一、归一化水体指数
归一化水体指数（NDWI）是遥感领域中用于监测植被冠层液态水含量的有效指数，通常通过近红外（NIR）波段与短波红外（SWIR）波段的比值来计算。NDWI的值范围从-1.0到1.0，其中值越接近1.0，表示水体的存在越明显。该指数在水体监测、植被健康状况评估等领域具有广泛应用。
二、GEE代码
基于Landsat数据生成NDWI年复合图像，并导出每年的栅格数据，同时绘制年际变化的折线图，需要的同学仅需要更改研究区和时间段。
// 定义几何区域var geometry = table;Map.centerObject(geometry, 6);// 加载数据集var dataset = ee.ImageCollection("LANDSAT/COMPOSITES/C02/T1_L2_ANNUAL_NDWI");// 定义年份范围var startYear = 1984;var endYear = 2024;var years = ee.List.sequence(startYear, endYear);// 创建一个函数计算每年的NDWI均值var annualMeanNDWI = years.map(function(year) {year = ee.Number(year);var startDate = ee.Date.fromYMD(year, 1, 1);var endDate = ee.Date.fromYMD(year, 12, 31);// 筛选数据并计算均值var meanNDWI = dataset.filterDate(startDate, endDate).select('NDWI').mean().reduceRegion({reducer: ee.Reducer.mean(),geometry: geometry,scale: 1000,maxPixels: 1e13}).get('NDWI');// 返回年份和均值return ee.Feature(null, {year: year,meanNDWI: meanNDWI});});// 转换为FeatureCollectionvar annualMeanNDWICollection = ee.FeatureCollection(annualMeanNDWI);// 打印结果到控制台print('Annual Mean NDWI:', annualMeanNDWICollection);// 可视化折线图var chart = ui.Chart.feature.byFeature({features: annualMeanNDWICollection,xProperty: 'year',yProperties: ['meanNDWI']}).setChartType('LineChart').setOptions({title: 'Annual Mean NDWI (1984-2024)',hAxis: { title: 'Year' },vAxis: { title: 'Mean NDWI' },lineWidth: 2,pointSize: 4});// 将折线图添加到面板print(chart);// 导出每年NDWI均值影像至Google Driveyears.getInfo().forEach(function(year) {var startDate = year + '-01-01';var endDate = year + '-12-31';var yearCollection = dataset.filterDate(startDate, endDate).select('NDWI').mean().clip(geometry);Export.image.toDrive({image: yearCollection,description: 'NDWI_' + year,fileNamePrefix: 'NDWI_' + year,scale: 100,region: geometry,maxPixels: 1e13,crs: "EPSG:4326",folder: 'NDWI_Exports'});});
三、成为会员
