CARBIS final report : detecting soil carbon and its spatial variability by imaging spectroscopy

Soil Organic Carbon (SOC) stock have been the objects of a growing literature last decades due to their role in the conservation of soil quality and in the global C cycle. However, the study of their temporal evolution remains difficult due to a strong intra- and inter-field variability masking the signal with a lot of noise. As a result, the detection of SOC stock changes in soil monitoring or modelling studies require a high sampling that is rarely achieved without resorting to expensive and time consuming routine soil analysis methods. New analytical methods are needed that would allow a rapid sampling and instant determination of SOC contents. Visible Near Infrared (VNIR) diffuse reflectance spectroscopy has been extensively explored in the laboratory as a rapid means to quantify various soil properties and OC in particular. For the time being, Portable field Spectroscopy (PS) and Imaging Spectroscopy (IS) have been less studied as SOC analytical tools. The objective of this study is to compare the predictive ability of lab-, field- and airborne-based VNIR spectroscopy to determine SOC contents in cropland using Partial Least Square Regressions (PLSR) and try to map SOC with IS. The stability of the calibrations across time and space has also been addressed. To achieve these goals, several spectral datasets have been collected during three hyperspectral field campaigns financed by the BELSPO along the period 2003-2005.