Calculate stdev while reducing resolution in Google Earth Engine

Question

I have a MODIS image that I'd like to resample to 12km resolution. For each 12km pixel, I'd like two pieces of information: (1) the mean of the MODIS pixels within the 12km pixel and (2) the standard deviation of the MODIS pixels within the 12km pixel.

Consider the following example:

var imageCollection = ee.ImageCollection("UMT/NTSG/v2/MODIS/NPP");    
var data = imageCollection.first().select("annualNPP")
    
var data_mean =data .reproject({ crs: 'EPSG:4326', scale: 12000})
                                        .reduceResolution({
                                          reducer: ee.Reducer.mean(), 
                                          maxPixels: 65535  }).rename("mean")

var data_stdev =data .reproject({ crs: 'EPSG:4326', scale: 12000})
                                        .reduceResolution({
                                          reducer: ee.Reducer.stdDev(), 
                                          maxPixels: 65535  }).rename("stdev")
Map.addLayer(data_mean,{},"mean")
Map.addLayer(data_stdev,{},"stdev")

This gives me an image with the mean of the MODIS pixels within the 12km pixel but the standard deviation at each 12km pixel is zero.

I thought maybe the standard deviation was small, so I tried multiplying the data_stdev image by 1,000, but that did not solve the problem.

Perhaps there is another way to approach this?

Answer 1

The reproject goes after the reduceResolution.