Vegetation Index · Chlorophyll / Red-edge

CIREDGE – Chlorophyll Index Red Edge

CIREDGE is a chlorophyll-sensitive vegetation index based on the red-edge and NIR bands. It is optimized to estimate leaf chlorophyll content and detect subtle changes in vegetation stress, especially in crops and forests.

1. Scientific Definition

The Chlorophyll Index Red Edge (CIREDGE) exploits the high sensitivity of the red-edge region to leaf chlorophyll content. It uses Near-InfraRed (NIR) and a red-edge band to enhance chlorophyll-related changes in vegetation canopies.

Formula

A commonly used formulation of CIREDGE is:

CIREDGE = (NIR / RedEdge) − 1 Dimensionless (typically 0 to >5)

Where:

  • NIR: Near-InfraRed reflectance
  • RedEdge: red-edge band reflectance (around 705 nm)

Typical Interpretation

CIREDGE Range Interpretation
< 0 Non-vegetated or noisy pixels / water / clouds
0 – 1 Very low chlorophyll content / stressed or sparse vegetation
1 – 3 Moderate chlorophyll content / normal vegetation
> 3 High chlorophyll content / very healthy dense vegetation

Key Applications

  • Leaf chlorophyll estimation in crops and forests
  • Early detection of vegetation stress (water, nutrients, disease)
  • Precision agriculture – variable rate fertilization
  • Monitoring phenology and canopy development

2. Data & Bands for CIREDGE

Common Sensors & Bands

  • Sentinel-2 (ESA) – 20 / 10 m
    • Red-edge: B5 (~705 nm) or B6 (~740 nm)
    • NIR: B8 (~842 nm) or B8A (~865 nm)
  • Hyperspectral / Multispectral sensors
    • Use a band in the red-edge region (~700–740 nm) and a NIR band (~800–900 nm).

Good Practice

  • Always use atmospherically corrected surface reflectance (e.g., Sentinel-2 SR).
  • Mask clouds, cloud shadows and snow using appropriate QA bands.
  • Clip the CIREDGE raster to your AOI before exporting.
  • Compare CIREDGE values for similar phenological stages when doing multi-temporal analysis.

Palette Suggestion

Suggested CIREDGE palette: [ "#440154", "#3b528b", "#21908c", "#5dc963", "#fde725" ]

3. Google Earth Engine Code – CIREDGE for Any AOI

Steps: open code.earthengine.google.com → New Script → paste the code → draw your AOI as geometry on the map → click Run. Then export CIREDGE as GeoTIFF to Google Drive. 

// CIREDGE (Chlorophyll Index Red Edge) for any AOI using Sentinel-2 SR
// -------------------------------------------------------------------
// Formula: CIREDGE = (NIR / RedEdge) - 1
// Here we use Sentinel-2 B8 (NIR) and B5 (Red Edge ~705 nm)

// 1. Define Area of Interest (AOI)
var roi = geometry;  // Draw geometry on the map, it will appear as 'geometry'

// Center map
Map.centerObject(roi, 11);

// 2. Define time range
var startDate = '2023-01-01';
var endDate   = '2023-12-31';

// 3. Load Sentinel-2 SR collection
var s2 = ee.ImageCollection('COPERNICUS/S2_SR')
  .filterBounds(roi)
  .filterDate(startDate, endDate)
  .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 20))
  .select(['B5', 'B8']);  // RedEdge (B5), NIR (B8)

// Create median composite and clip to AOI
var image = s2.median().clip(roi);

// 4. Compute CIREDGE
// CIREDGE = (NIR / RedEdge) - 1
var ciredge = image.expression(
  '(NIR / RE) - 1',
  {
    'NIR': image.select('B8'),
    'RE':  image.select('B5')
  }
).rename('CIREDGE');

// 5. Visualization
var ciredgeVis = {
  min: 0,
  max: 5,
  palette: [
    '#440154', // low chlorophyll
    '#3b528b',
    '#21908c',
    '#5dc963',
    '#fde725'  // high chlorophyll
  ]
};

Map.addLayer(ciredge, ciredgeVis, 'CIREDGE (Sentinel-2)', true);

// Optional: True Color background
var s2_rgb = ee.ImageCollection('COPERNICUS/S2_SR')
  .filterBounds(roi)
  .filterDate(startDate, endDate)
  .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 20))
  .select(['B4','B3','B2'])
  .median()
  .clip(roi);

Map.addLayer(s2_rgb, {min:0, max:3000}, 'True Color (RGB)', false);

// 6. Export CIREDGE as GeoTIFF to Google Drive
Export.image.toDrive({
  image: ciredge,
  description: 'CIREDGE_Export',
  fileNamePrefix: 'CIREDGE_Export',
  region: roi,
  scale: 10,
  crs: 'EPSG:4326',
  maxPixels: 1e13
});

// End of script