|Title (Primary)||Towards disentangling heterogeneous soil moisture patterns in cosmic-ray neutron sensor footprints|
|Author||Rasche, D.; Köhli, M.; Schrön, M.; Blume, T.; Güntner, A.|
|Journal||Hydrology and Earth System Sciences|
|Topic||T5 Future Landscapes|
neutron sensing (CRNS) allows for non-invasive soil moisture estimations at the
field scale. The derivation of soil moisture generally relies on secondary
cosmic-ray neutrons in the epithermal to fast energy ranges. Most approaches
and processing techniques for observed neutron intensities are based on the
assumption of homogeneous site conditions or of soil moisture patterns with
correlation lengths shorter than the measurement footprint of the neutron
detector. However, in view of the non-linear relationship between neutron
intensities and soil moisture, it is questionable whether these assumptions are
In this study, we investigated how a non-uniform soil moisture distribution within the footprint impacts the CRNS soil moisture estimation and how the combined use of epithermal and thermal neutrons can be advantageous in this case. Thermal neutrons have lower energies and a substantially smaller measurement footprint around the sensor than epithermal neutrons.
Analyses using the URANOS (Ultra RApid Neutron-Only Simulation) Monte Carlo simulations to investigate the measurement footprint dynamics at a study site in northeastern Germany revealed that the thermal footprint mainly covers mineral soils in the near-field to the sensor while the epithermal footprint also covers large areas with organic soils.
We found that either combining the observed thermal and epithermal neutron intensities by a rescaling method developed in this study or adjusting all parameters of the transfer function leads to an improved calibration against the reference soil moisture measurements in the near-field compared to the standard approach and using epithermal neutrons alone. We also found that the relationship between thermal and epithermal neutrons provided an indicator for footprint heterogeneity. We, therefore, suggest that the combined use of thermal and epithermal neutrons offers the potential of a spatial disaggregation of the measurement footprint in terms of near- and far-field soil moisture dynamics.
|Persistent UFZ Identifier||https://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=25546|
|Rasche, D., Köhli, M., Schrön, M., Blume, T., Güntner, A. (2021):
Towards disentangling heterogeneous soil moisture patterns in cosmic-ray neutron sensor footprints
Hydrol. Earth Syst. Sci. 25 (12), 6547 - 6566