The in situ reflectance spectra in the 400-2500 nm wavelength region were obtained using a portable radiometer over a range of land surfaces including burnt fields, crop canopies, and fallow vegetation at different community ages in slash-and-burn ecosystems in Laos. Normalized difference spectral indices (NDSI[i,j]=[Rj- Ri]/[Rj+Ri]) were derived using reflectance Ri and Rj at i and j nm wavelengths for a thorough combination (14 706 pairs) of 172 wavebands (10-nm resolution). The separability of burnt fields from dry/senescent vegetation was highest at NDSI[1090, 2390], whereas it was highly discriminated from fallow and crop vegetation by NDSI[760, 1970]. NDSIs using 730-760 nm with 1970-1990 nm showed the largest differences between dry/senescent vegetation and fallow or crop vegetation. None of the NDSIs was useful in discriminating between fallow and crop vegetations or between slashed/senescent vegetation and crop residue/ abandoned field. Community age and biomass of fallow vegetation could not be inferred directly from spectral information, since no NDSIs showed any significant differences among crop and fallow vegetation that had a large variability in the amount of green vegetation. Results would provide useful information for various applications of optical satellite sensor images especially in assessments of land use or post-fire regeneration of vegetation.
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