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Temperature and salinity are essential ocean variables for understanding the oceans' physical processes. The conductivity and temperature measurements are used for deriving ocean salinity. Conductivity-temperature (CT) sensors mounted on moored buoys are widely used to collect sustained time-series observations of temperature and salinity. However, these measurements are prone to drifts that need to be corrected to ensure data quality. The present study evaluates a field validation technique to correct the drift in subsurface temperature and conductivity measurements that can potentially complement the standard calibration procedure performed by the original equipment manufacturer. The advantage of field validation is that it could be carried out soon after retrieving CT sensors, which ensures that the physical conditions and configuration of the retrieved CT sensors remain unaltered from that of the in-situ conditions. The drift in the CT sensors was analyzed by pre-deployment and post-retrieval field validation of CT sensors. A correction is applied to the raw data assuming a linear trend in drift with time. An ice test to identify and correct the errors in the timestamp of CT measurements is also discussed.

Precise and accurate monitoring of atmospheric pressure by barometric pressure sensors used in moored buoys in the Indian Ocean is a key factor in cyclone monitoring and climate studies. Underperformance of these sensors has significant impacts on societal protection, weather predictions, and climate modeling. Experimental studies are carried out on the barometric pressure sensors used in moored buoys to quantitatively estimate the uncertainties due to sensor accuracy, drift, static pressure head, and satellite telemetry resolution. The overall measurement uncertainty of the pressure sensors is identified to be ±0.13 hPa, which is within the accuracy limits recommended by the World Meteorological Organization (WMO).

The 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.

Based on the in-situ subsurface thermal and salinity measurements from the Ocean Moored Buoy Network for Northern Indian Ocean (OMNI) during the passage of very severe tropical cyclones (TCs) in the Bay of Bengal, we have identified that the depth of ocean‐atmosphere interaction is limited by the depth of the pycnocline. During the TC Vardha and Phailin with cyclone-period-averaged wind speeds of 8 and 21 m/s, respectively, the maximum possible rates of water-vapor generation during the cyclone period, computed based on the salinity changes and considering precipitation, are 1.0 and 9.3 kg/m2/h, respectively. For the same wind speeds, based on the ocean heat content (OHC) changes, it is quantified that ~78% and 89% of the OHC changes are in the form of latent heat. The real-time availability of the in-situ subsurface parameters can be used in the ocean-atmosphere coupled models and intensification studies.

Reliable performance is the key requirement for deep ocean wave measurement buoys as failures lead to loss of data and expensive reinstallations. From more than 0.37 million demanding offshore wave measurement buoy-hours, the data returns from the buoys operating in the Bay of Bengal and the Arabian Sea were 88% and 95%, respectively. The mean time between failures of the buoys was 1.8 years in the Bay of Bengal and 3.8 years in the Arabian Sea, and the mean time to restore was 90 and 68 days, respectively. The offshore failure events, the technical developments for improving the performance, and the strategies adopted to mitigate the failures are presented in detail. The significance of the technical features incorporated for improving the reliability of the wave measurement buoy subsystems is quantitatively represented through fault tree modeling and simulations based on standards and the field failure data.

Sustained real-time ocean observation systems using moored data buoys are vital for understanding ocean dynamics and variability, which are essential for improving oceanographic services including weather prediction, ocean state forecast, cyclone tracking, tsunami monitoring, and climate change studies. This paper describes the significant rapid restoration techniques implemented to increase the availability of the Indian Ocean observation networks over the past two decades. The efforts have helped in achieving availability of 97.9%, 82.3%, and 98.7% for the meteorological sensors, subsea surface oceanographic sensors, and tsunami buoy network, respectively.

With land-based resources depleting fast, sustained harvesting of ocean resources with an appropriate trade-off between economic growth, social needs, and the health of the ocean environment is essential. India, with an over 7600-km-long coastline, an exclusive economic zone of 2.3 million km2, and seeking extension for additional 560 km, has initiated blue economic policies for leveraging the growth of the national economy. The first part of the paper presented in the OCEANS '18 conference in Kobe discussed the technology initiatives to harness the vast living and nonliving blue economic resources in India, including deep-ocean minerals, hydrocarbons, renewable energy, ocean desalination, and bioprospecting. This paper describes the activities carried out related to the activities undertaken by the National Institute of Ocean Technology (NIOT) in the areas of coastal protection, cyclone and tsunami early warning systems, coral habitat observations, sustainable fishing, and numerical studies carried out to understand the influence of natural gas leaks on deep-ocean ecology.

Over the past two decades, the Indian Ocean moored surface buoy observation networks have expanded in the spatiotemporal domain and technologically matured with system reliability, availability, cost optimization, and precision measurement of meteorological and oceanographic parameters as the key targets. Based on the return of experiences in the development, operation, and maintenance of the moored buoy observation networks over two decades, this paper for the first time summarizes the reliability metrics achieved by the National Institute of Ocean Technology (NIOT)-operated moored buoy networks, the healthiness monitoring interval implemented to achieve the highest level of on-demand reliability, the methodologies adopted to ensure highest possible system availability, and data returns. The tsunami buoy network with two buoys and the meteorological buoy with cyclone tracking sensors are found to have a mean time between failure of 1.27 years and 0.5 years, respectively. The identified performances provide a baseline for defining the technical improvement targets, identifying alternate technologies, incorporating redundancies, cost optimization, and maintenance planning. The approach serves as a reference for reliability assessment and integrity management of similar moored buoy ocean observation networks and for evolving standards for oceanographic systems.

