Uncertainty, sensitivity and improvements in soil moisture estimation with cosmic-ray neutron sensing

Baroni, Gabriele; Scheiffele, Lena; Schrön, Martin; Ingwersen, Joachim; Oswald, Sascha E.

doi:10.1016/j.jhydrol.2018.07.053

Cited by 69 publications

(56 citation statements)

References 57 publications

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“…Profile shape correction procedure Baroni et al (2018) proposed a simple profile shape correction to apply to CRNS-derived soil moisture. It accounts for the sensitivity of the sensor to the depth-dependent distribution of soil moisture within the profile.…”

Section: 3mentioning

confidence: 99%

A profile shape correction to reduce the vertical sensitivity of cosmic‐ray neutron sensing of soil moisture

Scheiffele

Baroni

Franz

et al. 2020

Vadose Zone Journal

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In recent years, cosmic-ray neutron sensing (CRNS) has shown a large potential among proximal sensing techniques to monitor soil moisture noninvasively, with high frequency and a large support volume (radius up to 240 m and sensing depth up to 80 cm). This signal is, however, more sensitive to closer distances and shallower depths. Inherently, CRNS-derived soil moisture is a spatially weighted value, different from an average soil moisture as retrieved by a sensor network. In this study, we systematically test a new profile shape correction on CRNS-derived soil moisture, based on additional soil moisture profile measurements and vertical unweighting, which is especially relevant during pronounced wetting or drying fronts. The analyses are conducted with data collected at four contrasting field sites, each equipped with a CRNS probe and a distributed soil moisture sensor network. After applying the profile shape correction on CRNS-derived soil moisture, it is compared with the sensor network average. Results show that the influence of the vertical sensitivity of CRNS on integral soil moisture values is successfully reduced. One to three properly located profile measurements within the CRNS support volume improve the performance. For the four investigated field sites, the RMSE decreased 11-53% when only one profile location was considered. We therefore recommend to install along with a CRNS at least one soil moisture profile in a radial distance <100 m and a measurement depth down to 50 cm. Profile-shape-corrected, CRNS-derived soil moisture is an unweighted integral soil moisture over the support volume, which is easier to interpret and easier to use for further applications.

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Section: 3mentioning

confidence: 99%

A profile shape correction to reduce the vertical sensitivity of cosmic‐ray neutron sensing of soil moisture

Scheiffele

Baroni

Franz

et al. 2020

Vadose Zone Journal

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“…The spatial interpolation was performed using local ordinary kriging (exponential model, nugget = 0.02, sill = 0.006, range = 39.3) with a maximum point distance of 50 m. Due to high vegetation cover, some parts of the SoilNet were inaccessible, thus causing gaps in the interpolated field. Since the vertical soil water profile is an important factor for CRNS measurements (Baroni et al, ), it is necessary to account for the exponentially decreasing neutron sensitivity with depth (Köhli et al, ). Therefore, we applied the vertical weighting approach presented by Schrön et al () and obtained weights of 0.58 and 0.42 for the 5 and 20 cm layers in the SoilNet area, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…We use information about soil bulk density ϱ bd and additional water equivalent θ offset (lattice water and organic carbon) from the SoilGrids database (Hengl et al, ; see values in Table ). Since bulk density is one of the most informative factors for the volumetric soil moisture product (Baroni et al, ), we use locally measured soil properties where available, for example, in the SoilNet area.…”

Section: Methods and Datamentioning

confidence: 99%

Synergies for Soil Moisture Retrieval Across Scales From Airborne Polarimetric SAR, Cosmic Ray Neutron Roving, and an In Situ Sensor Network

Fersch

Jagdhuber

Schrön

et al. 2018

Water Resources Research

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The consistent determination of soil moisture across scales is a persistent challenge in hydrology. Several measurement methods exist at distinct scales, each of which is challenging in terms of data processing, removal of vegetation and surface effects, and calibration. While in situ measurements are trusted at the point scale, distributed sensor networks extend the areal representation to the field scale. At this scale, also cosmic ray neutron sensing (CRNS) has become an established method to derive volume‐averaged, root zone soil moisture over several tens of hectometers, but the signal is often biased due to biomass water. With airborne synthetic aperture radar (SAR) remote sensing, it is possible to cover regional scales, but the method is limited to the topmost soil layer and sensitive to vegetation parameters. In this study, the performance and synergistic potential of these complementary methods is investigated for the determination of soil moisture within a 55 km2 Alpine foothill river catchment in Southern Germany. The individual approaches are evaluated and brought into synergy for a 9 ha grassland and several other locations within the catchment. The results indicate that the sensor network data provide valuable information to calibrate the mobile CRNS rover, and to optimize the vegetation removal within the polarimetric SAR retrieval algorithm. The root‐mean‐square errors for polarimetric SAR soil permittivity are 9.32 with the standard agriculture approach, 4.29 with the semi‐stand‐alone approach, and 0.31 with the sensor network optimized approach. Furthermore, the CRNS soil moisture product was improved by considering the remotely sensed cross‐polarized backscatter product as a biomass water proxy.

