Camera sightline pointing requirements for aerial inspection of overhead power lines

This paper considers the image quality requirements for video inspection of overhead power distribution lines from a helicopter. The use of video surveillance techniques for routine inspection of overhead lines is seen as a means of automating the process as well as improving the depth and coverage by provision of permanent visual records. One of the principal difficulties of remote video surveillance from a helicopter is the degradation of the image due to the motion of the camera sightline. The work reported here introduces simulated motion blur onto sharp images to show that the tolerable motion is of the order of 1-2% of the field of view for static images. An expression is obtained for the maximum allowable amplitude of (sinusoidal) sightline perturbation for a given value of image blur. The results of an experimental assessment of the quality of images subject to sightline motion are presented and it is shown that the tolerable motion for dynamic viewing is similar to that for static images. It is concluded that optical stabilisation of the order of 100 mur is necessary for satisfactory inspection detail. (C) 2001 Elsevier Science B.V. All rights reserved.