New Applications in Archeology for TDR Probes Measuring Water Content
Recently, I spent a day at the University of Birmingham in the UK where I talked with Dr. Nicole Metje and researchers in the Civil Engineering department. They are working on a project called, “Mapping the Underworld,” (Curioni G., Chapman D.N., Metje N., Foo K.Y., Cross J.D. (2012) Construction and calibration of a field TDR monitoring station. Near Surface Geophysics, 10, 249-261) where they are using TDR probes to help locate buried objects that require maintenance.
Currently, people use rudimentary tools to poke around and figure out where the buried object is. A more effective high-tech solution is GPR (Ground Penetrating Radar) that is pulled over the top of the soil and creates a 2D image of permittivity below the ground surface. The problem is GPR only provides relative depth information and must have ancillary data to produce actual values. To address this issue, their group uses TDR probes (time domain reflectometry) which measure dielectric permittivity to ground truth the GPR. Using this method they hope to be able to predict the depth to anomalies that are observed in the 2D GPR output.
After working on this for some time, the engineers at the University of Birmingham continue to deal with challenges related to TDR signal, interpretation, and maintenance. One challenge is that TDR systems are complex and power hungry. Thus, the researchers were interested in learning more about soil moisture sensing and different technologies that would help them meet their project goals. My first inclination was to solve their problem with water potential sensors. Many people who work in environmental applications want to know the fate and distribution of water where water potential is the driver. Interestingly, this is one of the few cases where people actually do need permittivity measurements (the value used to derive volumetric water content, VWC) instead of water potential because they use the actual permittivity signal to ground truth the GPR. This realization spawned a four-hour discussion on the frontiers of permittivity measurement in soil and the use of advanced analysis techniques to tease out important soil properties such as bulk density, electrical conductivity, and mineralogy.
I hadn’t given much thought to using soil science instrumentation to locating buried infrastructure. I’m excited to see what the combination of a new technology like GPR and dielectric measurement can do to help us solve everyday problems like where to start digging.
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