ndwi: Normalized Difference Water Index
In ASIP: Automated Satellite Image Processing

Description Usage Arguments Value Note References Examples

Normalized Difference Water Index (NDWI) is used to monitor changes related to water content in water bodies proposed by McFeeters (1996).

1	ndwi(directory = getwd(), crop = "n", ext2crop = "none")

ext2crop, crop, directory

Same as mentioned in arvi.

Computed NDWI product

1. NDWI = (r_green - r_nir) / (r_nir + r_green)

where, "r_" denotes TOA reflectance band.

2. There is another NDWI to monitor changes in water content of leaves proposed by Gao (1996). User should understand the requirements and run accordingly.

Other important notes are mentioned in custom.eqn.

McFeeters, S.K. (1996) The Use of the Normalized Difference Water Index (NDWI) in the Delineation of Open Water Features. International Journal of Remote Sensing, 17, 1425-1432. doi:10.1080/01431169608948714.

Gao Bo-cai (1996) NDWI-A normalized difference water index for remote sensing of vegetation liquid water from space. Remote Sensing of Environment, 58 (3), 257-266. doi:10.1016/S0034-4257(96)00067-3.

library (raster)
library (rgdal)
# Finding the path of the sample satellite image directory.
# User may define paths directly like "/home/ur_folder" or "C:/ur_folder"
path <- system.file ("TM_sample", package = "ASIP")
shapefil <- paste0 (path, "/test.shp")
op <- ndwi (directory = path, crop = "y", ext2crop = shapefil)