Urbanization Index · Settlement Detection

ISU – Index of Settlement / Urbanization

ISU enhances built-up areas by combining NDBI and NDVI, suppressing vegetation and highlighting impervious surfaces. Useful for urban expansion and settlement mapping.

1. Scientific Definition

The ISU – Index of Settlement/Urbanization is a normalized built-up index derived from the contrast between SWIR-based urban reflectance (NDBI) and vegetation reflectance (NDVI).

Formula

ISU = (NDBI − NDVI) / (NDBI + NDVI)

Component Indices

  • NDVI = (NIR − Red) / (NIR + Red)
  • NDBI = (SWIR − NIR) / (SWIR + NIR)

Interpretation

  • ISU < 0 → vegetation / water / non-built
  • 0 – 0.2 → low-density built-up
  • 0.2 – 0.4 → moderate urban areas
  • > 0.4 → dense built-up urban core

Applications

  • Urban growth and expansion mapping
  • Settlement density detection
  • Impervious surface estimation

2. Data Requirements

Sentinel-2 Bands

  • Red → B4
  • NIR → B8
  • SWIR1 → B11

Landsat 8/9

  • Red → B4
  • NIR → B5
  • SWIR1 → B6

Suggested Palette

[ "#0b1220", "#1c2d4a", "#32598a", "#5c8ccd", "#a3d3ff" ]

3. Google Earth Engine Code – ISU


// ISU = (NDBI - NDVI) / (NDBI + NDVI)

var roi = geometry;
Map.centerObject(roi, 11);

// Load Sentinel-2 SR
var s2 = ee.ImageCollection("COPERNICUS/S2_SR")
  .filterBounds(roi)
  .filterDate("2023-01-01", "2023-12-31")
  .filter(ee.Filter.lt("CLOUDY_PIXEL_PERCENTAGE", 20))
  .select(["B4","B8","B11"]); // Red, NIR, SWIR

var img = s2.median().clip(roi);

// NDVI
var ndvi = img.normalizedDifference(["B8","B4"]).rename("NDVI");

// NDBI
var ndbi = img.normalizedDifference(["B11","B8"]).rename("NDBI");

// ISU formula
var isu = ee.Image().expression(
  "(NDBI - NDVI) / (NDBI + NDVI)",
  {
    "NDBI": ndbi,
    "NDVI": ndvi
  }
).rename("ISU");

// Visualization
var vis = {
  min: -1, max: 1,
  palette: ["#0b1220","#1c2d4a","#32598a","#5c8ccd","#a3d3ff"]
};

Map.addLayer(isu, vis, "ISU");

Export.image.toDrive({
  image: isu,
  description: "ISU_export",
  fileNamePrefix: "ISU_index",
  region: roi,
  scale: 20,
  crs: "EPSG:4326",
  maxPixels: 1e13
});