Abstract: Precipitation is closely related to clouds. Artificial weather stations and weather forecast radar detection are the primary means of cloud observation, but the means are sometimes unable to obtain the comprehensive and accurate cloud cover data due to the natural constraints and human error. Reference to a variety of domestic and foreign cloud detection methods, in this study the multispectral cloud detection algorithm based on the combination of index method and spectral threshold method was used to detect cloud cover conditions over Xinjiang using MODIS1, 6, 26-channel data. The analyzed results show that the average annual cloud cover duration in Xinjiang in 2009 was 82 days, in which the average annual cloud cover duration was 101 days in the mountainous regions and 69 days in the plains, respectively.

Key words: MODIS, cloud detection, cloud cover duration, mountainous region, Xinjiang