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“…The neutron intensity at ground level strongly depends on the incoming cosmic-ray neutron flux. Nevertheless, open questions about the suitability of neutron monitor data for local CRNS applications still exist, as pointed out by Schrön (2017) and Baroni et al (2018). To build the basis for a more thorough analysis in future studies, we take advantage of additional neutron detector instruments during the study period in Fendt, the so-called Mini-NM (Krüger et al, 2008), and Bonner Spheres (Bramblett et al, 1960;Rühm et al, 2012).…”

Section: Local Neutron Monitor and Bonner Spheresmentioning

confidence: 99%

“…Soil moisture profile probes were installed throughout the study area in order to monitor the vertical distribution of soil moisture over time. The vertical distribution pattern is not only affecting the vertical CRNS footprint (Köhli et al, 2015), but also allows to better constrain vertical water movement and thus groundwater recharge (Baroni et al, 2018).…”

Section: Soil Moisture Profile Probesmentioning

confidence: 99%

A dense network of cosmic-ray neutron sensors for soil moisture observation in a pre-alpine headwater catchment in Germany

Fersch

Francke

Heistermann

et al. 2020

Preprint

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Abstract. Monitoring soil moisture is still a challenge: it varies strongly in space and time and at various scales while well established sensors typically suffer from a small spatial support. With a sensor footprint up to several hectares, Cosmic-Ray Neutron Sensing (CRNS) is an emerging technology to address that challenge. So far, the CRNS method has typically been applied with single sensors or in sparse national scale networks. This study presents, for the first time, a dense network of 24 CRNS stations that covered, from May to July 2019, an area of just 1 km2: the pre-alpine Rott headwater catchment in Southern Germany which is characterized by strong soil moisture gradients in a heterogeneous landscape with forests and grasslands. With substantially overlapping sensor footprints, that network was designed to study root zone soil moisture dynamics at the catchment-scale. The observations of the dense CRNS network were complemented by extensive measurements that allow to study soil moisture variability at various spatial scales: roving (mobile) CRNS units, remotely sensed thermal images from Unmanned Areal Systems (UAS), permanent and temporary wireless sensor networks, profile probes as well as comprehensive manual soil sampling. Since neutron counts are also affected by hydrogen pools other than soil moisture, vegetation biomass was monitored in forest and grassland patches, as well as meteorological variables; discharge and groundwater tables were recorded to support hydrological modeling experiments. As a result, we provide a unique and comprehensive dataset to several research communities: to those who investigate the retrieval of soil moisture from cosmic-ray neutron sensing, to those who study the variability of soil moisture at different spatio-temporal scales, and to those who intend to better understand the role of root-zone soil moisture dynamics in the context of catchment and groundwater hydrology, as well as land – atmosphere exchange processes. The data set is available through EUDAT, splitted into the two subsets https://doi.org/10.23728/b2share.85fe0f9dac0f48df9215c17e65d1f1e1 (Fersch et al., 2020a) and https://doi.org/10.23728/b2share.93ed99e486904d48a8a6a68083066198 (Fersch et al., 2020b).

show abstract

Uncertainty, sensitivity and improvements in soil moisture estimation with cosmic-ray neutron sensing

Cited by 69 publications

References 57 publications

A profile shape correction to reduce the vertical sensitivity of cosmic‐ray neutron sensing of soil moisture

A profile shape correction to reduce the vertical sensitivity of cosmic‐ray neutron sensing of soil moisture

Synergies for Soil Moisture Retrieval Across Scales From Airborne Polarimetric SAR, Cosmic Ray Neutron Roving, and an In Situ Sensor Network

A dense network of cosmic-ray neutron sensors for soil moisture observation in a pre-alpine headwater catchment in Germany

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