利用GEE计算遥感生态指数(RSEI)

淩亂°似流年 2023-09-27 23:56 162阅读 0赞

城市生态与人类生活息息相关，快速 、准确 、客 观地了解城市生态状况已成为生态领域的一个研究重点 。基于遥感技术，提出一个完全基于遥感技术 ，以自然因子为主的遥感生态指数 (RSEI)来对城市的生态状况进行快速监测与评价 。该指数利用主成分分析技术集成了植被指数 、湿度分量、地表温度和建筑指数等 4个评价指标，它们分别代表了绿度、湿度、热度和干度等4大生态要素。  
本文基于GEE平台，实现RSEI算法。  
运行结果：  
![在这里插入图片描述][f08c1f6d4ef04faf9a54c83a372fc468.png]

第一步：定义研究区，自行更换自己的研究区  
第二步：加载数据集,定义去云函数  
第三步：主函数,计算生态指标  
第四步：PCA融合，提取第一主成分  
第五步：利用PC1，计算RSEI，并归一化

### 完整代码 ###

代码如下（示例）：

// 第一步:定义研究区，自行更换自己的研究区
    var roi = 
        /* color: #98ff00 */
        /* displayProperties: [
          {
            "type": "rectangle"
          }
        ] */
        ee.Geometry.Polygon(
            [[[120.1210075098537, 35.975189051414006],
              [120.1210075098537, 35.886229778229115],
              [120.25764996590839, 35.886229778229115],
              [120.25764996590839, 35.975189051414006]]], null, false);
              
    Map.centerObject(roi);
     
    // 第二步：加载数据集,定义去云函数
    function removeCloud(image){
      var qa = image.select('BQA')
      var cloudMask = qa.bitwiseAnd(1 << 4).eq(0)
      var cloudShadowMask = qa.bitwiseAnd(1 << 8).eq(0)
      var valid = cloudMask.and(cloudShadowMask)
      return image.updateMask(valid)
    }
    
    // 数据集去云处理
    var L8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA')
               .filterBounds(roi)
               .filterDate('2018-01-01', '2019-12-31')
               .filterMetadata('CLOUD_COVER', 'less_than',50)
               .map(function(image){
                        return image.set('year', ee.Image(image).date().get('year'))                           
                      })
               .map(removeCloud)
     
    
    // 影像合成
    var L8imgList = ee.List([])
    for(var a = 2018; a < 2020; a++){
       var img = L8.filterMetadata('year', 'equals', a).median().clip(roi)
       var L8img = img.set('year', a)
       L8imgList = L8imgList.add(L8img)
     }
    
    // 第三步：主函数,计算生态指标
    var L8imgCol = ee.ImageCollection(L8imgList)
                     .map(function(img){
                          return img.clip(roi)
                       })
                     
    L8imgCol = L8imgCol.map(function(img){
      
      // 湿度函数:Wet
      var Wet = img.expression('B*(0.1509) + G*(0.1973) + R*(0.3279) + NIR*(0.3406) + SWIR1*(-0.7112) + SWIR2*(-0.4572)',{
           'B': img.select(['B2']),
           'G': img.select(['B3']),
           'R': img.select(['B4']),
           'NIR': img.select(['B5']),
           'SWIR1': img.select(['B6']),
           'SWIR2': img.select(['B7'])
         })   
      img = img.addBands(Wet.rename('WET'))
      
      
      // 绿度函数:NDVI
      var ndvi = img.normalizedDifference(['B5', 'B4']);
      img = img.addBands(ndvi.rename('NDVI'))
      
      
      // 热度函数:lst 直接采用MODIS产品
      var lst = ee.ImageCollection('MODIS/006/MOD11A1').map(function(img){
                    return img.clip(roi)
               })
               .filterDate('2014-01-01', '2019-12-31')
      
      var year = img.get('year')
      lst=lst.filterDate(ee.String(year).cat('-01-01'),ee.String(year).cat('-12-31')).select(['LST_Day_1km', 'LST_Night_1km']);
          
      // reproject主要是为了确保分辨率为1000
      var img_mean=lst.mean().reproject('EPSG:4326',null,1000);
      //print(img_mean.projection().nominalScale())
      
      img_mean = img_mean.expression('((Day + Night) / 2)',{
          'Day': img_mean.select(['LST_Day_1km']),
          'Night': img_mean.select(['LST_Night_1km']),
           })
      img = img.addBands(img_mean.rename('LST'))
      
      
      // 干度函数:ndbsi = ( ibi + si ) / 2
      var ibi = img.expression('(2 * SWIR1 / (SWIR1 + NIR) - (NIR / (NIR + RED) + GREEN / (GREEN + SWIR1))) / (2 * SWIR1 / (SWIR1 + NIR) + (NIR / (NIR + RED) + GREEN / (GREEN + SWIR1)))', {
          'SWIR1': img.select('B6'),
          'NIR': img.select('B5'),
          'RED': img.select('B4'),
          'GREEN': img.select('B3')
        })
      var si = img.expression('((SWIR1 + RED) - (NIR + BLUE)) / ((SWIR1 + RED) + (NIR + BLUE))', {
          'SWIR1': img.select('B6'),
          'NIR': img.select('B5'),
          'RED': img.select('B4'),
          'BLUE': img.select('B2')
        }) 
      var ndbsi = (ibi.add(si)).divide(2)
      return img.addBands(ndbsi.rename('NDBSI'))
    })
     
     
    var bandNames = ['NDVI', "NDBSI", "WET", "LST"]
    L8imgCol = L8imgCol.select(bandNames)
     
