Re: TDR use in varying temperature

[Jason Sun <jason@esica.com>]

Jon:

One of my friend and colleague did a detailed study on the effect of soil
temperature on soil moisture measurements using TDR. The result was
published on SSSA journal (94 or 95?), and the author's name was Dr. Steeve
Pepin.

The bulk density has less influence on moisture measurement using TDR
comparing to using other methods such as neutron probe. Should a bulk
density calibration be conducted depends on the accuracy requirement. If the
time delay is expressed as T/Tair (the ratio of travel time in soil to that
in free space over the same distance), then the effect of bulk density can
be corrected using a formula during data processing.

Jason Sun Ph.D.

Research Scientist
ESI Environmental Sensors Inc.
Victoria, BC, Canada
V8Z 4B9

Tel: 250-479-6588
Fax: 250-479-1412
e-mail: jason@esica.com

-----Original Message-----
From: owner-sowacs@aqua.ccwr.ac.za <owner-sowacs@aqua.ccwr.ac.za>
Date: June 25, 1999 3:57 PM
Subject: TDR use in varying temperature

>Hello,
>
>My name is Jon Southen and I am a graduate student at
>the University of Western Ontario.  I'm undertaking
>research looking at water transport due to temperature
>gradients beneath landfills.  As part of this
>research, I will be doing some column tests on silty
>soil subjected to a significant temperature gradient.
>I would like to measure soil water content, soil
>matric potential (suction) as well as temperature.
>Although TDR seems to be the "best" way to measure
>water content, I have concerns regarding the
>dependence of the dielectric constant of soil on
>temperature and density.  Since both of these
>variables change during the course of my testing, I
>need to be able to calibrate moisture content readings
>to both of these factors.  This approach seems to be
>potentially difficult.
>Does anyone have any suggestions as to the best way to
>approach this problem?  Would another method of water
>content / matric potential measurement be more
>suitable?  I need undisturbed measurements at various
>times over an approximately one month period.  Any
>suggestions would be appreciated.
>===
>Jon Southen, B.E.Sc.
>Graduate Student,
>Department of Civil Engineering
>University of Western Ontario
>jmsouthe@julian.uwo.ca
>PHONE : (519) 661-2111 ext. 8291
>FAX   : (519) 661-3942
>_________________________________________________________

>