radargram

A radargram is a two-dimensional image produced from radar data, most commonly from ground-penetrating radar (GPR). It displays reflected radar energy as a function of distance along a survey line (horizontal axis) and two-way travel time (vertical axis). Radar data are gathered by moving a transmitting and receiving antenna along the line, recording many traces that are then combined to form a cross-sectional view of the subsurface.

Interpretation relies on the contrast in dielectric properties between subsurface materials. Reflections occur at interfaces such as soil–rock boundaries, moisture changes, voids, or buried objects. The vertical axis indicates travel time, which can be converted to depth if the subsurface wave velocity is known. Depth conversion often uses velocity estimates derived from calibration data, such as boreholes or known horizons.

Radargrams reveal various features: continuous reflectors may indicate stratified layers; dipping or disrupted reflectors suggest faults or disturbances; hyperbolic reflections can signify point-like targets such as pipes or cavities. Data processing steps, including time-zero correction, background removal, dewow filtering, gain adjustments, and sometimes migration, enhance interpretability.

Limitations include attenuation of signals in conductive soils (which reduces penetration depth and clarity), the finite resolution set by the radar frequency, and surface clutter. Accurate interpretation depends on reliable velocity models and, when possible, independent confirmation.

Applications span archaeology (mapping walls and floors), civil and geotechnical engineering (utility mapping, road and pavement assessment, slope stability), hydrology (wetting patterns and moisture distribution), and environmental surveys. Radargrams remain a primary tool for non-invasive subsurface imaging due to their speed, depth range, and relatively low cost.