01.引言
由于经常需要批量下载某些指定日期的sentinel image和ndvi，故研究一下，写个函数方便以后项目的高效复用。现借助GEE的request功能来实现，话不多说，详见代码。
02.定义函数文件【.js】
exports.get_s2a = function get_s2a(timelist,geometry,buffer,folder){var S2A = ee.ImageCollection("COPERNICUS/S2")// buffervar area = geometry.map(function(roi){return roi.buffer(buffer)})// ndvivar s2_ndvi = function(image){return image.addBands(image.normalizedDifference(["B8","B4"]).rename("NDVI"));};function get_ndvi(start_time){var end_time = ee.Date(start_time).advance(1,'day')var s2 = S2A.map(s2_ndvi).filterBounds(area).filterDate(start_time,end_time)// .filterMetadata("CLOUD_COVERAGE_ASSESSMENT","less_than",60)// .sort("CLOUD_COVERAGE_ASSESSMENT");var new_ndvi = s2.max().clip(area).select("NDVI");return new_ndvi;};// imagefunction get_image(start_time){var end_time = ee.Date(start_time).advance(1,'day')var s2 = S2A.filterBounds(area).filterDate(start_time,end_time).filterMetadata("CLOUD_COVERAGE_ASSESSMENT","less_than",80).sort("CLOUD_COVERAGE_ASSESSMENT");var new_image = s2.mosaic().clip(area);return new_image;}// exportfunction export_tiff(input, till,folder){var exp = Export.image.toDrive ({image: input,description:till,fileNamePrefix:till,scale:10,region:area,maxPixels:9999999999999,crs:'EPSG:4326',folder:folder});return exp;};var res = ee.List([])for(var i=0;i<timelist.length;i++){var start_time = timelist[i]var ndvi = get_ndvi(start_time)var image = get_image(start_time)var res = res.add(image.select(['B2','B3','B4','B8','B11']).toUint16())var res = res.add(ndvi.toFloat())export_tiff(image.select(['B2','B3','B4','B8','B11']).toUint16(),'image'+start_time)export_tiff(ndvi.toFloat(),'ndvi'+start_time)};return res};
var sentinel = require('users/mxhoubo/requires:get_sentinel_ndvi.js')var imageVisParam4 = {"opacity":1,"bands":["B8","B4","B3"],"min":1251.4,"max":3046.6,"gamma":1.915}var geometry = ee.FeatureCollection('users/mxhoubo/china/city').filterMetadata('CityName','equals','潍坊市')var timelist = ['2022-05-21','2022-06-20','2022-06-25']var res= sentinel.get_s2a(timelist,geometry,2000,'weifang')var res = ee.ImageCollection.fromImages(res)print(res)var images = res.first()print(images)Map.addLayer(images,imageVisParam4,'image')Map.addLayer(geometry)Map.centerObject(geometry,8)
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