• Space-based system using GPS satellites

    From ScienceDaily@1:317/3 to All on Thu Apr 28 22:30:46 2022
    Space-based system using GPS satellites could warn of incoming tsunamis


    Date:
    April 28, 2022
    Source:
    University College London
    Summary:
    A new method for detecting tsunamis using existing GPS satellites
    orbiting Earth could serve as an effective warning system for
    countries worldwide, according to a new study.



    FULL STORY ==========================================================================
    A new method for detecting tsunamis using existing GPS satellites orbiting Earth could serve as an effective warning system for countries worldwide, according to a new study by an international team led by UCL researchers.


    ========================================================================== Initial tsunami waves are typically a few centimetres high but nonetheless cause a disturbance in the Earth's upper atmosphere by pushing up air
    and creating an acoustic wave that is amplified as it goes higher.

    This leads to a change in the ionosphere, 300km above the surface of the
    Earth, in which the density of electrons in the area is reduced. This
    in turn affects radio signals sent by GPS satellites to GPS receivers
    on the ground, delaying or speeding up different parts of the signal,
    or changing the signal's direction, depending on frequency.

    For the new study, published in Natural Hazards and Earth System Sciences, researchers from UCL and universities in Japan developed a new way to
    detect this dip in electron density from the altered GPS signals.

    Looking at GPS data at the time of the devastating 2011 Tohoku-Oki
    earthquake and tsunami, they found that a tsunami warning could have been issued with confidence within 15 minutes of the earthquake occurring --
    that is, at least 10 minutes prior to the first tsunami hitting Japan's
    east coast.

    They also found that a warning could have been issued using data from
    only 5% of Japan's 1,200 GPS receivers -- meaning that the method could
    be used in countries with a sparser GPS network than Japan's.



    ========================================================================== Professor Serge Guillas (UCL Statistical Science and the Alan Turing Institute), senior author of the paper, said: "Current tsunami warning
    systems are not as effective as they should be as they often cannot
    accurately predict the height of a tsunami wave. In 2011, Japan's
    warning system underestimated the wave's height. A better warning may
    have saved lives and reduced the widespread destruction that occurred,
    allowing people to get to higher ground and further away from the sea.

    "Our study, a joint effort by statisticians and space scientists,
    demonstrates a new method of detecting tsunamis that is low-cost, as it
    relies on existing GPS networks, and could be implemented worldwide, complementing other ways of detecting tsunamis and improving the
    accuracy of warning systems." Lead author and PhD researcher Ryuichi
    Kanai (UCL Statistical Science and the Alan Turing Institute) said:
    "Our calculations suggest the size and shape of the wave could be
    inferred from the disturbance in the ionosphere and so the next step in
    the research will be to investigate this further to see if the method
    could be used for more precise predictions of tsunami size and range.

    From my experience of working for the Japanese government in the past
    and seeing the damage caused by the tsunami, I believe that if this
    research comes to fruition, it will surely contribute to saving lives."
    The researchers used statistical techniques to reconstruct the depression
    in electron density in the atmosphere based on scattered points provided
    by GPS data, as well as to quantify the uncertainty inherent in the
    modelling.

    The acoustic wave caused by the initial rise in water took about seven
    minutes to reach 300km high in the ionosphere and the depression in
    electron density that occurs as a consequence could be detected via
    satellite signals in 10 to 15 minutes, the researchers found.



    ========================================================================== Tsunami waves are low in deep water but can travel at the speed of a jet
    (up to 800km an hour in a deep sea) and as they enter shallower waters,
    they slow down, growing in height.

    Many existing tsunami warning systems infer tsunami waves from
    earthquakes, but this proposed method could be used to predict incoming tsunamis with non- earthquake sources, such as landslides and volcanic eruptions.

    While some tsunamis reach coasts in under 10 minutes, the researchers
    pointed out that the method could also be used to predict second or
    third waves, helping to determine whether a tsunami warning should be
    cancelled or maintained after the first wave.

    The ionosphere stretches from 48 km to 965 km above the Earth's surface
    (where the Earth's atmosphere meets space). Heat from the Sun cooks the
    gases until they lose electrons (i.e. they become ionised), creating a
    sea of charged particles that includes an abundance of free electrons.

    The study was carried out by researchers at UCL, the Alan Turing
    Institute, Tokai University and the University of Shizuoka, Japan. It was supported by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Earthquake Research Institute at the University
    of Tokyo, the UK's Engineering and Physical Sciences Research Council
    (EPSRC), and the Japan Science and Technology Agency (JST).


    ========================================================================== Story Source: Materials provided by University_College_London. Note:
    Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Ryuichi Kanai, Masashi Kamogawa, Toshiyasu Nagao, Alan Smith, Serge
    Guillas. Robust uncertainty quantification of the volume of
    tsunami ionospheric holes for the 2011 Tohoku-Oki earthquake:
    towards low-cost satellite-based tsunami warning systems. Natural
    Hazards and Earth System Sciences, 2022; 22 (3): 849 DOI:
    10.5194/nhess-22-849-2022 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220428104005.htm

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