Chemistry Reference
In-Depth Information
Fig. 7.
Ratio of slick-covered relaxation rate to clean surface relaxation rate
(drawn), compared to ratio of spectral values (dotted), for wind speed
U
10
= 15
m/s
As a first step, the equilibrium wave spectra were calculated for the
slick-free and slick covered surfaces, respectively (Figs. 1 and 3). Because
of the negative values occurring in the relaxation rates calculated in section
3, these could not be used in the radar modelling. It was therefore neces-
sary to resort to the Plant and Wright relaxation rates again. With the equi-
librium spectra, the form of the source term (Eq. 23) and the relaxation
rates available, the actual spectral values of all wave components were cal-
culated by integrating the action balance equation along the cross cut, i.e.,
by integrating
d
N
1
N
P
(
N
N
)
,
(26)
eq
d
x
c
N
g
eq
starting at
x
= 0 with
N
=
N
eq
. This yields the wave spectrum at each point
along the cross cut. For this the relaxation model mentioned in the intro-
duction ('element 3') was used with a zero current field.
From these calculated wave spectra, the normalised radar cross sections
(
ı
0
) were calculated using the VIERS-1 radar backscatter module (Janssen
et al. 1998). This is a more or less 'standard' composite model which in-
cludes the two-scale effect (Bragg backscatter influenced by longer wave
