Deciduous forest mapping in Cambodia II

Make your probability map using machine learning

The code snippets below describe how to import the data, calculate the covariates and run the machine learning model.

step 1: copy the functions to calculate the covariates to your script.

/*Copyright (c) 2019 SERVIR-Mekong

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var ndCovariatesList = [
  ['blue', 'green'],
  ['blue', 'red'],
  ['blue', 'nir'],
  ['blue', 'swir1'],
  ['blue', 'swir2'],
  ['green', 'red'],
  ['green', 'nir'],
  ['green', 'swir1'],
  ['green', 'swir2'],
  ['red', 'swir1'],
  ['red', 'swir2'],
  ['nir', 'red'],
  ['nir', 'swir1'],
  ['nir', 'swir2'],
  ['swir1', 'swir2']
];

var rCovariatesList = [
  ['swir1', 'nir'],
  ['red', 'swir1']
];

var ComputeNDCovariatesList = function () {
  var list = [];
  for (var index in ndCovariatesList) {
    var list_ = [ndCovariatesList[index][0], ndCovariatesList[index][1]];
    list.push(list_);
  }
  return list;
};

var addNDCovariates = function (image){
  var list = ComputeNDCovariatesList();
  print(list)
  for (var index in list) {
    image = image.addBands(image.normalizedDifference(list[index]).rename('ND_'+ ndCovariatesList[index][0] + '_' + ndCovariatesList[index][1]));
  }
  return image;
};

var ComputeRCovariatesList = function () {
  var list = [];
  for (var index in rCovariatesList) {
    var list_ = [rCovariatesList[index][0], rCovariatesList[index][1]];
    list.push(list_);
  }
  return list;
};

var addRCovariates = function (image) {
  var list = ComputeRCovariatesList();
  for (var index in list) {
    image = image.addBands(image.select(list[index][0]).divide(image.select(list[index][1]))
            .rename('_R_' + rCovariatesList[index][0] + '_' + rCovariatesList[index][1]));
  }
  return image;
};

var addTopography = function (image) {

  // Calculate slope, aspect and hillshade
  var topo = ee.Algorithms.Terrain(elevation);

  // From aspect (a), calculate eastness (sin a), northness (cos a)
  var deg2rad = ee.Number(Math.PI).divide(180);
  var aspect = topo.select(['aspect']);
  var aspect_rad = aspect.multiply(deg2rad);
  var eastness = aspect_rad.sin().rename(['eastness']).float();
  var northness = aspect_rad.cos().rename(['northness']).float();

  // Add topography bands to image
  topo = topo.select(['elevation','slope','aspect']).addBands(eastness).addBands(northness);
  image = image.addBands(topo);
  return image;
};

var addJRCDataset = function (image) {
  // Update the mask.
  jrcImage = jrcImage.unmask(0);

  image = image.addBands(jrcImage.select(['occurrence']).rename(['occurrence']));
  image = image.addBands(jrcImage.select(['change_abs']).rename(['change_abs']));
  image = image.addBands(jrcImage.select(['change_norm']).rename(['change_norm']));
  image = image.addBands(jrcImage.select(['seasonality']).rename(['seasonality']));
  image = image.addBands(jrcImage.select(['transition']).rename(['transition']));
  image = image.addBands(jrcImage.select(['max_extent']).rename(['max_extent']));

  return image;
};

var addEVI = function (image) {
  var evi = image.expression('2.5 * ((NIR - RED) / (NIR + 6 * RED - 7.5 * BLUE + 1))', {
    'NIR' : image.select('nir'),
    'RED' : image.select('red'),
    'BLUE': image.select('blue')
  }).float();
  return image.addBands(evi.rename('EVI'));
};

var addSAVI = function (image) {
  // Add Soil Adjust Vegetation Index (SAVI)
    // using L = 0.5;
    var savi = image.expression('(NIR - RED) * (1 + 0.5)/(NIR + RED + 0.5)', {
    'NIR': image.select('nir'),
    'RED': image.select('red')
    }).float();
    return image.addBands(savi.rename('SAVI'));
};

var addIBI = function (image) {
  // Add Index-Based Built-Up Index (IBI)
  var ibiA = image.expression('2 * SWIR1 / (SWIR1 + NIR)', {
    'SWIR1': image.select('swir1'),
    'NIR'  : image.select('nir')
  }).rename(['IBI_A']);

  var ibiB = image.expression('(NIR / (NIR + RED)) + (GREEN / (GREEN + SWIR1))', {
    'NIR'  : image.select('nir'),
    'RED'  : image.select('red'),
    'GREEN': image.select('green'),
    'SWIR1': image.select('swir1')
  }).rename(['IBI_B']);

  var ibiAB = ibiA.addBands(ibiB);
  var ibi = ibiAB.normalizedDifference(['IBI_A', 'IBI_B']);
  return image.addBands(ibi.rename(['IBI']));
};

Step 2: import the data

// import data
var elevation = ee.Image("USGS/SRTMGL1_003");
var jrcImage = ee.Image("JRC/GSW1_0/GlobalSurfaceWater");
var composites = ee.ImageCollection("projects/servir-mekong/yearlyComposites");
var rubberData = ee.FeatureCollection("projects/servir-mekong/referenceData/CambodiaRubber");
var tccCollection = ee.ImageCollection("projects/servir-mekong/UMD/tree_canopy");
var countries = ee.FeatureCollection("USDOS/LSIB_SIMPLE/2017");
var cambodia = countries.filter(ee.Filter.eq("country_na","Cambodia"));
var trainingSample = ee.FeatureCollection("projects/servir-mekong/ReferenceData/DecidiousTraining");

Step 3: Set the date

var y = 2018;

var start = ee.Date.fromYMD(y,1,1)
var end = ee.Date.fromYMD(y,12,31)
<span id="mce_SELREST_start" style="overflow:hidden;line-height:0"></span>

Step 4: Filter your image collection and add all covariates

var image = ee.Image(composites.filterDate(start,end).first()).divide(10000)
var tcc = ee.Image(tccCollection.filterDate(start,end).first()).rename("tcc");

image = image.addBands(tcc);
image = addEVI(image);
image = addSAVI(image);
image = addIBI(image);
image = addTopography(image);
image = addJRCDataset(image);
image = addNDCovariates(image);

Step 6: Run the random forest model and show the map

var bandNames = image.bandNames();
var classifier = ee.Classifier.randomForest(25,0).setOutputMode('PROBABILITY').train(trainingSample,"land_class",bandNames);

var classification = image.classify(classifier).multiply(100)

Map.addLayer(classification.clip(cambodia),{min:20,max:90,palette:"white,gray,black"},"Rubber primitive")