While values for water-leaving radiance or reflectance are of some interest in themselves, their main significance lies in what they can tell us about the optical properties of the medium, and thus about the concentrations of the optically significant constituents in the water. A route by which such information may be acquired makes use of the approximate relations, derived from theoretical modelling of the underwater light field (§ 6.4), that exist between radiance reflectance (Lu/Ed), or irradiance reflectance (Eu/Ed), and the ratio of backscattering coefficient to absorption coefficient. From eqn 7.4, and explicitly recognizing that Lw and pw are functions of solar angle, satellite viewing angle and azimuth, we obtain n û Û pLw (1,0O,0V' f) /"7 1ÇA
The downward irradiance at the surface, Ed(0+, 1), is a function of the extraterrestrial irradiance, F0(1), solar zenith angle, and the irradiance transmittance of the atmosphere, in accordance with
so we can substitute for F0(1) cos 00 in eqn 7.18 to obtain a a a A\ pt(6>0' 1) Lw(1AA, f) ,
To simplify notation, Morel and Gentili (1996) introduced the term, <(0), which combines all the reflection and refraction effects, in accordance with
(1 - P)[1 - p(ff, f)] 2 <(0 )=-n2(1 - Rr)--(7:22)
Using this notation, and substituting also for rrs (the subsurface remote sensing reflectance) from eqn 6.11, we obtain
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