You can get the timeseries for daily data filtering by day. Inclusively, you can also plot the chart in GEE, however, you need a monthly aggregation because it can have a large amount of data (> 5000; limit in GEE). For a dates range between "2001-01-01" and "2022-12-31", following code looks as follows for an arbitrary area in Namibia (because your asset was not available).
var table = ee.Geometry.Polygon(
[[[15.011233342458334, -23.5446045392341],
[15.011233342458334, -23.56789330398866],
[15.072859776784506, -23.56789330398866],
[15.072859776784506, -23.5446045392341]]], null, false);
//gonna try and use imerg
//add polygon
//if you do this with mulitpile features it wont work
var geometry = ee.FeatureCollection(table);
Map.addLayer(geometry,{color:'green'},'Border');
Map.centerObject(geometry);
//SETUP DATES
var startYear = 2001;
var endYear = 2021;
var startDate = ee.Date.fromYMD(startYear, 01,01);
var endDate = ee.Date.fromYMD(endYear + 1, 12,31);
var dataset = ee.ImageCollection('NASA/GPM_L3/IMERG_V06')
.filterDate(startDate, endDate)
.select(['precipitationCal']);
var nDays = ee.Number(endDate.difference(startDate,'day').round());
print(nDays);
var byDays = ee.ImageCollection(
ee.List.sequence(0, nDays).map(function (n) {
var ini = startDate.advance(n,'day');
var end = ini.advance(1,'day');
return dataset.filterDate(ini,end)
.select(0).sum()
.set('system:time_start', ini);
}));
print(byDays.limit(5000));
var months = ee.List.sequence(1,12);
var nMonths = ee.Number(endDate.difference(startDate,'month')).round();
var byMonth = ee.ImageCollection(
ee.List.sequence(0, nMonths).map(function (n) {
var ini = startDate.advance(n,'month');
var end = ini.advance(1,'month');
return dataset.filterDate(ini,end)
.select(0).sum()
.set('system:time_start', ini);
}));
print(byMonth);
var precip = ui.Chart.image.seriesByRegion(
byMonth, // Image collection
geometry, // Region
ee.Reducer.mean(), // Type of reducer to apply
'precipitationCal',
11132);
var plotprecip = precip; // Data
print(plotprecip);
After running it in GEE code editor, I got result of following picture. There are 8034 daily images in this dates range and, in the Console Tab, it was printed 5000 of these images. Chart reflects a monthly aggregation.
Best Answer
This appears to be just the stddev/mean of each image, plotted. Something like this: