A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

The Potential of Combined SAR Data and Optical VI´s for Vegetation Mapping inthe Brazilian CerradoLaerte G. Ferreira 1 , Edson E. Sano 2 and Alfredo R. Huete 31Instituto de Estudos Socio-Ambientais (IESA/UFG), Campus Samambaia – Cx.Postal 131, CEP: 74001-970, Goiania-GO Brazil E-mail: laerte@iesa.ufg.br2 Empresa Brasileira de Pesquisa Agropecuaria, BR-020 Km 18 Cx. Postal08223, CEP: 73301-970 Planaltina, DF Brazil3 Department of Soil, Water, and Environmental Sciences, University of Arizona, Tucson AZ85721The Brazilian Cerrado covers more than 208 million hectares in the central part of thecountry and presents a well-defined seasonality. Approximately 40% of the Cerradohave been already converted. In order to evaluate the potential of optical and syntheticaperture radar data to map and monitor Cerrado’s vegetative cover, we acquired dry andwet seasons Landsat/TM and JERS-1 SAR data over the Brasilia National Park, a30.000 ha, preserved area located in northern Brasilia. The georeferenced SAR and TMimages were overlaid with the vector format, vegetation map of the Park to facilitate theextraction of representative SAR and optical digital numbers in each Cerrado unit(savanna grassland; shrub savanna; savanna grassland or shrub savanna with“termiters”; wooded savanna; savanna woodland; and gallery forest). The TM digitalcounts were transformed in top-of-canopy, nadir reflectance values by using the 6Sradioactive transfer model. Normalized Difference Vegetation Index (NDVI) andEnhanced Vegetation Index (EVI) were derived from the reflectance data. SAR digitalcounts were transformed in backscattering coefficients. Scatter plots betweennormalized SAR and TM data as well as statistical analyses (discriminant analysis andANOVA) showed overall better performance of radar data to map Cerrado’sphysiognomies, in comparison to the VIs. However, the performance improvedsignificantly when we combined the two types of data. The discrimination capability of69% obtained by the radar data, regardless of season, increased up to 85% when wecombined SAR and optical data.