NDTITool.txt

//--------------------------------------------------------------------
//                        Description
//--------------------------------------------------------------------
// Master Code for Landsat NDTI
// OSA Water Resources Project (III)
// NASA Develop, Fall 2018

//--------------------------------------------------------------------
//                        QA Band
//--------------------------------------------------------------------

// Apply Quality Assurance (QA) for the Landsat8 image collection
// (Copied from Google developers tutorial)
function maskL8sr(image) {
// Bits 3 and 5 are cloud shadow and cloud, respectively.
  var cloudShadowBitMask = (1 << 3);
  var cloudsBitMask = (1 << 5);
// Get the pixel 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.updateMask(mask);
}

//--------------------------------------------------------------------
//                  Loading Landsat / calculate NDTI
//--------------------------------------------------------------------
// Define Study Area

// Golfo Dulce
var geometry1 = /* color: #00ffff */ee.Geometry.Polygon(
        [[[-83.5467529296875, 8.666367420201201],
          [-83.4545668023759, 8.5244700149549],
          [-83.2940673828125, 8.370380467910778],
          [-83.13102996826171, 8.35000000000004],
          [-83.05071001857476, 8.502660887924105],
          [-83.05102996826167, 8.639214211082377],
          [-83.1492248157208, 8.691613945525585],
          [-83.28059250414674, 8.739494442673303],
          [-83.34219449287639, 8.774251572143942],
          [-83.46502431668944, 8.776686632150142],
          [-83.5456804566154, 8.74801644611116]]]);

// Terraba Sierpe
var geometry2=ee.Geometry.Polygon([[-83.62425772568696, 8.949467045670827],
           [-83.64708868889954, 8.789356481972188],
           [-83.64365546134292, 8.763569466438419],
           [-83.39302984980031, 8.825998100328574],
           [-83.43646017836784, 8.949636617198099]]);

// Osa Peninsula
var geometrymask = /* color: #bf04c2 */ee.Geometry.Polygon(
        [[[-83.75, 8.95],
          [-83.75, 8.35],
          [-83.05, 8.35],
          [-83.05, 8.95]]]);

    
var year, geometry, i;
for (i=1; i<3; i++) {
for (year=1986; year<2018; year+=5) {
  if(i===1) {geometry=geometry1;}
  if(i===2) {geometry=geometry2;}
  print(year);
  var yr = year.toString();
  
  if (yr < 2000) {
    var imc = ee.ImageCollection('LANDSAT/LT05/C01/T1_SR')
      .filterDate(yr+'-08-01', yr+'-11-30')
      .filterBounds(geometry)
      .map(maskL8sr);
  } else if (yr>=2000 & year<2014) {
    var imc = ee.ImageCollection('LANDSAT/LE07/C01/T1_SR')
      .filterDate(yr+'-08-01', yr+'-11-30')
      .filterBounds(geometry)
      .map(maskL8sr);
  } else {
    // Load Landsat 8 image colection and filter date and region of images
    var imc = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
      .filterDate(yr+'-08-01', yr+'-11-30')
      .filterBounds(geometry)
      .map(maskL8sr);
  }
  
  // Calculate median of all images    
  var im = imc.reduce(ee.Reducer.median());
  print(im);
  
  // Calculating Normalized Difference Turbidity Index (NDTI)
  if (yr >2014) {
    // For Landsat 8, B4 = red and B3 = green
    var ndti = im.normalizedDifference(['B4_median', 'B3_median']).unmask(9999);
  } else {
    // For Landsat 5 and 7, B3 = red and B2 = green
    var ndti = im.normalizedDifference(['B3_median', 'B2_median']).unmask(9999);
  }
  print(ndti);
  //Save Image
Export.image.toDrive({
  image: ndti.clip(geometry),
  description: 'ndti' + yr + '_wet' + i,
  region: geometry,
  scale: 30,
  folder: 'GEE_export',
});
  //--------------------------------------------------------------------
  //                          Add Land Mask
  //--------------------------------------------------------------------
  // Add land mask (obtained and slightly modified from GEE tutorial)
  // Load or import the Hansen et al. forest change dataset.
  var hansenImage = ee.Image('UMD/hansen/global_forest_change_2015');
  // Select the land/water mask.
  var datamask = hansenImage.select('datamask');
  // Create a binary mask (1 is land and 2 is water)
  var maskl = datamask.eq(1);
  // Update the composite mask with the water mask.
  var maskedLand =im.updateMask(maskl).select('B3_median');
  var maskedNDTI =ndti.updateMask(maskl).unmask(-9999);
  // Visualize the defined mask
  var vismask = {bands: ['B3_median'], max: 0.5,"palette":["000000"]};
  
  
  //--------------------------------------------------------------------
  //                          Create maps
  //--------------------------------------------------------------------
  // Define color palette for NDTI
  var viz = {min:-0.5, max: 0, palette: ['#00abff','#95bd00','e5e700','#cc2900','#a400c3']};
  // Apply color palette to calculated NDTI
  // Map.addLayer(maskedNDTI, null, 'maskedndti2');
  Map.addLayer(ndti, viz, 'ndti ' +yr);
  // Add mask to the map
  if (year > 2015) {
    Map.addLayer(maskedLand, vismask, 'masked');
  // Define map center and zoom level
  Map.setCenter(-83.12, 8.57, 10); // Center on Osa Peninsula
  }
}}


//--------------------------------------------------------------------
//                          Color Scale
//--------------------------------------------------------------------

// Color Scale
// set position of panel
var legend = ui.Panel({
  layout: ui.Panel.Layout.flow('vertical'),
  style: {
    position: 'bottom-left',
    padding: '30x 30px',
    color: '000000'
  }
});
 
// Create legend title
var legendTitle = ui.Label({
  value: 'NDTI',
  style: {
    fontWeight: 'bold',
    fontSize: '18px',
    margin: '0 0 0 0',
    padding: '0'
    }
});

 // Add the title to the panel
legend.add(legendTitle); 

// create the legend image
var lon = ee.Image.pixelLonLat().select('latitude');
var gradient = lon.multiply((viz.max-viz.min)/100.0).add(viz.min);
var legendImage = gradient.visualize(viz);

// create text on top of legend
var panel = ui.Panel({
    widgets: [
      ui.Label(viz['max'])
    ],
  });

legend.add(panel);
  
// create thumbnail from the image
var thumbnail = ui.Thumbnail({
  image: legendImage,
    params: {bbox:'0,0,10,100', dimensions:'20x200'},  
    style: {padding: '1px', position: 'bottom-center'},
  });

// add the thumbnail to the legend
legend.add(thumbnail);

// create text on top of legend
var panel = ui.Panel({
    widgets: [
      ui.Label(viz['min'])
    ],
   });

legend.add(panel);
// Add color scale to the map
Map.add(legend, 'color_scale');


//--------------------------------------------------------------------
//                          Export Images
//--------------------------------------------------------------------

//Save Image
Export.image.toDrive({
  image: maskedLand,
  description: 'mask_data',
  region: geometrymask,
  scale: 30,
  folder: 'GEE_export',
});
//Save Image
Export.image.toDrive({
  image: maskedNDTI,
  description: 'mask_vis',
  region: geometrymask,
  scale: 30,
  folder: 'GEE_export',
});