[DEPRECATED] Vegetation growing season length 2000-2016

The raster files are the annual above ground growing season length time-series and the derived linear trends for the period 2000-2016. The data set addresses trends in the season length of land surface vegetation derived from remote sensing observed time series of vegetation indices. The vegetation index used in the indicator is the Plant Phenology Index (PPI, Jin and Eklundh, 2014). PPI is based on the MODIS Nadir BRDF-Adjusted Reflectance product (MODIS MCD43 NBAR. The product provides reflectance data for the MODIS “land” bands (1 - 7) adjusted using a bi-directional reflectance distribution function. This function models values as if they were collected from a nadir-view to remove so called cross-track illumination effects. The Plant Phenology Index (PPI) is a new vegetation index optimized for efficient monitoring of vegetation phenology. It is derived from radiative transfer solution using reflectance in visible-red (RED) and near-infrared (NIR) spectral domains. PPI is defined to have a linear relationship to the canopy green leaf area index (LAI) and its temporal pattern is strongly similar to the temporal pattern of gross primary productivity (GPP) estimated by flux towers at ground reference stations. PPI is less affected by presence of snow compared to commonly used vegetation indices such as Normalized Difference Vegetation Index (NDVI) or Enhanced Vegetation Index (EVI). The product is distributed with 500 m pixel size (MODIS Sinusoidal Grid) with 8-days compositing period.本数据集包含2000-2016年时段的逐年地表植被生长季时长时间序列数据，以及由此推导得到的线性趋势结果。本数据集聚焦于基于遥感植被指数观测时间序列反演得到的陆地地表植被生长季时长变化趋势。本指标所采用的植被指数为植物物候指数（Plant Phenology Index, PPI，Jin与Eklundh，2014）。该指数基于MODIS天底视角双向反射分布函数校正反射率产品（MODIS MCD43 NBAR）。此产品提供经过双向反射分布函数校正的MODIS“陆地”波段（1至7波段）反射率数据。该校正函数将反射率模拟为天底视角下的观测值，以消除所谓的跨轨光照影响。植物物候指数（PPI）是一款专为高效监测植被物候而优化的新型植被指数。它基于辐射传输模型，利用可见光-红光（RED）与近红外（NIR）光谱波段的反射率计算得到。PPI被定义为与冠层绿叶叶面积指数（Leaf Area Index, LAI）呈线性相关，其时间变化特征与地面参考站点通量塔观测反演得到的总初级生产力（Gross Primary Productivity, GPP）高度相似。相较于归一化差分植被指数（Normalized Difference Vegetation Index, NDVI）与增强型植被指数（Enhanced Vegetation Index, EVI）等常用植被指数，PPI受积雪影响程度更低。该数据集产品采用500米分辨率（MODIS正弦网格投影），合成周期为8天。