Ground Penetrating Radar profile showing indications of two large underground storage tanks at a former gas station. Interpreted old soil horizons and former excavated areas are also labeled.
Looking for underground storage tanks (USTs) at a former gas station using GPR. The green line denotes the line along which the data below was collected. The two red outlines correspond to the suspected locations of the USTs. East is to the right.
A radar profile is a series of radar reflection pulses stacked side-by-side in the direction of the antenna movement.  Lateral variations are clearly discernable along the length of the graphic profile.  Like seismic reflection, radar reflection events are represented by several positive and negative pulses in the signal.  The depth of the reflector is determined by measuring the time (in nanoseconds) between the first cross-over in the surface pulse and the first cross-over in the target pulse; this value times the velocity of the material yields depth.  Often average velocities (or two-way travel times) for common soil and rock types are sufficient to estimate depth to the target reflection.  If more accurate velocities are required, velocity may be determined from a target at a known depth or special field tests made with two antennas.

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