VARION (Variometric Approach for Real-Time Ionosphere Observation)
It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric TEC (Total Electron Content) measurements collected by continuously operating ground-based receivers from the GNSS (Global Navigation Satellite Systems). - The notion that gravity waves generated by tsunami waves (even with wave heights of a few centimeters in deep ocean) can propagate upward in the atmosphere and ultimately cause perturbations in the TEC of the ionosphere was first established by Daniels, and was theoretically further developed by Hines. Peltier and Hines subsequently showed that these TEC variations can be detected through ionosonde measurements. 1)
Using this solid foundation and the abundance of GPS observations, researchers have set out goals to develop models and establish observational systems to provide reliable tsunami forecasts before the actual tsunami waves reach coastlines. It has been demonstrated that effects of an ocean tsunami can potentially be remotely observed as TIDs (Traveling Ionospheric Disturbances) produced by the gravity waves. These TIDs were detected using different methods of observation, including ground-based GPS receivers 2) 3) , Jason-1 radar altimeter 4) 5), ISR (Incoherent Scatter Radar) at Arecibo 6) and space-based measurements. 7) 8)
A team of scientists from the University of Rome"La Sapienza", Rome, Italy, and NASA/JPL (Jet Propulsion Laboratory) in Pasadena, California, has developed a new approach to assist in the ongoing development of timely tsunami detection systems, based upon measurements of how tsunamis disturb a part of Earth's atmosphere. 9)
The new approach, called VARION (Variometric Approach for Real-time Ionosphere Observation), uses observations from GPS and other GNSS (Global Navigation Satellite Systems) to detect, in realtime, disturbances in Earth's ionosphere associated with a tsunami. The ionosphere is the layer of Earth's atmosphere located from about 80 to 1,000 km above Earth's surface. It is ionized by solar and cosmic radiation and is best known for the aurora borealis (northern lights) and aurora australis (southern lights).
When a tsunami forms and moves across the ocean, the crests and troughs of its waves compress and extend the air above them, creating motions in the atmosphere known as internal gravity waves. The undulations of internal gravity waves are amplified as they travel upward into an atmosphere that becomes thinner with altitude. When the waves reach an altitude of between 300 to 350 km, they cause detectable changes to the density of electrons in the ionosphere. These changes can be measured when GNSS signals, such as those of GPS, travel through these tsunami-induced disturbances.
VARION was designed under the leadership of Sapienza's Mattia Crespi. The main author of the algorithm is Giorgio Savastano, a doctoral student in geodesy and geomatics at Sapienza and an affiliate employee at JPL, who conducted further development and validation of the algorithm. The work was outlined recently in a Sapienza- and NASA-funded study published in Nature's Scientific Reports Journal (Ref.1).
In 2015, Savastano was awarded a fellowship by CNI (Consiglio Nazionale degli Ingegneri) and Italian Scientists and Scholars in North America Foundation (ISSNAP) for a two-month internship at JPL, where he joined the Ionospheric and Atmospheric Remote Sensing Group under the supervision of Attila Komjathy and Anthony Mannucci.
"VARION is a novel contribution to future integrated operational tsunami early warning systems," said Savastano. "We are currently incorporating the algorithm into JPL's Global Differential GPS System, which will provide real-time access to data from about 230 GNSS stations around the world that collect data from multiple satellite constellations, including GPS, Galileo, GLONASS and BeiDou." Since significant tsunamis are infrequent, exercising VARION using a variety of real-time data will help validate the algorithm and advance research on this tsunami detection approach.
Savastano says VARION can be included in design studies for timely tsunami detection systems that use data from a variety of sources, including seismometers, buoys, GNSS receivers and ocean-bottom pressure sensors.
Once an earthquake is detected in a specific location, a system could begin processing real-time measurements of the distribution of electrons in the ionosphere from multiple ground stations located near the quake's epicenter, searching for changes that may be correlated with the expected formation of a tsunami. The measurements would be collected and processed by a central processing facility to provide risk assessments and maps for individual earthquake events. The use of multiple independent data types is expected to contribute to the system's robustness.
"We expect to show it is feasible to use ionospheric measurements to detect tsunamis before they impact populated areas," said Komjathy. "This approach will add additional information to existing systems, complementing other approaches. Other hazards may also be targeted using real-time ionospheric observations, including volcanic eruptions or meteorites."
