Chemistry Reference
In-Depth Information
monics and freely propagating Bragg waves, whereas the Ka-band back-
scatter is caused mainly by freely propagating Bragg waves. In particular,
the generation of freely propagating wind waves results in a reduction of
the X-band Doppler shift at wind speeds of 4.5-5 m s
-1
, which is less dis-
tinct at Ka-band.
When comparing the results obtained by different authors, one has to
take into account the different experimental set-ups, which may lead to dif-
ferent results. In particular, the existence of bound (Bragg) waves does not
only depend on the wind speed and frequency of the gravity waves but
also, for example, on the fetch length and the wave age (which may strong-
ly differ in different experimental set-ups). Therefore, we suspect that on
the open ocean X- and Ka-band Bragg waves are encountered that are both
freely propagating and bound to gravity waves (which in turn may be
modulated by the long ocean waves).
Fig. 7.
Measured X- and Ka-band Doppler shifts as function of the reference wind
speed. The measurements were performed with a slick-free water surface. Addi-
tionally inserted into each diagram are the theoretical curves assuming bound
(dashed line) and freely propagating (solid line) Bragg waves
The X- and Ka-band Doppler shifts measured from wind-generated
waves on a water surface covered with oleyl alcohol (OLA) are shown in
Figure 8. It is obvious that the coverage of the water surface with a sur-
