I'm new to GEE. I'm currently working on NDVI data analysis. So this is my code for MODIS Ndvi. I want to know how to divide all the images there inside ImageCollection by 10000 to get real NDVI values.

How do I get this work done?

var ndvi = ee.ImageCollection('MODIS/006/MOD13Q1');
var modisNDVI = ndvi.select('NDVI');
var collection = ee.ImageCollection(modisNDVI.filterDate('2017-07-01', '2018-12-31'));
var clipped = collection.mean().clip(fc)

You should create a custom function and map() over the collection:

var NDVI = function(image) {
  return image.expression('float(b("NDVI")/10000)')

var collection = ee.ImageCollection('MODIS/006/MOD13Q1');
var col = ee.ImageCollection(collection.filterDate('2017-07-01', '2018-12-31'));
var modisNDVI = col.map(NDVI);
var clipped = modisNDVI.mean().clip(fc)

Also, I changed the steps order (is better to filter a date range before to apply map())

  • Thanks @aldo_tapia. It worked but i try to create a time series chart. its not executing. Error generating chart: No features contain non-null values of "system:time_start". Code { print(ui.Chart.image.series(clipped, Phenology, ee.Reducer.mean(), 30)); } – Aravind S Nov 8 '18 at 6:20
  • @AravindS please, ask one question per post. You can open another thread to ask this – aldo_tapia Nov 8 '18 at 10:41

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