On-Line Vehicle Motion Estimation from Visual Terrain Information Part I: Recursive Image Registration

The authors address estimation of motion from the optical flow observed by an airborne down-looking electro-optical sensor. The development and analysis of a velocity-to-height ratio estimation algorithm and its principal error characteristics are described. The algorithm implements recursive registration of successive images by using the gradient of a similarity function between them to control the tracking of their relative shift. The shift estimate provides velocity/height information. Substantial saving in memory and computation as compared to conventional full-frame registration is achieved by using only a single line in the TV frame. Stochastic mathematical models for the image, terrain and vehicle velocity perturbations are used in the analysis. The choice of the most appropriate similarity function in the registration algorithm is addressed. Performance analysis indicates very small error variances, as illustrated by numerical examples.