Abstract
Identifying fire-affected areas is of key importance to support post-fire management strategies and account for the environmental impact of fires. The availability of high spatial and temporal resolution optical satellite data enables the development of procedures for detailed and prompt post-fire mapping. This study proposes a novel approach for integrating multiple spectral indices to generate more accurate burned area maps by exploiting Sentinel-2 images. This approach aims to develop a procedure to combine multiple spectral indices using an adaptive thresholding method and proposes an agreement index to map the burned areas by optimizing omission and commission errors. The approach has been tested for the burned area classification of four study areas in Italy. The proposed agreement index combines multiple spectral indices to select the actual burned pixels, to balance the omission and commission errors, and to optimize the overall accuracy. The results showed the spectral indices singularly performed differently in the four study areas and that high levels of commission errors were achieved, especially for wildfires which occurred during the fall season (up to 0.93) Furthermore, the agreement index showed a good level of accuracy (minimum 0.65, maximum 0.96) for all the study areas, improving the performance compared to assessing the indices individually. This suggests the possibility of testing the methodology on a large set of wildfire cases in different environmental conditions to support the decision-making process. Exploiting the high resolution of optical satellite data, this work contributes to improving the production of detailed burned area maps, which could be integrated into operational services based on the use of Earth Observation products for burned area mapping to support the decision-making process.
Highlights
From the 1980s onwards, because of climate change conditions [1] and the increase in drought and land degradation phenomena [2], fires have become an important cause of land cover modifications around the world [3], affecting landscape patterns and functions [4,5,6], ecosystem processes [7,8], and air quality [9]
This study aims to propose a procedure for burned area mapping through the combination of multiple SIs that i) identifies the best SI to be used to define SI thresholding based on the fire season and site conditions; ii) use an adaptive SI thresholding method which is flexible enough to be adapted to the local conditions, and iii) introduce a spatially explicit agreement index that can be consistently used for areas with different environmental conditions in all fire seasons
Having obtained the highest M value, dNBR and dNBR2 were selected as the best SIs to serve as reference for the summer dry season study cases (Roccagorga and Gravina in Puglia), while dMIRBI and dNBR2 were selected as reference SIs for the fall dry season (Trivero and Bussoleno)
Summary
From the 1980s onwards, because of climate change conditions [1] and the increase in drought and land degradation phenomena [2], fires have become an important cause of land cover modifications around the world [3], affecting landscape patterns and functions [4,5,6], ecosystem processes [7,8], and air quality [9]. Earth Observation (EO) has proven to be a suitable technology for identifying areas affected by fire [10], from global [11,12] to local scales [13]. From this perspective, EO data have been used in the identification of active fires [14,15,16], for delimiting the perimeters of burned areas [12,13,17], to monitor the recovery of vegetation after the event [18,19,20,21], and to determine the distribution of the plume in the atmosphere [22]. The global interannual variability in terrestrial ecosystem fluxes and in atmospheric CO2 are strongly influenced by forest fire emissions [23,24]
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