Assessment of the potential of SAC-C/MMRS imagery for mapping burned areas in Spain

Abstract

Early and detailed information regarding the location and extension of areas affected by forest fires is a critical issue for assessing their effects at several scales. Remote sensing is a valuable tool for burned area mapping, providing spatially explicit information on the scorched areas, even for remote regions. Various sensors have been used for burned land mapping in recent years, covering local (10–30 m pixel size) and global scales (500–1000 m pixel size). Regional inventories require higher detail than global studies, but typically cover larger territories than local studies. For this purpose, the use of medium spatial resolution sensors (100–300 m pixel size) is highly advisable. Few studies have evaluated these sensors, and none have specifically assessed the performance of images acquired by the Argentinian Satellite for Scientific Applications-C/Multispectral Medium Resolution Scanner (SAC-C/MMRS) for mapping burned areas, which is the main objective in this paper. Since information on calibration parameters was not available, raw data was converted into ground reflectance values after a “cross-calibration” method, using Landsat Enhanced Thematic Mapper (ETM+) data as reference. Estimated radiance values showed very high correlation with those for the ETM+ ( r 2>0.9). Several spectral indices were generated and tested. The Burned Area Index (BAI), derived from red and near infrared (NIR) reflectances showed the greatest sensitivity to discriminate burned areas from other land cover types, although the Normalized Difference Infrared Index (NDII), based on the Red and Short Wave Infrared (SWIR) bands also provided good discrimination capability. Image segmentation was performed by using a multi-threshold approach, based on the BAI and the NDII since these two spectral indices have the highest sensitivity to (1) discriminate burned areas and (2) to avoid confusion with water and cloud shadows. Burned perimeters delineated using a seeded region growing algorithm showed good agreement with the perimeters digitised on Landsat ETM+ data, providing accurate estimation of the burned areas compared to statistics provided by the Spanish forest fire authorities. In the first study area (Almerı́a, south-eastern Spain), the perimeters showed a 90% agreement. In the second study site (Madrid), two fires were studied. The first one (Cadalso, south–west of Madrid) showed an agreement of 64%, and for the second one (Patones, north–east of Madrid), the agreement was 84%. The lower accuracy of the former was caused by the great spatial discontinuity of that fire, which includes many patches of unaffected vegetation within the scar perimeter.