I am using a PR2 Profile Probe (Delta-T Devices) to monitor changes of the volumetric water content in compacted sandy soils at laboratory scale. I need some papers which deal the calibration of this kind of probe, with particular regards to the reliability and accuracy of measurements. The default calibration curve (e.g., mineral soils) does not provide an accurate estimation of the volumetric water content for the type of soil that I am using.
Those sensors are usually manufacturer-calibrated for a specific type of soil (usually some type of loam). You are likely to need a local calibration of the sensor, and I doubt that there are papers out there already that discuss this particular one, as it is quite new. They claim that they are not very temperature sensitive, but I would do a test in wet soils to confirm that. In sandy soils, that shouldn't be much of a problem, in any case, but I would try to be on the safe side.
Check out the papers below, one is a comparison of technologies, the other one a paper specifically on FDR calibration.
http://www.sciencedirect.com/science/article/pii/S0022169412000844
http://www.sciencedirect.com/science/article/pii/S0022169409008403
They also contain plenty of references that can help you further.
Thank you for your response and for the interesting papers. I am working with limestone sands and I am going to calibrate the FDR probe into a sand box by using different known dry density values. The effect of temperature and electrical conductivity of water will be taken into account but I think that the common tap water (450 microS/cm) should not deeply affect the measurements.
Hi Lucio, it's not the salinity of the water, but what may already be in the soils that can greatly affect the factory-calibrations. The soil's salt could be dissolved by adding water. Checking for the soil salinity is a simple test that can be found in any standard dealing with soil tests. I used to do both, the temperature and salinity tests first, before working out any new calibration.
Thank you. In the sandy soil that I am using, no appreciable changes of water salinity occur. Overall these changes are of up to 50-100 microSiemens/cm with respect to that of tap water.
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