Question

我有一个Landsat 5的图像集合和一个包含数千个多边形和点的要素集合（在示例中，我只有三个）。我想计算一段时间内每个多边形的NDVI（和NDWI）平均值，就像我正在使用的那样： ui.Chart.image.series ;

如果我仅使用此代码测试一个多边形：

var p1= ee.Geometry.Point([-78.55995626672507,35.05443673532838])
var pol = ee.Geometry.Polygon([[[-78.57239414626946,35.01247143741747], 
[-78.57186843330254,35.012559309453266], 
[-78.57199717933526,35.01277020195395], 
[-78.57253362113823,35.01272626606113],
[-78.57239414626946,35.01247143741747]
]]);

var ens = [
ee.Feature(pol, {name: 'Thiessen'})
];

var col =  ee.FeatureCollection(ens)
print(col)

// NDVI: B4 and B3
var addNDVI = function(image) {
var ndvi = image.normalizedDifference(['B4', 'B3']).rename('NDVI');
return image.addBands(ndvi);
};

// Apply the cloud mask and NDVI function to Landsat 5 imagery and   print the chart
 var l5 = ee.ImageCollection("LANDSAT/LT05/C01/T1_TOA")
      .filter(ee.Filter.calendarRange(1985,2007,'year'))
      .filter(ee.Filter.calendarRange(1,1,'month'))
      .filterBounds(p1)
      .map(addNDVI) 

print(ui.Chart.image.series(l5.select('NDVI'), col, ee.Reducer.mean(), 30));

使用此代码，我获得了this figure。我想获得具有多个多边形的相同类型的图形（一个图形包含多边形的所有时间序列）。

我尝试了以下代码：

var p1= ee.Geometry.Point([-78.55995626672507,35.05443673532838])
var p2= ee.Geometry.Point([-78.5725093420931,35.05908805245044])
var pol = ee.Geometry.Polygon([[[-78.57239414626946,35.01247143741747], 
[-78.57186843330254,35.012559309453266], 
[-78.57199717933526,35.01277020195395], 
[-78.57253362113823,35.01272626606113],
[-78.57239414626946,35.01247143741747]
]]);

var ens = [
ee.Feature(p2, {name: 'Thiessen'}),
ee.Feature(pol, {name: 'Thiessen'})
];

var col =  ee.FeatureCollection(ens)
print(col)

// NDVI: B4 and B3
var addNDVI = function(image) {
var ndvi = image.normalizedDifference(['B4', 'B3']).rename('NDVI');
return image.addBands(ndvi);
};

// Apply the cloud mask and NDVI function to Landsat 5 imagery and    print the chart
var l5 = ee.ImageCollection("LANDSAT/LT05/C01/T1_TOA")
      .filter(ee.Filter.calendarRange(1985,2007,'year'))
      .filter(ee.Filter.calendarRange(1,1,'month'))
      .filterBounds(p1)
      .map(addNDVI) 

//Create a graph of the time-series.
var graph = ui.Chart.image.seriesByRegion({
imageCollection: l5, 
regions: col, 
reducer: ee.Reducer.mean(),
scale: 30,
})
print(graph)

此代码提供了this figure

最后一个代码按照我的意愿显示了图形。但是，它不计算我想要的。对于多边形pol，我应该使用两个代码具有相同的图形，但事实并非如此。我如何用代码1进行相同的计算，但以代码2表示？

Answer 1

您需要在第二个调用中添加'band'参数，如下所示：

var graph = ui.Chart.image.seriesByRegion({
  imageCollection: l5, 
  regions: col, 
  band: 'NDVI',
  reducer: ee.Reducer.mean(),
  scale: 30,
})

如何为Google Earth引擎的要素集中包含的每个多边形创建时间序列（NDVI）？

1 个答案: