Assimilation of cosmic‐ray neutron counts for the estimation of soil ice content on the eastern Tibetan Plateau

Samuel Mwangi, Yijian Zeng*, Carsten Montzka, Lianyu Yu, Zhongbo Su

*Corresponding author for this work

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Abstract

Accurate observations and simulations of soil moisture phasal forms are crucial in cold region hydrological studies. In the seasonally frozen ground of eastern Tibetan Plateau, water vapor, liquid, and ice coexist in the frost‐susceptible silty‐loam soil during winter. Quantification of soil ice content is thus vital in the investigation and understanding of the region's freezing‐thawing processes. This study focuses on the retrieval of soil ice content utilizing the in situ soil moisture (i.e., liquid phase) and cosmic ray neutron measurements (i.e., total water including liquid and ice), with Observing System Simulation Experiments. To derive the total soil water from neutron counts, different weighting methods (revised, conventional, and uniform) for calibrating the cosmic‐ray neutron probe (CRNP) were intercompared. The comparison showed that the conventional nonlinear method performed the best. Furthermore, to assimilate fast neutrons using the particle filter, the STEMMUS‐FT (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) model was used as the physically based process model, and the COSMIC model (Cosmic‐ray Soil Moisture Interaction Code) used as the observation operator (i.e., forward neutron simulator). Other than background inputs from disturbed initializations in the STEMMUS‐FT, model uncertainties were predefined to assimilate fast neutrons. We observed that with enough spread of uncertainties, the updated states could mimic the CRNP observation. In all setups, assimilating CRNP measurements could enhance total soil water analyses, which consequently led to the improved detection of soil ice content and therefore the freezing thawing‐process at the field scale.
Original languageEnglish
Article numbere2019JD031529
Pages (from-to)1-23
Number of pages23
JournalJournal of geophysical research : Atmospheres
Volume125
Issue number3
Early online date24 Jan 2020
DOIs
Publication statusPublished - 16 Feb 2020

Fingerprint

neutron probe
plateau
ice
soil moisture
soil
liquid
soil water
COSMIC
frozen ground
cold region
cosmic ray
simulation
simulator
freezing
momentum
water vapor
assimilation
filter
winter
energy

Keywords

  • ITC-ISI-JOURNAL-ARTICLE
  • ITC-HYBRID
  • UT-Hybrid-D

Cite this

@article{2eedb136b8774b2ba62d564a13b81106,
title = "Assimilation of cosmic‐ray neutron counts for the estimation of soil ice content on the eastern Tibetan Plateau",
abstract = "Accurate observations and simulations of soil moisture phasal forms are crucial in cold region hydrological studies. In the seasonally frozen ground of eastern Tibetan Plateau, water vapor, liquid, and ice coexist in the frost‐susceptible silty‐loam soil during winter. Quantification of soil ice content is thus vital in the investigation and understanding of the region's freezing‐thawing processes. This study focuses on the retrieval of soil ice content utilizing the in situ soil moisture (i.e., liquid phase) and cosmic ray neutron measurements (i.e., total water including liquid and ice), with Observing System Simulation Experiments. To derive the total soil water from neutron counts, different weighting methods (revised, conventional, and uniform) for calibrating the cosmic‐ray neutron probe (CRNP) were intercompared. The comparison showed that the conventional nonlinear method performed the best. Furthermore, to assimilate fast neutrons using the particle filter, the STEMMUS‐FT (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) model was used as the physically based process model, and the COSMIC model (Cosmic‐ray Soil Moisture Interaction Code) used as the observation operator (i.e., forward neutron simulator). Other than background inputs from disturbed initializations in the STEMMUS‐FT, model uncertainties were predefined to assimilate fast neutrons. We observed that with enough spread of uncertainties, the updated states could mimic the CRNP observation. In all setups, assimilating CRNP measurements could enhance total soil water analyses, which consequently led to the improved detection of soil ice content and therefore the freezing thawing‐process at the field scale.",
keywords = "ITC-ISI-JOURNAL-ARTICLE, ITC-HYBRID, UT-Hybrid-D",
author = "Samuel Mwangi and Yijian Zeng and Carsten Montzka and Lianyu Yu and Zhongbo Su",
year = "2020",
month = "2",
day = "16",
doi = "10.1029/2019JD031529",
language = "English",
volume = "125",
pages = "1--23",
journal = "Journal of geophysical research : Atmospheres",
issn = "2169-897X",
publisher = "Wiley-Blackwell",
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}

Assimilation of cosmic‐ray neutron counts for the estimation of soil ice content on the eastern Tibetan Plateau. / Mwangi, Samuel; Zeng, Yijian; Montzka, Carsten; Yu, Lianyu; Su, Zhongbo.

