NDVI MAC

type: ImageCollection
id: LANDSAT/LC08/C01/T1_TOA
version: 1597756871742431
bands: List (12 elements)
properties: Object (39 properties)
type: FeatureCollection
id: users/gyzeternal/changtingshpedge
version: 1591521504384129
columns: Object (4 properties)
properties: Object (1 property)




//定义addNDVI函数，该函数的输入是image，然后对image执行NDVI计算，并将结果命名为ndvi
//并将生成的ndvi添加到原有的image中
var addNDVI = function(image) {
  var ndvi = image.normalizedDifference(['B5', 'B4']).rename('NDVI');
  return image.addBands(ndvi);
};
//选择2019年的lc8影像
var lc82018 = l8.filterDate('2018-01-01', '2018-12-31');
//将筛选出来的2019年的影像均执行NDVI计算并添加该结果至原影像
var withNDVI = lc82018.map(addNDVI);
//利用qualityMosaic()函数执行NDVI最大值筛选，并用gz的边界进行裁剪
var greenest = withNDVI.qualityMosaic('NDVI').clip(ct);
//对筛选出来的像素，执行NDVI计算（由于筛选出来的是包含所有波段
//所以可以直接输出全波段影像而不仅仅是NDVI）
//接下来显示NDVI最大值合成的结果，可以有2个方案：
var bestndvi2018 = greenest.select('NDVI').rename('bestNDVI');
//或者重新计算一次
//var bestndvi = greenest.normalizedDifference(['B5', 'B4']).rename('bestNDVI');
//添加生成的最优NDVI到图层窗口

//选择2019年的lc8影像
var lc82017 = l8.filterDate('2017-01-01', '2017-12-31');
var withNDVI = lc82017.map(addNDVI);
var greenest = withNDVI.qualityMosaic('NDVI').clip(ct);
var bestndvi2017 = greenest.select('NDVI').rename('bestNDVI');

var lc82016 = l8.filterDate('2016-01-01', '2016-12-31');
var withNDVI = lc82016.map(addNDVI);
var greenest = withNDVI.qualityMosaic('NDVI').clip(ct);
var bestndvi2016 = greenest.select('NDVI').rename('bestNDVI');

var lc82015 = l8.filterDate('2015-01-01', '2015-12-31');
var withNDVI = lc82015.map(addNDVI);
var greenest = withNDVI.qualityMosaic('NDVI').clip(ct);
var bestndvi2015 = greenest.select('NDVI').rename('bestNDVI');

var lc82014 = l8.filterDate('2014-01-01', '2014-12-31');
var withNDVI = lc82014.map(addNDVI);
var greenest = withNDVI.qualityMosaic('NDVI').clip(ct);
var bestndvi2014 = greenest.select('NDVI').rename('bestNDVI');



Export.image.toDrive({
  image: bestndvi2018,
  description: "l8_2018MVC", 
  fileNamePrefix: "NDVI_MVC_2018",
  scale: 30,
  region:ct,
  crs:  "EPSG:4326",
  maxPixels: 1e13
}); 

Export.image.toDrive({
  image: bestndvi2017,
  description: "l8_2017MVC", 
  fileNamePrefix: "NDVI_MVC_2017",
  scale: 30,
  region:ct,
  crs:  "EPSG:4326",
  maxPixels: 1e13
}); 


Export.image.toDrive({
  image: bestndvi2016,
  description: "l8_2016MVC", 
  fileNamePrefix: "NDVI_MVC_2016",
  scale: 30,
  region:ct,
  crs:  "EPSG:4326",
  maxPixels: 1e13
}); 


Export.image.toDrive({
  image: bestndvi2015,
  description: "l8_2015MVC", 
  fileNamePrefix: "NDVI_MVC_2015",
  scale: 30,
  region:ct,
  crs:  "EPSG:4326",
  maxPixels: 1e13
}); 


Export.image.toDrive({
  image: bestndvi2014,
  description: "l8_2014MVC", 
  fileNamePrefix: "NDVI_MVC_2014",
  scale: 30,
  region:ct,
  crs:  "EPSG:4326",
  maxPixels: 1e13
});