SOWACS: TDR and below zero temperatures

["Ioan C. Paltineanu" <icpaltin@msn.com>]

"Ioan C. Paltineanu" writes to the sowacs list:
===8<==============

Dear Hans:

One of the similarities in behavior of different electromagnetic methods
(Capacitance, TDR, etc..) using the relative dielectric constant (Ka) versus
soil-air-water mixture relationship, is the response to the change of water
status from liquid to solid (ice), and back to liquid form. It is generally
recognized that dielectric constant of pure liquid water, at 20 deg Celsius
and atmospheric pressure, is 80.4 (temperature variation), 3 to 7 of the
solids in soil matrix,. and that of air is 1. The dielectric constant of ice
is 3, and of the bound water is 4.

As soon as soil water is freezing, the dielectric constant drops and masks
the "real soil water content". With a proper placement of sensors you may
see the advancement of the "freezing front" with the soil depth. When
thawing is taking place (solid to liquid form of water), an "increase" in
soil water content data for that particular sensor is showing, going up to
the previous data depending on the soil temperature increase. Working with
the multisensor capacitance probes in multiyear (1995-1997), and year around
monitoring of soil water content under different soil tillage methods, the
same behavior (freeze/thaw) is shown in Fig 4.6.8. (Paltineanu I. C., and J.
L. Starr, 2000. "Real-Time Soil Water Dynamics", Chapter 4 Hydrology,
Section 4, in J. H. Lehr - editor, Standard Handbook of Environmental
Science, Health and Technology, McGraw-Hill, pp:4.45 - 4.57.

As we suggested in our paper: Paltineanu I. C., and J. L. Starr: 1997.
Real-time Soil Water Dynamics Using Multisensor Capacitance Probes:
Laboratory Calibration, Soil Sci. Soc. Am. J. 61:1576-1585, "more
calibration research is needed ... and for extremes of soil temperature that
can occur diurnally with bare surface soils and seasonally in many climates"

Please, make sure your TDR sensors were working within the recommended
temperature range.

Best regards,

IOAN

IOAN CATON PALTINEANU, Ph.D. - President
PALTIN International Inc.
6309 Sandy St.
Laurel, Maryland 20707
U.S.A.
Voice & Fax: (301) 725-0604
Email: icpaltin@msn.com
www.paltin.com



----- Original Message -----
From: "Johannes Deelstra" <johannes.deelstra@jordforsk.no>
To: <brooz@pobox.com>
Sent: Tuesday, March 18, 2003 4:17 AM
Subject: SOWACS: TDR and below zero temperatures


>
> "Johannes Deelstra" writes to the sowacs list:
> ===8<==============
> Is there anyone who can tell me about how TDR-equipment functions when
> soil temperatures drop below zero.
> I have continuous readings with TDR-equipment in addition to soil
> temperatures. During the winter season when the soil temperature drops
> below zero, one can notce a sudden drop in moisture conten.
> TDR measures the water but can one say that the reading provided by the
> TDR-equipment when soil temperatures are below zero is the water content
> or is it influenced by the ice content.
>
>
> regards
>
> Johannes (Hans) Deelstra
>
> Jordforsk
> Frederik A. Dahls vei 20,
> 1432 ‰s
>
> tel: +47 64948100(8173)
> fax: +47 64948110
>
> johannes.deelstra@jordforsk.no
> www.jordforsk.no

===8<==============
NOTE:  To get off this list, send an email to list@sowacs.com
with the subject line:
unsubscribe_sowacs

For full instructions see this page:
<http://www.sowacs.com/subscribe/index.html>