The combined use of reflectance, emissivity and elevation Aster/Terra data for tropical soil studies

Fábio Marcelo Breunig,Lênio Soares Galvão,Eduardo Guimarães Couto,Antonio Roberto Formaggio

doi:10.1590/s0100-06832009000600027

Abstract

Reflectance, emissivity and elevation data of the sensor ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer)/Terra were used to characterize soil composition variations according to the toposequence position. Normalized data of SWIR (shortwave infrared) reflectance and TIR (thermal infrared) emissivity, coupled to a soil-fraction image from a spectral mixture model, were evaluated to separate bare soils from nonphotosynthetic vegetation. Regression relationships of some soil properties with reflectance and emissivity data were then applied on the exposed soil pixels. The resulting estimated values were plotted on the ASTER-derived digital elevation model. Results showed that the SWIR bands 5 and 6 and the TIR bands 10 and 14 measured the clay mineral absorption band and the quartz emissivity feature, respectively. These bands improved also the discrimination between nonphotosynthetic vegetation and soils. Despite the differences in pixel size and field sampling size, some soil properties were correlated with reflectance (R² of 0.65 for Al2O3 in band 6; 0.61 for Fe2O3 in band 3) and emissivity (R² of 0.65 for total sand fraction in the 10/14 band ratio). The combined use of reflectance, emissivity and elevation data revealed variations in soil composition with topography in specific parts of the landscape. From higher to lower slope positions, a general decrease in Al2O3 and increase in total sand fraction was observed, due to the prevalence of Rhodic Acrustox at the top and its gradual transition to Typic Acrustox at the bottom.

Highlights

Remote sensing instruments with improved spectral resolution have opened new perspectives for several applications, including for the study of soils
Inspection of the pixel spectra and fieldwork showed that several areas of bright sandy soils were expressed as nonphotosynthetic vegetation in the model, which required an additional criterion to discriminate between these two classes
By using the soil fraction (0.65) and SWIR and TIR threshold values (0.07 and 3, respectively), an image of exposed soils was produced, which served as a basis for the subsequent analysis of the soil property estimates using reflectance and emissivity data

Summary

Introduction

Remote sensing instruments with improved spectral resolution have opened new perspectives for several applications, including for the study of soils. In spite of not being able to capture information from the diagnostic subsurface horizon, remote sensors may provide useful data from the soil surface to optimize fieldwork and mapping. ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), onboard the Terra Platform, launched in December 1999, has three bands in the VNIR (visible and near infrared), six bands in the SWIR (shortwave infrared) and five bands in the TIR (thermal infrared) with 15, 30 and 90 m of spatial resolution, respectively (Yamaguchi et al, 2001). The SWIR reflectance bands can detect hydroxyl absorption bands associated with clay minerals, whereas the TIR emissivity bands can identify reststrahlen features (Vaugham et al, 2005; Ducart et al, 2006). ASTER data may be useful to discriminate bare soils from soils with senescent vegetation on the surface (French et al, 2000)

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Results

Conclusion