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IN-field NIR spectroscopy for Carbon Accounting (INCA)

IN-field NIR spectroscopy for Carbon Accounting (INCA)

Summary
In order to limit climate change due to increasing content of the atmosphere greenhouse gas emissions, the Kyoto Protocol proposes to setup trading carbon market that corresponds to verified reduction of removal of greenhouse gas from the atmosphere. One of the main options for carbon mitigation is the sequestration of carbon in soils. This assumes that a method for accurately and inexpensively measuring the carbon stock in soil is available. Here, the objective of the INCA project is to develop a method and a device for measuring the volumic concentration of soil carbon using Near Infrared Spectroscopy (NIRS).
Near Infrared Spectroscopy is a well-know technique used for more than 40 years for measuring the quality and composition of agricultural and food products. It has also been experimented for soil analysis purposes but has not reached the routine analysis phase yet. If quantification of different components or certain functions (weight content of organic and inorganic carbon, nitrogen, cation exchange capacity, particle size ...) has been the subject of numerous publications, several methodological and technological issues must be addressed to make an analytical method for routine accounting credits C. First, NIRS must be implemented in field, to avoid the costs generated by the extraction and sample preparation and allowing repeated measurements. On the other hand, the critical point of the NIRS - particularly for soils - is the calibration process. Several research questions have to be addressed: (i) which optical architecture optimizes the quality of the in-situ measured spectra? (ii) What is the sensitivity of the measurement regarding different variable of influence (moisture, temperature, aggregate, particle size etc.). ? and how can be the measure robust ? (iii) How can the quality of the measurement be evaluated?
With the aim to provide answers to these questions, a partnership gathering specialists in soil science and in NIRS instrumentation has been set up in the frame of the multidisciplinary INCA project.
The research focused on both the development of a suitable optical setup to measure soils and on the assessment of the potential of different calibration methods. The different calibrations were made from spectral database build in the frame of the project and including over 2000 samples representative of the metropolitan area associated with the carbon content. The major results of INCA are: (i) a new method for measuring the chemical absorbance of scattering materials, which can be applied to both soils than on other media ; (ii) a signal quality indicator, SQi, also generic and (iii) INCA has defined the most relevant strategies in terms of calibration , while stressing the importance of acquiring a signal of good quality.

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Contact
IRSTEA (Véronique Bellon-Maurel and Alexia Gobrecht)

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