HR: 1340h
AN: U43C-1403    [Abstracts]
TI: Effects of Carbon Depth Profile on INS Measurement
AU: * Wielopolski, L
EM: lwielo@bnl.gov
AF: Brookhaven National Laboratory, Environmental Sciences Department, Bldg. 490D, Upton, NY 11973, United States
AB: Inelastic Neutron Scattering (INS) is a new system for measuring carbon in soil in situ that is non-destructive. In addition the INS can be used in stationary or scanning modes of operation enabling type of measurements not possible till now. It is based on counting 4.44 MeV characteristic gamma rays emitted from carbon nuclei undergoing inelastic neutron scattering with fast, 14 MeV, neutrons. Because of the attenuation of the neutrons, on their way in, and of the gamma rays, on their way out, the large volume of about 0.3 m³ sampled by the INS system causes it to respond preferentially to carbon atoms located near the surface. Thus, the carbon signal depends on the variations in the carbon depth profile; however, this dependence is reduced by an averaging process resulting from the large footprint of about 1 m² of the INS system. The encountered variability in the depth profiles on small 30 cm scale and on large field size scale is presented for various fields. We also show results of Monte Carlo simulations of the INS response to various carbon depth profiles. Experimentally we show that depending on the field conditions, i.e. profound variability in the carbon depth profile or extensive changes in the carbon distribution in the field, the scanning results with the INS system may differ from the mean value calculated from few INS discrete stationary measurements. Since the static measurements are analogous to conventional chemical analysis using soil cores, it raises the question which type of measurement is more representative of the field carbon content; the discrete chemical analysis using geostatistical considerations or continuous field scanning made possible with the INS system. Clearly the new INS methodology introduces novel capabilities for soil carbon analysis not possible with the conventional approach of dry combustion. The advantages and pitfalls of the INS system with the need to defining practical new calibration concepts for it are discussed in the forthcoming presentation.
DE: 0428 Carbon cycling (4806)
DE: 0452 Instruments and techniques
DE: 0466 Modeling
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1622 Earth system modeling (1225)
SC: Union [U]
MN: 2007 Fall Meeting