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| Titel |
The COsmic-ray Soil Moisture Interaction Code (COSMIC) for use in data assimilation |
| VerfasserIn |
J. Shuttleworth, R. Rosolem, M. Zreda, T. Franz |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 17, no. 8 ; Nr. 17, no. 8 (2013-08-14), S.3205-3217 |
| Datensatznummer |
250085910
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| Publikation (Nr.) |
 copernicus.org/hess-17-3205-2013.pdf |
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| Zusammenfassung |
| Soil moisture status in land surface models (LSMs) can be updated by
assimilating cosmic-ray neutron intensity measured in air above the surface.
This requires a fast and accurate model to calculate the neutron intensity
from the profiles of soil moisture modeled by the LSM. The existing Monte
Carlo N-Particle eXtended (MCNPX) model is sufficiently accurate but too
slow to be practical in the context of data assimilation. Consequently an
alternative and efficient model is needed which can be calibrated accurately
to reproduce the calculations made by MCNPX and used to substitute for MCNPX
during data assimilation. This paper describes the construction and
calibration of such a model, COsmic-ray Soil Moisture Interaction Code (COSMIC), which is simple, physically based and
analytic, and which, because it runs at least 50 000 times faster than MCNPX, is
appropriate in data assimilation applications. The model includes simple
descriptions of (a) degradation of the incoming high-energy neutron flux
with soil depth, (b) creation of fast neutrons at each depth in the soil,
and (c) scattering of the resulting fast neutrons before they reach the soil
surface, all of which processes may have parameterized dependency on the
chemistry and moisture content of the soil. The site-to-site variability in
the parameters used in COSMIC is explored for 42 sample sites in the
COsmic-ray Soil Moisture Observing System (COSMOS), and the comparative
performance of COSMIC relative to MCNPX when applied to represent
interactions between cosmic-ray neutrons and moist soil is explored. At an
example site in Arizona, fast-neutron counts calculated by COSMIC from the
average soil moisture profile given by an independent network of point
measurements in the COSMOS probe footprint are similar to the fast-neutron
intensity measured by the COSMOS probe. It was demonstrated that, when used
within a data assimilation framework to assimilate COSMOS probe counts into
the Noah land surface model at the Santa Rita Experimental Range field site,
the calibrated COSMIC model provided an effective mechanism for translating
model-calculated soil moisture profiles into aboveground fast-neutron
count when applied with two radically different approaches used to remove
the bias between data and model. |
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