William Dungan Jr.. A terrain and cloud computer image generation model. In Thomas A. DeFanti, Bruce H. McCormick, Bary W. Pollack, Norman I. Badler, S. H. Chasen, editors, Proceedings of the 6th Annual Conference on Computer Graphics and Interactive Techniques, SIGGRAPH 1979, Chicago, Illinois, USA, August 8-10, 1979. pages 143-150, ACM, 1979. [doi]