Snow-sky and water-sky luminance at an Arctic station

Abstract

Luminance measurements of water-sky and snow-sky were carried out at Ny-Alesund, Svalbard. The luminance of a well-developed water-sky is found to be about 40% of that of the adjacent snow-sky. Once the‘luminance level’of a comparatively pure snow-sky is reached, there is only a very slight further luminance increase towards zenith. This is in good agreement with FRITZ’theory as well as with the light conditions experienced during‘white-out’situations. By measuring the angular elevation of the border between water-sky and snow-sky and the height of the cloud base, good estimates are obtained of the distance to the corresponding border on the ground between snow surface and open water.