利用表達式計算一個數(shù)據(jù)集的增強結(jié)果

主要功能

對數(shù)據(jù)集的所有數(shù)據(jù)執(zhí)行多項式計算獲得計算結(jié)果進行展示

代碼

// Map an expression over a collection.
//
// Computes the mean NDVI and SAVI by mapping an expression over a collection
// and taking the mean.  This intentionally exercises both variants of
// Image.expression.

// Filter the L7 collection to a single month.
var collection = ee.ImageCollection('LANDSAT/LE07/C01/T1_TOA')
    .filterDate('2002-11-01', '2002-12-01');

// A function to compute NDVI.
var NDVI = function(image) {
  return image.expression('float(b("B4") - b("B3")) / (b("B4") + b("B3"))');
};

// A function to compute Soil Adjusted Vegetation Index.
var SAVI = function(image) {
  return image.expression(
      '(1 + L) * float(nir - red)/ (nir + red + L)',
      {
        'nir': image.select('B4'),
        'red': image.select('B3'),
        'L': 0.2
      });
};

// Shared visualization parameters.
var vis = {
  min: 0,
  max: 1,
  palette: [
      'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718',
      '74A901', '66A000', '529400', '3E8601', '207401', '056201',
      '004C00', '023B01', '012E01', '011D01', '011301'
  ]
};

Map.setCenter(-93.7848, 30.3252, 11);

// Map the functions over the collection, reduce to mean and display.
Map.addLayer(collection.map(NDVI).mean(), vis, 'Mean NDVI');
Map.addLayer(collection.map(SAVI).mean(), vis, 'Mean SAVI');

步驟分析

1. 創(chuàng)建數(shù)據(jù)集對象，使用名稱，日期來篩選獲得LE07特定數(shù)據(jù)
2. 定義函數(shù)，實現(xiàn)輸入影像數(shù)據(jù)，返回NDVI計算結(jié)果
3. 定義函數(shù)，實現(xiàn)輸入影像數(shù)據(jù)，返回調(diào)節(jié)植被指數(shù)SAVI計算結(jié)果
4. 設(shè)置顯示參數(shù)
5. 設(shè)置地圖中心，縮放等級
6. 添加NDVI圖層，展示結(jié)果
7. 添加SAVI圖層，展示結(jié)果