This paper assesses the reliability of data reception of the offshore moored Indian meteorological buoys equipped with INSAT telemetry and used for monitoring the Indian seas. Based on 11,952 data transmissions spanning 4.2 buoy-years, the data reception performance of the INSAT-based telemetry system is found to be 98.74%, with a corresponding data “mean time to failure” (MTTF) of 51 h. It is also identified that the moored buoy telemetry hardware conforms to an IEC 61508 Safety Integrity Level 4. The identified reliability results serve as a guideline for offshore system designers using INSAT telemetry. Meteorological data buoys with INSAT telemetry shall provide an opportunity for collecting extensive and cost-effective oceanographic data, which are used for improving the effectiveness of the Indian Ocean monitoring programs and for cost-effective integrity management of critical systems used for tsunami early warnings.

Sustained and real-time ocean observation systems using moored data buoys are vital for understanding ocean dynamics and the variability required for improving oceanographic services, including weather prediction, ocean state forecast, and climate change studies. This paper presents the effectiveness of India's moored data buoy network in capturing the response in the ocean during the cyclonic disturbances formed in the Bay of Bengal (BoB) and the Arabian Sea (AS) during the last 5-year period. The moored buoy network provided critical information about the evolution and intensification of low-pressure systems and supported the India Meteorological Department to improve prediction capabilities by incorporating real-time data. The lowest mean sea-level pressure of 920 hPa was recorded in the BoB during the very severe cyclonic storm Phailin. The warning systems adopted for the effective dissemination of the ocean forecast services to the user community have significantly reduced the loss of life and property in coastal states.

This paper analyses the reliability of the Indian Tsunami Early Warning System (ITEWS), comprising a 24 × 7 manned and automated center capable of monitoring the seismic, open sea water level and coastal tide levels and disseminating tsunami bulletins with the aid of proven prerun scenario models during a tsunamigenic earthquake. Since its inception in 2007, the ITEWS has undergone technological maturity with reliability as the prime objective. The system is expected to be in operation throughout the year and alerting the entire Indian Ocean rim countries in the event of a tsunami. Based on International Electrotechnical Commission (IEC) 61508 standards and field failure data, quantitative reliability modeling is done for the subsystems, and it is found that the seismic network, tsunami buoy network, and distress information dissemination systems conform to Safety Integrity Level SIL4, while tide gauge stations conform to SIL4 with a maintenance interval of 45 days. In case of the tsunami buoy network, the failure of one tsunami buoy degrades the network to SIL3 and needs to be restored within 8 months. The study provides confidence on ITEWS's reliable support to tsunami early warning.

This paper describes the Advanced Data Reception and Analysis System (ADDRESS) used for monitoring Indian Ocean moored buoys and the reliability analysis done on the data reception and dissemination performances. The system needs to be highly reliable, as the critical real-time data received from the tsunami and meteorological buoys are used for societal protection decision support systems during tsunami and cyclonic events. Driven by demanding societal needs, the developed ADDRESS with a 24/7 manned and automated Mission Control Center and the implemented system integrity proof test interval is found to conform with the IEC 61508 SIL 4 safety and reliability levels and to have an availability of 99.9938%. The graphical display capabilities developed are used for buoy deployment support, early restoration of failed moorings, and for up-keep of system components operating in remote harsh offshore environments by monitoring their performance over time.

This paper details the evolution of reliable and cost-effective data buoy power systems used for environment monitoring applications in the Indian seas. A reliable power system is the key requirement for offshore moored buoys involved in meteorological and tsunami monitoring missions, as unavailability of the operating power results in loss of time-critical data and can have serious impact on societal protection and, in addition, results in costly repairs and reinstallations. As a significant development and driven by stringent IEC 61508 Safety Integrity Level (SIL) standards, a Generation III power system was able to meet the required SIL 4 reliability requirements compared to the Generation I system that complied only with SIL 1. It is found that by using a suggested four slot annual maintenance plan, an operating Generation III hybrid power system, and lead acid batteries powered by solar energy and backed by Lithium thionyl chloride batteries, in addition to meeting the required SIL 4 reliability levels, the energy cost of transmission is reduced to U.S. $1.7 per data set, compared to U.S. $2.7 in the Generation II systems. Ongoing efforts in increasing the green footprint in futuristic systems are detailed. The study provides confidence in the power system’s reliable, cost-effective and eco-friendly support to India’s Ocean Observation Network program.

Underwater technology is advancing with the development of instruments capable of measuring continuous data for longer durations for diversified ocean data collection. A bottom pressure recorder is deployed on the seabed to measure the water level for tsunami early warning, thus playing a critical role in saving lives. Recently, many countries have installed their warning systems. Here, we report an unusual corrosion of such an instrument deployed in the deep sea (3,250 m) in the Bay of Bengal, which led to severe damage of the instrument. This paper reports for the first time on the investigation and possible causes for this unusual corrosion of an instrument made from highly marine corrosion-resistant aluminum alloy and duplex stainless steel material.