Capacitive array resistivity with an inductive source

Adams, C 2008, Capacitive array resistivity with an inductive source, Doctor of Philosophy (PhD), Applied Sciences, RMIT University.

Document type: Thesis
Collection: Theses

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Title Capacitive array resistivity with an inductive source
Author(s) Adams, C
Year 2008
Abstract The aim of this research was to develop an instrument that fills a niche in geophysical instrumentation for a tool that is fast, non-contact or minimal contact, and specifically optimised for discrete, near-surface, electrically resistive targets in resistive and conductive environments. This aim was sought to be achieved through the development of a new Capacitive Array Resistivity with Inductive Source (CARIS) system.

Two CARIS systems were produced and thoroughly tested. A first prototype instrument CARIS-1, operating at 100KHz, was developed for proof of concept in the laboratory and initial field testing. A second prototype CARIS-2, operating at 5kHz, was developed for further fielding testing and trial mapping experiments.

Several major conclusions have been reached through the development and testing of the CARIS systems. Firstly, the CARIS system can clearly detect objects in a conductive homogeneous liquid, with high repeatability of data. This result reinforced the concept of the CARIS method, and established the stability of the instrumentation in laboratory environments. The approach was validated by close correlation between measurements and modelling. Secondly, the CARIS system is able to measure responses to near-surface conductivity variation in field conditions with high repeatability. Data collected also showed spatial consistency with GPR, Resistivity and mapped culture. It was determined that properties of the near surface, such as moisture content and soil consolidation, can significantly affect the electrical homogeneity of the medium and thus the uniformity of the background reading. The CARIS systems thus had a limitation that they proved to be quite sensitive to variations of this nature. Thirdly, foll owing from the second conclusion, although the aim of the CARIS system was to detect the presence of discrete buried objects, CARIS proved to be more responsive to the effects of the burial process rather than the objects themselves. It was concluded therefore that the method of excavation, burial, and refill material were of high significance in CARIS interpretation. This conclusion was reinforced by the results of theoretical modelling which showed that shallow boundaries of small conductivity contrast could quite easily produce more significant anomalies than target objects which are deeper and have higher contrast.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Geophysics -- Measurement
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