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- - Figure 1: Aerial photograph of the site location from Google Maps showing the parking lot outlined in red at 3245 New Brighton Rd in Arden Hills GEOPHYSICAL INVESTIGATION Ground penetrating radar (GPR) is a geophysical method where electromagnetic waves are propagated away from an antenna, into the ground, and at each change in electromagnetic properties some energy is transmitted while some is reflected. The reflected energy is received by another antenna. The data is therefore amplitude versus two-way travel time (TWTT). GPR has the advantage of being the only shallow geophysical technique that can easily detect non-metallic targets, but it has the disadvantage of being very site dependent in its performance. The ability to detect targets depends on the contrast in electrical permittivity while the depth of penetration is dependent on the electrical conductivity of the soil. If the soil is very conductive then the GPR may have very limited penetration depth and data may not be useful for interpretation as to the location in plan view of tire fill. Olson plans to utilize an ImpulseRadar PinpointR system with dual frequency 400 and 800 MegaHertz (MHz) antennas. All ImpulseRadar GPR systems have real time sampling (RTS) capability, which is a significant improvement over the older and more common equivalent -time - sampling (ETS) approach to data digitization. An ETS system digitizes a single point on each GPR Olson Proposal No. P2023149.1 GP Page 2