Observing the ionosphere, and how terrestrial weather below it interfaces with space above, continues to be an important focus for NASA. Two new missions — the ICON (Ionospheric Connection Explorer) and the GOLD (Global-scale Observations of the Limb and Disk) — are planned to launch by early 2018 to observe the ionosphere, which should ultimately improve a wide array of models used to protect humans on the ground and satellites in space.
Figure 1: Real-time detection of perturbations of the ionosphere caused by the Oct. 27, 2012, Queen Charlotte Island tsunami off the coast of British Columbia, Canada, using the VARION algorithm (image credit: NASA)
Figure 2: Animation of Oct. 27, 2012, Queen Charlotte Island tsunami as it crossed Hawaii. As the wave (dark blue/white lines approaching from the northeast) moved, it perturbed the atmosphere and changed the density of ionospheric electrons as reflected by navigation satellite signal changes (colored dots), image credit: Sapienza University/NASA-JPL/Caltech
1) Giorgio Savastano, Attila Komjathy, Olga Verkhoglyadova, Augusto Mazzoni, Mattia Crespi, Yong Wei, Anthony J. Mannucci, "Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: A Preliminary Feasibility Demonstration," Nature, Scientific Reports, Vol. 7, Article number: 46607 (2017), doi:10.1038/srep46607, Published online: 21 April 2017, URL: https://www.nature.com/articles/srep46607.pdf
2) Lucie M. Rolland, Giovanni Occhipinti, Philippe Lognonne, Anne Loevenbruck, "Ionospheric gravity waves detected offshore Hawaii after tsunamis," Geophysical Research Letters, Volume 37, Issue 17, Sept. 2010, DOI: 10.1029/2010GL044479
3) David A. Galvan, Attila Komjathy, Michael P. Hickey, Philip Stephens, Jonathan Snively, Y. Tony Song, Mark D. Butala, Anthony J. Mannucci, "Ionospheric signatures of Tohoku-Oki tsunami of March 11, 2011: Model comparisons near the epicenter," Radio Science, Vol. 47, RS4003, doi:10.1029/2012RS005023, 2012
4) Giovanni Occhipinti, Philippe Lognonne, E. Alam Kherani, Helene Hebert, "Three-dimensional waveform modeling of ionospheric signature induced by the 2004 Sumatra tsunami," Geophysical Research Letters, Vol. 33, Issue 20, October 2006, DOI: 10.1029/2006GL026865
5) Chao-Lun Mai, Jean-Fu Kiang, "Modeling of ionospheric perturbation by 2004 Sumatra tsunami," Radio Science, Vol. 44, Issue 3, June 2009, DOI: 10.1029/2008RS004060
6) M. C. Lee, R. Pradipta, W. J. Burke, A. Labno, L. M. Burton, J. A. Cohen, S. E. Dorfman, A. J. Coster, M. P. Sulzer, S. P. Kuo, "Did Tsunami-Launched Gravity Waves Trigger Ionospheric Turbulence over Arecibo?," Journal of Geophysical Research: Space Physics, Vol. 113, Issue A1, January 2008, DOI: 10.1029/2007JA012615
7) Pierdavide Coïsson, Philippe Lognonne, Damian Walwer, Lucie M. Rolland, "First tsunami gravity wave detection in ionospheric radio occultation data," Earth and Space Science, Vol. 2, Issue 5, May 2015, DOI: 10.1002/2014EA000054, URL: http://onlinelibrary.wiley.com/doi/10.1002/2014EA000054/epdf
8) Yu-Ming Yang, X. Meng, A. Komjathy, O. Verkholyadova, R. B. Langley, B. T. Tsurutani, A. J. Mannucci, "Tohoku-Oki earthquake caused major ionospheric disturbances at 450 km altitude over Alaska," Radio Science, Volume 49, Issue 12, Dec. 2014, pp: 1206 - 1213, DOI: 10.1002/2014RS005580
9) Alan Buis, Tony Greicius, "Scientists Look to Skies to Improve Tsunami Detection," NASA/JPL, May 17, 2017, URL: https://www.jpl.nasa.gov/news/news.php?release=2017-143
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).