Abstract
Landsat-5 had acquired 12, 328 data in total over Japan (42 scenes) during 17 working years.That means 293.5 data in average for one scene were registered in that period. However, examining Cloud Coverage Ratio (CCR) in whole data, clear images were very limited because optical sensor was hindered by cloud. The highest sites of clear sky frequency through year (CCR≤20; CCR less than 20%) were Kanto (WRS 107-35), fo11owed by northeastern Hokkaido (WRS 106-29), 13.71% and 11.42%, respectively (Fig.1) .The worst two were northern Okinawa (WRS 113-41) and southern Okinawa (WRS 113-42), 1.52% and 1.78%, respectively. Dividing Japan into 6 blocks, Kanto & Tokai block wascharacterized as high during winter seasons (12.72%), while Hokkaido & Tohoku Pacific side was high in summer seasons (6.99%) .Comparing with some arid areas in foreign countries, there was a drastic difference. CCR0 (no cloud cover) and CCR20 (1-20%) were 14.00% and 39.00% for southern Australia (WRS96-82), 16.91% and 27.94% for Inner Mongolia of China (WRS 124-29, 30), and 1.27% and 4.90% for Japan (42 scenes), respectively.Under this situation, special devices and efforts are necessary for thepractical use in agriculture and forestry fields.
