Preprints
https://doi.org/10.5194/hess-2023-169
https://doi.org/10.5194/hess-2023-169
24 Jul 2023
 | 24 Jul 2023
Status: this preprint is currently under review for the journal HESS.

Technical Note: revisiting the general calibration of cosmic-rayneutron sensors to estimate soil water content

Maik Heistermann, Till Francke, Martin Schrön, and Sascha E. Oswald

Abstract. Cosmic-ray neutron sensing (CRNS) is becoming increasingly popular for monitoring soil water content (SWC). To retrieve SWC from observed neutron intensities, local measurements of SWC are typically required to calibrate a location-specific parameter, N0, in the corresponding transfer function. In this study, we develop a generalized conversion function that explicitly takes into account the different factors that govern local neutron intensity. That way, the parameter N0 becomes location-independent, i.e., generally applicable. We demonstrate the feasibility of such a "general calibration function" by analysing 75 CRNS sites from four recently published datasets. Given the choice between the two calibration strategies – local or general – users will wonder which one is preferable. To answer this question, we estimated the resulting uncertainty of the SWC by means of error propagation. While the uncertainty of the local calibration depends on both the local reference SWC itself and its error, the uncertainty of the general calibration is mainly governed by the errors of vegetation biomass and soil bulk density. An interactive online tool is provided to support the decision decide which calibration strategy – local or general – is preferable in the user-specific application context (https://cosmic-sense.github.io/local-or-global).

Maik Heistermann et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'missing supplementary?', Jingnuo Dong, 16 Aug 2023 reply
    • AC1: 'Reply on CC1', Maik Heistermann, 17 Aug 2023 reply
      • CC2: 'Reply on AC1', Jingnuo Dong, 17 Aug 2023 reply
  • RC1: 'Comment on hess-2023-169', Anonymous Referee #1, 28 Aug 2023 reply
    • AC2: 'Reply on RC1', Maik Heistermann, 11 Sep 2023 reply

Maik Heistermann et al.

Maik Heistermann et al.

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Short summary
Cosmic-ray neutron sensing (CRNS) is a non-invasive technique to obtain estimates of soil water content (SWC) at a horizontal footprint of around 150 m and a vertical penetration depth of around 30 cm. However, typical CRNS applications require the local calibration of a function which converts neutron counts to SWC. As an alternative, we propose a generalized function as a way to avoid the usage of local reference measurements of SWC and hence a major source of uncertainty.