METHOD FOR CLOUD BASE HEIGHT MEASURING AND DEVICE FOR POLARIZATION MEASURING

摘要

The invention is a method for measuring cloud-base distance comprising the steps of taking linear polarization images of a sky-portion from essentially the same point of view and at essentially the same time by means of at least three linear polarizing filters with different transmission directions, selecting points equivalent to each other on the linear polarization images, determining a degree of linear polarization and a total intensity of an incident light beam arriving on the points equivalent to each other by means of the respective intensities of the points, and determining a relative cloud-base distance for the points equivalent to each other based on the degree of linear polarization and on the total intensity, as well as on a pre-determined degree of linear polarization and on a pre-determined total intensity belonging to a cloudless sky. Further, the invention is an apparatus for measuring polarization, comprising an optical device generating a light beam (34) from a sky-portion, an image recording device (24) capable of receiving the light beam (34) and taking an image thereof, at least three linear polarizing filters (26, 26', 26") with different transmission directions and the polarizing filters (26, 26', 26") are arranged affecting different parts of the light beam (34), which parts of the light beam are projected onto a common image recording device (24).