A laboratory calibration of time domain reflectometry for soil water measurement including effects of bulk density and texture

Jacobsen, O. H.; Schjønning, Per

doi:10.1016/0022-1694(93)90233-y

Cited by 203 publications

(121 citation statements)

References 6 publications

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“…However, Roth et al (1992) and Jacobsen and Schjønning (1993) indicate that a different calibration is required for soils with high organic matter contents and low bulk densities, which is the case in the top soil layer at our site. Therefore, the measurement at 4 cm is corrected following the relationship of Roth et al (1992):…”

Section: Description Of the Site And Experimental Datamentioning

confidence: 89%

Analysis of the Surface Energy Budget at a Site of GAME/Tibet using a Single-Source Model

Yang

Koike

Ishikawa

et al. 2004

Journal of the Meteorological Society of Japan

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In the GAME/Tibet project, the Anduo site is a typical plateau prairie area that is covered by short and sparse vegetation. From May to September 1998, we measured all the surface energy fluxes at this site to quantitatively describe the surface energy budget, but it was still questionable because of low energy closure ratios in most days of the rainy season.To clarify the surface energy budget at this site, this study proposes a single-source energy partition model, to simplify the processes of heat and water vapor transfer from the surface. The model does not distinguish the contribution of turbulent fluxes from the vegetation, and the one from the ground, and thus has fewer parameters to be calibrated comparing to a dual-source model. The main model parameters are: the soil surface evaporation resistance, the parameter kB À1 (the logarithm of the ratio of the aerodynamic roughness length to the thermal roughness length), and the surface emissivity. Their values are calibrated by minimizing the discrepancy between measured and model-predicted values of soil temperatures.This tuned single-source model is then validated by the agreement between the measured and simulated net radiation flux, surface soil heat flux, sensible heat flux, and latent heat flux on the days with high energy closure ratios. This model also reproduces these measured fluxes, except latent heat flux on the days with low closure ratios. The simulated latent heat flux is much higher than the measured one. We further show that the measured latent heat flux is untrustable due to an instrumental limitation, while the model provides a reasonable surrogate. Therefore, the single-source concept is applicable to the heat and water vapor transfer on the Tibetan plateau sparse-vegetation surface, and would contribute to a further research on the land-atmosphere interactions over the plateau.

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Section: Description Of the Site And Experimental Datamentioning

confidence: 89%

Analysis of the Surface Energy Budget at a Site of GAME/Tibet using a Single-Source Model

Yang

Koike

Ishikawa

et al. 2004

Journal of the Meteorological Society of Japan

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“…Roth et al, 1990), percentage of organic matter and bulk density (e.g. Jacobsen & Schj0nning, 1993;Hook & Livingston, 1996), electrical conductivity (e.g. Dalton, 1992;Sun et al, 2000;Persson et al, 2000), and temperature (e.g.…”

