To eliminate the influence of objects on the ground surface other than an object, the reflection or radiation characteristic of the atmosphere, etc., on image signals by correcting the image signals based on the damping amount by atmospheric propagation measured from solar spectra, scattered light in the atmosphere, and reflected light from clouds in the sky.

Solar rays 13 reflected by the high- or low-reflectivity reflecting plate 11 or 12 of a sensitivity correcting plate 5 form an image in a photoelectric conversion section 1 and the image is stored in a memory 7 after A/D conversion. Then laser transmission and reception are performed into and from the atmosphere by driving λ1 laser transmitting sections 18 and 22 and λ3 laser receiving sections 19 and 23 and the damping amount of scattered light 36 by atmospheric propagation is calculated by means of relational operator sections 24 and 25. Simultaneously, reflected light rays 31 from clouds in the sky are taken in as two-dimensional pictures by means of a TV camera 30 and only sky parts are segmented and inputted to a calibrating data generating section 17. The section 17 generates calibrating data which are used for correcting the picked-up image of an object based on the sky parts and a main arithmetic section 35 corrects the image date of the object stored in an image memory 8 with the calibrating data.