今天来分享下如何在GEE中批量下载以MODIS为数据源的NPP产品。在GEE所调用的的数据为MODIS/006/MOD17A3HGF，
NPP是指陆地植被净初级生产力，是地球表面绿色植物在单位时间内单位面积上由光合作用所产生的有机物质总量中扣除自养呼吸后的剩余部分，从本质上看，植被净初级生产力的形成主要涉及碳的固定与消耗，与全球碳平衡和碳扰动等有着密切的关系，是表征陆地生态过程的关键参数.
GEE调用代码如下:

var roi = ee.FeatureCollection("users/lilei655123/shanxi");
var year_list=ee.List.sequence(2000,2019);
year_list=year_list.map(function(num){
  var time=ee.Date.fromYMD(num, 1, 1)
  var year_image=ee.ImageCollection("MODIS/006/MOD17A3HGF")
                  .filterDate(time,ee.Date(time).advance(1,'year'))
                  .max();
  var year_npp=year_image.select('Npp');
  return  year_npp.addBands(ee.Image.constant(num).toFloat());                 
}
  )
var img_collection=ee.ImageCollection.fromImages(year_list);
var linearFit = img_collection.select(['constant', 'Npp'])
  .reduce(ee.Reducer.linearFit());
print(year_list)
print(img_collection)
var trendVis = {
  min: -100,
  max: 100,
  palette: [
"fff5f0","fee0d2","fcbba1","fc9272","fb6a4a","ef3b2c","cb181d","a50f15","67000d",
"f7fcf5","e5f5e0","c7e9c0","a1d99b","74c476","41ab5d","238b45","006d2c","00441b"
  ],
};
var batch = require('users/fitoprincipe/geetools:batch')//下载所需的调用接口
batch.Download.ImageCollection.toDrive(img_collection,"result", {
scale: 500,//分辨率为500m
region: roi,                //研究区域
maxPixels:34e10,            //此处值设置大一些，防止溢出
type:"int16" });
Map.centerObject(roi);
Map.addLayer(linearFit.select('scale').clip(roi),trendVis);

显示结果如下:


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