Preprints
https://doi.org/10.5194/hess-2022-123
https://doi.org/10.5194/hess-2022-123
 
11 Apr 2022
11 Apr 2022
Status: this preprint was under review for the journal HESS. A revision for further review has not been submitted.

On soil bulk density and its influence to soil moisture estimation with cosmic-ray neutrons

Mandy Kasner, Steffen Zacharias, and Martin Schrön Mandy Kasner et al.
  • UFZ – Helmholtz Centre for Environmental Research GmbH, Leipzig, Germany

Abstract. Cosmic-ray neutron sensing (CRNS) is a non-invasive technique that is used to quantify soil moisture in a representative footprint of 10–20 ha and 15–80 cm depth. In a stationary mode, CRNS is widely employed to monitor the moisture dynamics on agricultural land, which may undergo active changes of the soil compartments, e.g. due to plowing. On mobile platforms, CRNS measurements aim at mapping the spatial soil moisture distribution across various types of soil and land use. To date, the potential effect of variable soil bulk density on the neutron measurements has not been investigated in detail. In fact, most sensors are calibrated only once on site-specific soil properties. Therefore we hypothesize that unaccounted spatiotemporal changes of soil bulk density may have impact on the quality of CRNS soil moisture products.

In this study, we quantify the effect of the soil density on the neutron response by neutron transport simulations and a dedicated lab experiment. The results indicate a significant dependency of neutrons on soil bulk density, which also depends on the soil moisture state. For the hypothetical cases with constant ratio between soil density and water content, the neutron intensity remains unaffected.

Correction functions are proposed to improve the performance of two widely used approaches to convert neutrons to soil moisture (Desilets et al. 2010, and Köhli et al. 2021). The latter approach together with the proposed correction can be recommended for practical use, as it accurately represented the simulated neutron response to soil moisture and soil bulk density with a constant – and potentially universal – calibration parameter.

Mandy Kasner et al.

Status: closed (peer review stopped)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-123', Anonymous Referee #1, 10 May 2022
    • AC1: 'Reply on RC1', Martin Schrön, 24 Jul 2022
  • RC2: 'Comment on hess-2022-123', Anonymous Referee #2, 13 Jun 2022
    • AC2: 'Reply on RC2', Martin Schrön, 24 Jul 2022
  • EC1: 'Comment on hess-2022-123 - Start interacting', Nunzio Romano, 21 Jun 2022
  • RC3: 'Comment on hess-2022-123', Anonymous Referee #3, 26 Jun 2022
    • AC3: 'Reply on RC3', Martin Schrön, 24 Jul 2022

Status: closed (peer review stopped)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-123', Anonymous Referee #1, 10 May 2022
    • AC1: 'Reply on RC1', Martin Schrön, 24 Jul 2022
  • RC2: 'Comment on hess-2022-123', Anonymous Referee #2, 13 Jun 2022
    • AC2: 'Reply on RC2', Martin Schrön, 24 Jul 2022
  • EC1: 'Comment on hess-2022-123 - Start interacting', Nunzio Romano, 21 Jun 2022
  • RC3: 'Comment on hess-2022-123', Anonymous Referee #3, 26 Jun 2022
    • AC3: 'Reply on RC3', Martin Schrön, 24 Jul 2022

Mandy Kasner et al.

Mandy Kasner et al.

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Short summary
Cosmic-ray neutron sensing (CRNS) is a non-invasive technique that is used to quantify field-scale root-zone soil moisture. We hypothesize that unaccounted spatiotemporal changes of soil density may have impact on the quality of CRNS soil moisture products. Our results indicate a significant dependency of neutrons on soil density, which also depends on the soil moisture state. A correction approach is provided that can be recommended for practical use.