In: Journal of geophysical research : Atmospheres, Vol. 125, No. 3, e2019JD031529, 16.02.2020, p. 1-23.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Assimilation of cosmic‐ray neutron counts for the estimation of soil ice content on the eastern Tibetan Plateau

AU - Mwangi, Samuel

AU - Zeng, Yijian

AU - Montzka, Carsten

AU - Yu, Lianyu

AU - Su, Zhongbo

PY - 2020/2/16

Y1 - 2020/2/16

N2 - Accurate observations and simulations of soil moisture phasal forms are crucial in cold region hydrological studies. In the seasonally frozen ground of eastern Tibetan Plateau, water vapor, liquid, and ice coexist in the frost‐susceptible silty‐loam soil during winter. Quantification of soil ice content is thus vital in the investigation and understanding of the region's freezing‐thawing processes. This study focuses on the retrieval of soil ice content utilizing the in situ soil moisture (i.e., liquid phase) and cosmic ray neutron measurements (i.e., total water including liquid and ice), with Observing System Simulation Experiments. To derive the total soil water from neutron counts, different weighting methods (revised, conventional, and uniform) for calibrating the cosmic‐ray neutron probe (CRNP) were intercompared. The comparison showed that the conventional nonlinear method performed the best. Furthermore, to assimilate fast neutrons using the particle filter, the STEMMUS‐FT (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) model was used as the physically based process model, and the COSMIC model (Cosmic‐ray Soil Moisture Interaction Code) used as the observation operator (i.e., forward neutron simulator). Other than background inputs from disturbed initializations in the STEMMUS‐FT, model uncertainties were predefined to assimilate fast neutrons. We observed that with enough spread of uncertainties, the updated states could mimic the CRNP observation. In all setups, assimilating CRNP measurements could enhance total soil water analyses, which consequently led to the improved detection of soil ice content and therefore the freezing thawing‐process at the field scale.

AB - Accurate observations and simulations of soil moisture phasal forms are crucial in cold region hydrological studies. In the seasonally frozen ground of eastern Tibetan Plateau, water vapor, liquid, and ice coexist in the frost‐susceptible silty‐loam soil during winter. Quantification of soil ice content is thus vital in the investigation and understanding of the region's freezing‐thawing processes. This study focuses on the retrieval of soil ice content utilizing the in situ soil moisture (i.e., liquid phase) and cosmic ray neutron measurements (i.e., total water including liquid and ice), with Observing System Simulation Experiments. To derive the total soil water from neutron counts, different weighting methods (revised, conventional, and uniform) for calibrating the cosmic‐ray neutron probe (CRNP) were intercompared. The comparison showed that the conventional nonlinear method performed the best. Furthermore, to assimilate fast neutrons using the particle filter, the STEMMUS‐FT (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) model was used as the physically based process model, and the COSMIC model (Cosmic‐ray Soil Moisture Interaction Code) used as the observation operator (i.e., forward neutron simulator). Other than background inputs from disturbed initializations in the STEMMUS‐FT, model uncertainties were predefined to assimilate fast neutrons. We observed that with enough spread of uncertainties, the updated states could mimic the CRNP observation. In all setups, assimilating CRNP measurements could enhance total soil water analyses, which consequently led to the improved detection of soil ice content and therefore the freezing thawing‐process at the field scale.

KW - ITC-ISI-JOURNAL-ARTICLE

KW - ITC-HYBRID

KW - UT-Hybrid-D

UR - https://ezproxy2.utwente.nl/login?url=https://library.itc.utwente.nl/login/2020/isi/zeng_ass.pdf

U2 - 10.1029/2019JD031529

DO - 10.1029/2019JD031529

M3 - Article

VL - 125

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JO - Journal of geophysical research : Atmospheres

JF - Journal of geophysical research : Atmospheres

SN - 2169-897X

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M1 - e2019JD031529

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