Navigation Links
New radar satellite technique sheds light on ocean current dynamics
Date:1/24/2008

Ocean surface currents have long been the focus of research due to the role they play in weather, climate and transportation of pollutants, yet essential aspects of these currents remain unknown.

By employing a new technique based on the same principle as police speed-measuring radar guns to satellite radar data, scientists can now obtain information necessary to understand better the strength and variability of surface current regimes and their relevance for climate change.

Scientists at the SeaSAR 2008 workshop held this week in ESRIN, ESA's European Centre for Earth Observation in Frascati, Italy, demonstrated how this new method on data from the Advanced Synthetic Aperture Radar (ASAR) instrument aboard ESAs Envisat, enabled measurements of the speed of the moving ocean surface.

Synthetic Aperture Radar (SAR) instruments, such as ASAR, record microwave radar backscatter in order to identify roughness patterns, which are linked to varying surface winds, waves and currents of the ocean surface. However, interpreting radar images to identify and quantify surface currents had proven very difficult.

By using the new information embedded in the radar signal the Doppler shift of the electromagnetic waves reflected from the water surface Dr Bertrand Chapron of the French Research Institute for Exploitation of the Sea (IFREMER), Dr Johnny Johannessen of Norways Nansen Environmental and Remote Sensing Centre (NERSC) and Dr Fabrice Collard of France's BOOST Technologies were able to determine how surface winds and currents contribute to the Doppler shift.

The Doppler shift occurs due to changing relative velocities, experienced in everyday life in the way the pitch of a siren on a passing ambulance goes up as it approaches, then goes down as the vehicle recedes away.

The shift is introduced by the relative motion between the satellite platform, the rotation of the Earth and the velocity of the particular facets of the sea surface from which the SAR signal scatters back to orbit. The initial two values are well known particularly for Envisat, with its very stable satellite orbit and attitude and can be simply subtracted to extract the useful sea surface velocity information.

Chapron first demonstrated the concept in 2005 with initial tests carried out over the Gulf Stream. Although the results were promising, repeat acquisitions and careful validation were not possible. However, based on these conclusions ESA upgraded its ASAR ground segment in July 2007 to systematically process and disseminate a Doppler grid product, a regularly spaced collection of individual Doppler information, for all Wide Swath acquired images.

The Doppler grid, embedded in ESA standard products, is now regularly tested on a number of so-called super-sites, including regions of the Gulf Stream and the greater Agulhas Current, both among the strongest western boundary currents of the worlds oceans.

"These measurements are very useful for advancing the understanding of surface current dynamics and mesoscale variability, as well as for determining surface drift, important for oil dispersion and pollution transport and for wave-current interaction, probably influencing the existence of extreme waves," Johannessen said.

"The method at this very high resolution could also complement the use of additional information sources to improve 3-D ocean models. Its use for sensor synergy with radiometry, spectrometry and altimetry is very promising," Chapron added.

The ground segment upgrade is also allowing the scientists to examine the anticipated Doppler shift signal of the river outflow at the mouth of the Amazon delta to monitor river runoff and improve our understanding of hydrological processes.

Chapron and Collard also presented their Near Real Time global swell wave observations to the workshop, attended by 150 participants from 25 countries. Using standard processed SAR ESA wave mode products, the team produces three hourly animations every morning for the Atlantic, Pacific and Indian Oceans and makes them available online.

Tracking swell waves from space is very important because they are generally preceded by calm water, making it impossible to detect their arrival from shore. Envisats Wave Mode acquires 10 by 5 km small images, or 'imagettes', of the sea surface every 100 km along the satellite orbit. These small images, which depict the wave groups, are then mathematically transformed into wave energy and direction, called ocean-wave spectra.

ESA has provided SAR data to some 500 oceanography projects since 1998 and remains committed to providing continuity to its SAR missions. As part of its Global Monitoring for Environment and Security (GMES) programme, the agency will launch the Sentinels the first series of operational satellites responding to the Earth Observation needs of GMES, a joint initiative of the European Commission and ESA.

Sentinel-1, expected to be launched in 2011, will ensure the continuity of C-band SAR data with ESA's ERS-2 and Envisat satellites. Important applications driving the mission concept include marine - vessel detection, oil spill mapping and sea ice mapping. With these new findings, Sentinel-1 is expected to provide additional information, such as consistent wind, wave and current products.


'/>"/>

Contact: Mariangela D'Acunto
mariangela.dacunto@esa.int
39-069-418-0856
European Space Agency
Source:Eurekalert

Related biology news :

1. Satellites witness lowest Arctic ice coverage in history
2. UNCCD recognizes importance of satellites for combating desertification
3. Satellites help ensure efficient use of pesticides
4. Telemedicine: Health alert via satellite
5. ASU researchers use NASA satellites to improve pollution modeling
6. New technique can be breakthrough for early cancer diagnosis
7. University of Leicester scientists discover technique to help friendly bacteria
8. New technique reveals subtle force-induced changes in biomolecules conformation
9. New magnetic separation technique might detect multiple pathogens at once
10. New technique captures chemical reactions in a single living cell at unprecedented resolution
11. Software Techniques Inc. Selects M2SYS Fingerprint Software to Meet Continuous Growth and Demand for Desktop Biometric Time & Attendance Solutions
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:12/6/2016)... Valencell , the leading innovator in ... a third consecutive year of triple digit growth for ... with a 360 percent increase in companies who have ... driven by sales of its wrist and ear Benchmark™ ... technology for hearables for fitness and healthcare applications. ...
(Date:12/2/2016)... India , December 1, 2016 ... Authentication type (Fingerprint, Voice), Future Technology (Iris Recognition ... and Region - Global Forecast to 2021", published ... USD 442.7 Million in 2016, and is projected ... at a CAGR of 14.06%.      ...
(Date:11/30/2016)...  higi SH llc (higi) announced today the ... brands, industry thought-leaders and celebrity influencers looking to ... taking steps to live healthier, more active lives. ... has built the largest self-screening health station network ... who have conducted over 185 million biometric screenings.  ...
Breaking Biology News(10 mins):
(Date:12/6/2016)... Ind. , Dec. 6, 2016 Zimmer ... "Company") today announced the pricing terms of its ... to $1.25 billion aggregate purchase price (excluding accrued and ... settlement date and excluding fees and expenses related ... the debt securities identified in the table below ...
(Date:12/6/2016)... ... December 06, 2016 , ... ... company focused on discovery and development of precision treatments for neurodegenerative diseases, ... for Alzheimer’s disease (AD) inhibited the direct neurotoxic effect of prion-like forms ...
(Date:12/5/2016)... ... 05, 2016 , ... This composition patent, U.S. Patent No. ... The composition claims are not limited to any particular process to make or ... carbon fibers, graphene, and other materials. A continuation application, U.S. Patent App. ...
(Date:12/5/2016)... ... ... In anticipation of AxioMed’s exclusive cleanroom manufacturing facility in ... Lubinski will be traveling to Germany on December 6th. Mr. Lubinski will meet ... discuss the benefits of a viscoelastic total disc replacement. , AxioMed received its ...
Breaking Biology Technology: