Introduction➢ Quantifying surface and root-zone soil moisture spatial variability remains

decisive in agriculture, hydrology, ecology, and climatology.

➢ There is a gap between traditional point-level sensors and remote sensing soil moisture products.

➢ A roving Cosmic-ray Soil Moisture Observing System (COSMOS) has great potential to monitor soil moisture at the hectometer scale and to bridge the gap between existing technologies.

➢ COSMOS a non-invasive soil moisture sensing technology based on background epithermal neutrons (EN).

➢ EN are moderated mainly by hydrogen atoms, thus a direct relationship can be established with soil water content.

➢ The are under study had a spatial domain of 77 km2 and was located near Gypsum, KS.

➢ The COSMOS rover was used to conduct bi-weekly transects of 160 km of soil and gravel county roads.

Objetive: calibrate the roving COSMOS probe and analyze the sensitivity of

the instrument to different soil moisture conditions

Figure 2: Aerial image of the study area. Orange dots show the rover transect, blue dots indicate calibration sites, and yellow dot indicates the Kansas Mesonetstation. (Photo by GoogleEarth).

➢ Three calibration sites were selected. Radial volumetric soil sampling (0 to 15cm depth) was used to calibrate the sensor.

➢ Neutron counts were corrected and calibrated to estimate volumetric water content.

Figure 1: COSMOS rover mounted on the truck while conducting a field calibration field (A), taking measures next to the Mesonet station at Gypsum, KS (B), taking volumetric soil samples(C) .

Conclusions

Sensitivity Calibration Spatial analysis

Figure 4: Calibrated curve for corrected neutrons curve to volumetric water content.

➢ COSMOS rover was able to capture soil moisture spatial patterns across the studied landscape, resolution 30x30 meters.

➢ COSMOS rover was capable of detecting soil moisture spatial patterns at the landscape scale, which can be used to i) validate coarse-resolution remote sensing soil moisture products; ii) inform hydrological and crop models; and iii) upscale in situ soil moisture monitoring stations.

➢ Future work will be focused on better understanding the factors controlling soil moisture spatial variability at the landscape scale.

Figure 5: Volumetric soil water content estimated from Cosmos. Black dots denote the rover transect. Date 08/02/17.

Figure 6: Volumetric soil water content estimated from Cosmos. Black dots denote rover transect. Date 10/17/17.

Acknowledgement: Kansas Soybean Commission / Farmer: Justin Knopf & Garrett Kennedy

Results

Materials and Methods

➢ Neutron counts ranged from 215 cpm to 409 cpm, indicating high sensitivity to changes in soil moisture conditions.

Landscape-scale Soil Moisture Monitoring Using Cosmic-ray NeutronsPedro Rossini1, Samuel Long1, Vibhavi Jayasinghe1, Andres Patrignani1

1Department of Agronomy, Kansas State University, 2004 Throckmorton Hall, Manhattan, KS, 66506prossini@ksu.edu

Φ0= neutron count dry soil, W𝑙𝑎𝑡=water lattice, WSOC= water in the Organic matter, 𝜌𝑏= bulk density

Φ0 = 550 cpmRMSE= 0.015

Figure 3: Distribution of corrected neutron counts through different water conditions.

Before rainfall event After rainfall event

A

B C