Evaluation of a low-cost soil water content sensor for wireless network applications (original) (raw)
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Journal of Hydrology, 2008
This study evaluated the family of ECH 2 O sensors (EC-5 and ECH 2 O-TE) for measurement of soil moisture content (h), bulk electrical conductivity (EC b ) and temperature for a range of soils, across a range of measurement frequencies between 5 and 150 MHz. Measurement frequency is one of the primary factors affecting the sensitivity of capacitance sensor measurements to soil variables such as soil texture, electrical conductivity, and temperature. Measurements in both soil and solution demonstrated that the ECH 2 O EC and TE measurements were accurate. Using a measurement frequency of 70 MHz, a single calibration curve was determined for a range of mineral soils, independent of soil salinity, suggesting there might be no need for a soil specific calibration. When combining all data for each soil type, the R 2 values remained high (R 2 = 0.98) with little probe to probe variability. After laboratory calibration, the error for h was about 2%, independent of soil EC b , up to a soil solution EC of about 12 dS/m. Our results showed that a single calibration curve could be used for all tested mineral soils, independent of soil salinity. The bulk soil EC b -water content data were excellently described by a polynomial expression. Measurements of temperature sensitivity to soil water content and EC b were sufficiently small. For example, for a temperature change of 10°C, measurements of h and EC b were affected by about 0.02 cm 3 cm À3 and 0.02 dS/m, respectively. Limited sensor calibration requirements are important, when large networks of soil moisture sensors are being deployed. It is concluded that an accurate, cost-effective soil moisture sensor is available that operates at a measurement frequency of 70 MHz, with a low sensitivity to confounding soil environmental factors. ª
Evaluation of Standard Calibration Functions for Eight Electromagnetic Soil Moisture Sensors
Vadose Zone Journal, 2013
An increasing number of electromagnetic (EM) sensors are deployed to measure volumetric soil water content (q) for agricultural, ecological, and geotechnical applications. While impedance and capacitance sensors generally operate at frequencies between 20-300 MHz, time domain-reflectometry (TDR) and-transmissometry (TDT) function in the GHz range. In general, lower frequency sensors are less expensive but more sensitive to confounding effects of salinity, temperature, and soil textural variations. To simplify sensor application, factory-supplied calibrations are often provided for different porous media types such as mineral, organic, and saline soils, or soilless-substrates. The objective of the presented study was to evaluate the performance of eight commercially available EM moisture sensing systems (TDR 100, CS616, Theta Probe, Hydra Probe, SM300, Wet2, 5TE, 10HS) in seven well-characterized and texturally varying soils using a standardized approach. The validity of factory supplied-calibration relationships was evaluated and the influence of soil properties on the EM responses for q measurements was observed. Results indicate that the factory-supplied calibration relationships for groups of mineral and organic soils in general performed well, but some inconsistences were identified and suggestions for improvement are discussed. Soil-specific calibrations from this study yielded accuracies of around 0.015 m 3 m −3 for 10HS, SM300, and Theta Probe, while lower accuracies of about 0.025 m 3 m −3 were found for TDR100, CS616, Wet2, 5TE, and the Hydra Probe. These results are based on mineral soils having a large variation in texture, electrical conductivities below 2 dS m −1 , organic matter below 10%, and specific surface areas of less than 50 m 2 g −1 .
