What is NBR? (Normalized Burn Ratio)
What is NBR?
NBR, the Normalized Burn Ratio, is a satellite index tuned to detect burned vegetation and assess fuel condition before a fire. It uses the same near-infrared band as NDVI but pairs it with a deeper shortwave-infrared band (SWIR2) that is especially sensitive to ash, charred material, and dry woody fuel.
It serves two distinct purposes: NBR (single snapshot) measures current vegetation dryness and fuel condition — low NBR means dry, fire-prone vegetation. dNBR (differenced NBR) compares pre-fire and post-fire NBR to measure how badly an area burned — this is the standard used by fire agencies worldwide.
How it’s calculated
Healthy vegetation reflects strongly in near-infrared and absorbs shortwave-infrared. Burned or very dry vegetation does the opposite: NIR reflectance collapses and SWIR2 reflectance rises. NBR turns this contrast into a number:
NBR = (NIR − SWIR2) / (NIR + SWIR2)On Sentinel-2 these are Band 8 (NIR) and Band 12 (SWIR2, ~2.2 µm). The ratio structure normalizes brightness across scenes.
For the differenced version used after a fire:
dNBR = NBR_pre-fire − NBR_post-fireA larger positive dNBR means a more severe burn — the canopy lost more of its healthy reflectance between the two dates.
Typical value ranges
Pre-fire NBR for fuel condition and fire risk:
| NBR range | Meaning | Fire risk |
|---|---|---|
| > 0.4 | Lush, wet vegetation | Very low |
| 0.2 – 0.4 | Healthy vegetation | Low |
| 0.0 – 0.2 | Drying vegetation | Moderate |
| −0.1 – 0.0 | Dry, stressed | High |
| Below −0.1 | Very dry / burned / bare | Extreme |
Post-fire dNBR burn severity (USGS standard):
| dNBR range | Severity class | What it means on the ground |
|---|---|---|
| < 0.1 | Unburned / enhanced | Vegetation regrowth or no burn |
| 0.1 – 0.27 | Low severity | Surface fire, canopy largely intact |
| 0.27 – 0.44 | Moderate–low severity | Partial canopy mortality |
| 0.44 – 0.66 | Moderate–high severity | Heavy canopy mortality |
| > 0.66 | High severity | Stand-replacing fire, total canopy loss |
When to use it
Use NBR for pre-fire risk assessment: low values before fire season indicate dry, flammable fuel. Combine with NDMI (moisture) for a complete fuel-condition picture. Use dNBR after a fire to classify burn severity for insurance claims, reforestation planning, and erosion risk assessment.
For dNBR, pre-fire image selection matters critically. Trustworthy pipelines select cloud-free imagery 5–90 days before the fire and 5–60 days after. Before 5 days, smoke contaminates the image; after 60 days, fast vegetation recovery can mask the true severity. Other land-cover changes (logging, harvest, senescence) can also lower NBR — a real burn assessment cross-references the timing of the drop against the fire event.
Comparison with other indices
NBR is the fire-specialist index. NDMI measures leaf water content (primary fire risk indicator), while NBR measures fuel condition and burn severity — the two complement each other in fire-danger scoring. NDVI tracks green canopy density and recovers after fire, but NBR is far more sensitive to char and ash because of the SWIR2 band. For post-fire damage assessment, dNBR is the international standard that NDVI and NDMI cannot replace.
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Frequently asked questions
What is the difference between NBR and dNBR?
NBR is a single snapshot of current vegetation condition — low values indicate dry, fire-prone fuel. dNBR is the difference between a pre-fire and post-fire NBR image, used to measure how severely an area burned. NBR is for risk assessment before a fire; dNBR is for damage assessment after.
What is a good dNBR value?
There is no “good” dNBR — lower is less severe. Below 0.1 is considered unburned or enhanced (regrowth). 0.1–0.27 is low-severity surface fire. Above 0.66 is high-severity, stand-replacing fire. The USGS classification is the international standard.
Can NBR predict wildfires?
Not on its own. NBR measures fuel condition — how dry and flammable the vegetation is — but ignition depends on weather, human activity, and lightning. NBR (fuel) combined with NDMI (moisture) and weather data gives a meaningful risk score, but no satellite index predicts ignition.
How soon after a fire can I assess burn severity?
Typically 5–60 days after the fire date, once the smoke has cleared and before significant regrowth or senescence distorts the reading. Before 5 days, smoke and active fire contaminate the image; after 60 days, fast vegetation recovery can mask the true severity.