Cosmogenic particles, such as neutrons and muons, have many practical applications in the earth and environmental sciences. One important application is measuring water content at and below the land surface using low-energy neutrons. The field of cosmic-ray hydrology provides the tools to measure soil water, snow water equivalent, or vegetation water, and water fluxes related to these reservoirs, such as precipitation and infiltration.

Cosmic-ray hydrology has its roots in cosmogenic geochronology, which uses cosmogenic isotopes to date depositional and erosional features on the land surface. In cosmic-ray paleohydrology geological proxy records are used to reconstruct past hydrologic conditions, such as precipitation rates or the distribution and size of water reservoirs. Such proxies should be clearly related to the environment, such as precipitation rates, lake levels, or river discharge in the geological past. This presentation will discuss several examples of geological records of ancient water systems, including mountain moraines, paleolake shorelines, river terraces, valley incisions, and ocean paleo-beaches. The combination of mountain moraine positions and their corresponding ages provides valuable information about the temperature and precipitation rates that allowed the glacier to reach the position marked by the moraines. Paleolake shorelines, dated with cosmogenic isotopes, offer insights into the size of the reservoir, which is useful in water mass balance reconstructions and paleoclimate studies. The height of river terraces indicates past river discharge rates at times determined through cosmogenic dating of the deposits. Dated valley incisions provide information on the last significant erosion episode, which is linked to high river discharge. Dated ocean paleobeaches provide a record of sea-level changes in the geological past.

Although measuring water reservoirs and fluxes today uses different tools than those which are used in paleohydrology, the two are linked by the cosmogenic particles that are at the heart of these tools.

How to cite: Zreda, M.: Cosmic-ray paleohydrology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22534, https://doi.org/10.5194/egusphere-egu24-22534, 2024.

While the sun, as the primary source of energy on earth, is considered to have a constant energy output, small fluctuations can be observed over time. Historical records of solar activity (e.g., sunspot numbers) are however scarce, and only available over the last 400 years. Cosmogenic nuclides stored in tree rings (¹⁴C) or ice cores (¹⁰Be, ³⁶Cl) can be used as proxies for solar activity and allow solar reconstructions reaching much further back in time^1,2. However, only recently the presence of the eleven-year solar cycle could be revealed in an annually resolved ¹⁴C record from tree-rings covering the past 1000 years. The amplitude of this so called Schwabe cycles is found to correlate with the general level of the solar activity with high amplitudes during periods of strong solar activity and vice versa³.

Here, we present the solar activity, and specifically the 11-year cycles, reconstructed from ¹⁴C in tree-rings covering two grand solar minima, one around 400 BCE and another one around 3400 BCE. The results will be compared with the two previously analysed grand solar minima (Spörer and Maunder) of the last millennia, coinciding with the Little Ice Age.

¹ Bard, E. et al. (2000) Solar irradiance during the last 1200 years based on cosmogenic nuclides. Tellus Series B-Chemical and Physical Meteorology 52, 985-992.

² Muscheler, R. et al. (2007) Solar activity during the last 1000 yr inferred from radionuclide records. Quaternary Science Reviews 26, 82-97.

³ Brehm N. et al. (2021) Eleven-year solar cycles over the last millennium revealed by radiocarbon in tree rings. Nature Geoscience. 14(1), 10-15.

How to cite: Wacker, L., Brehm, N., Christl, M., Synal, H.-A., Pearson, C. C., Nicolussi, K., Pichler, T., Bayliss, A., Brown, D., and Bleicher, N.: Uncovering variations in solar activity through tree-ring radiocarbon measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15539, https://doi.org/10.5194/egusphere-egu24-15539, 2024.

A prerequisite to applying ¹⁰Be in natural archives for solar and geomagnetic reconstructions is to know how ¹⁰Be deposition reflects atmospheric production changes. However, this relationship remains debated. To address this, we use two state-of-the-art global models GEOS-Chem and ECHAM6.3-HAM2.3 with the latest beryllium production model. During solar modulation, both models suggest that ¹⁰Be deposition reacts proportionally to global production changes, with minor latitudinal deposition biases (<5%). During geomagnetic modulation, however, ¹⁰Be deposition changes are enhanced by ~15% in the tropics and attenuated by 20%-35% in subtropical and polar regions compared to global production changes. Such changes are also hemispherically asymmetric, attributed to asymmetric production between hemispheres. For the extreme solar proton event in A.D. 774/5, ¹⁰Be shows a 15% higher deposition increase in polar regions than in tropics. This study highlights the importance of atmospheric mixing when comparing ¹⁰Be from different locations or to independent geomagnetic field records.

