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

Abstract

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%), OPEN ACCESSRemote Sens. 2015, 7 1321 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.

COSMO-SkyMed potential to detect and monitor Mediterranean maquis fires and regrowth: a pilot study in Capo Figari, Sardinia, Italy

“…When pixel number did not reach the 10% of those of the area, the values was not considered (indicated with "n/a" Vaglio for low-biomass forests. Different researches highlighted the usefulness of optical and SAR data for burnt area detection, also used in conjunction in the Mediterranean region (Stroppiana et al 2015). Although optical data have been more frequently used, recent studies have been also conducted with different SAR data types, as shown by the Gitas et al (2012) review.…”

Processing Optical and SAR data for burned forests mapping: An integrated framework

“…A binary burned area map (0-unburned, 1-burned) can be derived by applying a threshold to the fuzzy score map [3]. By assessing the accuracy of the burned/unburned area maps as a function of the threshold applied to the fuzzy score map, we found that errors vary between two extremes: a map where areas identified as burned are highly reliable, i.e.…”

“…Partial positive and negative evidence brought by the optical and SAR data have been integrated by using Ordered Weighted Averaging (OWA) operators [4,5] and a region growing algorithm has been subsequently applied. For a more detailed description the reader is referred to [3].…”

“…cloud and topographic shadows, low density unburned vegetation, wetlands). Specifically, six spectral indices are taken into account (CSI, EVI, EVI2, MIRBI, NBR, NBR2, NDVI, SAVI) [3]. The evidence of burn given by each index (i.e., partial positive evidence) is quantified by using fuzzy membership functions.…”

“…The adopted approach relies on the use of fuzzy sets theory for the interpretation and integration of spectral indices and scattering signature [1], [3] and a region growing algorithm. This approach is theoretically based on the concept of the reinforcement of burn evidence [1]: spectral indices derived from the multi-spectral images acquired by optical satellite sensors can provide consistent and coherent information over burned areas, whereas they may have a complementary, incoherent behavior over confusing surfaces (e.g.…”