Effective Calibration of Low-Cost Soil Water Content Sensors

Soil water content is a key variable for understanding and modelling ecohydrological processes. Low-cost electromagnetic sensors are increasingly being used to characterize the spatio-temporal dynamics of soil water content, despite the reduced accuracy of such sensors as compared to reference electromagnetic soil water content sensing methods such as time domain reflectometry. Here, we present an effective calibration method to improve the measurement accuracy of low-cost soil water content sensors taking the recently developed SMT100 sensor (Truebner GmbH, Neustadt, Germany) as an example. We calibrated the sensor output of more than 700 SMT100 sensors to permittivity using a standard procedure based on five reference media with a known apparent dielectric permittivity (1 < Ka < 34.8). Our results showed that a sensor-specific calibration improved the accuracy of the calibration compared to single “universal” calibration. The associated additional effort in calibrating each sensor individually is relaxed by a dedicated calibration setup that enables the calibration of large numbers of sensors in limited time while minimizing errors in the calibration process.

[1]  Steven R. Evett,et al.  The Soil Moisture Active Passive Marena, Oklahoma, In Situ Sensor Testbed (SMAP‐MOISST): Testbed Design and Evaluation of In Situ Sensors , 2016 .

[2]  Guoqing Zhou,et al.  Estimation of Soil Moisture from Optical and Thermal Remote Sensing: A Review , 2016, Sensors.

[3]  Wenting Han,et al.  A survey on wireless sensor network infrastructure for agriculture , 2013, Comput. Stand. Interfaces.

[4]  Y. Kerr,et al.  State of the Art in Large-Scale Soil Moisture Monitoring , 2013 .

[5]  Robert B. Jackson,et al.  A Global Analysis of Groundwater Recharge for Vegetation, Climate, and Soils , 2012 .

[6]  Harry Vereecken,et al.  Sensor‐to‐Sensor Variability of the ECH2O EC‐5, TE, and 5TE Sensors in Dielectric Liquids , 2010 .

[7]  H. Hendricks Franssen,et al.  An empirical vegetation correction for soil water content quantification using cosmic ray probes , 2015 .

[8]  Yoshihiro Kawahara,et al.  Low-Cost Soil Moisture Profile Probe Using Thin-Film Capacitors and a Capacitive Touch Sensor , 2016, Sensors.

[9]  Johan Alexander Huisman,et al.  The integrated water balance and soil data set of the Rollesbroichhydrological observatory , 2016 .

[10]  Jan Vanderborght,et al.  Predicting subgrid variability of soil water content from basic soil information , 2015 .

[11]  Tissa H. Illangasekare,et al.  Empirical two‐point α‐mixing model for calibrating the ECH2O EC‐5 soil moisture sensor in sands , 2008 .

[12]  A. Western,et al.  Seasonal and event dynamics of spatial soil moisture patterns at the small catchment scale , 2012 .

[13]  J. Miller,et al.  Measurement of Soil Water Content Using a Simplified Impedance Measuring Technique , 1996 .

[14]  Johan Alexander Huisman,et al.  Correction of Temperature and Electrical Conductivity Effects on Dielectric Permittivity Measurements with ECH2O Sensors , 2011 .

[15]  H. Vereecken,et al.  Effects of Soil Hydraulic Properties on the Spatial Variability of Soil Water Content: Evidence from Sensor Network Data and Inverse Modeling , 2014 .

[16]  Gerrit H. de Rooij,et al.  Methods of Soil Analysis. Part 4. Physical Methods , 2004 .

[17]  A. P. Annan,et al.  Electromagnetic determination of soil water content: Measurements in coaxial transmission lines , 1980 .

[18]  R. Schulin,et al.  Calibration of time domain reflectometry for water content measurement using a composite dielectric approach , 1990 .

[19]  Günter Blöschl,et al.  Preferred states in spatial soil moisture patterns: Local and nonlocal controls , 1997 .

[20]  R. Knight,et al.  Soil Moisture Measurement for Ecological and Hydrological Watershed‐Scale Observatories: A Review , 2008 .

[21]  H. Vereecken,et al.  A terrestrial observatory approach to the integrated investigation of the effects of deforestation on water, energy, and matter fluxes , 2014, Science China Earth Sciences.

[22]  C. G. Gardner,et al.  High dielectric constant microwave probes for sensing soil moisture , 1974 .

[23]  Scott B. Jones,et al.  Standardizing Characterization of Electromagnetic Water Content Sensors: Part 1. Methodology , 2005 .

[24]  Irena Hajnsek,et al.  TERENO - Long-term monitoring network for terrestrial environmental research , 2012 .

[25]  Svatopluk Matula,et al.  Laboratory Performance of Five Selected Soil Moisture Sensors Applying Factory and Own Calibration Equations for Two Soil Media of Different Bulk Density and Salinity Levels , 2016, Sensors.

[26]  Peter Dietrich,et al.  Spatial and Temporal Dynamics of Hillslope‐Scale Soil Moisture Patterns: Characteristic States and Transition Mechanisms , 2015 .

[27]  Johan Alexander Huisman,et al.  Emerging methods for noninvasive sensing of soil moisture dynamics from field to catchment scale: a review , 2015 .

[28]  Mark S. Seyfried,et al.  Measurement of soil water content with a 50-MHz soil dielectric sensor , 2004 .

[29]  Udo Kaatze,et al.  Dielectric Relaxation Spectrometry of Mixtures of Water with Isopropoxy- and Isobutoxyethanol. Comparison to Unbranched Poly(ethylene glycol) Monoalkyl Ethers , 1996 .

[30]  Heather McNairn,et al.  Calibration and Evaluation of a Frequency Domain Reflectometry Sensor for Real‐Time Soil Moisture Monitoring , 2015 .

[31]  Yves Tramblay,et al.  Assessment of initial soil moisture conditions for event-based rainfall–runoff modelling , 2010 .

[32]  Mike Schwank,et al.  Laboratory Characterization of a Commercial Capacitance Sensor for Estimating Permittivity and Inferring Soil Water Content , 2006 .

[33]  M. G. Hodnett,et al.  The dielectric calibration of capacitance probes for soil hydrology using an oscillation frequency response model , 1998 .

[34]  John S. McCartney,et al.  Calibration of Capacitance Sensors for Compacted Silt in Non-Isothermal Applications , 2016 .

[35]  S. Seneviratne,et al.  Investigating soil moisture-climate interactions in a changing climate: A review , 2010 .

[36]  S. Jones,et al.  A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry , 2003 .

[37]  Scott B. Jones,et al.  Standardizing Characterization of Electromagnetic Water Content Sensors: Part 2. Evaluation of Seven Sensing Systems , 2005 .

[38]  Johan Alexander Huisman,et al.  Calibration of a Novel Low‐Cost Soil Water Content Sensor Based on a Ring Oscillator , 2013 .

[39]  Scott B. Jones,et al.  A time domain transmission sensor with TDR performance characteristics , 2005 .

[40]  Rachel Cardell-Oliver,et al.  Wireless soil moisture sensor networks for environmental monitoring and vineyard irrigation , 2009 .

[41]  H. Vereecken,et al.  Evaluation of a low-cost soil water content sensor for wireless network applications , 2007 .

[42]  Jan W. Hopmans,et al.  Frequency, electrical conductivity and temperature analysis of a low-cost capacitance soil moisture sensor , 2008 .