Google Earth Engine（GEE）——Landsat8/modis/sentinel2 NDVI时序影像差异对比分析图表

var  AOI = 
    /* color: #d63000 */
    /* displayProperties: [
      {
        "type": "rectangle"
      }
    ] */
    ee.Geometry.Polygon(
        [[[-103.60307723271508, 44.88240786607988],
          [-103.60307723271508, 44.88233802278273],
          [-103.60242947923798, 44.88233802278273],
          [-103.60242947923798, 44.88240786607988]]], null, false),
    Point_1 = /* color: #98ff00 */ee.Geometry.Point([-103.60279560076852, 44.88238125911955]);
var AOI = AOI, Point_1 = Point_1;
//Sentinel 2 Image ------------------------------------------------------------
var startDateS2 = ee.Date.fromYMD(2016,1,1);
var endDateS2 = ee.Date.fromYMD(2016,8,29);
 
 
var collectionS2 = ee.ImageCollection("COPERNICUS/S2").filterDate(startDateS2,endDateS2).filterBounds(AOI).filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 0.1);
 
 
var S2 = collectionS2.median().clip(AOI)
Map.addLayer(S2, {min:0, max: 3000, bands:"B4,B3,B2"}, 'S2');
Map.centerObject(AOI);
 
var s2_ndvi = S2.normalizedDifference(['B8', 'B4']).rename('NDVI')
 
var ndviParams = {min: -0.2, max: 0.8, palette: ['red', 'yellow', 'green']};
Map.addLayer(s2_ndvi, ndviParams, 'NDVI');
 
//
 
 
 
 
//TimeSeries ---------------------------------------------
 
var startDate = ee.Date.fromYMD(2018,1,1);
var endDate = ee.Date.fromYMD(2019,12,31);
 
var months = ee.List.sequence(1,12)
var years = ee.List.sequence(2018, 2019);
 
//Sentinel 2 < 15% clouds -----------------------------------------
 
var S2_nocloud = ee.ImageCollection("COPERNICUS/S2").filterDate(startDate,endDate)
                                            .filterBounds(AOI)
                                            .filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 15)
                                     
                                           
var S2_NDVI_nocloud = S2_nocloud.map(function(image){
  return image.normalizedDifference(['B8', 'B4']).rename('NDVI').copyProperties(image, ['system:time_start']);
})
 
 
 
//Chart
 
var titleS2_nocloud = {
  title: 'S2 NDVI < 15% cloud',
  hAxis: {title: 'Time'},
  vAxis: {title: 'NDVI'},
};
 
 
var S2_chart_nocloud = ui.Chart.image.seriesByRegion({
  imageCollection: S2_NDVI_nocloud,
  regions: Point_1,
  reducer: ee.Reducer.mean(),
  band: 'NDVI',
  scale: 20,
  seriesProperty: 'NDVI'
}).setOptions(titleS2_nocloud)
 
print(S2_chart_nocloud);
 
// Sentinel 2 Monthly ------------------------------------------------------------
 
function maskS2clouds(image) {
  var qa = image.select('QA60');
 
  // Bits 10 and 11 are clouds and cirrus, respectively.
  var cloudBitMask = 1 << 10;
  var cirrusBitMask = 1 << 11;
 
  // Both flags should be set to zero, indicating clear conditions.
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0)
      .and(qa.bitwiseAnd(cirrusBitMask).eq(0));
 
  return image.updateMask(mask).divide(10000).copyProperties(image, ['system:time_start']);
}
 
var S2 = ee.ImageCollection("COPERNICUS/S2").filterDate(startDate,endDate)
                                            .filterBounds(AOI)
                                            .map(maskS2clouds);
 
