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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 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