One of the most successful applications of satellite-borne radar altimeter
data over the oceans in recent years has been the extraction of information
about long-wavelength baroclinic Rossby (or planetary) waves, which play a
significant role in ocean circulation and climate dynamics. These waves cr
oss ocean basins from east to west at speeds of a few centimeters per secon
d at midlatitudes. The cross-basin propagation time may therefore be severa
l months or even years, and an accurate estimation of the speed of the wave
s is important. Methods are reviewed for obtaining information on Rossby wa
ve velocity from altimetry data, particularly the two-dimensional Radon tra
nsform. Unfortunately, the use of longitude-time plots, although it allows
the estimation of the zonal phase speeds, does not give any information on
the velocity vector when the propagation of the waves is not purely zonal (
east-west). As shown here, the two-dimensional Radon transform can be gener
alized to three dimensions, enabling not only the true propagation velocity
component to be determined but also the direction of the waves and thus an
y deviation from the pure-westward case. As examples of the application of
this extended technique, maps of direction, speed, and energy of Rossby wav
es in the North Atlantic Ocean are shown.