On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variation
Abstract Dielectric techniques are fundamental methods for measuring soil water content, and they commonly rely on the conventional laboratory calibration of the dielectric permittivity models between a dielectric constant and water content. As a non‐negligible factor, porosity has been constructed...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Wiley
2021-01-01
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| Series: | Vadose Zone Journal |
| Online Access: | https://doi.org/10.1002/vzj2.20096 |
| _version_ | 1818434675262095360 |
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| author | Xicai Pan Yudi Han Kwok Pan Chun Jiabao Zhang Donghao Ma Hongkai Gao |
| author_facet | Xicai Pan Yudi Han Kwok Pan Chun Jiabao Zhang Donghao Ma Hongkai Gao |
| author_sort | Xicai Pan |
| collection | DOAJ |
| description | Abstract Dielectric techniques are fundamental methods for measuring soil water content, and they commonly rely on the conventional laboratory calibration of the dielectric permittivity models between a dielectric constant and water content. As a non‐negligible factor, porosity has been constructed differently in some models as a calibration constant, but the systematic porosity variations during the laboratory model calibration and field applications are not yet well addressed. Based on time‐domain reflectometer laboratory calibration experiments, this study investigated this issue using three preestablished dielectric permittivity models: the Purdue calibration equation (American Society for Testing and Materials model [ASTM]), the complex refractive index model (CRIM), and a piecewise CRIM model (CRIMP). Results demonstrate that a generalized porosity constant used in the calibration would bring in additional structural bias compared with the calibration using variable porosities, and its magnitude varies with the model structure. The deviation of the generalized porosity constant can further amplify the structural bias of ASTM and CRIM for soils with low clay content, but it is insensitive for the soils with high clay content due to the overwhelming role of model structure error. Only the model CRIMP with a “perfect” model structure can effectively cope with the systematic porosity variation and keep a stable built‐in capability for estimating calibration constants from readily available soil data. These findings highlight ignoring porosity variation should not be taken for granted for calibrating and applying the preestablished models. |
| first_indexed | 2024-12-14T16:40:45Z |
| format | Article |
| id | doaj.art-158cf3f1264347f6899634441c39677e |
| institution | Directory Open Access Journal |
| issn | 1539-1663 |
| language | English |
| last_indexed | 2024-12-14T16:40:45Z |
| publishDate | 2021-01-01 |
| publisher | Wiley |
| record_format | Article |
| series | Vadose Zone Journal |
| spelling | doaj.art-158cf3f1264347f6899634441c39677e2022-12-21T22:54:20ZengWileyVadose Zone Journal1539-16632021-01-01201n/an/a10.1002/vzj2.20096On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variationXicai Pan0Yudi Han1Kwok Pan Chun2Jiabao Zhang3Donghao Ma4Hongkai Gao5State Key Lab. of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 ChinaState Key Lab. of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 ChinaDep. of Geography Hong Kong Baptist Univ. Hong Kong ChinaState Key Lab. of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 ChinaState Key Lab. of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 ChinaSchool of Geographical Sciences East China Normal Univ. Shanghai 200241 ChinaAbstract Dielectric techniques are fundamental methods for measuring soil water content, and they commonly rely on the conventional laboratory calibration of the dielectric permittivity models between a dielectric constant and water content. As a non‐negligible factor, porosity has been constructed differently in some models as a calibration constant, but the systematic porosity variations during the laboratory model calibration and field applications are not yet well addressed. Based on time‐domain reflectometer laboratory calibration experiments, this study investigated this issue using three preestablished dielectric permittivity models: the Purdue calibration equation (American Society for Testing and Materials model [ASTM]), the complex refractive index model (CRIM), and a piecewise CRIM model (CRIMP). Results demonstrate that a generalized porosity constant used in the calibration would bring in additional structural bias compared with the calibration using variable porosities, and its magnitude varies with the model structure. The deviation of the generalized porosity constant can further amplify the structural bias of ASTM and CRIM for soils with low clay content, but it is insensitive for the soils with high clay content due to the overwhelming role of model structure error. Only the model CRIMP with a “perfect” model structure can effectively cope with the systematic porosity variation and keep a stable built‐in capability for estimating calibration constants from readily available soil data. These findings highlight ignoring porosity variation should not be taken for granted for calibrating and applying the preestablished models.https://doi.org/10.1002/vzj2.20096 |
| spellingShingle | Xicai Pan Yudi Han Kwok Pan Chun Jiabao Zhang Donghao Ma Hongkai Gao On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variation Vadose Zone Journal |
| title | On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variation |
| title_full | On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variation |
| title_fullStr | On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variation |
| title_full_unstemmed | On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variation |
| title_short | On the laboratory calibration of dielectric permittivity models for agricultural soils: Effect of systematic porosity variation |
| title_sort | on the laboratory calibration of dielectric permittivity models for agricultural soils effect of systematic porosity variation |
| url | https://doi.org/10.1002/vzj2.20096 |
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