HORIZON DETECTOR

PURPOSE:To detect the horizon stably and to prevent false detection even when meteological conditions change, by detecting a candidate for the horizon from shift difference data after pattern classification of a peripheral distribution and by adopting the characteristic amounts of the peripheral distribution and the shift difference as the conditions of selection. CONSTITUTION:A peripheral distribution is determined by a peripheral distribution computing circuit 9 from image data 8 obtained by differentiating digital image data 8 by a differentiating circuit 7, and classification of patterns of the peripheral distribution is conducted by using average values of the sky and the sea and sea clutter informations. Then, shift difference data 20 are determined by a shift difference computing circuit 19, a zero-cross point and a peak point to be a candidate for the horizon are detected from these data 20, and the characteristic amount of the peripheral distribution and that of the shift difference being used as the conditions of selection, the horizon is detected by a horizon detecting-determining circuit 27. Even when meteological conditions change, accordingly, stable detection can be executed, and when detection is hard to be executed due to bad weather, it is judged impossible to execute detection, whereby false detection is prevented.