How to cite: Zheng, M., Adolphi, F., Ferrachat, S., Mekhaldi, F., Lu, Z., Nilsson, A., and Lohmann, U.: Modeling atmospheric transport of cosmogenic radionuclide ¹⁰Be using GEOS-Chem 14.1.1 and ECHAM6.3-HAM2.3: implications for solar and geomagnetic reconstructions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2846, https://doi.org/10.5194/egusphere-egu24-2846, 2024.

Muography uses cosmic ray muons to image the inner structure of large
objects like geological formations or artificial buildings.
Cosmic muons have wide energy spectrum, while their slow energy loss is
proportional to the density and length of the traversed rock.
Counting these muons one measures the absorption of the overburden rock,
images its inner density structure and reveals anomalies (eg: ore, caves,
tunnels).
This multidisciplinary technology requires expertise in particle
physics instrumentation, geological knowledge, and industrial design,
to became a novel tool for geophysical surveys.
In the last decade several research groups started on various methods
to develop and demonstrate its practical usability.

The Innovative Gaseous Detector R&D Group in the Wigner RCP in Hungary is
a well-known team of the muography community that focuses on
technological advancement and applications. The group has used this
measurement technique in a number of mining, archaeological, and
speleological investigations. I will present the series of
measurements made for these subsurface applications with the results and
practical experiences of our group.

The success of any measurement is based on the right plan,
especially in muography, where devices are mounted into hardly-accessible
territories while measurements take up to several weeks or months.
Choosing the most suitable muograph type and geometry, and
estimate the required measurement time for expected anomalies are
essential. While in practice it is usually done by experience and educated
guess, for new challenges and complex structure it requires mathematical
modeling and computation, that could even be used to planning for
tomographic inversion series.
I will present the developed model for the direct problem,
verify it with laboratory measurements and underground raw data as well.

How to cite: Stefán, B. A., Balázs, L., Hamar, G., Surányi, G., and Varga, D.: Application of MWPC based muography in geophysics, experiments and planning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1013, https://doi.org/10.5194/egusphere-egu24-1013, 2024.

As Cosmic Ray Neutron Sensing (CRNS) gains increasing importance in Hydrology and other fields related to measurement of water in various form (notably Soil Moisture, Snow Water Equivalent, Biomass Water Equivalent), its large-scale application risks to be hindered by the complex calibration of site-specific parameters.

The success of CRNS comes from its ability to straightforwardly determine the amount of water content in soil and snow, overcoming limitations in scale representativity of more traditional technologies like point probes and satellites. A single, autonomous probe placed over the ground is in fact capable of delivering a real-time estimation of the Soil Moisture (SM) on a large scale (hectares) and in depth (tens of cm in soil, meters in snow).

CRNS is based on the fact that neutrons strongly interact with hydrogen, of which water is rich, therefore providing a correlation between the number of neutrons backscattered by the soil and the water content. The neutrons source is provided by the interaction of cosmic radiations with the atmosphere. Advantageous as it is to use a naturally available source, it comes with the drawback of having a natural variability that needs to be account for, which is usually done by refferring to a public network of cosmic neutrons observatories (the Neutron Monitor DataBase, NMDB). A second critical hurdle is calibration, requiring the determination of a site-specific reference value for the neutrons count rate through a complex campaign of soil sampling and analysis.

Finapp developed a patented detection technology characterized by the unique capability of contextually detecting muons, another kind of particle generated by cosmic rays. Since muons are not backscattered by the soil, their measurement is only related to the incoming flux. Years of measurements provide evidence of the correlation of local muons flux variations with the general trend of incoming neutrons as measured by NMDB stations.

Not only this offers the possibility to monitor the incoming flux variations locally without the need to rely on an external entity, but it furthermore suggests that the expected reference neutrons rate on a given site should be proportional to the measured muons flux. Although additional parameters will still need to be included to account for Additional Hydrogen Pools in the soil, this approach can greatly simplify the calibration procedure.

We will therefore present the state-of-the-art of the use of muons as a reference in CRNS and in particular early results of the novel muons-based calibration approach.

