Stereoscopic ground-based determination of the cloud base height: theory of camera position calibration with account for lens distortion

For the reconstruction of some geometrical characteristics of clouds a method was developed based on taking pictures of the sky by a pair of digital photo cameras and subsequent processing of the obtained sequence of stereo frames to obtain the height of the cloud base. Since the directions of the optical axes of the stereo cameras are not exactly known, a procedure of adjusting of obtained frames was developed which use photographs of the night starry sky. In the second step, the method of the morphological analysis of images is used to determine the relative shift of the coordinates of some fragment of cloud. The shift is used to estimate the searched cloud base height. The proposed method can be used for automatic processing of stereo data and getting the cloud base height. The earlier paper described a mathematical model of stereophotography measurement, poses and solves the problem of adjusting of optical axes of the cameras in paraxial (first-order geometric optics) approximation and was applied for the central part of the sky frames. This paper describes the model of experiment which takes into account lens distortion in Seidel approximation (depending on the third order of the distance from optical axis). We developed procedure of simultaneous camera position calibration and estimation of parameters of lens distortion in Seidel approximation.