Chen X, Tan Z, Schwartz M D, Xu C
Department of Urban and Environmental Sciences, Peking University, Beijing, China.
Int J Biometeorol. 2000 Aug;44(2):97-101. doi: 10.1007/s004840000056.
The objectives of this study are to explore the relationships between plant phenology and satellite-sensor-derived measures of greenness, and to advance a new procedure for determining the growing season of land vegetation at the regional scale. Three phenological stations were selected as sample sites to represent different climatic zones and vegetation types in northern China. The mixed data set consists of occurrence dates of all observed phenophases for 50-70 kinds of trees and shrubs from 1983 to 1988. Using these data, we calculated the cumulative frequency of phenophases in every 5-day period (pentad) throughout each year, and also drew the cumulative frequency distribution curve for all station-years, in order to reveal the typical seasonal characteristics of these plant communities. The growing season was set as the time interval between 5% and 95% of the phenological cumulative frequency. Average lengths of the growing season varied between 188 days in the northern, to 259 days in the southern part of the research region. The beginning and end dates of the surface growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from normalized difference vegetation index curves for 8-km2 pixels overlying the phenological stations. Our results show that, at the beginning of the growing season, the largest average greenness value occurs in the southern part, then in the northern, and finally the middle part of the research region. In contrast, at the end of the growing season, the largest average greenness value is measured in the northern part, next in the middle and lastly the southern part of the research region. In future studies, these derived NDVI thresholds can be applied to determine the growing season of similar plant communities at other sites, which lack surface phenological data.
本研究的目的是探讨植物物候与卫星传感器获取的绿度指标之间的关系，并提出一种在区域尺度上确定陆地植被生长季的新方法。选择了3个物候观测站作为样本点，以代表中国北方不同的气候带和植被类型。混合数据集包含了1983年至1988年期间50 - 70种乔木和灌木所有观测物候期的出现日期。利用这些数据，我们计算了每年每5天（候）物候期的累积频率，并绘制了所有站点年份的累积频率分布曲线，以揭示这些植物群落的典型季节特征。将生长季设定为物候累积频率5%至95%之间的时间间隔。研究区域北部生长季的平均长度为188天，南部为259天。然后，将每年地表生长季的开始和结束日期作为时间阈值，从物候观测站上方8平方公里像素的归一化植被指数曲线中确定相应的10天峰值绿度值。我们的结果表明，在生长季开始时，平均绿度最大值出现在研究区域的南部，然后是北部，最后是中部。相反，在生长季结束时，平均绿度最大值出现在研究区域的北部，其次是中部，最后是南部。在未来的研究中，这些推导得到的归一化植被指数阈值可用于确定其他缺乏地表物候数据站点类似植物群落的生长季。
