Involvement of altimetric information into planet surface relief reconstruction from a set of images

The photoclinometric method for surface topography reconstruction from images using known dependence of the facet brightness on its orientation was proposed by Van Diggelen in 1951. The method includes calculation of topography slope fields using available images and consequent solution of equations. This method is still widely used though in its initial (simplest) formulation, it is a mathematically incorrectly posed problem. With an improved photoclinometry (based on the accurate mathematical formulation of the problem in the frame of the Bayesian statistical approach), surface heights can be calculated up to an unknown constant. The height accuracy also depends on the noise level of image registration. To obtain the true surface heights, the relief reconstruction from images using the improved photoclinometry has to be accompanied with an account of a priori known heights in sites located in the surface area under study. Height measurements by altimeter are the most reliable method to get the true surface topography. However usually sparse net of measured points does not give detailed topography information. Altimetry data usually have high accuracy. They seem to be the most promising for the use together with relief reconstruction by the improved photoclinometry allowing calculation of true surface relief (advantage of the altimeter) with the spatial resolution as high as the resolution of initial images (advantage of the photoclinometry).