Soil Organic Carbon mapping of partially vegetated agricultural fields with imaging spectroscopy |
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| Authors: | Harm Bartholomeus Lammert Kooistra Antoine Stevens Martin van Leeuwen Bas van Wesemael Eyal Ben-Dor Bernard Tychon |
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| Institution: | 1. Centre for Geo-Information, Wageningen University, Droevendaalsesteeg 3, NL 6708 PB, Wageningen, The Netherlands;2. Department of Geography, Université catholique de Louvain, Place Pasteur 3, 1348 Louvain-La-Neuve, Belgium;3. Faculty of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada;4. Department of Geography, Tel-Aviv University, P.O. Box 39040, Ramat Aviv, Tel-Aviv, Israel;5. Department of Environmental Sciences and Management, University of Liège, Avenue de Longwy 185, B-6700 Arlon, Belgium |
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| Abstract: | Soil Organic Carbon (SOC) is one of the key soil properties, but the large spatial variation makes continuous mapping a complex task. Imaging spectroscopy has proven to be an useful technique for mapping of soil properties, but the applicability decreases rapidly when fields are partially covered with vegetation. In this paper we show that with only a few percent fractional maize cover the accuracy of a Partial Least Square Regression (PLSR) based SOC prediction model drops dramatically. However, this problem can be solved with the use of spectral unmixing techniques. First, the fractional maize cover is determined with linear spectral unmixing, taking the illumination and observation angles into account. In a next step the influence of maize is filtered out from the spectral signal by a new procedure termed Residual Spectral Unmixing (RSU). The residual soil spectra resulting from this procedure are used for mapping of SOC using PLSR, which could be done with accuracies comparable to studies performed on bare soil surfaces (Root Mean Standard Error of Calibration = 1.34 g/kg and Root Mean Standard Error of Prediction = 1.65 g/kg). With the presented RSU approach it is possible to filter out the influence of maize from the mixed spectra, and the residual soil spectra contain enough information for mapping of the SOC distribution within agricultural fields. This can improve the applicability of airborne imaging spectroscopy for soil studies in temperate climates, since the use of the RSU approach can extend the flight-window which is often constrained by the presence of vegetation. |
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| Keywords: | Imaging spectroscopy Soil Organic Carbon Residual Spectral Unmixing |
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