Attenuation
Definition
The reduction in radar signal amplitude with distance traveled. Electrically conductive materials (wet clay, saline soil) convert signal energy to heat, limiting useful depth. Attenuation rate is measured in dB/m and rises steeply with soil conductivity and frequency.
- Definition
- Reduction in radar signal amplitude with distance
- Measured in
- dB per metre
- Worsened by
- Wet clay, saline soil, higher frequency
- Mechanism
- Conductive material converts signal energy to heat
- Practical effect
- Limits maximum useful GPR survey depth
Common questions
Why does soil salinity matter so much for GPR survey planning?+
Saline groundwater raises electrical conductivity, and conductive material dissipates radar energy as heat rather than reflecting it back to the antenna, so a site with saline or clay-rich soil can limit useful penetration to a fraction of what the same equipment achieves in dry sandy soil.
How does an investigator compensate for high attenuation in the field?+
Common adjustments include using a lower-frequency antenna, which penetrates deeper at the cost of resolution, taking test scans over a known feature to calibrate expected depth before the main survey, and combining GPR with another detection method when attenuation is expected to be severe.
Related terms
- 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),...
- 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...