The use of hyperspectral imagery for digital soil mapping in mediterranean areas

Hyperspectral imagery is considered as a promising source of data to overcome the lack of soil information that often hamper digital soil mapping. We have tested it in the vineyard plain of Languedoc (southern France) using an 5×5m resolution HYMAP image and 52 calibration-validation points. Satisfactory predictions of clay content and calcium carbonate (CaCO3) content were first obtained from HYMAP spectra over bare soils, partial least-squares regression performing better than continuum removal technique. These predictions were however less precise than using laboratory spectra. An examination of the possible factors that could explain this decrease showed that calibration uncertainties of the HYMAP sensor and of atmospheric effects were largely predominant. Secondly, since the HYMAP image was largely covered by vegetation with few pure bare soil pixels, an interpolation-aggregation procedure was proposed to obtain a 100×100m digital soil map of the whole study area from a set of scattered bare soil fields with hyperspectral soil characterization. Interpolation was performed by a conditional simulation algorithm to estimate the within pixel soil pattern parameters. Validation results showed that satisfactory estimates of local means can be obtained whereas the variations of local variances were only partly represented.In the near future, a new proof-of-concept zone will be implemented in Tunisia to confirm these encouraging results and to examine how hyperspectral imagery can be used in association with soil legacy data and digital terrain models to produce digital maps of soil properties in the Mediterranean areas