A water index — 0 compatible sensors — Last revised June 1, 2025
TWI
Triangle Water Index
Triangle Water Index - A spectral index for water applications.
Used in water detection.
When to use
- Permanent and seasonal water body delineation
- Flood mapping and emergency response
- Wetland inventory and change detection
- Reservoir and lake water level monitoring
- Coastal shoreline change analysis
Limitations
- Dark surfaces (shadows, asphalt, dark soils) can produce false positives
- Suspended sediments and algae alter spectral response in shallow water
- Mixed pixels at water boundaries reduce edge accuracy
- Atmospheric correction quality directly impacts threshold selection
- Sun glint over open water can saturate sensors and bias values
- Requires four or more bands — limits portability across simpler sensors
What the values mean
-1 Definitely not water
-0.3 Dry / built-up surface
0 Possible moisture / wet soil
0.3 Open water
0.6 Deep / clear water
| Surface type | Typical TWI |
|---|---|
| Built-up, asphalt | -0.5 to -0.2 |
| Bare soil, vegetation | -0.2 to 0 |
| Wet soil, flooded fields | 0 to 0.3 |
| Open water, lakes | 0.3 to 0.7 |
General Formula
RE1 705
RE2 740
G 550
S2 2190
B 450
N 850
Sensor-Specific Formulas
Most-used sensors — click to show code below
| Sensor | Provider | Formula | Band Mapping |
|---|
Code Examples
twi_generic.py
TWI vs other water indices
| Index | Name | How it differs |
|---|---|---|
| LSWI | Land Surface Water Index | Alternative water index — different band combination |
| LWVI-1 | Leaf Water Vegetation Index 1 | Alternative water index — different band combination |
| LWVI-2 | Leaf Water Vegetation Index 2 | Alternative water index — different band combination |
| MNDWI | Modified Normalized Difference Water Index | Refined formulation for specific conditions |
Related Water Indices
References
https://doi.org/10.3390/rs14215289
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