Design and Development of Energy-efficient Data Acquisition System for Indian Tsunami Surface Buoy System

Sustained real-time ocean observation systems using moored data buoys are vital for the understanding of ocean dynamics and variability to improve oceanographic services such as weather prediction, ocean state forecast, cyclone tracking, tsunami monitoring, and climate change studies. The Indian Tsunami Buoy System (ITBS) developed and operated by the National Institute of Ocean Technology (NIOT) provides vital inputs to the Indian Tsunami Early Warning System (ITEWS) by confirming the propagation of tsunami in the deep ocean; estimating its travel time to the shore; assessing possible impacts on the coastline of the Indian Ocean rim countries during a Tsunamigenic earthquake. The ITBS presently comprises a network of 4 moored surface buoys (MSB); two systems (2) in the Bay of Bengal (BoB) and two systems (2) in the Arabian Sea. The MSB transmits the received data to the INMARSAT satellite terminal, which, in turn, transmits it to the NIOT and Indian National Center for Ocean Information Services (INCOIS) data analysis center, through the Land Earth Station and public networks. Continuous improvements in energy storage, satellite-based communication, deep ocean moorings & data analysis tools and by following standards & best practices, the Mean Time Between Failure (MTBF) of a tsunami buoy communicating from the location to the NIOT-Mission Control Center (NIOT-MCC) through INMARSAT telemetry has been increased from 0.3 years in 2007 to 0.9 years in 2015. They include processor health monitoring using health monitoring module in which the heart beat pulse of the Data Acquisition System (DAS) is monitored by the microcontroller and restores functions when there is a functional interruption. Features to reset the processor hardware during prolonged outages, remote calibration facility and mooring watch circle which are aimed at increasing the availability of the time-critical system are also incorporated. The 4 node network has recorded a MTBF of 1.62 years, with a system availability of 98.3%. The required minimum maintenance interval has increased from 12 months to 24 months. Based on the achieved MTBF, maintenance experiences and the ship availability, the tsunami buoy systems (TBS) are maintained based on a 4-slot annual maintenance program. A DAS with energy-efficient design helps in decreasing the energy consumption and increases the offshore endurance of the MSB thereby reducing the required ship time and the huge maintenance costs involved. A distributed battery configuration, in addition to reduced energy consumption has advantages in operating a section of the DAS during battery failures, which increases the partial availability of the DAS. In a scenario, when the battery pack powering the telemetry fails, the pressure sensor monitoring and processing circuit remains healthy, enabling data availability for post-event analysis. This article describes the development and performance validation of the energy-efficient and reliable data acquisition system (DAS) for ITBS. The moored surface buoy (MSB) with the customized DAS, data encryption techniques, distributed battery architecture with 6-hour reporting interval helps in reducing the MSB power consumption from 5.5Ah to 0.79Ah/day and DAC annual probability of failure from 2.6 to 0.4%. The field performance of the system is validated from April 2019 for 200 days of interruption-free continuous offshore operation in the prototype tsunami buoy system at the location 18° 38’ 9.6” N, 67° 11’ 34.8 E in the Arabian Sea. By implementing this development in the ITBS will improve the reliability and reduce energy costs.