Weathering sequence of soils developed from basalt as evaluated by laboratory (IRIS), airborne (AVIRIS) and orbital (TM) sensors

The aim of this investigation was to evaluate orbital and terrestrial spectral reflectance data of soils developed from basic rocks on a toposequence in Parana State, Brazil, focusing on their characterization, discrimination, attribute content estimation and relation to weathering. Rhodic Haplortox (RH) and Typic Argiudol (TA) soil samples were collected and submitted to a laboratory 450-2500 nm spectroradiometer for reflectance data acquisition, which were used to simulate AVIRIS (Airborne Visual and Infrared Imaging Spectrometer) bands. Digital numbers (DN) and reflectance data were extracted from Landsat-5 Thematic Mapper (TM) at the same place as the soil sample collecting sites. Although the spectral curves of the soils were similar, TA (little-weathered soil) presented higher reflectance intensity than RH (highly weathered soil) between 800 and 2500 nm, and both showed differences in absorption features at 850, 1900 and 2265 nm, due to granulometry and mineralogy constituents. Spectral data obtained in the laboratory were important to the validation of orbital data, which also discriminated the soils, especially band 7. We concluded that reflectance data extracted from TM represent soil spectral information better than DN. AVIRIS data were better than TM, as they identified gibbsite so as the laboratory sensor IRIS (Infrared Intelligent Spectroradiometer). It was possible to estimate clay and silt contents using the analysis of reflected energy of soil samples. Remote sensing is a very helpful alternative for soil investigation and for estimating element content.