NDWI
Definition
Normalised Difference Water Index. Computed from green and near-infrared or shortwave-infrared bands. Sensitive to water content in vegetation canopy and surface soil. A freshly disturbed, wetter-than-normal soil patch can show elevated NDWI.
- Full name
- Normalised Difference Water Index
- Bands used
- Green and near-infrared or shortwave-infrared
- Sensitive to
- Water content in vegetation and surface soil
- Forensic use
- Flagging freshly disturbed, wetter soil patches
Common questions
How does NDWI help locate a clandestine grave from aerial or satellite imagery?+
Disturbing soil to dig and refill a grave changes its moisture retention relative to the undisturbed surrounding ground, at least for a period after burial, and this shows up as an anomalous NDWI value that stands out from the background pattern in the surrounding area.
Is an elevated NDWI reading by itself proof of a grave?+
No. Irrigation, drainage, recent rainfall, or unrelated ground disturbance can all produce a similar signature, so an NDWI anomaly is treated as a lead that narrows a search area, to be followed up with ground-truthing such as probing or geophysical survey rather than as standalone evidence.
Related terms
- Ground Sampling Distance (GSD)
- The dimension on the ground represented by one pixel in an image. A 10 m GSD means each pixel covers a 10...
- NDVI
- Normalised Difference Vegetation Index. Computed as (NIR-Red)/(NIR+Red) from multispectral imagery. Values near 1 indicate dense healthy vegetation; values near 0 indicate bare...
- Synthetic Aperture Radar (SAR)
- An active microwave sensor that generates its own energy pulse and measures the return from the surface. Cloud-penetrating and day/night capable. Backscatter...
- Temporal Change Detection
- The comparison of multi-date images of the same area to identify pixels or features that have changed between acquisition dates. A disturbed...
- Thermal Infrared (TIR)
- Sensor bands measuring emitted heat radiation (approximately 8-14 micrometres). Decomposing organic matter generates heat; soil with high moisture retains heat longer than...