前言：主要介绍利用GEE获取Modis下的GPP数据。

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1.GPP

• 总初级生产力（Gross primary productivity，GPP）是指单位时间内生物（主要是绿色植物）通过光合作用所固定的有机碳量，又称总第一性生产。
• 本博客获取的Modis_GPP数据主要是通过遥感的方法来计算的GPP。

2.MOD系列和MYD系列区别

• Terra卫星的观测数据为MOD数据，Terra是于当地的上午10:30过境。
• aqua卫星观测数据为MYD数据，auqa是于当地下午1:30过境。
• A3是NPP数据，每一年进行合成。

3.MOD17A2H(500m/8天)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset = ee.ImageCollection('MODIS/006/MOD17A2H').filter(ee.Filter.date('2014-01-01', '2014-12-31'));
print(dataset)
var npp = dataset.select('Gpp');
var nppVis = {min: 0.0,max: 19000.0,palette: ['bbe029', '0a9501', '074b03'],
};
Map.addLayer(npp.mean().clip(geometry), nppVis, 'NPP');

4.MYD17A2H(500m/8天)

4.1 MYD17A2H下的指数

主要有Gpp、PsnNet、Psn_QC指数

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset = ee.ImageCollection("MODIS/006/MYD17A2H")
.filter(ee.Filter.date('2010-01-01', '2010-12-31'))
.filterBounds(geometry);
print(dataset);

4.2 遥感影像查看

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset = ee.ImageCollection("MODIS/006/MYD17A2H")
.filter(ee.Filter.date('2010-01-01', '2010-12-31'))
.filterBounds(geometry).select('Gpp');
print(dataset);
var gppVis = {min: 0.0, max: 600.0, palette: ['bbe029', '0a9501', '074b03']};
Map.addLayer(dataset.mean().clip(geometry), gppVis, 'Gpp');//2010年的均值

5.GPP日数据下载(以MYD17A2H为例)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset = ee.ImageCollection("MODIS/006/MYD17A2H")
.filter(ee.Filter.date('2010-01-01', '2010-12-31'))
.filterBounds(geometry).select('Gpp');
print(dataset);
function exportImageCollection(imgCol) {var indexList = imgCol.reduceColumns(ee.Reducer.toList(), ["system:index"]).get("list");indexList.evaluate(function(indexs) {for (var i=0; i<indexs.length; i++) {var image = imgCol.filter(ee.Filter.eq("system:index", indexs[i])).first();image = image.clip(geometry);//tif数据下载Export.image.toDrive({image: image,description: 'modis_gpp_'+indexs[i],fileNamePrefix: 'modis_gpp_'+indexs[i],folder: 'Modis',region: geometry,scale: 500,crs: "EPSG:4326",maxPixels: 1e13});}});
}
exportImageCollection(dataset);

6.GPP月数据下载(以MYD17A2H为例)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
var dataset = ee.ImageCollection("MODIS/006/MYD17A2H");
for(var i=2018;i<=2020;i++){for(var j=1;j<=12;j++){var data_collection = null;switch(j){case 1:case 3:case 5:case 7:case 8:case 10:case 12:data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-31').select('Gpp');break;case 4:case 6:case 9:case 11:data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-30').select('Gpp');break;case 2:data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-28').select('Gpp');break;}var YR_collection = data_collection.mean().clip(geometry);Export.image.toDrive({image: YR_collection,description: i+'-'+j,fileNamePrefix: i+'-'+j,scale: 500,region: geometry,maxPixels: 1e13,folder: 'Modis'})}
}

7.GPP年数据下载(以MYD17A2H为例)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
var dataset = ee.ImageCollection("MODIS/006/MYD17A2H");
for(var i=2018;i<=2020;i++){var data_collection = dataset.filterDate(i+'-01-01',i+'-12-31').select('Gpp');// print(data_collection)var YR_collection = data_collection.mean().clip(geometry);Export.image.toDrive({image: YR_collection,description: i,fileNamePrefix: i,scale: 500,region: geometry,maxPixels: 1e13,folder: 'Modis'});
}