA with copper filament, were developed for testing in the marine environment. The chlorine probes were designed into two groups: four utilizing standard FTO glass and four featuring FTO glass coated with platinum nanoparticles. Each set of probes employed different excitation currents for chlorine generation. All probes underwent laboratory calibration using formazine before deployment in a coastal environment for 97 days. The findings demonstrate a correlation with higher electrical power leading to prolonged operation intervals free from biofouling interference. Additionally, probes coated with platinum nanoparticles demonstrate higher performance in comparison to those with standard FTO glass. The copper probe did not effectively shield the optical transducers from microfouling, although it effectively demonstrated its efficacy in protecting the structural housing of the device. Overall, this work offers a compelling in situ demonstration of local chlorine generation as a promising strategy for enhancing the performance and longevity of optical oceanographic instruments in marine environments.

Abstract
Turbidity and suspended sediment concentration are crucial parameters indicative of water quality, playing pivotal roles in evaluating the well-being of aquatic ecosystems and the effectiveness of water treatment processes. This manuscript provides an in-depth review of various methods and instruments in use for in situ and inline applications. The exploration of optical instrumentation is central to this review, examining its widespread use and current challenges within standard methods, commercial instruments and scientific research. The study also delves into alternative techniques, such as acoustic and capacitive methods, elucidating their applications, calibration intricacies, and practical considerations. Furthermore, the paper scrutinizes the emerging importance of satellite and aerial imaging processing as a supplementary tool for turbidity monitoring, underscoring its potential to offer comprehensive insights on a larger scale. The review emphasizes the key accomplishments and challenges of the state-of-the-art technologies, providing a comprehensive overview of the current stage of the field and its prospects. and aims to provide valuable insights for researchers, practitioners, and decision-makers involved in environmental monitoring and water facility management, enabling a deeper comprehension of the significance of turbidity and suspended sediment concentration in safeguarding water quality and ecosystem health.