I. Introduction
A new imaging method for measuring the recession of ablative thermalprotection system (TPS) materials during arcjet testing has been developed and demonstrated [1]. The method, Photogrammetric Recession Measurement (PRM), combines concepts from stereo photogrammetry and particle image velocimetry (pIV): it uses standard photogrammetric transformations between image and object space, and it uses image cross correlation in lieu of fiducial marks to track the displacement of the model surface. It can measure the recession time history at each of an arbitrary number of points distributed over the face of a test article (“model”) for the entire time that the model is exposed to the arcjet flow. PRM is non-intrusive, requires no external light source (in particular, no lasers), and requires no modifications to the test article. The principal requirements of the method are, first, that the face of the model exhibit some texture as it ablates (required for image cross correlation), and, second, that the ablating surface can be imaged from at least twodirections.