Section: Open For Discussion Until 1 December 2001mentioning

confidence: 99%

Using neural networks for calibration of time-domain reflectometry measurements

Persson¹,

Berndtsson²,

Sivakumar

2001

Hydrological Sciences Journal

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Time-domain reflectometry (TDR) is an electromagnetic technique for measurements of water and solute transport in soils. The relationship between the TDR-measured dielectric constant (K a ) and bulk soil electrical conductivity (cr a ) to water content (8 W ) and solute concentration is difficult to describe physically due to the complex dielectric response of wet soil. This has led to the development of mostly empirical calibration models. In the present study, artificial neural networks (ANNs) are utilized for calculations of 9", and soil solution electrical conductivity (a w ) from TDR-measured K a and a" in sand. The ANN model performance is compared to other existing models. The results show that the ANN performs consistently better than all other models, suggesting the suitability of ANNs for accurate TDR calibrations.Key words neural networks; time-domain reflectometry; soil water content; electrical conductivity Utilisation de réseaux de neurones pour l'étalonnage de mesures par réflectométrie en domaine temporel Résumé La réflectométrie en domaine temporel (TDR) est une technique électro-magnétique de mesure de transferts d'eau et de solutés dans les sols. La relation entre la constante diélectrique (K") mesurée par TDR et la conductivité électrique volumique du sol (o" 0 ) d'une part, et la teneur en eau (0 W ) et la concentration en soluté d'autre part est difficile à décrire physiquement en raison de la complexité de la réponse diélectrique d'un sol humide. Cela a conduit au développement de modèles d'étalonnage essentiellement empiriques. Dans cette étude, nous utilisons des réseaux de neurones artificiels (RNA) pour le calcul de 0", et de la conductivité électrique de la solution du sol (a,,,) à partir de K a et rj" mesurés par TDR dans du sable. La performance du modèle à base de RNA est comparée à celle d'autres modèles existants. Les résultats montrent que les RNA donnent des résultats sensiblement meilleurs, suggérant la pertinence des RNA pour l'étalonnage précis de la mesure TDR.Mots clefs réseaux de neurones; réflectométrie en domaine temporel; humidité du sol; conductivité électrique

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“…EM signal propagation is affected by several soil physical properties, especially colloid (clay and organic matter) contents, electrical conductivity, bulk density and temperature (Jacobsen & Schjonning, 1993;Malicki et al, 1996;O'Connor and Dowding, 1999;Gong et al, 2003;Yuanshi et al, 2003). The authors have personal experiences of being consulted to explain obviously wrong readings (e.g., at one extreme, >100 % for a saturated clay soil).…”

Section: Introductionmentioning

confidence: 99%

Calibrating electromagnetic short soil water sensors

Loiskandl¹,

Buchan²,

Sokol³

et al. 2010

Journal of Hydrology and Hydromechanics

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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. Používanie elektromagnetických (EM) snímačov vlhkosti pôdy sa rýchlo rozširuje tak v terénnom výskume, ako aj v laboratóriu. Sú používané v praktických aplikáciách ako je riadenie závlah na farmách a záhradách, ako aj v hydrologickom monitoringu. Pre meranie vlhkosti pôdy (θ v ) sú dostupné početné typy komerčných EM snímačov, založených na viacerých princípoch merania a snímače majú rozdielnu veľkosť snímaných objemov pôdy. Kalibračné krivky takýchto snímačov (t.j. závislosti medzi reálnou vlhkosťou pôdy θ v a elektrickým výstupom snímača) sa môžu posúvať -niekedy podstatne -a to v závislosti od rozdielnych parametrov pôdy, ako je jej textúra, obsah organických látok, rozsah vlhkostí, elektrická vodivosť a teplota. Z toho vyplýva, že jednoznačná kalibračná krivka, dodávaná výrobcom je často neadekvátna, čo núti užívateľa snímač kalibrovať v špecifických podmienkach. Cieľom tohto príspevku je opísať procedúry, ktoré môžu byť použité užívateľmi pri rekalibrácii vybraných typov snímačov. Berúc do úvahy širokú paletu princípov EM snímačov, ilustrujeme tieto procedúry výsledkami vlastných kalibračných testov na piatich typoch krátkych snímačov (dĺžka od 5 do 20 cm). Užívateľom odporúčame rekalibráciu komerčných snímačov, ktorými získajú predbežné skúsenosti a spoľahlivejšie výsledky pri meraní vlhkosti pôdy.KĽÚČOVÉ SLOVÁ: snímače vlhkosti pôdy, elektromagnetické snímače, TDR, kalibrácia.

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A laboratory calibration of time domain reflectometry for soil water measurement including effects of bulk density and texture

Cited by 203 publications

References 6 publications

Analysis of the Surface Energy Budget at a Site of GAME/Tibet using a Single-Source Model

Analysis of the Surface Energy Budget at a Site of GAME/Tibet using a Single-Source Model

Using neural networks for calibration of time-domain reflectometry measurements

Calibrating electromagnetic short soil water sensors

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