Water and Moisture Indices in GeoIndexR

In GeoIndexR: Computation of Spectral and Geospatial Indices from Multispectral Raster Data

knitr::opts_chunk$set(
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Overview

Delineating water bodies and tracking moisture conditions are foundational tasks in hydrology, wetland monitoring, and irrigation management. GeoIndexR implements three key indices:

1. NDWI (Normalized Difference Water Index, McFeeters 1996)
2. MNDWI (Modified Normalized Difference Water Index, Xu 2006)
3. NDMI (Normalized Difference Moisture Index, Gao 1996)

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1. NDWI (McFeeters, 1996)

McFeeters designed NDWI to delineate open water features by maximizing green band reflectance and minimizing NIR reflectance:

$$\text{NDWI} = \frac{\text{GREEN} - \text{NIR}}{\text{GREEN} + \text{NIR}}$$

Water bodies typically have positive NDWI values ($\text{NDWI} > 0$), while terrestrial vegetation and dry soil display negative values.

library(GeoIndexR)
img <- get_example_data()

ndwi <- geo_index(img, "NDWI")
index_summary(ndwi)

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2. MNDWI (Xu, 2006)

In urbanized and complex landscapes, built-up surfaces often produce false positive signals under classical NDWI. Xu (2006) replaced the NIR band with the Shortwave Infrared (SWIR) band:

$$\text{MNDWI} = \frac{\text{GREEN} - \text{SWIR}}{\text{GREEN} + \text{SWIR}}$$

Because built-up areas reflect strongly in SWIR, their MNDWI values are negative, clearly separating urban structures from open water.

mndwi <- geo_index(img, "MNDWI")
index_summary(mndwi)

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3. NDMI (Gao, 1996)

The Normalized Difference Moisture Index monitors vegetation liquid water content:

$$\text{NDMI} = \frac{\text{NIR} - \text{SWIR}}{\text{NIR} + \text{SWIR}}$$

Higher values indicate well-hydrated vegetation canopies, whereas low or negative values signal drought or water stress.

ndmi <- geo_index(img, "NDMI")
index_summary(ndmi)

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Multi-Index Stack & Comparison

We can compute and compare water and moisture indices together:

water_stack <- geo_indices(img, c("NDWI", "MNDWI", "NDMI"))
index_summary(water_stack)

GeoIndexR documentation built on Oct. 10, 2026, 5:08 p.m.