Hari Vishnu

Research Fellow

Hari is a Research Fellow at ARL working on underwater acoustic signal processing and machine learning. His interests include machine learning for underwater applications, bio-acoustics and signal processing in impulsive noise. These are used in a wide range of underwater applications ranging from biodiversity or defense-related scenarios in shallow tropical waters infested with snapping shrimp noise, to the mineral resources in the depths of the ocean, to the Arctic ice sheets where glacier melt noise dominates the soundscape.

In 2019-2020, Hari also worked as a Visiting Scholar at the Scripps Institution of Oceanography, working on the acoustics of melting ice. He is currently focusing on machine-learning based marine-mammal quantification. Previously, he has also worked with modeling for deep-sea exploration.

He obtained his Ph.D degree from the Nanyang Technological University  (NTU), Singapore, in Computer Engineering. He did his B.Tech in EEE from National Institute of Technology, Calicut, in 2008. His Ph.D involved the development of algorithms for underwater signal processing. These included detection & localization, acoustic propagation modeling, vector sensor processing, and robust methods in impulsive noise.

He is the Chief Editor on the OES Science outreach magazine Earthzine. In 2019, he was awarded the IEEE Oceanic Engineering society’s YP-BOOST award which aims to encourage young professionals to participate in the leadership of the society by attending OES meetings, being involved in the diverse committees, and helping with different aspects of the IEEE OCEANS conferences.

He was the chair of the IEEE OES, Singapore chapter for 2018-2020, and Secretary of the Singapore AUV Challenge since 2016. Through 2015-2017, he was involved with IEEE OES in several roles such as Secretary, Webmaster and Executive committee member of the Singapore chapter.

Hari has been involved with student technical activities since his Bachelors days, where he served on the IEEE Student Branch at NIT Calicut as Public relations officer and Secretary. During this period, he was instrumental in helping give birth to robotics initiatives at NITC, and also in conducting the popular FOSS open source software meet at NITC.

In 2020, Hari was featured on two interviews by IEEE TryEngineering, on the importance of ocean awareness and education – they were showcased as part of the TryEngg. spotlight and TryEngg. Tuesday events.

Apart from research and volunteering activities, he enjoys reading, gardening, listening to music and playing the flute. He is also passionate about anime, movies and TV series.

Find me at:Google scholar .

Find Earthzine here .

Some of my code is public at my Github repo. I also contribute to ARL’s open source repositories at arlpy and UnderwaterAcoustics.jl

If you spot dolphins, dugongs or other marine mammals at Sisters Islands Marine Park in Singapore, please fill this form to help our lab’s research on marine-mammal acoustics:

