Applying Raster Calculation to Image Collection in Google Earth Engine

Question

I am trying to perform a raster calculation (EVI) on an imagery collection. This operation is seen on Line 130 and is based on:

https://developers.google.com/earth-engine/image_math (which I know is for single images). In addition to being an imageCollection, my version of this GEE provided code differs in that I've renamed my bands prior to calculating EVI.

I am having trouble finding the necessary format to apply a band math equation to an imagery collection.

Presently, I am receiving an error: "Cloudfiltered.expression is not a function"

Here is my script: https://code.earthengine.google.com/0e9ae4a031ddd2d46fe44d40cc03b05e

The Region of Interest: "ROI" was made with the Rectangle Tool in GEE and can be totally arbitrary; I don't know how to share it. Here is mine for context: https://i.sstatic.net/BbeWg.jpg

Answer 1

The way to add EVI to every image in an image collection in Earth Engine is to map() a function over the collection.

// First, create function
var addEVI = function(image) {
  var evi = ee.Image(0).expression(
    '2.5 * ((NIR - RED) / (NIR + 6 * RED - 7.5 * BLUE + 1))', {
      'NIR': image.select('NIR'),
      'RED': image.select('RED'),
      'BLUE': image.select('BLUE')
    });
  return image.addBands(evi.rename('evi'));
};

// Second, apply function over your collection
var mergedEVI = Cloudfiltered.map(addEVI);

The variable mergedEVI is an image collection in which every image has a band named "evi".

More information https://developers.google.com/earth-engine/ic_mapping