An intensive data collection campaign has been conducted in the coastal waters of the southern North Sea during which a variety of marine optical parameters have ben measured. This has enabled the angular distribution factor of spectral radiance or Q factor to be calculated from in situ measurements. The Q factor relates upwelled spectral radiance to upwelled spectral irradiance and its precise determination is of importance in ocean color remote sensing. Previous modeling studies, often based on the optical properties of case I waters, have proposed a value of 5 for Q. However, this study suggest that more turbid coastal waters may approach the Lambertian case of Q close to (pi) .