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 facet
|Contact: Mariangela D'Acunto|
European Space Agency