Google Earth Engine Tutorial: Download NDBI Images from Landsat 8

Google Earth Engine (GEE) is a powerful platform for analyzing satellite imagery and environmental data. One of the key metrics for urban area analysis is the Normalized Difference Built-Up Index (NDBI). This index highlights built-up areas using Landsat 8 imagery by leveraging shortwave infrared (SWIR) and near-infrared (NIR) bands. Below is a step-by-step tutorial to download NDBI images using GEE.

Step 1: Access Google Earth Engine

Log in to your Google account and visit the Google Earth Engine Code Editor. Open the editor and click on the “Console” tab to start coding.

Step 2: Load the Landsat 8 Dataset

Landsat 8 satellite data is available in GEE under the USGS Landsat 8 Collection 2 Tier 1 dataset. Use the following code to load the dataset:

var landsat8 = ee.ImageCollection("LANDSAT/LC08/C02/T1_L2");

Step 3: Define the Region of Interest (ROI)

Specify the area you want to analyze by drawing a polygon or using a predefined geometry. For example:

var roi = ee.Geometry.Rectangle([xmin, ymin, xmax, ymax]); // Replace with your coordinates

Step 4: Filter the Dataset

Filter images by date and the specified ROI to narrow down the data:

var filtered = landsat8.filterDate('2023-01-01', '2023-12-31')
.filterBounds(roi);

Step 5: Compute NDBI

The NDBI formula is (SWIR1 – NIR)/(SWIR1 + NIR), where SWIR1 corresponds to Band 6 and NIR to Band 5 in Landsat 8. Select the relevant bands and calculate the index:

var ndbi = filtered.select(['SR_B6', 'SR_B5']).map(function(image) {
  return image
    .addBands(image.select(['SR_B6']).rename('SWIR1'))
    .addBands(image.select(['SR_B5']).rename('NIR'))
    .expression('(SWIR1 - NIR)/(SWIR1 + NIR)', {SWIR1: image.select('SWIR1'), NIR: image.select('NIR')})
    .rename('NDBI');
});

Step 6: Visualize the NDBI Image

Add the NDBI layer to the map for visualization:

Map.addLayer(ndbi.first(), {min: -1, max: 1, palette: ['blue', 'white', 'red']}, 'NDBI');

Step 7: Export the Image

Export the calculated NDBI image to your Google Drive:

Export.image.toDrive({
  image: ndbi.first(),
  description: 'ndbi_export',
  folder: 'GEE_Exports',
  region: roi,
  scale: 30,
  maxPixels: 1e10
});

Replace the parameters with your specific requirements. The exported image will be available in your Google Drive under the GEE_Exports folder.

Step 8: View and Analyze the Downloaded Image

Download the exported GeoTIFF file and open it in GIS software like QGIS or ArcGIS for further analysis.