What is Drone Ground Penetrating Radar (Drone GPR)?
Drone Ground Penetrating Radar (Drone GPR or Airborne GPR) is a geophysical survey method flown on a drone (UAV) that uses pulses of electromagnetic radiation to image below the ground surface. As a non-intrusive and non-destructive survey method, drone GPR allows operators to investigate subsurface features without disturbing the ground. Consequently, it provides an effective solution for analysing a wide range of materials, including soil, concrete, masonry, and asphalt.
Drone GPR works by sending a tiny pulse of electromagnetic energy into a material and recording the strength and the time required for the return of any reflected signal.
A scan is a series of pulses over a single area. Whenever the energy pulse enters a material with different electrical conduction properties or Relative Dielectric Permittivity (RDP) from the material it left, part of the signal is reflected. The larger the contrast in the dielectric constants and conductivities of the two materials, the stronger the reflection. As a result, an electromagnetic pulse travelling from dry sand (dielectric value 5) to wet sand (dielectric value 30) produces a strong reflection, while moving from dry sand (5) to limestone (7) will produce a relatively weak reflection. Therefore, buried metallic objects often make excellent targets because they create significant contrasts in electromagnetic properties.
Materials and Relative Dielectric Permittivity (RDP)
| Material/soil type | RDP |
| Vacuum | 1.00 |
| Air | 1.00 |
| Snow (@ ρ=0.35 / 350 kg/m³) | 1.57 |
| Clayey soil (dry) | 2.00 |
| Petroleum (crude) | 2.10 |
| Oil | 2.40 |
| Sandy soil (dry) | 3.00 |
| Ballast | 3.14 |
| Ice | 3.14 |
| Soil (frozen) | 3.14 |
| Soil (very dry) | 3.14 |
| Mica | 4.00 |
| Railway ballast | 4.60 |
| Granite (dry) | 5.00 |
| Polyethylene (PE) | 5.00 |
| Rock (dry) | 5.00 |
| Sand (dry) | 5.00 |
| Soil (dry) | 5.00 |
| Concrete | 6.00 |
| Sandstone (saturated) | 6.00 |
| Glass | 7.00 |
| Granite (saturated) | 7.00 |
| Limestone (dry) | 7.00 |
| Soil (rocky) | 7.00 |
| Basalt (saturated) | 8.00 |
| Limestone (saturated) | 8.00 |
| Average Normal Soil | 9.00 |
| Till/moraine | 11.11 |
| Soil (wet) | 14.00 |
| Clayey soil (saturated) | 15.00 |
| Cultivated soil | 15.00 |
| Shales | 15.00 |
| Sandy soil (saturated) | 19.00 |
| Soil (very wet) | 23.00 |
| Sand (saturated) | 30.00 |
| Silts | 30.00 |
| Soil (saturated) | 30.00 |
| Clay | 40.00 |
| Peat | 56.00 |
| Gyttja/mud | 60.00 |
| Water | 81.00 |
| Metal | 1000000.00 |
High RDP Complications
When we consider the table and the values for heavy soils and water, it is no surprise to learn that ground-penetrating radar will not work well in clay soils, particularly if they are waterlogged. Furthermore, the GPR signal is unable to penetrate through metallic objects, including very dense material reinforcement. Consequently, when the GPR signal encounters a metallic object, it generates a strong reflection while absorbing or scattering the remaining energy. As a result, the system cannot detect objects directly beneath that target during the same scan.
The conductive properties of metal mean any GPR signal will not pass through it but will instead resonate within it until there is no energy present. In essence, the greater the electrical conductivity of the subsurface materials through which a given electromagnetic wave (the GPR signal) must pass, the more reduced the penetration depth the wave will reach. Additionally, signal power and antenna frequency both influence penetration depth.
Higher Frequencies = Shorter Wavelengths
Higher central frequencies provide a higher resolution but a limited depth. Consequently, higher-frequency GPR systems can identify smaller objects with greater detail. Conversely, a lower frequency GPR provides greater penetration depth along with lower resolution. Therefore, operators should select the antenna frequency according to the survey objective – choosing the appropriate central frequency significantly improves survey performance.
For example, it would be pointless using a 500 MHz GPR for studying typical soil strata below 5 m because the signal would simply not reach. However, using the same GPR to detect pipes buried at only 0.5 m would be beneficial. In the same way, utilising a 125 MHz GPR to detect small objects at 0.5 m would be pointless, as it would simply not have the resolution. However, the same GPR would be very effective for deep geophysical studies at 10 m or more, where large sediment layers were being studied.
