Google Earth Engine中的LandSat卫星数据

古城微笑少年丶 2021-07-25 14:58 1074阅读 0赞

## ee.ImageCollection.qualityMosaic（） ##

*  mosaic获取的是最后一个有值的像素，然后生成一张影像；
 *  qualityMosaic提取的是像素点的最大值，类似对集合使用max函数。在处理NDVI时可以有去云的效果；

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 1][]      ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 2][]

var l8 = ee.ImageCollection("LANDSAT/LC08/C01/T1_TOA");
    
    var l8_select=l8.filterBounds(ee.Geometry.Point(106.5,29.6))
                    .filterDate("2018-01-01","2018-12-31")
                    .select("B[3,4,5]")
                    
    function add_NDVI(image){
      var NDVI=image.normalizedDifference(["B5","B4"]).rename("NDVI")
      return image.addBands(NDVI)
    }
    
    var l8_ndvi=l8_select.map(add_NDVI)
    var ndvi_quality=l8_ndvi.qualityMosaic("NDVI")
    
    Map.setCenter(106.7,29.7,7)
    
    Map.addLayer(l8_ndvi,{"bands":["B5","B4","B3"],"max":0.5},"l8_ndvi")
    Map.addLayer(ndvi_quality,{"bands":["B5","B4","B3"],"max":0.5},"ndvi_quality")
    
    print(l8_ndvi,ndvi_quality)

### qualityMosaic（）处理NDVI去云 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 3][]

var l8 = ee.ImageCollection("LANDSAT/LC08/C01/T1_TOA");
    
    var l8_select=l8.filterBounds(ee.Geometry.Point(106.5,29.6))
                    .filterDate("2018-01-01","2018-12-31")
                    .select("B[3,4,5]")
                    
    function add_NDVI(image){
      var NDVI=image.normalizedDifference(["B5","B4"]).rename("NDVI")
      return image.addBands(NDVI)
    }
    
    var l8_ndvi=l8_select.map(add_NDVI)
    
    var ndvi_quality=l8_ndvi.qualityMosaic("NDVI").select("NDVI")
                    
    
    Map.setCenter(106.7,29.7,9)
    
    Map.addLayer(ndvi_quality,{"min":-1,"max":1,"palette":'FFFFFF, CE7E45, DF923D, F1B555, FCD163, 99B718, 74A901, 66A000, 529400,3E8601, 207401, 056201, 004C00, 023B01, 012E01, 011D01, 011301'},"ndvi_quality")

## simpleCloudScore() ##

有待研究

## simpleComposite() ##

取影像集中云层含量最小的栅格值作为选定值，再将所有选定值拼接成image

返回一个去了云的Image

注意：需要landsat中的row数据

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 4][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 5][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 6][]

var sichuan = ee.FeatureCollection("users/lcljv1066965/test/sichuan"),
        l8 = ee.ImageCollection("LANDSAT/LC08/C01/T1");
    
    
    var l8_select=l8.filterBounds(sichuan)
                    .filterDate("2018-01-01","2018-12-31")
                  
    var img_simpleComposite=ee.Algorithms.Landsat.simpleComposite({collection:l8_select,asFloat:true}).clip(sichuan)
    print("img_simpleComposite",img_simpleComposite)
    Map.centerObject(sichuan,6)
     
    Map.addLayer(img_simpleComposite,{bands:["B5","B4","B3"],max:0.3},"B543")
    Map.addLayer(img_simpleComposite,{bands:["B4","B3","B2"],max:0.3},"B432")

# 自定义函数去云 #

给影像集中的每个image都去云，并且返回一个去了云的影像集

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 7][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 8][]

又或者

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 9][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70 10][]

var sichuan = ee.FeatureCollection("users/lcljv1066965/test/sichuan");
    
    var maskL8 = function(image) {
      var qa = image.select('BQA');
      var mask = qa.bitwiseAnd(1 << 4).eq(0);
      return image.updateMask(mask);
    }
    
    var composite = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA')
        .filterDate('2018-01-01', '2019-1-1')
        .map(maskL8)
        .median();
    
    Map.addLayer(composite.clip(sichuan), {bands: ['B4', 'B3', 'B2'], max: 0.3});
    Map.centerObject(sichuan,6)

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70]: /images/20210725/2007cb486061495f8080d0a88b9b0208.png
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