GPR Concepts
© Radiodetection 2016
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RD1100 Operation Manual
Hyperbolas are best viewed when subsurface targets are crossed perpendicularly or at a 90
degree angle. The actual position of the object is located at the apex of the hyperbola.
7.3 Calculating Depth
Ground penetrating radar records the time it takes a radio wave to travel to a target and
back; it does not measure the depth to that target directly. Depth to target is calculated
based on the velocity with which the wave travels to the target and back.
To calculate depth:
𝐷 = 𝑉 𝑥 𝑇/2
𝑊ℎ𝑒𝑟𝑒 𝐷 𝑖𝑠 𝐷𝑒𝑝𝑡ℎ
𝑉 𝑖𝑠 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝑇 𝑖𝑠 𝑡ℎ𝑒 𝑇𝑤𝑜 − 𝑤𝑎𝑦 𝑡𝑟𝑎𝑣𝑒𝑙 𝑡𝑖𝑚𝑒
For the RD1100, velocity is indicated by the Soil Calibration Value, known as Soil Cal. Once
the Soil Cal values are set, the measured depths will be determined accurately (Section
8.6.6)
7.4 Soil Calibration values
Below is a table of common subsurface materials and their corresponding Soil Cal. This is only
a guideline and there is some variation based on the fact that there can be a mixture of different
materials in the subsurface. The soil water content has the biggest influence, by far, on Soil Cal
values.
Apex of hyperbola is where
the object is located
