(a) Irradiance of daylight at noon (CIE D65 illuminant) and noon daylight on a sunny day recorded at 3 m depth in the Aegean Sea. (b) Reflectance spectra of blue, orange, and red patches from a Macbeth ColorChecker (MCC). Reflectance is the ratio of reflected light to incoming light at each wavelength, and it is a physical property of a surface, unaffected by the ambient light field, unlike radiance. (c) Radiance of the same patches under noon daylight on land and (d) underwater.