GPR GPR Signal Processing & Analysis 1 — Questions and Answers
Question 1: What is the primary purpose of applying a time-zero correction in GPR data processing?
- To amplify weak reflections
- To align the first arrival wavelet to the surface interface (Correct answer)
- To remove horizontal banding artifacts
- To increase the scan frequency
Correct answer: To align the first arrival wavelet to the surface interface
Time-zero correction shifts the data so the direct wave aligns precisely with the air-ground interface, ensuring accurate depth calculations.
Question 2: Which processing step is used to compensate for signal attenuation with increasing depth in GPR data?
- Dewow filtering
- Bandpass filtering
- Gain function application (Correct answer)
- Migration
Correct answer: Gain function application
A gain function (such as SEC or AGC) amplifies signals at greater depths to compensate for energy loss due to geometric spreading and material absorption.
Question 3: What does 'dewow' filtering remove from GPR data?
- High-frequency noise
- Low-frequency drift or 'wow' in the time domain (Correct answer)
- Multiples and reverberations
- Surface clutter from air waves
Correct answer: Low-frequency drift or 'wow' in the time domain
Dewow filtering removes low-frequency DC drift (the 'wow' effect) introduced by inductive saturation of the receiver electronics.
Question 4: In GPR processing, what is the goal of migration?
- To convert time to depth using a velocity model
- To collapse hyperbolic diffractions to their true point source locations (Correct answer)
- To remove ringing caused by metallic objects
- To apply frequency filtering to improve resolution
Correct answer: To collapse hyperbolic diffractions to their true point source locations
Migration collapses hyperbolic diffraction tails back to their true subsurface positions, improving spatial accuracy of interpreted targets.
Question 5: A bandpass filter in GPR processing is primarily used to:
- Limit the frequency content to a range that reduces noise while preserving target reflections (Correct answer)
- Convert the signal from time domain to depth domain
- Remove all reflections below a specified depth
- Enhance horizontal coherence across traces
Correct answer: Limit the frequency content to a range that reduces noise while preserving target reflections
A bandpass filter passes frequencies within a defined range, suppressing out-of-band noise and improving signal-to-noise ratio for target identification.
Question 6: Which velocity analysis method uses the shape of hyperbolic diffractions to estimate subsurface EM velocity?
- Common midpoint (CMP) gather
- Hyperbolic fitting (Correct answer)
- Spectral analysis
- Cross-correlation
Correct answer: Hyperbolic fitting
Hyperbolic fitting matches a theoretical hyperbola to a diffraction event in the data, and the best-fit velocity provides the local EM propagation velocity.
GPR GPR Signal Processing & Analysis 1
What is the primary purpose of applying a time-zero correction in GPR data processing?