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Vertically displaced optical flow sensors to control the landing of a UAV

We report on an optical device to aid landing of Unmanned Aerial Systems. Optical flow calculates a measure of observed angular movement of the image seen by the sensor. Optical flow can be converted to range if speed of the sensor is known. Our approach eliminates this requirement by using two optical flow sensors displaced vertically to calculate range. The initial implementation was tested on an instrumented UAV with promising results. We show that the sensor provides useful range measurements at a height of several meters. We argue that this technique is comparable to vision techniques such as stereo in this application. We show alternate implementations with optics that do not require vertical displacement.