# Remote Sensing of Forest Burnt Area, Burn Severity, and Post-Fire Recovery: A Review
## 4 Results and Discussions
### BA and BS Estimates
#### 4.1.1 Spectral Indices and Mapping Techniques
Confirmed hotspots are then used to derive regional-level NDVI difference thresholds for BA mapping. As an alternative to the NDVI, a non-linear global environmental monitoring index (GEMI) [84] provided better results for discriminating burned areas in several forest ecosystems [85; 86; 87]. The GEMI was specifically designed to minimize problems of contamination of the vegetation signal by extraneous factors to monitor recently burned areas. Another non-linear burnt area index (BAI), which integrates the minimum reflectance of burnt vegetation in the NIR and the maximum in the red bands, \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Sensor** & **Index** & **Description** & **Temporal Period** & **Number of Studies** & **\% of Total Studies** \\ \hline MSS, TM, ETM+, OLI, AVHRR, MODIS, MISR, IRS WIFS, QuickBird, Ikons OSA, Sentinel-2 MSI, SPOT VGT, RapidView-2,3 & NDVI & Normalised Differenced Vegetation Index & 2000–2020 & 128 & 23.4 \\ RapidView REIS, GeoEye GIS, WorldView-2,3 & & & & & \\ TM, ETM+, OLI, MODIS, QuickBird, MSI, VGT, REIS, WorldView-2/3 & & & & & \\ TM, ETM+, OLI, MODIS, QuickBird, MSI, VGT, REIS, WorldView-2/3 & & & & & \\ TM, ETM+, OLI, MODIS, QuickBird, MSI, VGT, REIS, WorldView-2/3 & & & & & \\ TM, ETM+, MSI, AVHRR, MODIS & CBI & Composite Burn Index & 2005–2020 & 34 & 6.2 \\ TM, ETM+, OLI, MSI & RdNBR & Relative Differenced Normalized Burn Ratio & 2007–2020 & 32 & 5.8 \\ ETM+, SPOT VGT, MODIS, QuickBird & dNDVI & Delta Normalised Differenced Vegetation Index & 2006–2020 & 22 & 4.0 \\ TM, ETM+, MODIS, WorldView-2/3 & EVI & Enhanced Vegetation Index & 2010–2020 & 21 & 3.8 \\ TM, ETM+, MODIS, WorldView-2/3, IRS AWIFS, QuickBird & BAI & Burn Area Index & 2002–2020 & 18 & 3.3 \\ TM, ETM+, MSI, MODIS & NDWI & Normalized Difference Water Index & 2003–2020 & 17 & 3.1 \\ TM, ETM+, WorldView-2/3, QuickBird & SAVI & Soil Adjusted Vegetation Index & 2002–2020 & 13 & 2.4 \\ TM, ETM+, MODIS & GEMI & Global Environmental & 2002–2020 & 12 & 2.2 \\ TM, ETM+, MODIS & MIRBI & Mid-Infrared Burnt Index & 2006–2020 & 12 & 2.2 \\ TM, ETM+, WorldView-2/3, & MAGVI & Modified Soil Adjusted Vegetation Index & 2012–2020 & 12 & 2.2 \\ QuickBird & Vegetation Index & & & & \\ TM, ETM+, OLI & NBR2 & Normalized Burn Ratio 2 (ND4/5) & 2005–2020 & 9 & 1.6 \\ TM, ETM+, MODIS & LST & Land Surface Temperature & 2014–2020 & 8 & 1.5 \\ TM, MODIS, WorldView-2/3 & GeoCBI & Geometrically structured Composite Burn Index & 2010–2020 & 7 & 1.3 \\ TM, ETM+, MODIS, WorldView-2/3, MSI & LAI & Leaf Area Index & 2008–2020 & 6 & 1.1 \\ TM, ETM+ & CSI & Char Soil Index & 2012–2020 & 6 & 1.1 \\ MODIS & BAIM & MODIS Burned Area Index & 2009–2020 & 5 & 0.9 \\ MSI, OLI & RBR & Relative Burn Ratio & 2018–2020 & 5 & 0.9 \\ ETM, SPOT VGT & SWVI & Normalized short-wave-based vegetation index & 2002–2020 & 4 & 0.7 \\ TM, ETM+ & NBRT & Normalised Burn Ratio Thermal & 2018–2020 & 4 & 0.7 \\ AVHRR, MODIS & BBFI & Burned Boreal Forest Index & 2012–2020 & 3 & 0.5 \\ TM, ETM+, WorldView-2 & RVI & Ratio Vegetation Index & 2012–2020 & 3 & 0.5 \\ TM, ETM+, OLI & DI & Disturbance index & 2014–2020 & 3 & 0.5 \\ TM, ETM+ & BSI & Burn Scar Index & 2011–2020 & 3 & 0.5 \\ TM, ETM+ & NDII & Normalized Difference Infrared Index & 2014–2020 & 3 & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Spectral indices used for the review. was initially developed for BA discrimination in NOAA-AVHRR images [88]. The BAI was adapted to MODIS NIR and SWIR bands (BAIM) for mapping recently burned areas in Mediterranean ecosystems [89; 90; 91]. The mid-infrared bi-spectral index (MIRBI) [92], which applies to SWIR wavelengths, also showed strong spectral separation between burned and unburned areas [93; 94]. Some researchers found that the MIRBI proved to be reliable to reduce confusions with mixed pixels found in water-land borders and areas affected by previous wildfires [28; 95]. Several global BA detecting products have been developed over the past decades based on medium- and high-resolution sensors.