Lecture 4C - GPR applications and Interpretations

Flashcards reviewing GPR applications, data interpretation, hyperbolic reflection patterns, and velocity estimation.

What is a primary advantage of GPR in environmental applications?

It provides high-resolution near-surface measurements.

What feature makes hydrological boundaries suitable for GPR?

Strong contrasts in permittivity.

What is a major limitation of GPR regarding depth penetration?

Limited depth penetration, especially in areas of high conductivity.

In a processed GPR profile, what do strong parallel returns typically represent?

The ground surface or ground wave.

What do multiple parallel black and white lines representing a single interface indicate in a GPR profile?

Multiple oscillations in the individual transmitted pulse.

What do parallel white and dark bands represent in a GPR profile?

A consistent interface or a boundary between layers of contrasting permittivity.

What causes multiples in GPR data?

The radar signal reflecting multiple times between the surface and a reflector.

Why do hyperbolic curves appear in GPR reflection profiles?

They are an artifact of the common offset profiling method over small discrete reflectors.

How does the radar signal radiate from the transmitter?

Like a cone into the ground.

When does the reflected path length reach a minimum when using GPR?

When the instrument is directly over the anomaly.

What does the shape of a hyperbola indicate in GPR data?

The velocity of the radar wave.

At what angle should a profile cross a pipe to be represented as a hyperbola?

90 degrees.

What does the peak of a hyperbolic pattern indicate when surveying a pipe?

The location of the pipe.

What might hyperbolas in the uppermost layer of a GPR profile represent?

Discrete features acting as individual strong reflectors, like large boulders.

What estimated velocity was used to convert the vertical axis from time to depth in the example?

0.154 meters per nanosecond

What is the purpose of constructing a line drawing from a GPR profile?

To clearly represent subsurface reflectors and extract important information.

What should you be careful not to misinterpret as dipping reflectors?

The edges of hyperbolas.

In the Borth Bog example, what was the aim of the GPR survey?

Assessing the depth of the peat and, if possible, determine characteristics such as water content.

What velocity was estimated from the hyperbolas in the Borth Bog example?

0.035 meters per nanosecond.

What relative permittivity was estimated for the upper layer of the peat bog, suggesting high water content?

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