Research Interests


Journal Articles

  1. H. Vishnu, G. Deane, M. Chitre, O. Glowacki, D. Stokes, and M. Moskalik, “Vertical directionality and spatial coherence of the sound field in glacial bays in Hornsund Fjord,” Journal of the Acoustical Society of America, vol. 148, no. 6, 2020. © 2020 Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America. [ DOI | .pdf ]. See a video describing this paper here. PlumX metrics.
  2. L. J. Wong, B. Kalyan, M. Chitre and V. N. Hari, “Acoustic Assessment of Polymetallic Nodule Abundance Using Sidescan Sonar and Altimeter,” IEEE Journal of Oceanic Engineering, 2020, DOI: 10.1109/JOE.2020.2967108 [ http | .pdf ]PlumX metrics.
  3. C. Wei, Whitlow W. L. Au, D. R. Ketten, H. Vishnu and Abel Z. Z Ho, “Sound propagation in the near and far-field of a broadband echolocating dolphin and a narrowband echolocating porpoise,” Proceedings of Meetings on Acoustics, 2019, DOI: 10.1121/2.0001036 [ http ]PlumX metrics.
  4. C. Chi, V. Hari, T. B. Koay and Mandar Chitre, “Utilizing Orthogonal Coprime Signals for Improving Broadband Acoustic Doppler Current Profilers,” IEEE Journal of Oceanic Engineering, 2020, vol 45, No. 4, pp. 1516 – 1526, DOI: 10.1109/JOE.2019.2925922 [ http |.pdf ]PlumX metrics.
  5. M Chitre, J Tian and V. Hari, “On Ambiguity Function Shaping for Broadband Constant-Modulus Signals,” Signal Processing, vol. 166, 2020, DOI: 10.1016/j.sigpro.2019.07.017 [ http |.pdf ]PlumX metrics.
  6. C. Chi, V. Hari, T. B. Koay and Mandar Chitre, “Robust Resolution of Velocity Ambiguity for Multifrequency Pulse-to-Pulse Coherent Doppler Sonars,” IEEE Journal of Oceanic Engineering, 2020, vol 45, No. 4, pp 1506 – 1515, DOI: 10.1109/JOE.2019.2925919 [ http| .pdf ]PlumX metrics.
  7. S. L. Rigel Goh, V. Hari and Ngan Kee Ng, “The sounds of fighting: contests between violet vinegar crabs, Episesarma versicolor (Decapoda: Brachyura: Sesarmidae) are resolved through acoustic communication,” Journal of Crustacean Biology, 2019, [ DOI ]PlumX metrics.
  8. V. N. Hari, B. Kalyan, M. Chitre, and V. Ganesan, “Spatial modeling of deep-sea ferromanganese nodules with limited data using neural networks,” IEEE Journal of Oceanic Engineering, vol. PP, no. 99, pp. 1–18, 2017. [ DOI  | .pdf  ]PlumX metrics.
  9. A. Mahmood, M. Chitre, and V. Hari, “Locally-Optimal Inspired Detection in Snapping Shrimp Noise,” IEEE Journal of Oceanic Engineering, 2017, vol. 24, No. 4, Oct 2017, DOI: 10.1109/JOE.2017.2731058 [ http | .pdf ] © IEEE 2017PlumX metrics.
  10. V. Hari and M. Chitre, “Robust estimation of modulation frequency in impulsive acoustic data,” IEEE Transactions on Aerospace and Electronic Systems, vol. 53, no. 4, pp. 1932–1946, 2017. [ DOI  | .pdf  ]PlumX metrics.
  11. V. N. Hari, G. V. Anand and A. B. Premkumar, “Narrowband signal detection techniques in shallow ocean by acoustic vector sensor array”, Digital Signal Processing, vol. 23 pp. 1645-1661, June 2013,[ http | .pdf ]©ElsevierPlumX metrics.
  12. V. N. Hari, A. B. Premkumar, and X. Zhong, “A Decoupled Approach for Near-Field Source Localization Using a Single Acoustic Vector Sensor”, Circuits, Systems, and Signal Processing, vol. 32, no. 2, pp. 843–859, Oct. 2012. [ http | .pdf ] ©SpringerPlumX metrics.
  13. V. N. Hari, G. V. Anand, A. B. Premkumar, and A. S. Madhukumar, “Design and performance analysis of a signal detector based on suprathreshold stochastic resonance”, Signal Processing, vol. 92, no. 7, pp. 1745–1757, Jul. 2012. [ http | .pdf ]  ©Elsevier .PlumX metrics.

Invited Conference Talks

  1. G. Deane, O. Glowacki, Hari Vishnu, D. Stokes, M. Chitre, H. Johnson, J. Tegowski, “Recent Progress in Monitoring Tidewater Glaciers with Passive Cryoacoustics,” in 6th Underwater Acoustics conference and exhibition, Greece, June 2021. (Invited). [ .http ]
  2. A. Mahmood, V. N. Hari and M. Chitre, “Model Based Signal Detection in Snapping Shrimp Noise”, Underwater Communications and Network (UComms 2016), Lerici, Italy, September 2016 [http] [.pdf]
  3. G. V. Anand, V. N. Hari and Z. Madadi, “Signal detection in non-Gaussian noise”, SYMPOL 2011, Kochi, 2011

