Geology · Iron Oxide Mapping

FERRIC – Ferric Iron Index

The Ferric Iron Index enhances Fe³⁺-bearing minerals (iron oxides) by contrasting Red and Blue reflectance. Commonly used for iron oxide and alteration mapping in geological remote sensing.

1. Scientific Definition

The FERRIC Index highlights ferric iron (Fe³⁺) rich minerals such as hematite and goethite by using the higher Red reflectance relative to the Blue band.

Formula

FERRIC = (Red − Blue) / (Red + Blue)

  • Red — Red band reflectance
  • Blue — Blue band reflectance

Interpretation

  • > 0 → ferric-oxide rich surfaces / iron staining
  • < 0 → vegetation / water / low iron content

Applications

  • Iron oxide mapping
  • Hydrothermal alteration detection
  • Lithological and structural geological studies
  • Iron ore exploration

2. Required Bands

Sentinel-2

  • Blue → B2
  • Red → B4

Landsat 8/9

  • Blue → B2
  • Red → B4

Suggested Palette

[ "#0b1220", "#3c2f3b", "#7c4a47", "#c47a4f", "#f2c27b" ]

3. Google Earth Engine Code – FERRIC


// FERRIC = (Red - Blue) / (Red + Blue)

var roi = geometry;
Map.centerObject(roi, 10);

// 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(["B2","B4"]); // Blue, Red

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

// Compute Ferric Index
var ferric = img.expression(
  "(R - B) / (R + B)",
  {
    "R": img.select("B4"),  // Red
    "B": img.select("B2")   // Blue
  }
).rename("FERRIC");

var vis = {
  min: -1,
  max: 1,
  palette: ["#0b1220","#3c2f3b","#7c4a47","#c47a4f","#f2c27b"]
};

Map.addLayer(ferric, vis, "FERRIC Index");

// Export
Export.image.toDrive({
  image: ferric,
  description: "FERRIC_export",
  fileNamePrefix: "FERRIC_Index",
  region: roi,
  scale: 10,
  crs: "EPSG:4326",
  maxPixels: 1e13
});