The bulk properties of natural waters are often divided into inherent and apparent optical properties, respectively. Inherent optical properties (IOPs) include the beam absorption, beam scattering, and beam attenuation coefficients (a, b, and c, respectively). By definition, IOPs depend only upon the medium, including its dissolved and suspended components. The geometry or magnitude of the incident light field does not influence them. Apparent optical properties (AOPs) also are determined by the medium, but additionally are influenced by the geometry and magnitude of the incident light field because they are based on irradiances, rather than field radiances. Apparent optical properties include irra-diance reflectance (R), remote sensing reflectance (Rrs), and the coefficients of vertical light attenuation (K-functions). When we divide Eu by Ed we obtain the irradiance reflectance at the point of measurement, which is important for remote sensing purposes. The coefficient of vertical light attenuation defines the relative loss of light with increasing depth.
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