如何在谷歌地球引擎中以智能的方式获得本月和上月的差异图像

Question

如何在谷歌地球引擎中智能获取本月与上月的差异图像

研究区域25E-75E，5S-35N

// study area 25E-75E，5S-35N。
var geometry = 
ee.Geometry.Polygon(
[[[25, 35],
[25, 5],
[75, 5],
[75, 35]]], null, false);
var regions = ee.FeatureCollection([
ee.Feature(geometry)
]);

//imgCol

var now = ee.Date(Date.now());
var NDVICollection=ee.ImageCollection('MODIS/006/MOD13Q1')
.filterDate('2010-01-01',now)
.filterBounds(regions)
.select('NDVI'); 
var col = NDVICollection.map(function(img){
return img.multiply(0.0001)
.copyProperties(img,['system:time_start','system:time_end']);
});
// grouped by month 
var months = ee.List([11,12,1,2]);
var byMonth = ee.ImageCollection.fromImages(
months.map(function (m) {
return col.filterDate('2019-11-01',now).filter(ee.Filter.calendarRange(m, m, 'month'))
.select('NDVI').mean()
.set('month', m);
}));

掩模

var meanNDVI = byMonth.reduce(ee.Reducer.mean());
var mask = meanNDVI.gt(0.1);

创建差异图像

**var img12 = byMonth.filter(ee.Filter.eq('month', ee.Number(12))).first().updateMask(mask);
var img11 = byMonth.filter(ee.Filter.eq('month', ee.Number(11))).first().updateMask(mask);
var img1 = byMonth.filter(ee.Filter.eq('month', ee.Number(1))).first().updateMask(mask);
var img2 = byMonth.filter(ee.Filter.eq('month', ee.Number(2))).first().updateMask(mask);
var ndviChange_12 = img12.subtract(img11).set('name','ndviChange_12');
var ndviChange_1 = img1.subtract(img12).set('name','ndviChange_1');
var ndviChange_2 = img12.subtract(img1).set('name','ndviChange_2');
var ndviChange = ee.ImageCollection([ndviChange_12,ndviChange_1,ndviChange_2]);**

我想让它更聪明，我该怎么办？做一个函数或其他什么

显示图像

Map.centerObject(regions);
Map.addLayer(byMonth);
Map.addLayer(ndviChange);

Answer 1

我认为解决方案是对byMonth集合使用iterate。请在文档中查看此示例。https://developers.google.com/earth-engine/ic_iterating