Huge Waves From One Storm Slam Coasts Some 6000 Km Apart
Pastor Dale Morgan
Huge Waves From One Storm Slam Coasts Some 6000 Km Apart*
by Staff Writers
Paris (ESA) Jun 01, 2007
Huge waves that struck Reunion Island and coastlines across Indonesia
earlier this month all originated from the same storm that occurred
south of Cape Town, South Africa, and were tracked across the entire
Indian Ocean for some 10 000 kilometres over a nine-day period by ESA's
Envisat satellite.
Waves reaching up to 11 metres devastated France's Reunion Island in the
Indian Ocean when it slammed into the southern port of Saint Pierre on
12 May. Six days later waves created from the same storm measuring as
high as seven metres began crashing into Indonesia coastlines from
Sumatra to Bali, killing at least one person and causing some 1200
people to flee their homes.
Dr Bertrand Chapron of IFREMER, the French Research Institute for
Exploitation of the Sea, and Dr Fabrice Collard of France's BOOST
Technologies in Brest located and tracked the swells using standard
processed Synthetic Aperture Radar (SAR) ESA Wave Mode products, as
shown in the animation above.
"The extreme swell systems originated from the same storm, which moved
rapidly and had two main strong wind periods," Chapron said. "As
illustrated in the animation, the resulting waves were organised into
two main swell systems that followed each other across the entire Indian
Ocean, hitting Reunion Island, Mauritius, Australia and Indonesia."
The waves that hit Reunion Island were forecasted, but their intensity
was predicted to be 20 to 30% below measurements, Collard explained.
"Although swells are still surprise factors, these particular swells
were created by natural events so they could be tracked," Chapron said.
"By using the SAR Wave Mode product, we can locate and systematically
track swells globally, making it possible to put a network of early
warning systems in place in the near future."
"Because of its unique capacity to restitute wavelength and directional
information of the propagation of swells, the SAR instrument is about to
bring a remarkable contribution to the monitoring of energetic wave
systems," Collard said.
Chapron and Collard are working on a global swell-tracking project,
which was presented for the first time at the Envisat Symposium held in
Montreux, Switzerland, from 23 to 27 April 2007, using the Advanced
Synthetic Aperture Radar (ASAR) aboard Envisat to follow these waves in
order to refine their propagation paths and determine their arrival
times and intensities.
Once in place, this system will be the equivalent of deploying a global
network of virtual buoys that are able to detect and track large swell
systems carrying large energy from all available remote sensing
measurements of waves, such as SAR and radar altimetry.
Each virtual buoy will have the capacity to detect and measure the
wavelength and the direction of propagation as well as the height of the
swell systems crossing the oceans, complementing the sea forecast models
used by weather centres and allowing alarms to be raised a few hours
before these devastating swells hit coasts.
Storms are capable of generating waves of different wavelengths that
travel in several directions upon leaving the storm system, with the
longest wavelengths travelling the fastest. As these waves cross open
seas, they can accumulate energy at precise locations and become very
dangerous for marine safety.
In addition, wave systems slow down as they approach the coastline, and
individual waves increase to reach at least two times the mean average
of their initial wave height. For instance, a 5-metre significant wave
height system can hit the coast with the height of 10 metres.
Today, the ASAR Wave Mode acquires 10 by 5 km small images, or
'imagettes', of the sea surface every 100 km along the satellite orbit.
These small 'imagettes' are then mathematically transformed into
averaged-out breakdowns of wave energy and direction, called ocean-wave
spectra, which ESA makes available to scientists and weather centres.
As part of the Global Monitoring for Environment and Security (GMES), a
joint initiative of the European Commission and ESA, the space agency
has undertaken the development of Sentinel-1, a European polar-orbiting
satellite system for the continuation of SAR operational applications.
The Sentinel-1 SAR instrument will also have a dedicated enhanced Wave
Mode capability to double the present ASAR Envisat Wave Mode samplings,
to improve the actual demonstrations for a Near Real Time tracking and
forecasting of swell for European users.
ESA and IFREMER will sponsor an ocean wave data user workshop at IFREMER
in Brest, France, on 20 and 21 September 2007 that will address and
capture user requirements for a possible future wave data service.
In January 2008, ESA will host its second SAR oceanography workshop,
SEASAR 2008, entitled "Advances in SAR Oceanography from Envisat and ERS
missions," at ESRIN, ESA's Earth Observation centre, in Frascati, Italy.