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Calculate water indices including both NDWI variants

Source: R/03-water-indices.R
calculate_water_index.Rd

Calculate various water indices including NDWI (McFeeters 1996), MNDWI (Xu 2006), and NDMI (Gao 1996) for water body detection and moisture content. Updated formulas based on latest research and satellite missions (2024).

Usage

calculate_water_index(
  green,
  nir,
  swir1 = NULL,
  index_type = "NDWI",
  clamp_range = NULL,
  mask_invalid = TRUE,
  verbose = FALSE
)

Arguments

green

Green band SpatRaster or file path

nir

NIR band SpatRaster or file path

swir1

SWIR1 band SpatRaster or file path (for MNDWI, NDMI)

index_type

Index type: "NDWI", "MNDWI", "NDMI", "MSI", "NDII", "WI", "SRWI", "LSWI"

clamp_range

Optional range to clamp output values

mask_invalid

Mask invalid/extreme values

verbose

Print progress messages

Value

SpatRaster of water index

Details

Available water indices with their specific applications:

Primary Water Detection Indices:

  • NDWI (McFeeters 1996): (Green - NIR) / (Green + NIR) - Use: Open water body detection, flood mapping - Range: Values from -1 to 1, water bodies typically > 0.3 - Pros: Simple, effective for clear water - Cons: Sensitive to built-up areas, can overestimate water

  • MNDWI (Xu 2006): (Green - SWIR1) / (Green + SWIR1) - Use: Enhanced water detection, urban water bodies - Range: Values from -1 to 1, water bodies typically > 0.5 - Pros: Better separation of water from built-up areas - Cons: Requires SWIR band, less effective with turbid water

Vegetation Moisture Indices:

  • NDMI (Gao 1996): (NIR - SWIR1) / (NIR + SWIR1) - Use: Vegetation water content, drought monitoring - Range: Values from -1 to 1, higher values = more water content - Application: Agriculture, forest fire risk assessment

  • MSI: SWIR1 / NIR - Moisture Stress Index - Use: Plant water stress detection - Range: [0, 5+], lower values = higher moisture

  • NDII: (NIR - SWIR1) / (NIR + SWIR1) - Same as NDMI - Use: Alternative name for NDMI, vegetation moisture

Specialized Water Indices:

  • WI: NIR / SWIR1 - Water Index (simple ratio)

  • SRWI: NIR / SWIR1 - Simple Ratio Water Index

  • LSWI: (NIR - SWIR1) / (NIR + SWIR1) - Land Surface Water Index

Band Requirements by Satellite:

  • Landsat 8/9: Green=Band 3, NIR=Band 5, SWIR1=Band 6

  • Sentinel-2: Green=Band 3, NIR=Band 8, SWIR1=Band 11

  • MODIS: Green=Band 4, NIR=Band 2, SWIR1=Band 6

Examples

if (FALSE) { # \dontrun{
# These examples require external data files not included with the package
# Original NDWI for water body detection
ndwi <- calculate_water_index(green_band, nir_band, index_type = "NDWI")

# Modified NDWI for enhanced water detection (requires SWIR1)
mndwi <- calculate_water_index(green_band, nir_band, swir1_band, index_type = "MNDWI")

# NDMI for vegetation moisture monitoring
ndmi <- calculate_water_index(green_band, nir_band, swir1_band, index_type = "NDMI")

# With quality control
water_index <- calculate_water_index(
  green = "green.tif",
  nir = "nir.tif",
  swir1 = "swir1.tif",
  index_type = "MNDWI",
  clamp_range = c(-1, 1),
  mask_invalid = TRUE,
  verbose = TRUE
)
} # }