From NDVI to NBR
If you've read the NDVI guide, this is its twin. NDVI contrasts near-infrared with red; the Normalized Burn Ratio swaps red for shortwave-infrared (SWIR), the band that lights up over dry, charred ground:
Living vegetation: high NIR, low SWIR → high NBR. After a fire: NIR collapses (no healthy leaves), SWIR rises (exposed char and soil) → low NBR.
dNBR — measuring the change
A single NBR doesn't tell you severity; a desert has low NBR without ever burning. The trick is the difference between a pre-fire and post-fire scene:
A big positive dNBR = a big drop in greenness = a severe burn. The US Geological Survey bins it into standard classes — unburned, low, moderate, high — which is what fills a burn-severity map.
Play with it
The "before" is a healthy forest. Move the post-fire reflectances — drop the near-infrared (leaves gone) and raise the shortwave-infrared (exposed char) — and watch dNBR climb into the severe classes.
Do it yourself
The honest caveats
- Use clear scenes. Fresh smoke and cloud bias the bands — take the first clear post-fire image.
- dNBR is a proxy. Field plots (the Composite Burn Index) calibrate it; thresholds shift by ecosystem.
- Pre/post timing matters. Too long after, regrowth or rain changes NBR for reasons other than the fire.