// sentinel2 ndwi

//哨兵2去云处理

var s2_rmcloud = function(image) {

var quality = image.select("QA60").unmask();

return image.updateMask(quality.eq(0));

};

//在原影像中加入一个新的波段，命名为NDWI

var s2_ndwi = function(image) {

return image.addBands(image.normalizedDifference(["B3", "B8"]).rename("NDWI"));

};

//sentinel2 and roi 过滤筛选哨兵2影像

var s2_col = ee.ImageCollection("COPERNICUS/S2");

var roi = ee.Geometry.Point([117.0703125,38.09133660751176]);

var s2_nocloud = s2_col.map(s2_rmcloud)

                      .filterBounds(roi)

                      .filterDate("2017-01-01", "2017-09-24");

var ndwi = s2_nocloud.map(s2_ndwi).select("NDWI").reduce(ee.Reducer.mean());

var visParam = {

min: -0.5,

max: 0.5,

palette: ['00FFFF', '0000FF']

};

Map.addLayer(ndwi, visParam, "ndwi");

Map.centerObject(roi, 9);

//展示关心区域roi在1.1-9.23日之间的的NDWI值序列

var ndwi_list = s2_nocloud.filterDate("2017-01-01", "2017-09-23")

  .map(function(image) {

  var ndwi = image.normalizedDifference(['B3', 'B5']).rename('NDWI');

  return image.addBands(ndwi);

});

var chart1 = ui.Chart.image.series({

imageCollection: ndwi_list.select('NDWI'),

region: roi,

reducer: ee.Reducer.mean(),

scale: 30

}).setOptions({title: 'NDWI IMAGE SERIES'});

print(chart1);

var chart2 = ui.Chart.image.doySeries({

imageCollection: ndwi_list.select('NDWI'),

region:roi,

regionReducer: ee.Reducer.mean(),

scale:30

}).setOptions({title: "ROI NDWI EACH DAY SERIES"})

print(chart2)