Integration of Optical and SAR Data for Burned Area Mapping in Mediterranean Regions

Daniela Stroppiana,Ramin Azar,Riccardo Lanari,João Silva,Pasquale Imperatore,Pietro Brivio,Mirco Boschetti,Fabiana Calò,Antonio Pepe

doi:10.3390/rs70201320

Abstract

The aim of this paper is to investigate how optical and Synthetic Aperture Radar (SAR) data can be combined in an integrated multi-source framework to identify burned areas at the regional scale. The proposed approach is based on the use of fuzzy sets theory and a region-growing algorithm. Landsat TM and (C-band) ENVISAT Advanced Synthetic Aperture Radar (ASAR) images acquired for the year 2003 have been processed to extract burned area maps over Portugal. Pre-post fire SAR backscatter temporal difference has been integrated with optical spectral indices to the aim of reducing confusion between burned areas and low-albedo surfaces. The output fuzzy score maps have been compared with reference fire perimeters provided by the Fire Atlas of Portugal. Results show that commission and omission errors in the output burned area maps are a function of the threshold applied to the fuzzy score maps; between the two extremes of the greatest producer’s accuracy (omission error < 10%) and user’s accuracy (commission error < 5%), an intermediate threshold value provides errors of about 20% over the study area. The integration of SAR backscatter allowed reducing local commission errors from 65.4% (using optical data, only) to 11.4%, showing to significantly mitigate local errors due to the presence of cloud shadows and wetland areas. Overall, the proposed method is flexible and open to further developments; also in the perspective of the European Space Agency (ESA) Sentinel missions operationally providing SAR and optical datasets.

Highlights

Forest fires in the Mediterranean and Temperate Continental zones of Europe have strong ecological and socio-economic impacts [1]
The aim of this paper is to investigate how the distinctive features of the information conveyed by optical and Synthetic Aperture Radar (SAR) data can be combined to identify burned areas, through the development of an integrated multi-source framework for burned area maps production based on a fuzzy algorithm
To reduce the commission errors in burned area maps, SAR pre- and post-fire backscatter images (∆σ°) have been integrated into a burned area mapping fuzzy algorithm previously built on the exclusive use of optical data

Summary

Introduction

Forest fires in the Mediterranean and Temperate Continental zones of Europe have strong ecological and socio-economic impacts [1]. The application of improved and integrated monitoring tools is of crucial importance to assess and understand the effects of annually-occurring forest fires. It is nowadays possible to observe long-term global and regional changes from several imaging systems onboard satellite platforms, continuously monitoring our planet’s surface, including sensors operating in different regions of the electromagnetic spectrum. The different methodologies and techniques developed to study biomass, and burned areas, can be categorized according to the investigated spectral portion (i.e., visible, infrared and microwave). As far as the optical and infrared imaging sensors are concerned, several techniques have been exploited to map burned areas [2,3,4,5,6,7,8]. Large-scale studies have relied on the availability of coarse resolution satellite data, such as NOAA-AVHRR

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