Abstract The OMNI (Ocean Moored Buoy Network for northern Indian Ocean) buoy network comprises 12 buoy systems that measure surface meteorological parameters along with temperature and salinity profile measurements at discrete levels up to 500 m. All the OMNI buoy systems are deployed with slack-line moorings, which respond more to wind, wave, and current forcing compared to taut-line mooring. Subsurface temperature measurements are subject to change depending on both environmental condition and mooring design. The standard sensor fit of the OMNI buoy systems has only one pressure sensor fixed at 500 m, which shows significant depth variability. In order to see the spatial and seasonal variability in the vertical movement of the mooring line and the associated temperature variability, four deployments with additional pressure measurements at 200 m are analyzed. It is observed that the depth/temperature variability exhibits significant seasonality with maximum variability during pre-monsoon season. Also, the effect of this movement in the shallower depths is analyzed with four more pressure sensors in the mooring line for a 1-year period in the central Bay of Bengal. The analysis shows that the maximum value of average and root mean square (RMS) temperature deviations is 0.38 °C and 0.48 °C in the deepest interpolated depth at 400 m where the mooring line experiences a greater range of motion and the actual temperature variability in shallower depths is negligible particularly up to 75 m (<0.01°C). The study reveals the necessity of additional pressure measurements for better remapping of temperature profile measurements.

Oceans play a crucial role in regulating the global ecology. As a result, ocean monitoring is critical for understanding and forecasting natural hazards such as cyclonic storms, tsunamis, and other natural disasters. To collect continuous real-time data, several platforms such as moored buoy systems, Argo floats, drifters, and gliders are employed around the world. Moored buoys give simultaneous meteorological, surface, and subsurface measurements. The buoy systems are susceptible to vandalism, bio-fouling, corrosion, and external environmental forces due to cyclones. The design of a moored buoy with a tension recorder to gather the in-situ load caused by wind, wave, and current on the moorings is described in this paper. The numerical analysis was performed with OrcaFlex software, taking into account the moored buoy system's varied harsh sea environmental parameters. During the Amphan cyclone, the outcome is compared to the measured tension recorder value and a difference of 1% is attained.

Marine biofouling and corrosion are the two major challenges the maritime industry has been facing for over several millennia. As our dependence on marine resources increases, there is an increase in the technology development and deployment of structures to harness the resources. The absence of an ideal, cost-effective, and eco-friendly solution to prevent biofouling and corrosion remains a great challenge for the marine industry. As a vast number of research publications are available on the fundamentals of biofouling and corrosion, an attempt is made to provide a glimpse of the practical aspects and technological developments on materials used for marine applications and recent developments in material research for biofouling and corrosion prevention. The deep-sea environment with high pressure and low temperature cannot be simulated in the laboratory and hence the field test results are important. Underwater technology is advancing with the development of instruments, capable of measuring continuous data for longer durations for diversified ocean data collection. An attempt has also been made to present the operational challenges faced due to biofouling and corrosion on data buoys deployed by the National Institute of Ocean Technology, Ministry of Earth Sciences, Chennai as part of the ocean observation program, through two case studies.

The moored buoy network in the Indian Ocean revolutionized the observational programs with systematic time-series measurement of in situ data sets from remote marine locations. The real-time meteorological and oceanographic data sets significantly improved the weather forecast and warning services particularly during extreme events since its inception in 1997. The sustenance of the network requires persistent efforts to overcome the multitude of challenges such as vandalism, biofouling, rough weather, corrosion, ship time availability, and telemetry issues, among others. Besides these, the COVID-19 pandemic constrained the normal functioning of activities, mainly by delaying the maintenance of the network that resulted in losing a few expensive buoy system components and precious data sets. However, the improvements in the buoy system, in-house developed data acquisition system, and efforts in ensuring the quality of measurements together with “best practice methods” enabled 73% of the buoy network to be functional even when the cruises were reduced to 33% during the COVID-19 lockdown in 2020. The moored buoys equipped with an Indian buoy data acquisition system triggered high-frequency transmission during the Super cyclone Amphan in May 2020, which greatly helped the cyclone early warning services during the COVID-19 pandemic. The COVID-19 lockdown points toward the reliability and enhanced utility of moored buoy observations particularly when other modes of measurements are limited and necessitates more such platforms to better predict the weather systems. The present study analyzed the enhancement of the buoy program and improvisation of the buoy system that extended the life beyond the stipulated duration and enabled the high-frequency data transmission during cyclones amid the COVID-19 lockdown. The recommendations to better manage the remote platforms specifically in the event of a pandemic based on the operational experience of more than two decades were also presented.

