Testing of a commercial vector network analyzer as low-cost TDR device to measure soil moisture and electrical conductivity

Moret-Fernández, David ; Lera, Francisco (Universidad de Zaragoza) ; Latorre, Borja ; Tormo, Jaume (Universidad de Zaragoza) ; Revilla, Jesús

Resumen: Time Domain Reflectometry (TDR) is a non-destructive technique to determine the soil apparent dielectric constant, εa, the volumetric water content, θ, and bulk electrical conductivity, σ. However, the high cost of TDR devices may limit its use. This study evaluates two different low-cost Vector Network Analyzers (VNA) commercially available (NanoVNA), with 1.5 (VNA1.5) and 3.0 (VNA3.0) GHz maximum operating frequency. NanoVNA can be used for measurements of Frequency Domain Reflectometry (FDR) or, after suitable post-processing, for θ and σ TDR measures. Although FDR and TDR are dual procedures, TDR is easier to interpret for soil experiments. The TDR waveforms and εa measured with NanoVNA connected to 10 and 20 cm length three-rod probes immersed in air, distilled water, and a soil column with different θ were compared to those measured using a TDR100 (Campbell Sci.) instrument. The capacity of VNAs to measure σ was evaluated by immersing a 10 cm length three-rod probe in different NaCl-water solutions. Measurements obtained with the VNA and TDR100 were compared in a field test using two-rod 22 cm length TDR probes inserted in soil plots with increasing water content. A robust fit was observed between TDR waveforms registered with the two VNAs and the TDR100. Although VNA3.0 doubles the frequency range of VNA1.5, both devices allowed for good estimates of εa (εaVNA1.5, 3.0 = 1.001 εaTDR100 – 0.2125; R2 = 0.999). These results indicate that the low-cost VNA devices can measure soil water content with similar accuracy and precision as the TDR100. A good agreement (σVNA1.5, 3.0 = 0.999 σCM + 0.0023; R2 = 0.999) was also observed between the σ measured using a conductivity meter (CM) and that estimated with the VNAs. Finally, a good correlation was also observed between θ measured in the field experiment with TDR100 and the VNA1.5 and VNA3.0 devices.

Idioma: Inglés

DOI: 10.1016/j.catena.2022.106540

Año: 2022

Publicado en: Catena 218 (2022), 106540 [8 pp.]
ISSN: 0341-8162

Factor impacto JCR: 6.2 (2022)

Categ. JCR: GEOSCIENCES, MULTIDISCIPLINARY rank: 17 / 202 = 0.084 (2022) - Q1 - T1
Categ. JCR: SOIL SCIENCE rank: 7 / 37 = 0.189 (2022) - Q1 - T1
Categ. JCR: WATER RESOURCES rank: 12 / 103 = 0.117 (2022) - Q1 - T1

Factor impacto CITESCORE: 9.8 - Earth and Planetary Sciences (Q1)

Factor impacto SCIMAGO: 1.472 - Earth-Surface Processes (Q1)

Financiación: info:eu-repo/grantAgreement/ES/MINECO/PGC2018-094332-B-I00

Tipo y forma: Artículo (Versión definitiva)

Área (Departamento): Área Ecología (Dpto. CC.Agrar.y Medio Natural)
Área (Departamento): Área Teoría Señal y Comunicac. (Dpto. Ingeniería Electrón.Com.)