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Normalized burn ratio (NBR)

A spectral index used to identify burned areas.

Description

NBR (or NBI) is an index used to identify burned areas and measure burn severity.

Use cases

  • To identify burned areas.
  • To calculate burn severity in a vegetated area.

How it works

NBR is calculated using near-infrared (NIR) and shortwave infrared (SWIR) bands.

Healthy vegetation strongly reflects NIR, but not SWIR. Areas devastated by fire have the opposite reflectance rate. A fire trail with burned vegetation and soil will reflect strongly in the SWIR part of the spectrum.

NBR can be used to better understand burn severity when in comparison with data collected just before the fire.

NBR=NIR−SWIRNIR+SWIR\mathrm{NBR} = \frac{NIR - SWIR}{ NIR + SWIR}

NBR ranges between -1 and 1. A high NBR value indicates healthy vegetation. A low value indicates bare ground and recently burnt areas. Non-burnt areas usually have values close to zero.

Limitations

  • NBR is less effective if time has passed after the fire, and vegetation has started to regrow.
  • NBR requires the SWIR band, which limits the number of available remote sensors.
  • NBR is sensitive to phenological cycles and characteristics — for example, vegetation or soil moisture before and after the fire.

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