Sky luminance distributions for the upper and lower sky at ground level, 1.52 km and 6.10 km are presented for a clear day with a medium high sun. The directional luminous reflectances of a variety of natural terrains and man-made surfaces measured under a clear sky with a moderately high sun are also presented. These data are applicable for use in visibility calculations and supplement the data presented in an earlier article [S. Q. Duntley, J. I. Gordon, John H. Taylor, C. T. White, A. R. Boileau, J. E. Tyler, R. W. Austin, and J. L. Harris, Appl. Opt. 3, 549 (1964)].
Jacqueline I. Gordon and Peggy V. Church, "Sky Luminances and the Directional Luminous Reflectances of Objects and Backgrounds for a Moderately High Sun," Appl. Opt. 5, 793-801 (1966)