Statistical analysis of multiple optical flow values for estimation of unmanned aerial vehicle height above ground

For a UAV to be capable of autonomous low-level flight and landing, the UAV must be able to calculate its current height above the ground. If the speed of the UAV is approximately known, the height of the UAV can be estimated from the apparent motion of the ground in the images that are taken from an onboard camera. One of the most difficult aspects in estimating the height above ground lies in finding the correspondence between the position of an object in one image frame and its new position in succeeding frames. In some cases, due to the effects of noise and the aperture problem, it may not be possible to find the correct correspondence between an object's position in one frame and in the next frame. Instead, it may only be possible to find a set of likely correspondences and each of their probabilities. We present a statistical method that takes into account the statistics of the noise, as well as the statistics of the correspondences. This gives a more robust method of calculating the height above ground on a UAV.