 
 
var Monthly_S2 =  ee.ImageCollection.fromImages(
  years.map(function (y) {
    return months.map(function(m) {
       
      var filtered = S2.filter(ee.Filter.calendarRange(y, y, 'year'))
                    .filter(ee.Filter.calendarRange(m, m, 'month'))
      filtered = filtered.median()
      var NDVI = filtered.expression(
        '((NIR - RED) / (NIR + RED))', {
        'NIR': filtered.select('B8'),
        'RED': filtered.select('B4')
        }).rename('NDVI'); 
     
      return NDVI.set('year', y).set('month', m).set('system:time_start', ee.Date.fromYMD(y, m, 1));                 
    });
  }).flatten()
);
 
//Chart
 
var titleS2_M = {
  title: 'Mean Monthly S2 NDVI',
  hAxis: {title: 'Time'},
  vAxis: {title: 'NDVI'},
};
 
 
var S2_chart_M = ui.Chart.image.seriesByRegion({
  imageCollection: Monthly_S2,
  regions: Point_1,
  reducer: ee.Reducer.mean(),
  band: 'NDVI',
  scale: 20,
  seriesProperty: 'NDVI'
}).setOptions(titleS2_M)
 
print(S2_chart_M);
 
 
//MODIS NDVI --------------------------------------------------------------------------
 
var MD_NDVI = ee.ImageCollection('MODIS/MOD09GA_006_NDVI')
    .filterDate(startDate,endDate)
    .filterBounds(AOI)
    .select('NDVI');
 
 
 var Monthly_MD =  ee.ImageCollection.fromImages(
  years.map(function (y) {
    return months.map(function(m) {
       
      var filtered = MD_NDVI.filter(ee.Filter.calendarRange(y, y, 'year'))
                    .filter(ee.Filter.calendarRange(m, m, 'month'))
      filtered = filtered.median()
      return filtered.set('year', y).set('month', m).set('system:time_start', ee.Date.fromYMD(y, m, 1));                 
    });
  }).flatten()
);
 
//Chart
 
var titleMD = {
  title: 'Mean Monthly MODIS NDVI',
  hAxis: {title: 'Time'},
  vAxis: {title: 'NDVI'},
};
 
 
var MD_chart = ui.Chart.image.seriesByRegion({
  imageCollection: Monthly_MD,
  regions: Point_1,
  reducer: ee.Reducer.mean(),
  band: 'NDVI',
  scale: 60,
  seriesProperty: 'NDVI'
}).setOptions(titleMD)
 
print(MD_chart);
 
 
//Landsat 8 ------------------------------------------------------------
 
var L8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR').filterDate(startDate,endDate)
                                                     .filterBounds(AOI)
                                                    
                                                    
 
var L8_NDVI = L8.map(function(image){
  return image.normalizedDifference(['B5', 'B4']).rename('NDVI').copyProperties(image, ['system:time_start']);
})
//chart
 
var titleL8 = {
  title: 'L8 NDVI',
  hAxis: {title: 'Time'},
  vAxis: {title: 'NDVI'},
};
 
var L8_chart = ui.Chart.image.seriesByRegion({
  imageCollection: L8_NDVI,
  regions: Point_1,
  reducer: ee.Reducer.mean(),
  band: 'NDVI',
  scale: 30,
  seriesProperty: 'NDVI'
}).setOptions(titleL8)
 
print(L8_chart);
 
 
// export to CSV
 
var export_csv = function(img){
  var mon = img.get('month')
  var yea = img.get('year')
  var value = img.reduceRegion(ee.Reducer.mean(), Point_1, 500).get('NDVI')
  var ft = ee.Feature(null, {'year': yea,
                             'month': mon,
                             'value': value});
  return ft;
};
 
// Apply the function to each image in modisLST.
var MD_csv = Monthly_MD.map(export_csv);
 
Export.image.toDrive({
  image: s2_ndvi,
  description: 'Afework_Bibugne',
  scale: 10
});
Export.table.toDrive({collection: MD_csv, selectors: 'year, month, value',folder:"Time_Series", fileFormat:"CSV"});