    //定义归一化函数:归一化
    var img_normalize = function(img){
          var minMax = img.reduceRegion({
                reducer:ee.Reducer.minMax(),
                geometry: roi,
                scale: 1000,
                maxPixels: 10e13,
            })
          var year = img.get('year')
          var normalize  = ee.ImageCollection.fromImages(
                img.bandNames().map(function(name){
                      name = ee.String(name);
                      var band = img.select(name);
                      return band.unitScale(ee.Number(minMax.get(name.cat('_min'))), ee.Number(minMax.get(name.cat('_max'))));
                        
                  })
            ).toBands().rename(img.bandNames()).set('year', year);
            return normalize;
    }
    var imgNorcol  = L8imgCol.map(img_normalize);
     
     
    // 第四步:PCA融合，提取第一主成分
    var pca = function(img){
          
          var bandNames = img.bandNames();
          var region = roi;
          var year = img.get('year')
          // Mean center the data to enable a faster covariance reducer
          // and an SD stretch of the principal components.
          var meanDict = img.reduceRegion({
                reducer:  ee.Reducer.mean(),
                geometry: region,
                scale: 1000,
                maxPixels: 10e13
            });
          var means = ee.Image.constant(meanDict.values(bandNames));
          var centered = img.subtract(means).set('year', year);
          
          
          // This helper function returns a list of new band names.
          var getNewBandNames = function(prefix, bandNames){
                var seq = ee.List.sequence(1, 4);
                //var seq = ee.List.sequence(1, bandNames.length());
                return seq.map(function(n){
                      return ee.String(prefix).cat(ee.Number(n).int());
                  });      
            };
          
          // This function accepts mean centered imagery, a scale and
          // a region in which to perform the analysis.  It returns the
          // Principal Components (PC) in the region as a new image.
          var getPrincipalComponents = function(centered, scale, region){
                var year = centered.get('year')
                var arrays = centered.toArray();
            
                // Compute the covariance of the bands within the region.
                var covar = arrays.reduceRegion({
                      reducer: ee.Reducer.centeredCovariance(),
                      geometry: region,
                      scale: scale,
                      bestEffort:true,
                      maxPixels: 10e13
                  });
                
                // Get the 'array' covariance result and cast to an array.
                // This represents the band-to-band covariance within the region.
                var covarArray = ee.Array(covar.get('array'));
                
                // Perform an eigen analysis and slice apart the values and vectors.
                var eigens = covarArray.eigen();
            
                // This is a P-length vector of Eigenvalues.
                var eigenValues = eigens.slice(1, 0, 1);
                // This is a PxP matrix with eigenvectors in rows.
                var eigenVectors = eigens.slice(1, 1);
            
                // Convert the array image to 2D arrays for matrix computations.
                var arrayImage = arrays.toArray(1)
                // Left multiply the image array by the matrix of eigenvectors.
                var principalComponents = ee.Image(eigenVectors).matrixMultiply(arrayImage);
            
                // Turn the square roots of the Eigenvalues into a P-band image.
                var sdImage = ee.Image(eigenValues.sqrt())
                .arrayProject([0]).arrayFlatten([getNewBandNames('SD',bandNames)]);
            
                // Turn the PCs into a P-band image, normalized by SD.
                return principalComponents
                // Throw out an an unneeded dimension, [[]] -> [].
                .arrayProject([0])
                // Make the one band array image a multi-band image, [] -> image.
                .arrayFlatten([getNewBandNames('PC', bandNames)])
                // Normalize the PCs by their SDs.
                .divide(sdImage)
                .set('year', year);
            }
            
            // Get the PCs at the specified scale and in the specified region
            img = getPrincipalComponents(centered, 1000, region);
            return img;
      };
      
    var PCA_imgcol = imgNorcol.map(pca)
     
    Map.addLayer(PCA_imgcol.first(), {"bands":["PC1"]}, 'pc1')
     
    // 第五步：利用PC1，计算RSEI，并归一化
    var RSEI_imgcol = PCA_imgcol.map(function(img){
            img = img.addBands(ee.Image(1).rename('constant'))
            var rsei = img.expression('constant - pc1' , {
                 constant: img.select('constant'),
                 pc1: img.select('PC1')
             })
            rsei = img_normalize(rsei)
            return img.addBands(rsei.rename('rsei'))
        })
    print(RSEI_imgcol)
     
    var visParam = {
        palette: '040274, 040281, 0502a3, 0502b8, 0502ce, 0502e6, 0602ff, 235cb1, 307ef3, 269db1, 30c8e2, 32d3ef, 3be285, 3ff38f, 86e26f, 3ae237, b5e22e, d6e21f, fff705, ffd611, ffb613, ff8b13, ff6e08, ff500d, ff0000, de0101, c21301, a71001, 911003'
     };
     
    Map.addLayer(RSEI_imgcol.first().select('rsei'), visParam, 'rsei')

[f08c1f6d4ef04faf9a54c83a372fc468.png]: https://img-blog.csdnimg.cn/f08c1f6d4ef04faf9a54c83a372fc468.png