10 May 2007
SeaSondes® Part of India National Tsunami Early Warning System
The India National Institute of Ocean Technology (NIOT) is acquiring 10 additional
SeaSondes as part of a newly forming national Tsunami Early Warning System.
These instruments will be installed along the country's mainland coast and
Andaman Islands.
The SeaSonde network is intended to provide continuous surface current circulation
data during both normal and storm conditions with a parallel processing track
that will work to isolate tsunami wave train signatures from the ambient
ocean current regime. The information collected from HF radar not only has
the potential to detect the tsunami wave train presence prior to its run-up
at shore, but also to quantify the tsunami wave parameters that can be useful
for refining tsunami model forecasts.
SeaSondes deployed will have power sources both "on-the-grid",
as well as "off-the-grid" stand-alone power that will automatically
self-start and keep systems operational during a crisis situation. Communication
links for data retrieval are also designed with standard connections as well
as emergency backup satellite. Data collected by these systems will be automatically
sent to NIOT and Indian National Centre for Ocean Information Services (INCOIS)
offices.
System delivery and installation will take place during this year. ASB Systems
Pvt. Ltd., based in Mumbai, has been contracted for handling critical services
such as site preparation and providing ongoing local service support. Company
founder Mr. Arvind Buchar and his technical team have worked with HF radar
systems and CODAR Ocean Sensors starting from 1995.
HOW AN HF RADAR "SEES" A TSUNAMI WAVE
The most sensitive measurement the HF radar makes is velocity, from the Doppler
shift of the echo. However, what the HF radar sees is not the very fast propagation
speed of the tsunami wave (e.g., 150 km/hr at 180 m depth), but the "current
speed" of the orbital velocity at the crests and troughs, which may
be 30 km apart for a tsunami at this depth.
The HF signal is scattering from resonant Bragg waves that are 6 to 30 meters
long, depending on the radar transmitted frequency. These, in turn, are shifted
by any underlying currents. Near the crest and trough of any wave (including
a tsunami wave), the water undergoes an orbital motion: forward at the crest
and backward at the trough. As the tsunami moves into shallower water, this
orbital velocity will increase, while the spatial period decreases (between
crest and trough). So, as the tsunami wave gets closer to shore, into shallower
water even stronger currents with shorter spatial periods begin to emerge,
presenting an increasingly robust signal for the HF radar to detect.
FOR FURTHER READING
An investigation on using the early HF CODAR radars to detect or measure
the strength of tsunami surface signatures was conducted and published in
the late 1970s [Barrick, D. E. (1979), A coastal radar system for tsunami
warning, Remote Sensing of Environment , vol. 8, pp. 353-358]. More recently,
additional studies of the utility of SeaSondes in tsunami detection have
been published, also in peer-reviewed journals. The latest is B.J. Lipa et
al. (2006), HF Radar Detection of Tsunamis, Journal of Oceanography, vol.
62, pp. 705-716. These and other papers are available for download as PDFs
at the publications section of CODAR Ocean Sensors' website http://www.codaros.com/bib_00-04.htm.
POINTS
OF CONTACT
ASB Systems Pvt. Ltd. is the local India representative of CODAR Ocean Sensors.
Company President Mr. Arvind Bhuchar can be reached by phone at +91 22 2674
1919, or send e-mail to arvindb@vsnl.com.
|
