Classification of NDVI using Google Earth Engine

Question

I want to classify my NDVI raster using training data in Google Earth Engine. For that i am using the following code. But it is returning some error like ndvi is not a usable band. Please help in this

// Cloud Masking function
function maskS2clouds(image) {
  var qa = image.select('QA60');

  // Bits 10 and 11 are clouds and cirrus, respectively.
  var cloudBitMask = ee.Number(2).pow(10).int();
  var cirrusBitMask = ee.Number(2).pow(11).int();

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

  // Return the masked and scaled data.
  return image.updateMask(mask).divide(10000);
}

// AOI of Study Area
var boundary = ee.FeatureCollection('ft:1rbhNtC1TqDBvY9Rt2BZR-DjhpIPuC3nU5kmz49WW');//Jorhat Boundary
//var boundary = ee.FeatureCollection('ft:1ABffZYEE4XhMTOXsoSfWENKXBK2fQfOrdMplEaVo');//Midnapur Boundary

// Import of Images (Sentinel 2 multispectral)
var image = ee.ImageCollection(sent2img
  .filterDate("2017-12-01","2018-01-30")
  .filterBounds(boundary)
  .map(maskS2clouds)
  .sort("CLOUD_COVERAGE_ASSESSMENT")
  .median()
);

// Preprocessing 
var mosaic = image.mosaic()
var clip = mosaic.clip(boundary);
print(clip);

// FCC creation and visualisation of AOI     
Map.addLayer(clip, {bands: ['B8','B4','B3'], min: 0, max: 0.3},'clip');

// NDVI  calculation
var ndvi = clip.expression(
    ' ((NIR - RED) / (NIR + RED))', {
      'NIR': clip.select('B8'),
      'RED': clip.select('B4'),
}).rename('nd');

print(ndvi);

// Colour Palette
var palette = ['FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718',
               '74A901', '66A000', '529400', '3E8601', '207401', '056201',
               '004C00', '023B01', '012E01', '011D01', '011301'];

// Map display
Map.addLayer(ndvi, {min:0, max:1, palette: palette},"NDVI");

// Training Classes 
var newfc = wb.merge(plantation)
              .merge(agriland1)
              .merge(agriland2)
              .merge(habitation)
              .merge(sandyarea)
              .merge(deepplantation);
var bands = ['nd'];
var training = clip.select(bands).sampleRegions({
  collection: newfc, 
  properties: ['class'], 
  scale: 20,
  geometries:true
});

var classifier = ee.Classifier.cart().train({
  features: training, 
  classProperty: 'class', 
  inputProperties: bands
});

var classified = clip.select(bands).classify(classifier);

Map.addLayer(
  classified, 
  {min: 1, max: 7, palette: ['#0d1898', '#ff0841', '#138b11','#fff81c','#154c17','#529400','#F1B555']},
  'classification');

Answer 1

You forgot to add ndvi band to the image:

Do this:

// -----------  NDVI  calculation

var ndvi = clip.expression(
    ' ((NIR - RED) / (NIR + RED))', {
      'NIR': clip.select('B8'),
      'RED': clip.select('B4'),
}).rename('nd');

clip = clip.addBands(ndvi)

https://code.earthengine.google.co.in/64019c5b9fe1023f8633d182d2388d91