obtain a uniform di stribution of peri aps i s longitudes over the surface of Mars, and both Sand Xband data were used where possible to elimi nate charged part i c l e effects. I nc lu sion of-the Vik ing data arcs altered the Mart i an geoid features, as defined by previous short-arc analysis techniques of Mariner 9 data, by about 80 meters in the Southern Hemisphere 1 and about 140 meters i ...