Bi-directional reflectance spectroscopy of Fe-oxides minerals in mediterranean terra rossa soils: a methodological approach

Laboratory bi-direclional reflectance spectra of selected Terra Rossa soils (Puglia, south­em Italy) were parametrised using two different rnethods: the «convex-hull difference» normalisation and «derivative spectroscopy». The normalisation procedure was performed by subtracting from 100 the difference between the 'hull' (a continuum curve fit over the originai spectra) and the originai spectra. The following parameters were then quantified over the normalised spectra: band position, arnplitude, full-width at half maximum (FWI IM), asymmetry and area. First and second derivative curves were cal­culated from both origina! spectra and their remission functions. Position and amplitude of peaks over the derivative curves were then measured. Some significant correlations were found between the spec­tral parameters in the normalised spectra and derivative curves and soil iron oxides minerals (hematite and goethite). Relationships irnproved when the hematite and goethile contents were related to the organic rnatter content, thus highlìghting the considerable interference of the latter soil constituent on the inherent spectral behaviour of the two Fe-oxides, especially in the visible region (below 700 nm). Comparison between the two procedures of spectra paramctrisation showed that the normalisation pro­cedure performed better than derivative spectroscopy