We present a low-cost, reliable method for long-term in situ autonomous monitoring of subsurface resistivity and temperature in a shallow, moderately heterogeneous subsurface. Probes, to be left in situ, were constructed at relatively low cost with an electrode spacing of 5 cm. Once installed, these were wired to the CR-1000 Campbell Scientific Inc. datalogger at the surface to electrically image infiltration fronts in the shallow subsurface. This system was constructed and installed in June 2005 to collect apparent resistivity and temperature data from 96 subsurface electrodes set to a pole-pole resistivity array pattern and 14 thermistors at regular intervals of 30 cm through May of 2008. From these data, a temperature and resistivity relationship was determined within the vadose zone (to a depth of ~1 m) and within the saturated zone (at depths between 1 and 2 m). The high vertical resolution of the data with resistivity measurements on a scale of 5-cm spacing coupled with surface precipitation measurements taken at 3-min intervals for a period of roughly 3 years allowed unique observations of infiltration related to seasonal changes. Both the vertical resistivity instrument probes and the data logger system functioned well for the duration of the test period and demonstrated the capability of this low-cost monitoring system.
The United States Revolutionary War (1775–1783) resulted in numerous mass burials in the eastern United States, with deaths occurring not just directly related to the battles fought, but also from disease, starvation, and exposure. Current information relating to these mass burials is often gathered from myths and rumors, leaving the truth of the historical aspects of that time period ambiguous. Geophysical techniques are increasingly utilized in archaeologic and forensic studies to locate unmarked burials. GPR, magnetics, and electrical resistivity have been used to successfully identify burial locations around the world in a non-invasive manner. This paper aims to illustrate how different burials of the US Revolutionary War period can be detected and characterized with geophysics, providing important knowledge of a better historical understanding of that time period, as well as optimizing equipment instrumentation and processing procedures for such targeted investigations. Three case studies of Revolutionary War Era mass burial sites in Pennsylvania, USA are described here: the Paoli Battlefield Memorial, the Old Charlestown Cemetery, and Saint Peter's Church in the Great Valley. These sites are within 9 km of each other and have historic records that suggest mass burials during this period. Results show GPR to provide the most useful data overall, with supporting information gathered from the supplemental geophysical techniques of magnetometry and resistivity. 2D profiles tend to provide a more valuable image of the subsurface than 3D slices. Larger burials leave a greater footprint and have a higher chance of causing a geophysical disturbance that can be measured more than 200 years after the burial. Soil moisture content and vegetation type can impact quality of results. Study implications demonstrate the challenges and potential usefulness of geophysical techniques to successfully locate and characterize mass burials of this time period.
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