Displaying single band reflectance from Sentinel in GEE

Question

I have been able to display NDVI value in my project but I need some single certain band reflectance value for my data. I have tried in showing blue band (B2) but when I check the inspector tab, the number represent DN and not reflectance.

How do I display single band reflectance value in earth engine? Been searching and did not find the answer yet.

Below is my script:

var sentinelns = ee.ImageCollection('COPERNICUS/S2_SR')
                   .filterDate('2019-01-01', '2019-12-30')
                .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 95))
                .map(maskS2clouds)
                .median()
                .clip(geometry);
             
function maskS2clouds(image) {
  var qa = image.select('QA60');
  var cloudBitMask = 1 << 10;
  var cirrusBitMask = 1 << 11;
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0)
      .and(qa.bitwiseAnd(cirrusBitMask).eq(0));
  return image.updateMask(mask).divide(1);
}  

var SingleBandBlue = sentinelns.select(['B2']);
var BlueParam = { min: 0, max: 1000,};

Map.addLayer(SingleBandBlue, BlueParam, 'Sentinel B2');

Answer 1

You can find the detailed information for Sentinel 2 Level-2A collection here: https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S2_SR#bands

You can see that reflectance band's scale is 0.0001, which means that the value has been re-scaled using that factor. To get that value back you can simply multiply by the scale:

var sentinelns = ee.ImageCollection('COPERNICUS/S2_SR')
                   .filterDate('2019-01-01', '2019-12-30')
                .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 95))
                .map(maskS2clouds)
                .map(function(i){return i.multiply(0.0001)})
                .median()
                .clip(geometry);
             
function maskS2clouds(image) {
  var qa = image.select('QA60');
  var cloudBitMask = 1 << 10;
  var cirrusBitMask = 1 << 11;
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0)
      .and(qa.bitwiseAnd(cirrusBitMask).eq(0));
  return image.updateMask(mask).divide(1);
}  

var SingleBandBlue = sentinelns.select(['B2']);
// don't forget to change visualization parameters
var BlueParam = { min: 0, max: 0.2};

Map.addLayer(SingleBandBlue, BlueParam, 'Sentinel B2');