I've computed water area for each 8 days for about 20 years. I don't know how can I compute monthly area for these years? or How can I change 8 days product to the monthly in this code?
code link: https://code.earthengine.google.com/590d4cf09f90e591d69ed3a03039d4f7
Map.centerObject(geometry)
var modis = ee.ImageCollection('MODIS/006/MOD09A1')
.filterBounds(geometry)
.filterDate('2000-01-01','2020-01-01')
.select('sur_refl_b03','sur_refl_b02')
.map(function(img){
var id = img.id();
var scale = img.multiply(0.0001);
var clip = scale.clip(geometry);
var index = clip.normalizedDifference(['sur_refl_b03','sur_refl_b02']);
var thr = index.gte(0.1);
var mask = index.updateMask(thr);
var area = mask.multiply(ee.Image.pixelArea().divide(1000000.0));
return area
.copyProperties(img,['system:time_start','system:time_end'])
});
print(modis);
var chart = ui.Chart.image.series(modis, geometry,
ee.Reducer.sum(), 1000, 'system:time_start');
print(chart);