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The Wave Propagation Group was established simultaneously with the foundation of the Institute of Applied and Computational Mathematics in 1985. The main focus of the group is in the area of underwater acoustics with applications in oceanography and geophysics. Activity areas include forward propagation modelling, inverse problems such as ocean acoustic tomography, source localization, sea-bed reconstruction and inverse scattering, analysis of sonar performance, marine bioacoustics, statistical signal characterization and noise modelling. Further research interests refer to elastic and seismic waves. The group develops integrated software products to address problems in the above areas as well as for educational purposes (digital game-based learning) and also contributes to the education and training of students and young researchers. In addition to a large number of publications, the group has been organizing since 1996 a series of successful international conferences and workshops in underwater acoustics and wave propagation. Since 2000 the group maintains an underwater acoustic measurement laboratory for conducting  scaled propagation experiments in a custom-built water tank, acoustic measurements in the sea, calibration of acoustic transducers, and more recently development of experimental acoustic devices. The group also maintains a seismological station for continuous monitoring of the seismicity in the area of Heraklion.

Ocean acoustic propagation modelling: The core of the group’s activities is the development of mathematical models that simulate acoustic wave propagation in the underwater environment. These models solve boundary value  problems in unbounded domains based on the wave equation, the Helmholtz equation and its parabolic approximation and can be used to predict the acoustic field in environments of arbitrary bathymetry, bottom structure and sound-speed distribution. The development of efficient methods for the calculation of broadband acoustic fields and associated time-frequency analysis also belong to the activities of the group.

Ocean acoustic tomography: The group’s activity in ocean acoustic tomography (use of sound to sample sound-speed and temperature changes in the water column in the large scale) focuses on the development of enhanced analysis methods for tomographic data, based on wave-theoretic propagation modeling. Its contributions include modelling and sensitivity analysis of tomographic observables, methods for adaptive non-linear inversion, matched-field and matched-mode methods, statistical signal identification and inversion schemes, as well as schemes for automated analysis of tomography data. The group has participated in the design and analysis of large-scale tomography experiments in the Mediterranean Sea, the North Atlantic and the Arctic Ocean. Since the beginning of 2023 the group participates in an EU-funded  major international effort for acoustic thermometry and monitoring of climate change in the high Arctic.

Inverse scattering in waveguides: The research in this area focuses on the reconstruction of velocity inhomogeneities from point source data for the wave equation, and on the study of global uniqueness for the reconstruction of the refraction index from the DtN map for the Helmholtz equation, on complex geometric optics for waveguides as well as on the reconstruction of hard obstacles in homogeneous wave guides. Inverse problems for non-homogeneous acoustic and elastic waveguides are studied with new imaging functionals such as quantum fidelity and Loschmidt echo, by exploiting aspects of chaotic ray dynamics.

Sea-bed identification: The group’s activities include the development of inversion methods using either local reflections from the sea-bed or measurements of the sound field at long range. Inversion procedures based on optimization schemes have been developed. The group is using the tank facility of the hydroacoustics laboratory to perform experiments associated with local reflection problems and validate relative inversion schemes. The group has participated in the design and analysis of sea experiments aiming at the classification of the sea-bed in the Haro Strait (Canada), the Central Atlantic Ocean and the Edukki lake in India.

Underwater acoustic signal processing, detection and localization: Underwater acoustic propagation modelling is combined with statistical signal processing, detection and estimation theory for the analysis of underwater acoustic surveillance (SONAR) systems, active (monostatic and multistatic) and passive (broadband and LOFAR). Further, new methods for statistical characterization of underwater acoustic signals are developed as a means towards the development of enhanced tomographic and geoacoustic surveillance methods. Methods for the localization of sound sources from their acoustic field using ray- and wave-theoretic propagation modeling are developed based on matched-field processing.

Marine bioacoustics: The group’s activity in ocean bioacoustics began in 2001, focusing on sounds by marine mammals, sperm whales and Cuvier's beaked whales, in particular, in collaboration with PELAGOS Cetacean Research Institute. The group uses its expertise on underwater acoustics to develop methods and tools for the analysis and characterization of cetacean sounds as well as for passive localization of vocalizing animals. Recently it developed a real-time acoustic observatory for detection and lcocalization of sperm whales off SW Crete in the framework of the SAvEWhales project, see https://sites.google.com/view/savewhales. The group has also participated in projects involving experiments in fish tanks to record, identify and analyze sounds produced from marketable species, such as Sparus Aurata and Dicentrarchus Labrax.

Ambient noise: The group is active in the modelling of shipping noise since the late 1980s. In 2015 it developed an operational system for real-time prediction of shipping noise in the Eastern Mediterranean Sea using real-time AIS data and wave propagation modeling – that system provides hourly predictions of noise distribution over the whole basin at different depths. The group has also developed autonomous noise recorders that can be used for ambient noise monitoring in the framework of the MSFD (EU Marine strategy framework directive. In addition, the group works on the spatial coherence of ambient noise field, in connection with passive tomography relying on cross-correlation of the noise field at different locations and the emergence of the Green’s function.

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Underwater acoustic measurements laboratory: Established in 2000 it provides experimental support to the wave propagation group and also expands the activities of the institute in the field of applications and services. It includes an indoor facility (experimental tank) whereas it also has a capacity for acoustic measurements at sea. The laboratory activities include conduction of scaled ocean acoustic propagation experiments, measurement of reflection coefficients, calibration of acoustic transducers, non- destructive testing of materials, as well as outdoor measurements, including localization experiments, measurements of acoustic signatures and bioacoustic measurements in the audible and ultrasound regime. In recent years the laboratory infrastructure is exploited by the Wave Propagation Group for the development of experimental and operational acoustic devices such as autonomous ambient noise recorders and acoustic receiving stations for deployment at sea. For more information visit the laboratory website.

