Radargram
Definition
The cross-sectional image produced by a GPR survey. The horizontal axis represents distance along the survey line; the vertical axis represents two-way travel time, which is converted to depth once soil velocity is known.
- Source
- Ground-penetrating radar (GPR) survey
- Horizontal axis
- Distance along survey line
- Vertical axis
- Two-way travel time (converted to depth)
Common questions
How is travel time on a radargram converted to actual burial depth?+
The two-way travel time is divided by an estimated radar wave velocity for the soil, which depends on moisture and composition, so an inaccurate velocity estimate is a common source of depth error in GPR interpretation.
What does a buried object typically look like on a radargram?+
A discrete, compact reflector often appears as a hyperbolic signature, a curved arc caused by the radar detecting the object from multiple antenna positions as it passes overhead, distinct from the flatter reflections from natural soil layers.
Related terms
- Antenna Frequency
- The centre frequency of the radar pulse, typically expressed in megahertz. Higher frequencies give finer resolution but penetrate less deeply. Lower frequencies...
- Dielectric Permittivity
- A soil's capacity to store and transmit electric field energy. Higher water content raises permittivity and slows the radar wave. The contrast...
- Hyperbolic Anomaly
- The characteristic arch shape that point-like or cylindrical subsurface targets produce on a radargram. As the antenna passes over a discrete reflector...
- Two-Way Travel Time (TWT)
- The time from transmission of a pulse to receipt of its reflection. Depth is calculated as: depth = (velocity × TWT) /...
- Velocity Calibration
- The process of estimating the true electromagnetic wave velocity in the survey soil, usually by fitting a hyperbola to a known reflector...