ESA to use new radar satellite technique to shed light on ocean current dynamics

Paris, Jan 25: Scientists are going to use ESA’s (European Space Agency) new radar satellite technique to obtain information necessary to understand better the ocean current dynamics and their relevance for climate change.

According to ESA (European Space Agency), 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.

But, ESA's European Centre for Earth Observation in Frascati, Italy, demonstrated that how the new method on data from the Advanced Synthetic Aperture Radar (ASAR) instrument aboard ESA’s 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 till now.

By using the new information embedded in the radar signal, the team of scientists was 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.

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.

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 world’s oceans.

According to Dr Johnny Johannessen of Norway’s Nansen Environmental and Remote Sensing Centre (NERSC), “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."

"The method at this very high resolution could also complement the use of additional information sources to improve 3-D ocean models,” said Dr Bertrand Chapron of the French Research Institute for Exploitation of the Sea (IFREMER).

“Its use for sensor synergy with radiometry, spectrometry and altimetry is very promising," he added. (ANI)