Chemistry Reference
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rate. So the methodology used here for deriving a relaxation rate seems to
be valid.
Figures 6 and 7 show the effect of a slick on the computed relaxation
rate. The same slick as for Fig. 3 was used. In the saturation range, the
presence of the slick lowers the relaxation rate by the same order of magni-
tude as it lowers the spectrum. Around
k
= 100 rad m
-1
, the slick leads to a
more stable spectrum. In the capillary range (
k
> 200 rad m
-1
) the relaxa-
tion rate is reduced by exactly the same factor as the spectrum, regardless
whether
ȝ
is positive or negative.
Fig. 6.
Computed relaxation rates for a clean surface (drawn) and with oleic acid
slick present (dotted), for wind speed
U
10
= 15 m/s
4 Radar image modelling
On the basis of the extended VIERS wave spectral model presented above,
it was attempted to calculate the radar backscatter along a transect through
a slick on the sea surface. A slick of 50 m diameter of the same substance
as used in the previous sections (oleic acid) was taken, and the radar back-
scatter was calculated along a 150 m section centred on the slick. A wind
speed at 10 m height (
U
10
) of 5 m/s was used and the radar look direction
was downwind.
