Spectroscopy for the assessment of soil properties in reconstructed river floodplains

In order to deal with peak discharges of the river Rhine in the Netherlands more space is created. Floodplain surfaces are lowered and dikes are shifted, like in the Bakenhof floodplain near Arnhem. Fast assessment of soil properties in these areas is of great benefit for e.g. extraction and appropriate re-use of sand and clay, soil sanitation projects and nature development projects. The present study used partial least squares (PLS) regression to establish a relationship between soil reflectance spectra measured under field conditions and the organic matter and clay content of the soil. Several spectral pre-processing methods were employed to improve the performance and robustness of the models. Results indicate that, under varying surface conditions, field spectroscopy in combination with multivariate calibration does result in a qualitative relation for organic matter (R = 0.37) and clay content (R = 0.42). Soil moisture and vegetation cover had a negative influence on the prediction capabilities for both soil properties. Under laboratory conditions even more accurate results are obtained (R = 0.66 and 0.92 respectively) for these samples. Although the performance of the spectra measured in the field is not as accurate as those in the laboratory, the accuracy obtained is useful for rapid soil characterisation and implies that imaging spectroscopy can play a role in fast mapping of the surface of these areas.