Geoscience Reference
In-Depth Information
6.3 Tsunami Detection in the Open Ocean by Satellite Altimetry
Revelation of the place and time a tsunami wave originates is based on seismic in-
formation obtained immediately after the earthquake. The absence of observational
data on the tsunami parameters at the source leads to a low efficiency of the com-
putational models, determining the arrival time and amplitude of a wave at each
concrete point. As a result, the level of false tsunami warnings increases.
Thus, for example, during the Shikotan tsunami of October 4, 1994, which hap-
pened to be catastrophic for the Southern Kurils and the Hokkaido island, the inter-
national service sent a warning to the Hawaii islands about the possible approach of
a tsunami several meters high. Significant financial means (up to US$ 30 million)
were applied in evacuating thousands of people, although the height of the tsunami
turned out to be about half a metre. In these conditions the application of remote
satellite methods for registering tsunami waves would have permitted to obtain
the lacking information at the very moment of the earthquake or immediately af-
terwards.
Many thousands of human lives could have been saved during the tsunami of
December 26, 2004, if the system for satellite registration of tsunami waves had
already been functioning within the Indian Ocean.
Direct tsunami measurements, received by coastal-level recorders, contain oscil-
lations strongly distorting the initial record of a wave in the open ocean. The arrival
of a wave in shallow water and its reflection from the coast leads to enhancement
of its amplitude, but the spectrum (shape) of the signal is distorted by the resonance
properties of the shelf, bays and straits. The best in quality records of tsunamis in
the open ocean are provided by sensors of the bottom hydrostatic pressure [Kulikov,
Gonzalez (1995)]. However, such systems are very expensive and point-like mea-
surements do not provide for total coverage of probable zones of tsunami wave
origination. The rapid development of remote (satellite) methods opens up new pos-
sibilities for resolving problems of efficient tsunami forecasting.
At present, a cardinal way for resolving the problem of sea-level investiga-
tion not only near, but also at a significant distance from the coast with clear
connection to a unique geodetic reference system consists in the application of
satellite altimetry and, for example, high-precision radio-altimetry measurements
using the Earth's artificial satellites (EAS) GEOSAT, TOPEX/POSEIDON, ERS-
1,2, JASON-1 and ENVISAT. For this purpose, in the future, measurements can be
made use of, that were made by the Russian geodetic EAS 'Musson-2' and other
satellites with altimeters, designed in other countries. The accuracy, with which
the data on the sea level are correlated to the common system of heights is pro-
vided for by the receivers of one of the navigational systems, GLONASS, GPS or
DORIS, established on board the satellite. At present, the data of satellite altimetry
are widely applied in investigations of mesoscale variations of flows, tides, etc.
Modern systems and means of satellite altimetry are successfully applied for
studying properties of the oceanic lithosphere, determination the parameters of
lunar-solar tides in the ocean. The existence of a correlation has been established
between the level topography of the World Ocean and circulation of water masses