Conferences and Posters

  1. H. Vishnu, G. Deane, M. Chitre, O. Glowacki, D. Stokes, M. Moskalik and H. Johnson, “Spatial variation in acoustic field due to submarine melting in glacial bays,” (Accepted) in ASA meeting 2021, December 2021.
  2. H. Johnson, H. Vishnu, G. Deane, P. J. Tuckman, O. Glowacki, and M. Moskalik, “Depth dependence of acoustic signals produced by bubble release events in melting glacier ice,” in The Journal of the Acoustical Society of America – Acoustics Virtually Everywhere, vol. 148, pp. 2483–2483, December 2020. [ DOI | .pdf ]
  3. H. Vishnu, G. Deane, M. Chitre, D. Stokes, and O. Glowacki, “Vertical line array measurements of the sound radiated by melting glaciers in Hornsund Fjord,” in The Journal of the Acoustical Society of America – Acoustics Virtually Everywhere, vol 148, pp. 2483–2483, December 2020. [ DOI | .pdf ]
  4. Grant B. Deane, Oskar Glowacki, Dale M. Stokes, Mateusz Moskalik, Mandar Chitre and Hari Vishnu, “Measuring tidewater glacier melt rates with underwater noise”, Ocean Sciences meeting, Feb 2020 [http]
  5. L. J. Wong, V. Pallayil, P. Muthuvel, K. Amudha, B. Kalyan, V. Hari, M. A. Atmanand and M. Chitre, “Acoustic Backscattering Properties of Polymetallic Nodules from the Indian Ocean Basin: Results from a Laboratory Measurement”, IEEE Underwater Technology 2019, Kaouhsiong, Apr 2019 [http] [.pdf]
  6. V. Hari, V. Robert, B. Kalyan and M. Chitre, “A semi-supervised learning approach to polymetallic nodule parameter modeling”, IEEE Oceans 2018, Charleston, Oct 2018 [http] [.pdf]
  7. C. Chi, V. Hari and M. Chitre, “A Metric for Selecting Waveforms of Multi-User Wideband Active Sonars”, IEEE Oceans 2018, Charleston, Oct 2018 [http] [.pdf]
  8. C. Chi, V. Hari and T. B. Koay, “Resolving Velocity Ambiguity Based on Robust Chinese Remainder Theorem for Multi-Frequency Pulse-to-Pulse Coherent Doppler Sonar”, IEEE Oceans 2018, Charleston, Oct 2018 [http]
  9. B. Kalyan, R. Mishra, V. Hari and M. Chitre, “An Information Theoretic Approach to Polymetallic Nodule Exploration using AUVs”, (Accepted) Underwater Mining Conference 2018, Bergen, Norway.
  10. C. Chi, V. Hari and T. B. Koay, “Improving broadband acoustic Doppler current profiler with orthogonal coprime pulse pairs and robust chinese remainder theorem”, IEEE Oceans 2018, Kobe, May 2018 [http] [.pdf]
  11. S. Ahmed, V. Hari and M. Chitre, “Monostatic sonar performance using pulse compression waveforms”, IEEE Oceans 2018, Kobe, May 2018 [http] [.pdf]
  12. V. Hari , B. Kalyan and M. Chitre, “Spatial modeling and uncertainty characterization of polymetallic nodules in the Clarion-Clipperton zone”, IEEE Oceans 2017, Anchorage, Sep 2017 [http] [.pdf]
  13. V. Kalaiarasu, V. Hari, A. Mahmood and M. Chitre, “Predicting underwater acoustic network variability using machine learning techniques”, IEEE Oceans 2017, Anchorage, Sep 2017 [http] [.pdf]
  14. A. Mahmood, M. Chitre and V. Hari, “Spatial ambient noise inversion using a single hydrophone”, IEEE Oceans 2017, Anchorage, Sep 2017 [http] [.pdf]
  15. B. Kalyan, V. Ganesan, M. Chitre and V. Hari,” Optimal point planning for abundance estimation of polymetallic nodules”, IEEE Oceans 2017, Anchorage, Sep 2017 [http] [.pdf]
  16. Wong Liang Jie, B. Kalyan, M. Chitre and V. N. Hari, “Polymetallic Nodules Abundance Estimation using Sidescan Sonar: A Quantitative Approach using Artificial Neural Network”, IEEE Oceans 2017, Aberdeen, Scotland, Jun 2017 [http] [.pdf]
  17. M. Hoffman-Kuhnt, Abel Ho, V. N. Hari, M. Chitre and E. Matrai , Alice Tse, “Buzz that Rod ! Acoustic Analysis and patterns of the echolocation signals of a blindfolded bottlenose dolphin performing a horizontal and vertical angular resolution task”, Proceedings of 2015 Society for Marine Mammalogy Biennial Conference, San Francisco, Dec 13-18 [.pdf]
  18. K. C. Unnikrishnan and V. N. Hari, “A vector sensing scheme for underwater acoustics based on particle velocity measurements”, IEEE Oceans 2015, Washington DC, USA, Oct 2015 [http] [.pdf]
  19. X. Zhong, V. N. Hari, X. Shen, H. Wang, W. Wang, “Particle filtering for channel parameter tracking in a noisy shallow ocean environment using a vertical array”, Asia-Pacific Conference on Synthetic Aperture Radar 2015, Singapore, Sep 2015 [http]
  20. V. N. Hari, M. Chitre, Y. M. Too and V. Pallayil, “Robust passive diver detection in shallow ocean”, IEEE Oceans 2015, Genova, Italy [http] [.pdf]
  21. V. N. Hari, M. Chitre, “Robust signal processing in impulsive noise for Sonar”, DSO Tech-know exhibition, Singapore, Jul 2014
  22. V. N. Hari, X. Zhong, A. B. Premkumar, “Near-field/far-field source localization in ocean with an acoustic vector sensor array using polynomial rooting”, Proc. SYMPOL 2013, Kochi, India, Oct 2013 [.pdf[http] 
  23. V. N. Hari, G. V. Anand, and A. B. Premkumar, “Narrowband detection in ocean with impulsive noise using an acoustic vector sensor array” , in 20th European Signal Processing Conference (EUSIPCO 2012), 2012, pp. 1334–1339. [.pdf[http]
  24. X. Zhong, V. N. Hari and A. B. Premkumar, ” An Optimal Importance Sampling based Particle Filtering for Channel Parameter Estimation in Shallow Ocean”, Proc. IEEE Global Conference on Consumer Electronics 2012, Tokyo, Oct 2012. [http]
  25. V. N. Hari, G. V. Anand, A. B. Premkumar, and A. S. Madhukumar, “Underwater signal detection in partially known ocean using short acoustic vector sensor array”, in OCEANS 2011 IEEE – Spain, 2011, no. 65, pp. 1–9. [.pdf[http]
  26. X. Zhong, V. N. Hari, A. B. Premkumar, and A. S. Madhukumar, “Particle filtering with enhanced likelihood model for underwater acoustic source DOA tracking”, in OCEANS 2011 IEEE – Spain, 2011, pp. 1–6. [http]
  27. V. N. Hari, G. V. Anand, and A. B. Premkumar, “Preprocessor based on suprathreshold stochastic resonance for improved bearing estimation in shallow ocean”, in OCEANS 2009, MTS, 2009, no. 65, pp. 1–8. [.pdf[http]©IEEE 2009
  28. V. N. Hari, G.V. Anand , A. B. Premkumar, “Optimal suprathreshold stochastic resonance based nonlinear detector”, Proc. 17th European Signal Processing conference (EUSIPCO 2009), Glasgow, 2009, pp. 2062 – 2066. [.pdf]


