A HARMONIC-ANALYSIS OF MARTIAN TOPOGRAPHY

The topography of Mars is represented by a spherical harmonic model co mplete to degree and order 50. The data source is a recently revised U .S. Geological Survey compilation which encompasses a diverse array of spacecraft measurements and Earth-based radar ranges. Because of the disparate nature of the original data sources, it is difficult to obta in reliable estimates of the likely errors in Martian topography. Howe ver, the variance spectrum has a shape similar to that found for other terrestrial planets, and the topography correlates well with recent e stimates of the gravitational field of Mars. Both of these considerati ons suggest that the existing data provide a reasonable approximation to the true topography of Mars. Nevertheless, a detailed topographic m apping of the planet, such as will be provided by the Mars Global Surv eyor, will be required before significant advances are made in underst anding the relationship between topography and gravity on Mars.