GPR is a go-to tool for law enforcement professionals searching for buried forensic evidence. Here are a couple of tips when using GPR for forensic investigations.

1. Find Evidence, not Rocks

GPR technology is very sensitive to material changes which can result in many responses. The challenge is to differentiate responses from rocks, soil variations and other naturally-occurring subsurface objects from buried evidence such as containers of drugs, weapons or a body.  One way to boost interpretation confidence is to look at the ground response above an observed object.  Often it is possible to see a GPR response from disturbed soils strata where a hole was dug, particularly in layered soils. In the data example, the break in a horizontal layer directly above the GPR response from a buried object indicates the natural soil has been disturbed. Seeing this type of response helps determine that you have detected an object which was placed into the ground by excavating rather than something that has been buried by natural soil accumulation.

2. Evidence in a cross section

Most GPR operators are very familiar with looking at GPR cross sections and learn that upside-down U shapes (known as hyperbolas) are indicators of buried objects. However, when dealing with evidence such as buried bodies, investigators are less likely to see such typical shapes. Depending on the size, depth, GPR frequency and target orientation, cadavers tend to give a different response; it might be somewhat hyperbolic but the hyperbola is not usually well defined.  The response is often caused by reflection from the bottom of the excavation and shows a flatter response with the response dipping slightly down at each side.

While these tips provide information of what to look for on cross-sections, Sensors & Software recommends using grid searches that enable depth slice maps to be created as the primary method  for  forensic investigations. Cross sections can be used to confirm the targets identified in the depth slice images generated from the grid data.

For more information or training on forensic evidence searches with GPR, contact our forensic application specialists.

Figure 1: A Break in the Natural Soil

Figure 2: Subtle Evidence

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