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NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs Although I can't help you with your question, it sounds like a very valuable study. Knowing the porosity and assuming a particle density, the soil bulk density can be estimated, which would be useful for converting gravimetric moisture contents to volumetric moisture contents during the calibration of the TDR. Good luck to you!! Eric Harmsen University of Puerto Rico. -----Original Message----- From: owner-sowacs@aqua.ccwr.ac.za [mailto:owner-sowacs@aqua.ccwr.ac.za] Sent: Saturday, November 03, 2001 4:37 PM Subject: Dual Frequency TDR for Coincident Measurement of W C & porosity of Soil Sender: owner-sowacs@aqua.ccwr.ac.za Precedence: bulk NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs Dear List members, I have posted to this list about my interest on a TDR equipment with regulable rise-time. Now I am writing a bit more on the reasons why I am so interested. I wish to hear your opinion on a new line of TDR research that I suggest below: developing TDR (time-domain reflectometry) equipment to operate in two different rise-times, t' and t¥¥, for coincident measurement of water content and porosity of soil. The dielectric constants for water and solid soil, Kw and Ks, are t-dependent. (Am I correct?) Thus, t' and t" can be chosen in such a way that the ratio Kw'/ Ks' is considerably different from Kw"/ Ks". If this is done, then it might be possible to solve, for theta and phi, a system of two simultaneous equations of a mixing-model type, for instance: K'^1/2 = theta*Kw'^1/2 + (1-phi)*Ks'^1/2 + (phi-theta)*Ka'^1/2 (eq.1) K"^1/2 = theta*Kw"^1/2 + (1-phi)*Ks"^1/2 + (phi-theta)*Ka"^1/2 (eq.2) where theta stands for water content, a for air, phi for porosity. A sample of water would easily allow determination of Kw' and Kw". A dry sample of the soil, of known phi, could be used to determine Ks' and Ks" , using equations 1 and 2. Once Ks' and Ks" are known for that given soil, and Kw' and Kw" are also known, then the system of equations 1 and 2 could now be easily solved for phi and theta. *HENCE, SUCH AN INSTRUMENT COULD BE USED FOR SIMULTANEOUS TDR-DETERMINATION OF THETA AND PHI for a given soil -- which, as far as I know, has not yet been described in the literature.* (Is the idea really new? Has anyone read about something similar?) Other rise times, t'" and t"", could also be used to find further parameters, specially if a four-phase mixing model is used... I am myself very keen to test this idea. I am considering to prepare a project on this and submit it to some agency for financial support. *But*: I am rather inexperienced in TDR research, so I would very much appreciate listening to opinions on the feasibility of this idea before I invest more time and effort on it... I know the theory above is very much simplified. It is just a first approximation. I really want to confirm whether the central idea is correct... If it is correct, then other mixing-models could be considered, more sophisticated than eqs. 1 and 2. I will thank you very much for any comments/suggestions/criticism/etc, on this idea. Best regards, Elimoel A. Elias e-mail: elias@imagenet.com.br Website: http://elimoel.freeyellow.com/elimoel.html ICQ 109845414 Tel.: +55-19-432-9458 ----- Original Message ----- From: "EA Elias" <elias@imagenet.com.br> To: <owner-sowacs@aqua.ccwr.ac.za> Sent: Tuesday, October 16, 2001 11:05 AM Subject: TDR instrument with regulable risetime. Dear list members, I am seeking a TDR instrument with regulable risetime, covering a range as large as possible. Has anyone in this list ever used, or heard of, something like this? I am familiar with a TDR instrument operating at a fast rise time, <200 pS. I have also heard of instruments with faster rise times, <10 pS. I am seeking an instrument with a regulable risetime, covering a range as large as possible, perhaps from 10 to 200 pS. But I have been unable to find any information about this. I have emailed some companies: Soilmoisture Campbell Scientific Inc. Tektronix E.S.I. Environmental Sensors Inc. but I have only received negative answers. I will be grateful for any information on this matter. Elimoel A. Elias e-mail: elias@imagenet.com.br Website: http://elimoel.freeyellow.com/elimoel.html ICQ 109845414 Tel.: +55-19-432-9458