Planetary terminal descent hazard avoidance using optical flow

An algorithm that uses optical flow to detect landing hazards for a descending spacecraft is described. Image edge points are tracked between frames of a motion sequence, and the range to the points is calculated from the displacement of the edge points and the known motion of the camera. A novel variable-sized edge detector is used to compensate for the change in distance from one image to the next. Kalman filtering is used to incrementally improve the range estimates to those points and provide an estimate of the uncertainty in each range. Errors in camera motion and image point measurement are also modeled. A surface is then interpolated to these points, providing a complete map from which hazards such as steeply sloping areas can be detected. The algorithm has been applied to synthetic and real image sequences, with resulting range accuracy on the order of 1-3% of the range