Google Earth Engine——MODIS Combined 16-Day NDVI逐年合成影像循环下载

这里我们需要准备数据，看看影像的数据是如何的：

The Normalized Difference Vegetation Index is generated from the Near-IR and Red bands of each scene as (NIR - Red) / (NIR + Red), and ranges in value from -1.0 to 1.0. This product is generated from the MODIS/MCD43A4 surface reflectance composites.

Bands Table

* = Values are estimated

看代码：

//这里需要你自己加载自己的研究区，我这里是自己上传的矢量，不是公共数据集中，你没法使用
var hh= ee.FeatureCollection("users/bqt2000204051/shanxijie");

//定义一个变量数字作为循环的次数时间范围的界定

var years = ee.List.sequence(2000, 2020);
years.evaluate(function(y) 
{
  y.map(function(y) {
  var start = ee.Date.fromYMD(y, 1, 1);
  var stop &#