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As long as all your sensors are installed from surface, I would routinely do graviemetric determinations. I installed the CS615s at multiple depths and couldn't take soil samples for water content determinations except once upon installation. One thing I did do is install Campbell Scientific 229 heat dissipation sensors (measure matric suction) at the same depths as the CS615s and develop soil water characteristic curves (SWCC) in the lab for the soils at each depth. In theory, I could have backed the water content out of the suction data using the SWCC and compared that to the CS615 data (I didn't bother since I was more interested in water fluxes, gradients, etc. than in water content). In reality, I think the combination of errors in the 229 data and the SWCCs would combine to result in fairly large errors in calculated water content (at least to calibrate another sensor). It would be an easy, independant, and "automatable" method of determining water content. Depending on your work the ability to automate the procedure is important if you need real-time data or don't like calibrating sensors (i.e., manual gravimetric) when it was raining out, only when it was sunny and dry. Anyone have any comments of the accuracy of doing this? David At 05:58 PM 99-02-02 GMT, you wrote: >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 > >Hi All > >Currently I am using a TDR system supplied by Campbell Scientific and >comprises CS615 sensors and a CR10X logger. I need to measure the soil >water contents on different silvicultural treatments. Now these plots are >really large and I will need to have cables up to 200m in length between the >logger and sensor. Does the cable length affect the accuracy of the reading >and what is the maximum cable length that can be used with these sensors? >Second, I suppose like the neutron probe the best way to calibrate the >sensors is gravimetrically? Anyone else using the same equipment? > >Any comments or suggestions? > >Regards > >Luke > > >Luke Esprey >BSc (Hons), MSc (Hydrology) >>Soilwater Research Officer >>Institute for Commercial Forestry Research >>P.O. Box 100281, Scottsville, 3209, Republic of South Africa >> >e-mail lukes@icfr.unp.ac.za >Tel: Int+27 331 62314 >Fax: Int+27 331 68905 >URL: http://www.icfrnet.unp.ac.za/~lukes/index.ssi > ==> GPS : S29,37,575' E30,24.379' <== > > > ___________________________________________________________________ David A. Thomas EBA Engineering Consultants Ltd. 270, 200 Rivercrest Drive SE Calgary, AB T2C 2X5 phone:(403)203-3355 x349 fax:(403)203-3301 email:dthomas@eba.ca ___________________________________________________________________ "Black Holes are where God is dividing by zero"