Calculate NDVI for a Landsat collection

Question

I am trying to to calculate the ndvi for the full Landsat collection. At first I remove the clouds and then I try to calculate the ndvi index as follow. Unfortunately I do not get any results, does anyone has any ideas why the code does not work?

Thank you

Code:

// Function to cloud mask Landsat 8.
var maskL8SR = function(image) {

// Bits 3 and 5 are cloud shadow and cloud, respectively.
var cloudShadowBitMask = ee.Number(2).pow(3).int();
var cloudsBitMask = ee.Number(2).pow(5).int();

// Get the QA band.
var qa = image.select('pixel_qa');

// Both flags should be set to zero, indicating clear conditions.
var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0).and(
            qa.bitwiseAnd(cloudsBitMask).eq(0));
   return image

// Scale the data to reflectance and temperature.
   .select(['B4', 'B5'], ['Red', 'NIR']).multiply(0.0001)
   .updateMask(mask);
};


var lst8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
    .filterDate('2013-04-07', '2018-05-01')
    .filterBounds(geometry)  
    .map(maskL8SR)
    .map(addNDVI_l8).select('NDVI');

lst8 = lst8.map(addNDVI_l8);
lst8 = lst8.filterBounds(geometry);

It would be helpful if you share code that can be run and produces the problem you're experiencing. — Val, Oct 15 '18 at 12:43

score 2 · Answer 1 · answered Oct 23 '18 at 16:14

GEE has a built in function for computing NDVI

select image

var image = ee.Image(
  l8.filterBounds(point)
    .filterDate('2015-01-01', '2015-12-31')
    .sort('CLOUD_COVER')
    .first()
);

compute ndvi

var ndvi = image.normalizedDifference(['B5', 'B4']).rename('NDVI');

display image

Map.centerObject(image, 9);
var ndviParams = {min: -1, max: 1, palette: ['blue', 'white', 'green']};
Map.addLayer(ndvi, ndviParams, 'NDVI image');

without the function

var nir = image.select('B5');
var red = image.select('B4');
var ndvi = nir.subtract(red).divide(nir.add(red)).rename('NDVI');

over a collection

var addNDVI = function(image) {
  var ndvi = image.normalizedDifference(['B5', 'B4']).rename('NDVI');
  return image.addBands(ndvi);
};

var withNDVI = l8.map(addNDVI);

All these examples come from a very good tutorial that GEE has written, its worth looking at.