PURPOSE:To easily monitor snow soaring to occur when a train travels by using a special-purpose index and a television camera. CONSTITUTION:A special-purpose index 22, in which a plurality of round marks to become targets are arranged, is installed along a rail on which a train 20 travels. The index 22 is imaged by a television camera 21 before and immediately after the train passes the index 22, two pieces of picture information are processed by an image processor 23, soaring state of snow is obtained as a numeric value according to a difference of the number of the targets to be recognized by the picture information, and output to a monitor 24.
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