Drone Ground Penetrating Radar (Airborne GPR) Applications
Drone GPR supports a wide range of surveying applications across multiple sectors.
For example, organisations use drone GPR for:
- Utilities Mapping – pipe detection and backfill identification
- Mountain Rescue – avalanche support for Search & Recovery
- Archaeology Surveys – buried artefacts and architecture search
- Land Conservation – soil analysis, cavity, and sinkhole analysis
- Geological Studies – rock thickness and state of structure
- Waterway Conservation – fresh water bathymetry / infrastructure mapping
- Criminal Investigations – buried remains location
- Artic Surveys – snow, ice & permafrost thickness measurements
Drone GPR – Key Considerations
- Half of the signal strength of any flown GPR is lost through ground surface reflection, which means heavy soils are not ideal.
- Heavy soils (clay and loam) are not at all friendly to airborne GPR. Wet heavy soils will provide poor results.
- An RDP less than 9 is required for effective results. Ideal UK soil conditions are dry sandy soils.
- Fresh water bathymetry with airborne GPR is extremely effective and useful. However, it must be remembered that airborne GPR will not work in salt water.
Drone GPR – Fresh Water Bathymetry
Drone GPR utilises longer signal wavelengths that can penetrate 5-10 m depth of water and even penetrate sediments below the riverbed or lakebed. For example, using a RadSys LF GPR with a central frequency of 100 and 150 MHz, the GPR can take readings of a river’s depth, the depth of the soft sediments, the depth of the harder sediments below the softer sediments, and even the depth to bedrock.
RadarTeam Cobra SE-150 (124MHz) Profile for River Lule
Types of GPR Use and Their Central Frequency (MHz)
It is important to note that the central frequency is just that, a central frequency. The fact is, all GPRs operate with a range of frequencies, including the central frequency. However, for selection of a GPR, we use the central frequency. For example, concrete inspection surveys often require frequencies between 1500 and 2500 MHz because these frequencies deliver the resolution needed to identify very small cracks. Investigations of soil analysis and utility searches can use frequencies between 500 MHz and 1000 MHz. Additionally, for deeper geophysical investigations looking for large sediment changes at deeper depths, geophysicists typically select central frequencies of between 50 and 250 MHz.
UgCS Drone GPR – Standard Range
| GPR | Centre frequency, MHz |
| Radarteam Cobra Plug-In with SE-70 | 80 |
| Radarteam Cobra Plug-In with SE-150 | 124 |
| Radarteam CBD | 500 |
| Radar systems LF GPR (di-pole) | 50/85/100/150/300/400 |
| Radar Systems Zond Aero NG 500 | 500 |
| Radar Systems Zond Aero NG 1000 | 1000 |
Note: Further Frequencies on Request to Suit Project Needs
UgCS SkyHub & UgCS True Terrain Following (UgCS TTF)
The UgCS SkyHub solution is a hardware and software set designed to enhance UAV capabilities for commercial Ground Penetrating Radar (GPR) surveying and inspection purposes. In essence, SkyHub serves as the central onboard computer for the entire geophysical survey solution. When operators use a GPR payload, the system geotags and stores all survey data directly within the UgCS SkyHub. Furthermore, for maintaining an accurate AGL for your drone and sensor, the True Terrain Following Feature (UgCS TTF), and if fitted, the UgCS Obstacle Detection Radar (UgCS ODR), works with the UgCS SkyHub in complete harmony.
For more information on the SkyHub, TTF or ODR systems, click here.
Case Studies
To get access to any of these UAV GPR system case studies, please get in touch:
- Airborne GPR Integrated System: A way for safer and more efficient snow and ice studies.
- Evaluating airborne GPR’s potential for UXO and landmine detection in a controlled environment.
- Applicability of high-frequency UAV GPR system for bathymetric surveys.
- Detection of underground water distribution pipes by a UAV-embedded GPR system.
- Using a Drone-Based Ground Penetrating Radar for Avalanche Victim Search.
- Non-destructive Quality Control of Retaining Wall Construction with Drone-based GPR.
- 5 Mistakes In Utility Mapping that Airborne GPR Could Have Prevented.
- Subsurface Mapping: A Comparison of UAV and Ground-Based GPR by Medusa Explorations.
- UAV-Borne GPR Reveals Alpine Snowpack Variability for Improved Avalanche Risk Management.
- Mapping 112 km of GPR Data at Otemma Glacier in Four Days with True Terrain Following Support.
For further information on anything on this page, including access to case studies, follow this link: Get in touch.
Additionally, read more about drone ground-penetrating radar here, or sign up for the JBUAS Drone GPR Course.
