基于MODIS EVI时序数据的云南高原山地森林物候特征识别

Identifying Phenological Characteristics of Highland and Mountain Forests in Yunnan Using MODIS EVI Time-series Data

基于2000—2011年MOD13Q1产品的EVI时序,借助QA-SDS数据集消除云、阴影和冰雪等的影响后,采用非对称高斯函数拟合法进行时序重构,并运用动态阈值法提取云南高原山地典型森林植被的物候特征参数(即生长期开始时间、峰值时间、结束时间和生长期长度),进而分析了不同植被类型物候期规律及其主要控制因素。结果表明:1.从寒温性森林植被到热性森林植被的EVI值呈递增趋势;2.森林植被生长期开始时间、峰值时间和结束时间分别大致发生在3月中旬至4月中下旬、6月中旬至下旬和8月中旬至10月初,生长期长度为135～195 d;3.由寒温性植被向热性植被的生长期高峰时间和生长期结束时间总体呈延迟趋势,且生长期延长,生长期开始时间则由暖性植被向寒温性植被、暖性植被向热性植被双向提前;4.高原山地热量梯度决定了森林植被物候的空间格局,水分条件则主要控制着EVI和物候期的年际波动。

MOD13Q1 products from 2000 to 2011 covering highland and mountains in Yunnan were employed in this study. Noisy pixels due to cloud, shadow and ice/snow contamination were removed from original EVI time se- ries data by incorporating the QA - SDS dataset, and then the missing values of EVI time series data were interpola- ted by the asymmetric Gaussian function fitting method. Based on the reconstructed EVI time series data, phenolog- ical metrics （ greenup date, maturity date, senescence date and growing season length） of typical forest types were derived using dynamic threshold method. The results show that： 1. there is a positive EVI gradient from cold tem- perature to tropical forest vegetation. 2. greenup date, maturity date and senescence date of the studied forest vege- tation generally occur in mid - March to mid - to - late April, mid to late June and mid - August to early October, respectively, and growing season length of those are ca. 135 to 195 days. 3. from cold temperature to tropical for- est vegetation, maturity date and senescence date display a delayed tendency and growing season lengthen. There are the same earlier trend of greenup from warm-temperate to cold temperature forest vegetation and tropical to warm-temperate forest vegetation. 4. spatial pattern of forest phenology depends on heat flux gradient, whereas moisture condition mainly influences inter-annual variability of EVI values and phenological metrics of forest vegeta- tions.