Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2016-226
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
26 May 2016
Review status
A revision of this discussion paper was accepted for the journal Hydrology and Earth System Sciences (HESS) and is expected to appear here in due course.
Can canopy interception and biomass be inferred from cosmic-ray neutron intensity? Results from neutron transport modeling
Mie Andreasen1, Karsten H. Jensen1, Darin Desilets2, Marek Zreda3, Heye Bogena4, and Majken C. Looms1 1Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark
2Hydroinnova LLC, Albuquerque, New Mexico
3Department of Hydrology and Water Resources, University of Arizona, Arizona
4Agrosphere IBG-3, Forschungszentrum Juelich GmbH, Germany
Abstract. Cosmic-ray neutron intensity is inversely correlated to all hydrogen present in the upper decimeters of the subsurface and the first few hectometers of the atmosphere above the ground surface. This method has been used for measuring soil moisture and snow water equivalent, but it may also be used to identify and quantify canopy interception and biomass. We use a neutron transport model with various representations of the forest and different parameters describing the subsurface to match measured profiles and time series of thermal and epithermal neutron intensities at a field site in Denmark. A sensitivity analysis is performed to quantify the effect of forest canopy representation, soil moisture, complexity of soil matrix chemistry, forest litter, soil bulk density, canopy interception and forest biomass on neutron intensity. The results show that forest biomass has a significant influence on the neutron intensity profiles at the examined field site, altering both the shape of the profiles and the ground level thermal-to-epithermal neutron ratio. The ground level thermal-to-epithermal neutron ratio increases significantly with increasing amounts of biomass and minor with canopy interception. Satisfactory agreement is found between measurements and model results at the forest site as well as two nearby sites representing agricultural and heathland ecosystems. The measured ground level thermal-to-epithermal neutron ratios of the three site range from around 0.56 to 0.82. The significantly smaller effect of canopy interception on the ground level thermal-to-epithermal neutron ratio was modeled to range from 0.804 to 0.836 for a forest with a dry and a very wet canopy (4 mm of canopy interception), respectively. At the examined field site the signal of the canopy interception is lower than the measurement uncertainty.

Citation: Andreasen, M., Jensen, K. H., Desilets, D., Zreda, M., Bogena, H., and Looms, M. C.: Can canopy interception and biomass be inferred from cosmic-ray neutron intensity? Results from neutron transport modeling, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-226, in review, 2016.
Mie Andreasen et al.
Mie Andreasen et al.
Mie Andreasen et al.

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Short summary
The cosmic-ray method holds a potential for quantifying canopy interception and biomass. We use measurements and modeling of thermal and epithermal neutron intensity in a forest to examine this potential. Canopy interception is a variable important to forest hydrology, yet difficult to monitor remotely. Forest growth impacts the carbon-cycle and can be used to mitigate climate changes by carbon sequestration in biomass. An efficient method to monitor tree growth is therefore of high relevance.
The cosmic-ray method holds a potential for quantifying canopy interception and biomass. We use...
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