GPR Environmental & Geological Considerations 2

Question 1

What soil property most directly governs high-frequency GPR signal attenuation?

Accepted Answer

Electrical conductivity (σ)

Answer

Bulk density

Answer

Grain size distribution

Answer

Organic carbon content

Question 2

In what geological environment would GPR surveys typically be LEAST effective?

Accepted Answer

Coastal marine clay deposits with brackish groundwater

Answer

Desert sand dunes with dry aeolian deposits

Answer

Glacial outwash gravel plains

Answer

Karst limestone with dry cavities

Question 3

How does saturated peat soil affect GPR signal penetration?

Accepted Answer

Peat's high organic content and water retention cause significant signal attenuation

Answer

Peat is highly resistive, providing excellent penetration

Answer

Peat amplifies the signal due to its fibrous structure

Answer

Peat has identical GPR response to dry sand

Question 4

What dielectric permittivity value is commonly used for water when calibrating GPR velocity models?

Accepted Answer

Approximately 80

Answer

Approximately 4–6

Answer

Approximately 20–25

Answer

Approximately 1

Question 5

How does limestone bedrock typically appear in GPR profiles compared to granite bedrock?

Accepted Answer

Limestone may show complex reflections from dissolution features, voids, and fractures; granite typically presents a cleaner contact

Answer

Limestone shows a stronger, more continuous reflection because it is denser

Answer

Granite always shows deeper reflections because it is more resistive

Answer

Both materials produce identical GPR signatures

Question 6

Which condition can cause excessive multiple reflections (ringing) in GPR data that mask real subsurface features?

Accepted Answer

A highly reflective layer such as a shallow metal surface or pavement directly beneath the antenna

Answer

Presence of resistive dry gravel below the survey area

Answer

Deep water table at 10 m or more

Answer

Low-frequency antenna selection below 50 MHz

Question 7

Why does GPR performance typically degrade in coastal or tidal environments even above the water table?

Accepted Answer

Capillary rise of saline water elevates soil conductivity well above the water table

Answer

Sea breezes interfere with the radar antenna beam pattern

Answer

Coastal soils are always too dry for GPR to function

Answer

Salt particles in the air absorb GPR energy before it enters the ground