How to cite: Gazzola, E., Stevanato, L., Biasuzzi, B., Lunardon, M., Morselli, L., Gianessi, S., Zara, M., and Lorenzi, F.: Contextual detection of muons and neutrons as a way to self-referenced Cosmic Ray Neutron Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7468, https://doi.org/10.5194/egusphere-egu24-7468, 2024.

Cosmic Ray Neutron Sensing (CRNS) is a technique to measure water content, for example soil moisture, on the hectare scale through the measurement
of epithermal neutrons. The neutrons are results of particle showers in the earth’s atmosphere caused by cosmic rays impinging on it. The abundance and
global distribution of neutrons is changed in time through different factors. On the largest scale, the heliosphere and therefore the solar cycle greatly affect the amount of galactic cosmic rays that are able to reach earth. Large solar events, such as Forbush decreases, also cause rapid changes in the cosmic ray flux. The aim of any correction method is ultimately to account for these heliospheric changes.

The next smaller scale is the earth’s magnetic field. The biggest consequence here is an uneven distribution of neutrons across latitudes, as with increasing cut-off rigidity less cosmic rays are able to reach the atmosphere. This presents a challenge to correction methods based on neutron monitors, since any neutron measurement is always localised to specific geomagnetic and atmospheric conditions.

Lastly, the abundance of neutrons at different energy bands is strongly tied to the local conditions. In particular hydrogen abundance is of vital importance. The CRNS technique is based upon the sensitivity of neutrons to hydrogen, which is dependent on the energy of any given neutron. As these neutrons are still dependent on heliospheric and geomagnetic conditions, their measurement needs to be corrected for the amount and variation in incoming radiation. Neutron monitor based correction methods are tackling two challenges at the same time. Firstly, a neutron signal, free of local interference, needs to be extracted from the neutron monitor data. This signal is representative of the heliospheric conditions localised through the geomagnetic conditions to the neutron monitor site. Secondly, the signal needs to be localised to the point of the CRNS measurement, which rarely coincides with the position of a neutron monitor. Multiple correction methods have been evaluated and compared, with consideration towards both challenges.

How to cite: Hertle, L., Zacharias, S., and Schrön, M.: Comparison and evaluation of neutron monitor based incoming corrections for Cosmic Ray Neutron Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16578, https://doi.org/10.5194/egusphere-egu24-16578, 2024.

Accurate soil moisture estimation from Cosmic-ray neutron sensor (CRNS) entails necessary steps in pre-processing observed neutrons at the Earth's surface. One of the most important corrections to the measured neutron data is compensation for the influence of the atmosphere, also called the barometric effect (β). However, the correction for this effect is not universal, as values can vary depending on geographical location (i.e. cut-off rigidity), altitude, atmospheric conditions, and sensor type (i.e. energy range); hence, site-specific β values are required to reduce these offsets. In this study, 25 CRNS stations from around the world are used to estimate site-specific and to explore the sensitivity of β on soil moisture measurement with CRNS. The results obtained showed that β varied both spatially and temporally. Within the cut-off rigidity range of 1 to 4.5 GV where these sites are found, the average monthly for the investigated sites ranged between -0.53 to -0.96 %mbar. Although the cut-off rigidity range was small, we found an increasing relationship of β with increasing cut-off rigidity. In addition, we show how β affects soil moisture estimates through its effect on the atmospheric pressure correction during the CRNS calibration. The results of our study highlight the importance of site and sensor-specific for CRNS calibration and the correction of atmospheric effects on CRNS-derived soil moisture.

How to cite: Davies, P., Baatz, R., Bogena, H., Quansah, E., and Amekudzi, L.: Revisiting the barometric effect on cosmic-ray neutron soil moisture sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16814, https://doi.org/10.5194/egusphere-egu24-16814, 2024.

