Quasi-Inherent Characteristics Of The Diffuse Attenuation Coefficient For Irradiance

The diffuse attenuation coefficient for downwelling irradiance (Kd), the coefficient used to describe the attenuation of irradiance as a function of depth in natural waters, is an apparent optical property. As such, it is a function of the geometry of measurement and other factors which alter the radiance distribution as a function of depth. In spite of this, measurements of downwelling irradiance versus depth and sun zenith angle show that Kd is relatively insensitive to changes in sun angle, thus displaying "quasi-inherent" characteristics, except for very large sun zenith angles. Data will be shown to demonstrate this for a highly productive water type.