Envisat making first direct measurements of ocean surface
velocities For more than a decade space-based radar instruments
have been routinely observing ocean surface phenomena including
wind, waves, oil slicks, even the eyes of hurricanes. Now –
employing the same principle as police speed guns – satellite
radar has also begun to enable direct measurements of the speed
of the moving ocean surface itself. The oceans that cover 71% of
the Earth’s surface are constantly in motion. Ocean surface
currents can lead to strong interaction with wind and waves, and
through the transfer of heat influence the weather. Their
dynamic range in the mesoscale is broad, with features such as
current eddies and fronts, occurrences of filaments and jets,
and wind-driven coastal upwelling or downwelling. High-
resolution surface current observations on a large scale are
very difficult, although satellite altimeters permit monitoring
of sea level anomalies that are related to surface currents. Sea
surface temperature and ocean colo