Measurements of ultraviolet spectral radiance of the horizon sky

The spectral radiance of the horizon sky between 3000 A and 4200 A was measured in a maritime environment under clear and cloudy sky conditions. The spectral radiance was found to be mainly a function of the position of the sun and of the amount of cloud cover. A typical value for the spectral radiance at 3600 A at noon with clear sky is 5 microW cm(-2) sr(-2) nm(-1).