Vegetation Water Content · Moisture Index

NDII – Normalized Difference Infrared Index

NDII is a vegetation moisture index that uses NIR and SWIR1 to detect plant water content, drought stress, and hydrological conditions in agricultural and natural landscapes.

1. Scientific Definition

The NDII quantifies the level of moisture in vegetation using the difference between Near-InfraRed (NIR) and Short-Wave InfraRed (SWIR1), which is highly sensitive to leaf water content.

Formula

NDII = (NIR − SWIR1) / (NIR + SWIR1) Range: −1 → +1

Interpretation

NDII ValueMeaning
< -0.1Dry soil / built-up / rock
-0.1 – 0.1Low moisture / stressed vegetation
0.1 – 0.3Moderate vegetation moisture
> 0.3High water content / healthy vegetation

Main Applications

  • Vegetation moisture / drought monitoring
  • Agricultural health assessment
  • Forest drought stress mapping
  • Hydrological and eco-system studies

2. Required Data

Sentinel-2 Bands

  • NIR: B8
  • SWIR1: B11

Landsat 8 / 9

  • NIR: B5
  • SWIR1: B6

Best Practices

  • Use atmospherically corrected surface reflectance.
  • Mask clouds & shadows for accurate moisture detection.
  • Use NDII time series to detect drought events.

Suggested Palette

[ "#440154", "#414487", "#2a788e", "#22a884", "#7ad151", "#fde725" ]

3. Google Earth Engine Code – NDII


// NDII using Sentinel-2
// Formula: (NIR - SWIR1) / (NIR + SWIR1)

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(["B8","B11"]); // NIR, SWIR1

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

// Compute NDII
var ndii = img.expression(
  "(N - S) / (N + S)",
  {
    "N": img.select("B8"),
    "S": img.select("B11")
  }
).rename("NDII");

var vis = {
  min: -1,
  max: 1,
  palette: ["#440154","#414487","#2a788e","#22a884","#7ad151","#fde725"]
};

Map.addLayer(ndii, vis, "NDII");

// Export
Export.image.toDrive({
  image: ndii,
  description: "NDII_Export",
  region: roi,
  scale: 20,
  maxPixels: 1e13
});