该研究基于Savitzky_Golay滤波算法平滑了1982～1999年NOAA/AVHRR NDVI 时间序列影像，然后利用曲线拟合了锡林郭勒典型草原1982～1999年的每年物候期（返青期、黄枯期）及18年的平均物候期和生长季长度，并对1982～1999年的物候期进行了线性拟合，从而分析了物候期的变化趋势。结果表明：1）1982、1986、1992年的返青期处于正常水平，1985、1988、1989、1991年大部分地区的牧草返青期比正常年份有所提前。1984、1990、1993 年的黄枯期处于正常水平，大部分年份的黄枯期主要处于9月下旬至10月上旬（290～310 d）。2）在整个典型草原，返青期有较大的变异性，而黄枯期变化表现出了锡林郭勒典型草原的西南部较早、中部及东北部较晚的格局，生长季长度的变化格局为西南地区最短，中部地区最长。3）从1982～1999年，不同的地区表现出物候期及生长季长度提前或延迟的变化趋势，返青期大多数地区延迟时间集中在10～20 d，提前日期主要集中在10 d之内。锡林郭勒盟西南地区的黄枯期提前趋势最大。大部分地区的生长季长度变化呈缩短趋势，缩短日期小于 10 d，少部分地区的生长季延长，延长日期主要集中在0～10 d。4）对锡林浩特的物候期研究表明，牧草返青期提前日期小于10 d，黄枯期延迟大约14±5 d，生长季长度延迟大约1 5±5 d。最后利用野外观测数据对锡林浩特牧草返青期的拟合精度作出了评价。
Vegetation greenup is closely related to seasonal dynamics of the lower atmosphere and, therefore, is an important variable influencing the feedback mechanisms of global climate variation to terrestrial ecosystem. Detecting vegetation greenup using remotely sensed data at regional or global scale has become an advanced topic in geography and ecology. However, current methods of remote sensing based vegetation greenup detection are short of valid comparison and do not have a consistent results. This paper utilizes computer simulation technique to explore the seasonal dynamics of typical steppe grassland in Xilingole, Inner Mongolia, using NOAA/AVHRR NDVIdata from 1982 to 1999. Firstly, Savitzky_Golay filter algorithm is used to smooth NOAA/ AVHRR time_series images from 1982 to 1999. Secondly, the curve_fitting technique is applied to phenological phase (turning green date and wilting date) in each year and to the average phenological phase and length of growing season from 1982 to 1999 for the typical steppe grassland in Xilingole, Inner Mongolia. Finally, t he trend of change in phenological phase is analyzed for the typical steppe grassland in Xilingole during the 18 years.
The results indicate that 1) the turning green date in 1982, 1986 and 1992 was placed in normal level, but that in 1985, 1988, 1989 and 1991 was advanced in most areas. The wilting date in 1984, 1990 and 1993 was also placed in normal level and the wilting date in most years was mainly from the last ten_day of September to the first ten_day of October (290-310 days). 2) Turning green date of all typical steppe grassland showed large variability. The wilting date of southwestern area was earlier than that of central and northwestern area, but the length of growing season didn‘t show the same pattern of change. The length of growing season in southwestern area was the shortest and that in central area was the longest. 3) From 1982 to 1999, the phenological phase and length of growing season of the turning green date and the wilting date of typical steppe grassland showed the characteristics of advancing or delaying in different areas. The delay time for turning green date of typical steppe grassland in most areas mainly focused on 10-20 days, and the advance time for turning green date was less than 10 days. The advancing trend in wilting date was the greatest in northwestern area in Xilingole. The length of growing season showed a shortening trend and the shortening date was less than 10 days. Increase in the length of growing season was little in Xilingole, and it mostly focused on 0-10 days. 4)The research on phenology of the typical steppe grassland in Xilingole indicated that the turning green date of the typical steppe grassland advanced less than 10 days, the wilting date postponed for about 14±5 days, and the length of growing season in creased about 15±5 days. Lastly, the precision of phenology phase in Xilingole is evaluated by the observation data in the field.