Exploitation of Sentinel-2 Time Series to Map Burned Areas at the National Level: A Case Study on the 2017 Italy Wildfires

Federico Filipponi

doi:10.3390/rs11060622

Abstract

Satellite data play a major role in supporting knowledge about fire severity by delivering rapid information to map fire-damaged areas in a precise and prompt way. The high availability of free medium-high spatial resolution optical satellite data, offered by the Copernicus Programme, has enabled the development of more detailed post-fire mapping. This research study deals with the exploitation of Sentinel-2 time series to map burned areas, taking advantages from the high revisit frequency and improved spatial and spectral resolution of the MSI optical sensor. A novel procedure is here presented to produce medium-high spatial resolution burned area mapping using dense Sentinel-2 time series with no a priori knowledge about wildfire occurrence or burned areas spatial distribution. The proposed methodology is founded on a threshold-based classification based on empirical observations that discovers wildfire fingerprints on vegetation cover by means of an abrupt change detection procedure. Effectiveness of the procedure in mapping medium-high spatial resolution burned areas at the national level was demonstrated for a case study on the 2017 Italy wildfires. Thematic maps generated under the Copernicus Emergency Management Service were used as reference products to assess the accuracy of the results. Multitemporal series of three different spectral indices, describing wildfire disturbance, were used to identify burned areas and compared to identify their performances in terms of spectral separability. Result showed a total burned area for the Italian country in the year 2017 of around 1400 km2, with the proposed methodology generating a commission error of around 25% and an omission error of around 40%. Results demonstrate how the proposed procedure allows for the medium-high resolution mapping of burned areas, offering a benchmark for the development of new operational downstreaming services at the national level based on Copernicus data for the systematic monitoring of wildfires.

Highlights

Fire is an important disturbance factor in ecosystems that induce land-cover modification and change [1]
The main purpose of this paper is to introduce a multitemporal approach that could exploit the entire Sentinel-2 time series for the identification of burned areas, and to provide suggestions to address the future development of the procedure in order to refine it with additional methods
Based on the comparison with the Copernicus Emergency Management Service (EMS) product (Table 3), the procedure generated in Step A a high omission error of around 75% and a commission error of around 20–25%

Summary

Introduction

Fire is an important disturbance factor in ecosystems that induce land-cover modification and change [1]. Fire represents a significant source of gas and aerosols worldwide [3]. The large amounts of smoke emitted from fires impact air quality and affect global warming due to rising trace gas emissions [4]. Satellite data play a major role in supporting knowledge about fire severity by delivering rapid information to map fire-damaged areas in a precise and prompt way. Accurate and rapid mapping of fire-damaged areas is fundamental to support fire management, account for environmental loss, define planning strategies, and interpret cause–effect relations of post-hazard wildfire dynamics, as the specific case of vegetation restoration dynamics [5]. Fire severity is a qualitative measure of the immediate effects of fire on the non-anthropic ecosystem, related to the extent of mortality and survival of plant and animal life both aboveground and belowground and to the loss of organic matter [8]

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Conclusion