Seismic wave propagation - seismological station: The study of elastic and seismic waves are among the research interests of the group. Crete is an area of high seismic risk and monitoring its seismic activity is of vital importance. A seismological station was established in 2009 at FORTH for continuous monitoring of the seismicity in the area of Heraklion. The station is linked to the Hellenic Seismological Broadband Network of the National Observatory of Athens (NOA_HL). Statistical and probability based seismic signal characterization methods have been developed for the analysis of seismic records.

Software products: The ocean acoustic propagation and inversion codes developed by the group are integrated in user-friendly software environments. These environments are integrated in the sense that they provide a broad range of tools and data for properly defining and efficiently solving problems in underwater acoustics. The group has been developing integrated software products for applications such as sonar performance prediction, tomographic analysis, and operational passive acoustic localization, as well as for educational purposes.

International conferences: Since 1996 the group has been organizing a series of international conferences and workshops in underwater acoustics and wave propagation, among them the very successful 4 International Conferences on Underwater Acoustic Measurements – Technologies and Results (2005, 2007, 2009, 2011) followed by the 6 International Conferences on Underwater Acoustics (2013, 2014, 2015, 2017, 2019, 2021). In addition the Group Organized the International Conference on Theoretical and Computational Acoustics in 2007, the EURONOISE 2018 and the National Congress on Acoustics in 2006 while it hosted the annual meeting of the EC Technical Group of Noise (TG Noise) in 2019.

Education and Training: The group contributes to the education and training of undergraduate, graduate and post-graduate students as well as of PhD candidates and Postdoctoral researchers in the area of underwater acoustics and wave propagation. The group further develops educational software for interactive learning in these areas.

A. ONGOING PROJECTS

• HiAOOS: High Arctic Ocean Observation Systems - next generation of scientific instrumentation, tools and methods, EU–Horizon Europe, 2023-27

B. COMPLETED PROJECTS

• WHALES ‘24, Founding Agency: OceanCare, 1/6/2024 – 24/12/2024
• QUIETSEAS: Testing propagation models in critical areas of the Mediterranean Sea to be used for the traffic noise modeling, EU DG-Environment, 2021-2023.
  
• AUTOREC: Development of Underwater Acoustic Listeners, HCMR, 2020-2023.
• SAvEWhales: System for the avoidance of ship strikes with endangered whales. Development of a real-time acoustic observatory for sperm-whale detection and localization, Ocean Care, 2019-2022. https://sites.google.com/view/savewhales
• QUIETMED II: Consultation on the criteria to define thresholds for continuous noise measuring, EU DG-Environment, 2019-2021.
• PTSK: Peak-time sensitivity kernels for noise cross-correlation patterns, US-ONR, 2020-2021.
• SSK: Source sensitivity kernels: A new tool for noise cross-correlation studies, US-ONR, 2019-2020.
• GREEN: Green's function emergence through cross-correlation of shipping noise, US-ONR, 2018-2019.
• QUIETMED: Homogenization of ambient noise monitoring techniques for the Mediterranean Sea, EU DG-Environment, 2017-2018.
• PERAN: Innovative Actions in Environmental Research and Development, GSRT, 2017-2020.
• GREEN: Green’s function emergence through cross-correlation of shipping noise, US-ONR, 2018-2019.
• QUIETMED: Joint programme on noise for the implementation of the second cycle of the MSFD in the Mediterranean Sea, EU, 2017-2018
• E-RIHS: The European Research Infrastructure for Heritage Science, EU, 2017-2020
• PHASE-FS: Behavior and sensitivity of phase arrival times in the Fram-Strait area, US-ONR, 2016-2017.
• PHASE-2: Phase behavior and implications for travel-time observables , US-ONR, 2014-2015.
• SEA-EARS: Passive acoustic localization in the sea based on multipath (SEA-EARS), GSRT– Excellence-II Grants, 2014-2015
• EDELWEIS-14: Experiment for passive acoustic detection and localization of whales in the Ionian Sea, Ocean Care – CH, 2014.
• PEFYKA: Environment and natural hazards: New methods for monitoring and study of the ocean environment - GSRT– KRIPIS, 2013-2015.
• PHASE: Behavior and sensitivity of phase arrival times, US-ONR, 2013-2014.
  

RESEARCHERS

• Kalogerakis Michael, Collaborating Researcher
• Kouzoupis Spyros, Collaborating Researcher
• Makrakis George, Collaborating Researcher
• Papadakis Panagiotis, Senior Scientist
• Skarsoulis Emmanuel, Research Director
• Taroudakis Michael, Collaborating Researcher
• Xenaki, Angeliki, Principal Researcher

TECHNICAL SCIENTISTS

• Piperakis George, Technical Scientist
• Orfanakis Emmanuel, Collaborating Technical Scientist

For any information regarding the group please contact:

Wave Propagation Group,
Institute of Applied and Computational Mathematics,
Foundation for Research and Technology - Hellas
Nikolaou Plastira 100, Vassilika Vouton,
GR 700 13 Heraklion, Crete
GREECE

Tel: +30 2810 391800
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. (Mrs. Maria Papadaki)

Tel.: +30 2810 391805
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. (Mrs. Yiota Rigopoulou)