Abstract
Using N-LAND database system, the snow cover area in the Tohoku district in Japan is detected monthly in 1991. The N-LAND data system includes all the information of AVHRR/NOAA date and software to detect cloud area. The cloud cover area detection is based on the threshold method using all the AVHHR channel informations. Monthly free cloud covered image is created through synthesizing some images on near time. The detected snow area on the images are validated by the AMeDAS snow-depth data and the error is estimated to be less than 8%. The change of the snow cover area and distributions from Feburary to April, 1991 are investigated in the Tohoku district.
