A geophysical survey presents many challenges. A scientist must be able to notonly understand the theory and nature of the geophysics being applied but must also beable to identify features of interest in a dataset. It is also of extreme importance to beable to determine where, in the subsurface, the features identified in the data occur.This research is designed in an attempt to identify the locations of subsurfaceheterogeneities that affect geophysical instrument response. An experiment wasconducted in which topography, magnetics, ground-penetrating radar (GPR), andelectromagnetic induction (EM) data were collected over a defined survey line. Anexcavator with a modified flat-bladed bucket was used to remove, or skim, a 5 to 10 cmthick layer of material from the survey line. Upon removal of the material, datasets fromthe above mentioned instruments were again collected along the same survey line. Thisprocess was repeated for 10 skims, resulting in a total of 11 sets of data for eachinstrument.Having collected data with various instruments in the same location as materialwas progressively removed allowed for an empirical study with the goal of noting how the response of each instrument changed with respect to the removal of material. Byobserving how the anomalies changed in the data from one skim to the next, a betterunderstanding of the location of the causative heterogeneities could be had.Data for each instrument was compared to the equivalent data collected fromeach subsequent skim to determine how similar or different the data appeared as thedepth of the trench increased. The experiment also sought to determine if thetopographic variations, or roughness, along the survey line had any impact of thegeophysical signals. The data collected from each instrument were compared to thetopographic roughness of the survey line for the corresponding skim.
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