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

Authors

Lena M. Scheiffele, Institute of Environmental Science and Geography, University of Potsdam, GermanyFollow
Gabriele Baroni, University of Bologna, Bologna, Italy
Trenton E. Franz, University of Nebraska - LincolnFollow
Jannis Jakobi, Agrosphere Institute, Julich, Germany
Sascha E. Oswald, University of Potsdam, Potsdam, Germany

ORCID IDs

Lena M. Scheiffele https://orcid.org/0000-0003-3621-680X

Gabriele Baroni https://orcid.org/0000-0003-2873-7162

Trenton E. Franz https://orcid.org/0000-0003-2947-0906

Jannis Jakobi https://orcid.org/0000-0002-3695-010X

Sascha E. Oswald https://orcid.org/0000-0003-1667-0060

Document Type

Article

Date of this Version

10-4-2020

Citation

Vadose Zone J. 2020;19:e20083.

DOI: 10.1002/vzj2.20083

Comments

CC-BY

Abstract

n 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 distanceProfile-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.