Laboratory Evaluation of a Commercial Dielectric Soil Water Sensor
Vadose Zone Journal, 2003
to measure these changes. The TDR method, for example, is based on the determination of the changes in Development of management strategies for efficient water utilizathe velocity of an electromagnetic pulse sent through a tion of crop production requires measurements of changes in soil water content on a dynamic basis. Many of the methods currently probe (wave-guide) inserted into the soil. Differences used for measuring these changes are destructive, slow, or relatively in time required for the pulse to traverse the length of expensive for large-scale investigations. A commercially available, the wave-guide and return depend on the soil dielectric low-cost, nondestructive soil moisture sensor for measuring changes constant and consequently on the soil VWC. in soil volumetric water content (VWC) on the basis of changes in Another technique that depends on the changes in the dielectric constant of the soil water was evaluated under laboratory the soil dielectric constant to measure water content conditions for two soil series (Amarillo fine sandy loam [fine-loamy, is the capacitance method. Here a capacitor (probe) is mixed, superactive, thermic Aridic Paleustalfs] and Pullman clay loam subjected to a specific voltage and the charge time is [fine, mixed, thermic Torretic Paleustolls]) and a potting material measured. The charge time is a function of the capaciacross a wide range of water contents. Probes were placed in containtance of the probe, which is directly related to the dielecers filled with deionized water and soil. Containers with Amarillo fine sandy loam were placed in a programmable temperature chamber tric constant of the medium (soil). and subjected to a series of changes in both temperature and VWC. Both TDR and capacitance methods depend on Containers with Pullman soil and potting material were only subjected changes in the soil dielectric constant to measure soil to changes in VWC at a constant temperature. Probe output at a VWC. Therefore, ease of use, and other factors affecting constant temperature between air dry and a VWC of 0.25 m 3 m Ϫ3 was the output of the instruments (e.g., temperature, salinlinear for the Pullman soil and potting material and nonlinear for the ity) become considerations in the choice of methods Amarillo soil. When the Amarillo soil temperature varied between (Wraith and Or, 1999; Or and Wraith, 1999; Baumhardt 15.9 and 39.1؇C Ϫ1 at a constant VWC, probe output changed the et al., 2000). equivalent of 0.10 m 3 m Ϫ3. The temperature sensitivity was 0.5 mV A low-cost capacitance probe is currently being man-؇C Ϫ1 for air-dry and about 5 mV ؇C Ϫ1 for wet Amarillo soil. We ufactured and is commercially available for use in a conclude that probe output is soil specific and, given the nonlinear response to increasing water content on some soils and sensitivity to wide range of soil types. The objective of this study was temperature, will require soil-specific calibration equations. to evaluate the effect of changes in water contents for two soil series and a potting material on the output and sensitivity of these probes under controlled laboratory conditions. In our study we did not compare the capaci
Performance Analysis of Dielectric Soil Moisture Sensor
Soil and Water Research, 2019
Soil moisture (SM) varies greatly in the soil profile. We developed a low-cost sensor for SM monitoring at three vertical depths. The sensor function was based on dielectric theory to monitor SM. Three linear calibration models were established using different soils. The sensor for each depth showed acceptable statistics of validations. The linear fit coefficient of determination (R2) ranged from 0.95 to 0.99. Root mean square error (RMSE) ranged from 1.35 to 4.30. The sensor performed consistently for at least 4 months, and is suitable for continuous monitoring of in situ SM and irrigation scheduling.
Japan Agricultural Research Quarterly: JARQ, 2012
When calibration tests of dielectric soil water sensors are conducted in a laboratory, it is of great importance to know the appropriate sample size for each sensor used. In the current study, appropriate sample sizes for different dielectric sensors of time domain reflectometry (TDR) systems (TDR100 with CS605 probe and TRIME-EZ), water content reflectometer (WCR) systems (CS615 and CS616), and an ECH2O (EC20) were examined experimentally using air-dried packed soil (Andosol) columns with diameters ranging from 70 to 150 mm; surrounded initially by air and then water. Although the output values of all dielectric sensors increased independently of the sample diameters when the samples were surrounded by water, the significances of these increases depended on the sample diameters. The result showed that a sample diameter adequate for the effective sensor sampling area of the TDR100 with the CS605 was ≥80 mm. Similarly, appropriate sample diameters were ≥150 mm for the TRIME-EZ, ≥100 mm for the CS615 and CS616, and ≥70 mm for the EC20, respectively. The differences in the appropriate sample diameters among sensors are due to the distribution of the electromagnetic energy of probes linked to their design. The results suggest that approximately 70% of the electromagnetic energy or more must be within the sample diameter if the effective sampling area of the probe is to be included within the sample.