Continuous information on plant traits such as plant height, leaf area index (LAI), and above-ground biomass (AGB) is important in the study of plant growth and such information can help farmers achieve better yields while reducing agricultural inputs, e.g. through more efficient water use. Knowledge on plant traits is also key to further test and develop crop and land surface models. Cosmic-ray neutron sensors (CRNS) have primarily been used to determine soil moisture. Recently, Jakobi et al. (2022) found that thermal neutrons can be used to monitor aboveground biomass (ABG) and that the variations in measured thermal neutron intensity may also depend on the vegetation biomass and structure. However, different soil properties of the test sites may have influenced the results (e.g. related to differences in soil chemistry). In this follow-up study, a single agricultural field was investigated over a long measurement period (2015-2023) to avoid site-specific effects on the CRNS measurements. This new dataset contains different crop rotations with repetitions of the same crop and continuous measurements of plant height instead of sporadic biomass measurements. Based on this data, we developed regression models that take into account plant structure to predict traits (i.e. plant height and LAI) from observed thermal neutron intensity.

The annual regression models for plant height provided generally high R²-values (0.86 on average), with the highest values found for potato and winter wheat. An aggregation by crop type of the different seasons resulted in a slight reduction of the R² to 0.84 for winter wheat (3 seasons), 0.68 for sugar beet (2 seasons), and 0.75 for potato (2 seasons). The slope values of these regressions were distinctly different, thus supporting the assumption that the relationship between plant traits and thermal neutron intensity depends on vegetation structure. The root mean square error (RMSE) of the plant height predicted with thermal neutrons were 12 cm for winter wheat and 14 cm for both sugar beet and potato. In addition, we tested a prediction of LAI based on thermal neutrons. For this, we used a regression model that predicts LAI based on plant height (R²: 0.78). Using this model, we were able to predict the LAI for a period of 5 years with LAI observation data with an RMSE of 1.23 m/m, which is still within the uncertainty range of radiation-based LAI methods (Fang et al., 2019).  Independent validation was performed also against spatio-temporal LiDAR-based plant height and multispectral-based LAI measurements, each averaged for the CRNS footprint area. Our results demonstrate the potential of cosmic-ray neutron sensing for continuous monitoring of plant traits at the field scale.

Literature

Fang, H., F. Baret, S. Plummer and G. Schaepman‐Strub (2019): An overview of global leaf area index (LAI): Methods, products, validation, and applications. Reviews of Geophysics 57(3): 739-799. DOI: 10.1002/hyp.11274

Jakobi, J., J.A. Huisman, H. Fuchs, H. Vereecken and H. Bogena (2022): Potential of Thermal Neutrons to Correct Cosmic-Ray Neutron Soil Moisture Content Measurements for Dynamic Biomass Effects. Water Resour. Res. 58(8): e2022WR031972. DOI: 10.1029/2022WR031972

How to cite: Bogena, H., Jakobi, J., Brogi, C., Huisman, J. A., Bates, J., Montzka, C., and Schmidt, M.: A new application of cosmic neutron sensing for monitoring plant traits, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14860, https://doi.org/10.5194/egusphere-egu24-14860, 2024.

By 2050, the demand for food must increase by 50% to satisfy the needs of the expected 9 billion people. Precision agriculture, primarily driven by technology, aims to produce more with less input (i.e., water) by managing in-field soil and plant variability. Point measurement with traditional soil moisture sensors calls for a large number of sensors, thus increasing costs. The low spatial resolution and the limited measurement depth of the space-borne microwave sensors are not pertinent to field-scale and agricultural applications. Cosmic Ray Neutron Sensors (CRNS) emerge as an alternative technology for large-scale measurements of moisture (SM) content and biomass water equivalent (BWE). However, a lot of uncertainties are still in assessing the measurement footprint in space and depth. This work will explore the potential of combining high-resolution microwave L-band measurements using a UAV platform with CRNS to evaluate the spatial and temporal moisture content distribution. An experimental setup of one eddy covariance station and 2 Finapp CRNS (with and without Gadolinium) was installed on an alfalfa field  (Davis, California). TDR measurements were taken before and after irrigation at two different depths to calibrate both CRNS and Microwave L-band measurements. An on-site multispectral sensor (Arable) was used to monitor canopy development and to validate CRNS’ BWE and the microwave’s vegetation optical depth (VOD). The calibrated values were also compared with satellite measurements. Both CRNS and high-resolution microwave measurements showed promising results, especially when used in conjunction. However, research is still needed before unlocking the full commercial potential and mass adoption in the agricultural sector.    

How to cite: Daccache, A., Xu, N., and Puig, F.: Unleash the strength of precision irrigation with Portable L-band microwave and cosmic ray neutron sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16636, https://doi.org/10.5194/egusphere-egu24-16636, 2024.