Vision-augmented Gnc: Passive Ranging from Image Flow

Knowledge of range and closing velocity is known to enhance missile guidance, improve launch envelope, and reduce miss; however, scenarios exist where the range-to-target is unknown to the weapon. This paper provides the mathematical framework and algorithm for calculating range-to-target from sequential optical (intensity only) images. Such use of additional information from imaging seekers to assist GNC falls into the general category of Vision-Augmented GNC (VA-GNC), and a brief overview of this emerging field is provided. It has been shown that through use of the optical flow constraint (OFC), a range expression at each image pixel may be directly calculated from spatial-temporal gradients, known pixel angular location, and ownship motion. However, these optical flow/gradient-based passive ranging algorithms are subject to singularities, noise, and bogus range estimates for certain image content. In this work, a local median filtering approach is applied to the raw range estimates to remove outliers before segmentation. Using this approach provides the additional benefit of both intensity and range information for segmentation. Once segmented, the range to the target of interest is extracted and available for guidance or range-rate estimation. Finally, simulation performance results are presented using synthetic, analytically derived images for the case of a body-fixed ∗Associate Principal Engineer †Chief Scientist, Senior Member AIAA ‡Tech Fellow for Aerodynamics, Senior Member AIAA §Senior Member AIAA This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Drs. Matthew Markel, Juan Lopez, and Glenn Gebert are with Sverdrup Technology, P.O. Box 1935, Eglin AFB, FL 32542. Johnny Evers is with the U.S. Air Force Research Laboratory Munitions Directorate. camera. These results indicate that, for stationary ground targets, the technique yields range accuracy which is adequate for guidance and object tracking.