Chapter 1: INTRODUCTION
while the flux absorbed by the sea is equal to
1
d
r
b
d
I
I I
I
A
(1.57)
Fresnel’s formula can be used for an idealized plane sea surface to
calculate the reflectance coefficient, R s , which is independent of absorption
and scattering properties of the waters. Curve 1 in Figure 1-7 corresponds to
the idealized case of direct incident solar rays and flat ocean surface; curve 2
includes scattered solar radiation as well (cloudy sky). The reflectance
coefficient typically lies in the range of 5 to 7 % for a plane sea surface and
an overcast sky, but can exceed 30 % when the sun is low on the horizon of
a clear sky.
Cox and Munk (1956) and Saunders (1967a) studied reflectance
calculations in more complicated situations including rough seas and low
solar elevation. Their results are also shown in Figure 1-7 (curve 3). Note
that the solar elevation [ and solar zenith angle T are related by[
R
T
27
Figure 1-7. Reflectance coefficient (R s in our notation) as a function of the solar elevation [ҏ
Here: curve 1 is the idealized case of direct incident solar rays and flat ocean surface; curve 2
the case of total (direct and scattered) solar rays and flat ocean surface; curves 3 the case of
direct solar rays and rough seas. Curves 3 are calculated from the Cox and Munk (1956) data
for two different assumptions regarding multiple reflections at low sun elevations. (After
Ivanoff, 1977.) Copyright owner could not be found.