  • V. N. Hari, “Improved techniques for detection and localization of underwater acoustic sources using acoustic vector sensors”, Ph.D thesis, School of Computer Engineering, Nanyang Technological University, Singapore, 2013

Selected articles published on Earthzine

  1. H. Vishnu, “Understanding the Ocean through sound – JOE October 20 issue”, OES Earthzine, April 2021. [ http ]
  2. H. Vishnu, “Exploring Worlds beyond the coastline” OES Earthzine, January 2021. [ http ]
  3. H. Vishnu and G. Chia, “Inspiring young minds towards Oceanic Engineering – TryEngineering webinar” OES Earthzine, October 2020. [ http ]
  4. H. Vishnu, “AUV-related research articles in April issue of IEEE JOE” OES Earthzine, July 2020. [ http ]
  5. H. Vishnu, “UN Decade of Ocean Science for Sustainable development – Outreach (Part 1/2)” OES Earthzine, June 2020. [ http ]
  6. H. Vishnu, “Climate Science for the public – The IPCC report on Ocean and Cryosphere” OES Earthzine, March 2020. [ http ]
  7. L. J. Wong and H. Vishnu, “OCEANS ’19 Marseille: Analysis of the number of papers mentioning machine learning.” IEEE Earthzine, February 2020. [ http | .pdf ]
  8. H. Vishnu, “(Editorial) Earthzine announces Plastics theme for first quarter of 2020” OES Earthzine, January 2020. [ http ]
  9. H. Vishnu, “Data. To store or not to store, that is the question” OES Earthzine, October 2019. [ http ]
  10. H. Vishnu, “Arctic Research at Oceans 2019 – A summary” OES Earthzine, September 2019. [ http ]
  11. H. Vishnu, “(Editorial) Earthzine resumes operations” OES Earthzine, August 2019. [ http ]

Online webinars delivered

  1. Webinar delivered at TryEngineering Tuesday event, on Oceanic Engineering, “Try Engineering Tuesday featuring Hari Vishnu and Brandy Armstrong, Oceanic Engineering Society”, September 2020.
  2. Webinar delivered at TryEngineering Spotlight event, on careers in Oceanic Engineering, “Try Engineering Spotlight Featuring Hari Vishnu and Grace Chia, Oceanic Engineering Society”, July 2020.