Study of Vegetational Phenology by Using Global Remote-Sensing Data and Climatic Data Set

本文研究了由遥感影像数据探测到的全球植被的季节变化，并探讨了其与气候有关的原因。本文所使用的数据是美国NGDC编制的1986-1988年10分钟空间分辨率的归一化植被指数(NDVI)文件和30分钟空间分辨率的月温度和降水数据集。通过考虑地形效应，将气候数据内插到10分钟分辨率，即递减率和DEM。并在约束条件下将所有数据内插到半月度数据，以保持相同的年平均值或总值。用新建立的水量平衡和积雪融化模型计算了每半个月一次的供水量、实际蒸散量、蓄水量变化和合成径流。我们认为，该模型中使用的假设是在自然现象的范围内，通过比较计算的流域径流和观测的河流流量，仍有一种方法可以改进模型中的假设值。该项目利用一个新开发的系统将半月实际蒸散量和VI值的地图显示为动画图像。在动画地图上快速感知植被和气候参数的时间序列和空间变化，并对两者的空间相关性进行统计分析。我们发现，植被绿度的变化(鲜绿和落叶)同时或以半个月的延迟发生，直到超过实际蒸散的阈值。我们认为，全球植被的绿度受唯一的气候参数--实际蒸散量的控制，而不是温度和降水这两个独立的参数或两者的简单组合。

This report deals with the seasonal change of global vegetation detected by remotely sensed image data and pursues the cause in relation to climate. The data used in this study are NDVI(normalized vegetatin index) files for 1986-1988 in 10 minute spatial resolution, and monthly Temperature and Precipitation data set in 30 minute spatial resolution prepared by NGDC, USA. Climatic data were interpolated to 10 minute resolution by considering the topographic effect, that is, lapse rates and DEMs. And all were interpolated to semimonthly data under constraint to keep the same yearly average or total value. Water supply, actual evapotranspiration, water storage change and resultant runnoff for each pixsel were calculated at semimonthly intervals by a newly developed model of water balance and snow accumulation-melting. The assumptions used in this model are, we believe, in the range of natural phenomena and there remains a way to improve assumptive values in the model through comparing calculated basin runoff and observed river discharge. Maps of semimonthly actual evapotranspiration and VI values were showed as animated images by a newly developed system in this project. Not only time-serial but also spatial change of vegetation and climatic parameters were quickly percepted in the animated maps and then spatial correlation of the two were analyzed statistically. We found that vegetational greenness change (fresh green and defoliation) happens simultaneously or with semimonthly delay to crossing a threshold value of actual evapotranspiration. We conclude that greenness of global vegetation is under control of the unique climatic parameter, actual evapotranspiration, neither two independent parameters temperature and precipitation nor a simple combination of the two.