AbstractThe article proposes a novel and robust Continuously Homing Submerged Autonomous Tsunami Underwater System (CHATUR) in which the buoy is submerged at a depth of 300 m, collecting sea-level data during normal conditions and surfacing during a tsunami event to transmit the event data. By on-demand reliability analysis, a system in the Bay of Bengal requires health monitoring at an interval of 13 days. By offshore experiments and numerical simulations, the configuration increases the tsunami warning time by ~2 min.

This paper describes the development and performance validation of a cylindrical surface buoy (CSB) used for monitoring tsunamis in Indian seas. The buoy design with multiple compartments provides damage-tolerance curved top surface profile, the subsurface access ensures vandalism resistance, and the shape provides enough space for the power and control systems for an offshore endurance of two years. The scaled-down CSB is numerically modeled and experimentally validated for its stability in a wave basin. The validated numeric model is extended to a diameter of 2.4 m and the mooring loads are analyzed. The field scale prototype CSB is deployed in the open ocean, where the water depth is 2500 m. The performance of the CSB is validated from one year of failure-free performance and capability to remain within the watch circle under all environmental conditions, and it has detected the water level change events during the operational period.

Biofouling formation is one of the critical factors which affect the measurement of continuous real time data in offshore moored data buoy sensors. In order to understand the biofouling trend at different water depths, observations were conducted in instrumented data buoy system moored in the coastal waters and in the Northern Indian Ocean in water depths ranging from 2000 to 4500 m. It is identified that biofouling is predominant only up to a depth of 50 m and Lepas anatifera goose neck barnacle is the common biofoulant irrespective of location and water conductivity. The study also presents typical cases of conductivity sensors drifts due to biofouling and preventing techniques adopted for increasing the maintenance interval and to obtain quality data. The results shall serve as inputs for the design and maintenance of offshore facilities and instrumented moored data buoy systems. (C) 2016 Elsevier Ltd. All rights reserved.

Equipment and structures deployed in seawater and other marine environments are susceptible to marine growth. This marine biofouling is one of the critical factors that affects the measurement of continuous real-time data from the oceanographic sensors deployed for long-term observations. To understand the characteristics of biofouling on marine sensors, an investigation was conducted on sensors deployed in a moored buoy network deployed and maintained by the National Institute of Ocean Technology (NIOT) in the Arabian Sea and Bay of Bengal regions. The present paper attempts to elucidate the characteristics of biofouling on sensor components deployed at seven locations in the Bay of Bengal and five locations in the Arabian Sea, at varying depths ranging from the surface to 500-m depth. Biofouling on bare sensor surfaces and surfaces with various antifouling measures has been studied for 2 consecutive years (2015 and 2016), and the effect of antifouling measures is discussed in this paper. Among the locations studied, buoys deployed in the Arabian Sea exhibited a higher biofouling load compared to the buoys deployed in the Bay of Bengal. The study showed that the pedunculate barnacles Lepas anatifera Linnaeus, 1758, was the predominant biofouling species on these sensors. Furthermore, observations show that the use of copper- and zinc-based antifouling methods reduced the incidence of biofouling by 59% on average.

This paper discusses the analysis done on the meteorological ocean buoy mooring used for monitoring the Indian seas.Based on the extreme environmental parameters experienced by the buoys, mooring loads are analyzed using offshore dynamic analysis software.The results obtained are validated with the tension recorder installed in one of the moorings, and the results are found to comply with an accuracy of better than 1%.The successful on demand performance of the mooring during major cyclones in the Bay of Bengal and the vital meteorological and oceanographic information provided by the buoy during these disastrous cyclonic events validates the mooring design, and proves the data availability for societal needs.The time critical data assimilated in the cyclone prediction models have given confidence to improve the country's weather prediction and climate modelling capabilities.

The moored buoy network maintained by NIOT has crucial role in cyclone and Tsunami warning. It is significant to have continuous, reliable real time data from these moored buoy systems. This paper explains the evolution of effective power system attained after years of experience and extensive study of buoy power system. Non-rechargeable lithium batteries are being used as primary power source because the buoy systems with Lead Acid batteries charged by solar panels are prone to damage. Later a dual battery system was implemented wherein lead acid battery would power the buoy system and in case of failure, the primary lithium battery can take over. A study is being made on installation of wind turbine on the buoy system to cater the power required for redundant charging mechanism.