植被指数逐年获取 1. 常见的植被指数1.1 比值植被指数（Ratio vegetation index，RVI）1.2 归一化植被指数（Normalized Difference Vegetation Index，NDVI）1.3 增强植被指数（Enhanced Vegetation Index，EVI）1.4 土壤调节植被指数（Soil Adjusted Vegetation Index