The Seasonal Dynamics of AVHRR Spectrum Characteristics in Xilingol Grasslands,Inner Monglolia.

The seasonal dynamics of AVHRR_NDVI in four types of Xilingol grasslands,Inner Mongolia were analyzed.The averaged monthly NDVI was used to demonstrate the seasonal changes of four grasslands.It showed that there is very small variation for desert steppe in whole year,and this grassland has a low_flat NDVI pattern.In May,meadow steppe and typical steppe started to grow,but the NDVI of the other two steppes reached their nadir.June is an important period for NDVI acceleration.Taking April as NDVI baseline,by the end of June,81% of net NDVI increase had finished for meadow steppe,73% for steppe and 37% for sand grassland.But monthly NDVI alone is insufficient for grassland classification.Monthly AVHRR data(Ch1～Ch5)were used to check if there was any additional information for classification.Unlike monthly NDVI,there was little extra information from original data for classification in May, but in June, Ch33180 and Ch53100 could be good indicators to detect desert steppe and sand_steppe from steppe,and in August,Ch2210 can be used to distinguish meadow steppe from steppe.All decision rules were organized by a decision tree,and this classification can be used to classify four grasslands in Xilingol,Inner Mongolia.