Introduction
NIOT has developed expertise in the area of Ocean Acoustics in the last one and half decades and development of acoustic systems for ocean applications, ambient noise measurements in Indian deep and coastal waters and Polar regions, and underwater acoustic systems for source localization and strategic applications have been accomplished successfully. Further extensive data analysis on ocean ambient noise characterization and noise modelling have been carried out. A vector sensor and array has been developed and demonstrated successfully and is being enhanced towards coastal surveillance applications. The group also maintains an NABL (National Accreditation Board for Testing and Calibration Laboratories) accredited Acoustic Test Facility (ATF) for testing and calibration of underwater acoustic transducers.
Presently the group is focusing on
- Autonomous Ambient Noise Measurement System (ANMS) for polar region and long term measurements in the Arctic.
- Deep water noise measurements over long term for oceanographic as well as strategic applications.
- Vector Sensor Array (VSA) enhancements towards coastal surveillance applications.
- Upgradation and maintenance of ATF.
Deployment of ambient noise system in the Arctic
Ambient Noise Measurement System (ANMS) for polar region and Arctic measurements
Developed an autonomous ANMS for measurements in the Polar region for studying ice dynamics, bioacoustics, meteorological and other anthropogenic noise, through long term measurements, towards understanding climate change. The first autonomous Ambient Noise Measurement System (ANMS)for polar region was developed and deployed successfully along with IndARC mooring in July 2015 at Kongsfjorden Svalbard, Arctic with the support of OOS NIOT and NCPOR. The system is retrieved and redeployed in summer every year and four years data have already been obtained. ANMS was successfully deployed as an independent mooring in 2018
The retrieved data for the period July 2015 to July 2019 has been quality checked, analyzed and interpreted. Sound scape of Kongsfjorden has been analysed and variability in noise levels during open water and ice covered condition is examined. Sound propagation modeling is carried out to understand the variability in ambient noise levels. Ice melting in winter identified and causative factors analysed. Papers have been published in high rated peer reviewed journals including Nature- Scientific reports
Development of Deep Water Ambient Noise Measurement System (DANMS) and measurements in deep waters.
The objective is to record time series of ambient noise data in deep sea Indian ocean region particularly to gain knowledge on noise variability and noise field in deep water, for acoustic oceanographic and strategic applications. A deep water system was acquired and deployed as part of OMNI buoy of OOS, in Arabian sea and one year data obtained. Further indigenous development of DANMS has been accomplished. The system was tested and deployed successfully in Arabian sea and Bay of Bengal.
Deployment of deep water ambient noise system in the Arabian sea
Vector Sensor Array (VSA) enhancements towards coastal surviellance applications
Vector sensors have been increasingly used for Direction of Arrival estimation and parameter inference because it provides significantly high directivity with small aperture. A vector sensor measures acoustic particle velocity in addition to the acoustic pressure using single sensor thereby providing acoustic bearing to the sound source. In an array of vector sensors, the resolution of the angle will be improved and accuracy of localization of sound source will be higher. NIOT has developed three element vector sensor arrays for underwater source localization in shallow waters of the seas, towards surveillance applications.Algorithm for Direction of Arrival (DoA) estimation has been developed, tested and validated with actual field measurements.
VSA testing at Acoustic test Facility
Acoustic Test Facility (ATF)
The Acoustic Test Facility (ATF) established in the year 2002 to caters to the needs of underwater acoustic measurements, underwater acoustic transducer calibration and testing in the range 100Hz to 500 kHz by NIOT, R&D and industrial organizations, and academic institutes. ATF has been accredited by “National Accreditation Board for Testing and Calibration Laboratories (NABL)” since 2005. As part of quality control activity and in order to bring the ATF as a Nationally Designated Laboratory in underwater acoustics, Inter Laboratory Comparison (ILC) was carried out with internationally acclaimed laboratories in Russia and Germany. ILC results established that the hydrophone calibration at NIOT conforms with the International standards and on par with the internationally acclaimed laboratories. Further in 2018, ATF successfully participated in the key comparison of hydrophone calibration organized and conducted by NPL, UK with seven other countries.