Miniaturized wireless water content and conductivity soil sensor system
Computers and Electronics in Agriculture, 2019
Obtaining more data for the research/studies of plants growing may be easier realized when suitable nondestructive detection methods are available. We are here presenting the development of a miniaturised, lowpower, real-time, multi-parameter and cost-effective sensor for measurements in mini plugs (growth of seedling). The detection technique is based on measurement of electrical impedance at two frequencies for sensing two soil parameters, water content and water conductivity (dependent on e.g. total ions concentration). Electrical models were developed and comply with data at two frequencies. An easy and efficient calibration method for the sensor is established by using known liquids' properties instead of various soil types. The measurements show a good correlation between the sensor's readings and the traditional soil testing. This soil sensor can easily send data wirelessly allowing for spot checks of substrate moisture levels throughout a greenhouse/field, and/or enable sensors to be buried inside the soil/substrate for long-term consecutive measurements.
Sensors (Basel, Switzerland), 2012
Elements of design and a field application of a TDR-based soil moisture and electrical conductivity monitoring system are described with detailed presentation of the time delay units with a resolution of 10 ps. Other issues discussed include the temperature correction of the applied time delay units, battery supply characteristics and the measurement results from one of the installed ground measurement stations in the Polesie National Park in Poland.
Demonstrating the Potential of a Low-Cost Soil Moisture Sensor Network
Sensors, 2022
Soil moisture is a key parameter of the climate system as it relates to plant transpiration and photosynthesis and impacts land–atmosphere interactions. Recent developments have seen an increasing number of electromagnetic sensors available commercially (EM) for soil volumetric water content (θ). Their use is constantly expanding, and they are becoming increasingly used for agricultural, ecological, and geotechnical applications and climate research, providing decision support and high-resolution data for models and machine-learning algorithms. In this study, a soil moisture sensor network consisting of 10 Sense Cap capacitance-based sensors is evaluated. Analytical performance of the sensors was determined based on laboratory and field measurements with dielectric permittivity (ε) standards and soil media substrates. Sensor response normalisation to standards of known ε was found to reduce intersensor variability and provide robust estimates of θ in soil samples with known θ. Cross...
Calibrating electromagnetic short soil water sensors
Journal of Hydrology and Hydromechanics, 2000
The use of electromagnetic (EM) soil moisture probes is proliferating rapidly, in two broad domains: in field and laboratory research; and in strongly practical applications such as irrigation scheduling in farms or horticultural enterprises, and hydrological monitoring. Numerous commercial EM probes are available for measurement of volumetric water content (θ v), spanning a range of measurement principles, and of probe dimensions and sensing volumes. However probe calibration (i.e. the relationship of actual θ v to probe electrical output) can shift, often substantially, with variations in parameters such as soil texture, organic matter content, wetness range, electrical conductivity and temperature. Hence a single-valued, manufacturer-supplied calibration function is often inadequate, forcing the user to seek an application-specific calibration. The purpose of this paper is to describe systematic procedures which probe users can use to check or re-determine the calibration of their selected probe(s). Given the wide diversity of operating principles and designs of commercially-available EM probes, we illustrate these procedures with results from our own calibrations of five different short probes (length of 5 to 20 cm). Users are strongly recommended to undertake such calibration checks, which provide both a) pre-use experience, and b) more reliable in-use data.
On the Accuracy of Factory-Calibrated Low-Cost Soil Water Content Sensors
Sensors
Soil water content (SWC) monitoring is often used to optimize agricultural irrigation. Commonly, capacitance sensors are used for this task. However, the factory calibrations have been often criticized for their limited accuracy. The aim of this paper is to test the degree of improvement of various sensor- and soil-specific calibration options compared to factory calibrations by taking the 10HS sensor as an example. To this end, a two-step sensor calibration was carried out. In the first step, the sensor response was related to dielectric permittivity using calibration in media with well-defined permittivity. The second step involved the establishment of a site-specific relationship between permittivity and soil water content using undisturbed soil samples and time domain reflectometry (TDR) measurements. Our results showed that a model, which considered the mean porosity and a fitted dielectric permittivity of the solid phase for each soil and depth, provided the best fit between b...