Migration
Definition
A processing step that repositions reflections from their apparent location (a spread-out hyperbola) to their true subsurface location (a point or plane), sharpening the image. Hyperbolic diffraction patterns collapse to their apex position after migration.
- Purpose
- Repositions reflections to true subsurface location
- Effect on hyperbolas
- Collapses them to their apex point
- Requirement
- An accurate velocity model
- Category
- GPR data processing step
Common questions
Why do buried objects produce a hyperbola instead of a point in raw GPR data?+
As the antenna passes over a buried reflector, the two-way travel time is shortest directly above it and increases symmetrically to either side, tracing a curved hyperbolic pattern in the radargram even though the object itself occupies a single point.
What goes wrong if the velocity model used for migration is inaccurate?+
An incorrect velocity either under-collapses the hyperbola, leaving a smeared feature, or over-collapses it into a distorted shape, in both cases placing the apparent reflector depth or position incorrectly relative to its true location.
Related terms
- Attenuation
- The reduction in radar signal amplitude with distance traveled. Electrically conductive materials (wet clay, saline soil) convert signal energy to heat, limiting...
- Dielectric Permittivity (Epsilon)
- A material property that controls how fast electromagnetic waves travel through it and how strongly they reflect at a boundary. Water has...
- Hyperbolic Reflection
- The bowtie-shaped pattern in a GPR time section produced as the antenna passes over a point-like object. The shape is governed by...
- Time Window
- The total two-way travel time recorded by the GPR per trace, effectively setting the maximum depth sampled. The time window must be...
- Velocity Calibration
- The process of estimating the true electromagnetic wave velocity in the survey soil, usually by fitting a hyperbola to a known reflector...