Time Window
Definition
The total two-way travel time recorded by the GPR per trace, effectively setting the maximum depth sampled. The time window must be set longer than the expected depth of the target, with additional margin for a velocity slower than assumed.
- Parameter
- Total two-way travel time recorded per GPR trace
- Sets
- The maximum depth sampled
- Rule of thumb
- Set longer than expected target depth plus margin
- Margin needed for
- A velocity slower than the assumed value
Common questions
What happens if the time window is set too short?+
Reflections from below the target depth simply never get recorded, so a feature that lies deeper than the operator assumed will be invisible in the data regardless of how well everything else is configured.
Why build in margin for a slower-than-assumed velocity?+
Radar wave velocity depends on soil moisture and composition, which are rarely known precisely in advance. If the true velocity is slower than assumed, the same travel time corresponds to a shallower depth than expected, so extra window margin protects against underestimating depth.
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...
- Migration
- A processing step that repositions reflections from their apparent location (a spread-out hyperbola) to their true subsurface location (a point or plane),...
- Velocity Calibration
- The process of estimating the true electromagnetic wave velocity in the survey soil, usually by fitting a hyperbola to a known reflector...