Identyfikacja błędów pomiaru niskich wartości wilgotności gleby sondą reflektometryczną TDR

• Autorzy: Skierucha W. , Wilczek A.

Warianty tytułu

EN

Identification of errors of low soil water content measurements by TDR reflectometric sensors

• Języki publikacji: PL

Abstrakty

PL

W pracy podjęto próbę identyfikacji źródeł błędu pomiaru małych wartości wilgotności gleby sondą reflektometryczną TDR, które powstają na skutek efektu splotu sygnałów. Wykazano, że wybór mediów kalibracyjnych o wartościach przenikalności elektrycznej bliskich dolnemu i górnemu zakresowi pomiarowego przenikalności elektrycznej mierzonej gleby zmniejsza błąd pomiaru tej wielkości i w konsekwencji błąd pomiaru wilgotności gleby oraz umożliwia użycie sond TDR o różnych długościach prętów.

EN

Reflectometric TDR sensors working in time domain (TDR - Time Domain Reflectometry) are successfully used for laboratory and field measurements of the soil bulk dielectric permittivity and, indirectly, the soil water content. Commonly applied methods for calibrating these sensors use two media, in which the respective parallel waveguides of the TDR sensor are inserted into: air - for low and water - for high values of dielectric permittivity. However, the variability range of the soil bulk dielectric permittivity is much smaller than the one associated with these calibration media. Application of air to calibration of short TDR sensors causes output waveform overlapping errors of the pulse reflected from the rods beginning with the pulses reflected from the rods open termination, which results in a relative time shift of these pulses. In the paper there is shown the way how to minimise these errors, called convolution effect errors, by application of other than air and water calibration media. The authors try to identify the error sources of low soil water content values measured by a TDR reflectometric sensor caused by the convolution effect. It is shown that the proper choice of calibration media having dielectric permittivity values close to low and high limits of the measurement range of the measured porous medium (soil) decreases the dielectric permittivity measurement error and, consequently, the measurement error of water content as well as enables application of variable length TDR sensors.

Słowa kluczowe

PL

przenikalność elektryczna; wilgotność gleby; splot sygnałów; TDR

EN

dielectric permittivity; soil water content; convolution effect; TDR

• Wydawca: Wydawnictwo PAK
• Czasopismo: Pomiary Automatyka Kontrola
• Rocznik: 2010
• Tom: R. 56, nr 8
• Strony: 875--878
• Opis fizyczny: Bibliogr. 9 poz., rys., tab., wzory

Twórcy

autor

Skierucha W.

autor

Wilczek A.

• Instytut Agrofizyki im. Bohdana Dobrzańskiego PAN w Lublinie, ul. Doświadczalna 4, 20- 290 Lublin,

Bibliografia

• [1] Robinson D. A., Campbell C. S., Hopmans J. W., Hornbuckle B. K., Jones S. B., Knight R., Ogden F., Selker J., Wendroth O.: Soil moisture measurement for ecological and hydrological water-scale observatories: a review. Vadose Zone Journal, 7 (1), 358-389, 2008.
• [2] Malicki M. A., Plagge R., Roth C. H.: Reduction of soil matrix effect on TDR dielectric moisture determination by accounting for bulk density or porosity. European Journal of Soil Science, 47 (3), 357-366, 1996.
• [3] Topp G. C., Zegelin S., White I.: Impacts of the real and imaginary components of relative permittivity on time domain reflectometry measurements in soils. Soil Science Society of American Journal, 64, 1244-1252, 2000.
• [4] Skierucha W., Wilczek A., Aloghina O.: Calibration of a TDR probe for low soil water content measurements. Sensors and Actuators A. Physical, 147, 544-552, 2008.
• [5] van Gemert M. J. C.: High-frequency time-domain methods in dielectric spectroscopy, Philips Resources Report, 28, 530-572, 1973.
• [6] Heimovaara T. J. Design of triple-wire Time Domain Reflecto-metry probes in practice and theory, Soil Science Society of American Journal, 57, 1410-1417, 1993.
• [7] Jacobsen O. H., Schojnning P. A laboratory calibration of time domain reflectometry for soil water measurement including effects of bulk density and texture, Journal of Hydrology, 151, 147-157, 1993.
• [8] Or D., Wraith J.M.: Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry: a physical model, Water Resources Research, 35 (2), 371-383, 1999.
• [9] Topp G. C., Davis J. L., Annan A. P.: Electromagnetic determina-tion of soil water content: measurements in coaxial transmission lines, Water Resources Research, 16, 574-582, 1980.