## Pw1 pt1 Pr 1 [Pa1 Pramt1712

that component of total measured reflectance that is due to the water-leaving flux is obtained. It should be noted that the calculated values of pr(1) and [pa(1) + par(1)] include the contribution of skylight reflected at the water surface.

All the individual reflectances in eqn 7.12 can be expressed in terms of the corresponding radiance, and the extraterrestrial irradiance, in accordance with eqn 7.4. Applying this to pw(1) and rearranging, we obtain the water-leaving radiance

p i.e. the atmospheric correction procedure can provide values for pw(1) or Lw(1), as required. The water-leaving radiance is for some purposes converted to the normalized water-leaving radiance, [Lw(1)]N,486,480 which may be defined as the radiance that would exit the ocean in the absence of the atmosphere, with the Sun at the zenith, at the mean Earth-Sun distance. To arrive at Lw(1), [Lw(1)]N is first reduced by the factor cos y0 to allow for non-vertical Sun, and is then further reduced to take account of the attenuation of the downward solar flux through the atmosphere (pathlength 1/cos 0O) by Rayleigh scattering and ozone absorption (the contribution by aerosol being disregarded). The relationship between the two radiances is given by480,28

where tR and tOz are the Rayleigh and ozone optical thicknesses, respectively, and ec is a correction factor, applied to F0(4) and consequently to [Lw(4)]N, accounting for changes in the Earth-Sun distance. Equation 7.14 can be written, more simply, as

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