Aerial inspection of overhead power lines using video: estimation of imageblurring due to vehicle and camera motion

One of the principal difficulties of video inspection of overhead power dis tribution lines from a helicopter is the blurring of the image due to rotat ion of the camera in its gimbals and the translational motion of the helico pter. The author presents a kinematic model describing the sightline geomet ry which includes the effect of the helicopter's rectilinear motion in thre e degrees of freedom. It is shown that, except for locations very near to t he object being inspected the velocity flow field of the image is substanti ally uniform. The image Jacobian is used to predict how much blur is to be expected along a typical flight path during inspection operations. An impor tant conclusion is that this will be greater than the tolerable limit of 1- 2% unless the camera is rotated at a rate which compensates for the helicop ter's rectilinear motion - the implications for the design of an automated object tracking system are discussed. The maximum singular value of the ima ge Jacobian is proposed as a quality measure for inspection from various lo cations of the helicopter relative to the target object. It is found to be an useful figure of relative merit but too conservative to provide a realis tic upper bound on image blur.