Soil moisture - TDR (TRIME tube access probe)

Parameter to be measured:

Soil moisture after the method of Stacheder (1996) with an effective penetration depth of the probe T3 about 15 cm, of T3C 10 cm, calibration is necessary

Method:

TRIME (Time domain Reflectometry with Intelligent MicroElements) is a TDR-method (IMKO, 2000)

Equipment:

• TRIME-T3 access tube probe or TRIME-T3C for more saline soils with cable and TRIME-FM3 standard field measuring device, access tubes, drill set to install the tubes

Advantages:

• easy and fast measurement in access tube to the depth of the access tube
• manual as well as continuously logged measurements possible, but if logged measurement only in one depth
• accuracy comparable to neutron probes

Disadvantages:

• installation of access tube in gravel rich soils is complicated and the IMKO drill is useless in this soils.
• The contact between tube and soil has to be guarantied, otherwise a too dry value will be measured.
• There is no marking on the cable to control the direction of the probe, measurement in different directions has to be done carefully.
• Battery of reading device has to be carefully maintained otherwise it has a short durability.

What to watch out for:

• The measurement volume of the probe is not circularly around the probe. To measure the mean water content of one depth requires measurement in different directions.

Links

Projects that used the above equipment:

• TERENO
• CAOS

Other related web sites:

• IMKO: [1]

References

Evett, SR, Tolk, JA, Howell, TQ 2006. Soil profile water content determination: Sensor accuracy, axial response, calibration, temperature dependence, and precision. Vadose Zone 5, 894–907.

Imko GmbH, 2000. Theoretical Aspects on Measuring Moisture Using TRIME. http://www.imko.de/ENG/filebase/Publications/TRIME-THEORY.pdf

Laurent, J-P, Ruelle, P, Delage, L, Zairi, A, Nouna, BB, Adjmi, T 2005. Monitoring Soil Water Content Profiles with a Commercial TDR System: Comparative Field Tests and Laboratory Calibration. Vadose Zone Journal 4, 1030–1036.

Laurent, J-P and Evett, SR 2008. TRIME® FM3 MOISTURE METER AND T3 ACCESS TUBE PROBE, in: INTERNATIONAL ATOMIC ENERGY AGENCY, Field Estimation of Soil Water Content A Practical Guide to Methods, Instrumentation and Sensor Technology [2]

Stacheder, M, 1996. Die Time Domain Reflectometry in der Geotechnik, Messung von Wassergehalt, elektrischer Leitfähigkeit und Stofftransport, PhD Thesis, Schriftenreihe angewandte Geologie, Karlsruhe, 179p.