Use of Scanning Electron Microscopy for three dimensional stereo analysis of impact craters and modelling with Zernike polynomials

Examples will be presented to demonstrate the use of a Scanning Electron Microscope to obtain detailed measurements of hypervelocity impact craters and to obtain the shapes of craters in three dimensions by comparing stereo pairs. The depth of each crater is sampled at approximately 5000 points and the data is fitted using a set of polynomials orthogonal over a unit disc ( the Zernike polynomials). The specific application to be presented is the study of groups of craters produced under identical impact conditions by firing a quantity of projectiles as buckshot from a light gas gun. Analysis of the Zernike polynomial spectrum of the crater shapes will show quantitatively the variations in crater shapes, both within groups of identical craters and between groups corresponding to different impact conditions. In this way the potential of the method for inferring properties of impactors will be assessed, with the aim of applying the method to obtain velocity and density information from craters in retrieved space-exposed surfaces.