Integral quantification of seasonal soil moisture changes in farmland by cosmic-ray neutrons

Abstract

Abstract. Soil moisture at the plot or hill-slope scale is an important link between local vadose zone hydrology and catchment hydrology. However, so far only a few methods are on the way to close this gap between point measurements and remote sensing. One new measurement methodology that could determine integral soil moisture at this scale is the aboveground sensing of cosmic-ray neutrons, more precisely of ground albedo neutrons. The present study performed ground albedo neutron sensing (GANS) at an agricultural field in northern Germany. To test the method it was accompanied by other soil moisture measurements for a summer period with corn crops growing on the field and a later autumn-winter period without crops and a longer period of snow cover. Additionally, meteorological data and aboveground crop biomass were included in the evaluation. Hourly values of ground albedo neutron sensing showed a high statistical variability. Six-hourly values corresponded well with classical soil moisture measurements, after calibration based on one reference dry period and three wet periods of a few days each. Crop biomass seemed to influence the measurements only to minor degree, opposed to snow cover which has a more substantial impact on the measurements. The latter could be quantitatively related to a newly introduced field neutron ratio estimated from neutron counting rates of two energy ranges. Overall, our study outlines a procedure to apply the ground albedo neutron sensing method based on devices now commercially available, without the need for accompanying numerical simulations and suited for longer monitoring periods after initial calibration.

Investigating temporal field sampling strategies for site-specific calibration of three soil moisture–neutron intensity parameterisation methods

“…Although a number of investigations have used single calibration points from measured soil moisture profiles for each of the three methods (Rivera Villarreyes et al, 2011;Zreda et al, 2012;Franz et al, 2013c;Bogena et al, 2013;Baatz et al, 2014), to our record, there has been no previous study on whether this is feasible for each of these three methods at distinct sites. The fact that hydrogen pools (e.g.…”

“…The fact that hydrogen pools (e.g. biomass, litter layer water) vary differently over time than soil moisture content profiles, and that not all these hydrogen pools can always be monitored completely and accurately Rivera Villarreyes et al, 2011), could be a complicating factor. Therefore we posed the following research questions:…”

Estimating field-scale root zone soil moisture using the cosmic-ray neutron probe

“…Cosmic-ray neutron probes have been shown to be successful in measuring field-scale soil moisture in a variety of environments and regions (e.g. Rivera Villarreyes et al, 2011;Franz et al, 2012a;Bogena et al, 2013;Hawdon et al, 2014), and have potential for validating remote sensing data (Crow et al, 2012;Hornbuckle et al, 2012;Dong et al, 2014). The cosmic-ray neutron probe holds great promise; however, the effective measurement depth is less than 30 cm for most soils (Franz et al, 2012b), requiring upscaling with depth to be representative of the entire root zone.…”

Application of cosmic-ray neutron sensing to monitor soil water content in an alpine meadow ecosystem on the northern Tibetan Plateau

“…The analysis and correction of the influences of atmospheric pressure, water vapor, solar activity and aboveground biomass on the neutrons have been studied (Desilets and Zreda, 2001;Moraal et al, 2005;Rosolem et al, 2013;Coopersmith et al, 2014;McJannet et al, 2014;Baatz et al, 2015) and can improve the accuracy of the CRNS. These studies have built the foundation for the application of the CRNS method (Rivera villarreyes et al, 2011;Bogena et al, 2013;Han et al, 2014;Wang et al, 2015).…”