“Two maps in Aitoff equal area projection based on the 1958 observations (Fig. 6, 7) were prepared by Mr. J. Roth, using a photometrically checked step scale of 4 gray* to transfer to the maps the relative brightness or * tone * values of the dark and bright regions. The visual step-values (i. e., relative surface brightnesses on a logarithmic scale) of the various regions were derived from over 1,000 photometric estimates made during the 1958 opposition and previously reduced to a standard system”
G. de Vaucouleurs: Precision mapping of Mars. In: Physics of Planets. Proceedings of the 11th International Astrophysical Symposium Liege, July 9-12, 1962. 369-
Bad image quality due to scanning, original paper version is not available.
