Gridded GPR survey method is the more traditional approach and the natural partner of a high productivity GPR survey for areas which cannot be accessed with the towed system.
What is it
The use of one or more of the central antennas from our Stream EM GPR system, mounted on a hand pushed trolley. This is pushed across the survey area in a series of parallel lines both perpendicular and parallel to the survey area to form a survey grid. Typical spacing should be 0.5 or 1m between scans.*
* The majority of GPR surveys are operated in this method with the exception of on-site detection surveys where the ground is marked on-site.
Why use it
The principle advantages of a grid method GPR survey are
- High quality
- Excellent coverage
- High detection capability
- Ability to see through some rebar and detect smaller targets*
* depends on the frequency of the antenna.
Where is it suitable for
Gridded GPR surveys can be deployed in most environments but take considerably longer than a high productivity GPR survey. For this reason it is recommended for areas which cannot be serviced using high productivity GPR first:
- Urban roads (low speed) with traffic management – shorter lengths, dead ends and small roundabouts.
- Footpaths wider than 1.5m with traffic management.
- Irregular but mostly open areas
- Areas with some obstructions
- Flat surfaces and grass
The system can be used but is less ideal for:
- Large areas and major routes (suitable for high productivity GPR)
Who needs it
Grid method GPR surveys are suitable for:
- Surveying companies as part of a PAS128 compliant service
- Highways agency
- Local councils
- Large contractors
Not suitable for
GPR surveys are not suitable for all situations, in very small or narrow areas it is not possible to complete a meaningful GPR survey. Some of the areas not suitable for a grid method GPR survey include:
- Narrow footpaths (no perpendicular scans can be completed)
- Very large areas
- Reinforced concrete
- Rough ground
About our system
For gridded GPR surveys, GPR Pro uses the central antennas from our Stream EM high productivity GPR system, similar to the IDS RIS Hi Mod in its ‘as delivered’ configuration. We have found the performance to be reliable without additional modification.
When operating this equipment we typically favour survey grids over GPS or TS in most cases.
Note: ‘mini’ versions of high productivity GPR systems
GPR Pro has experimented with ‘mini’ versions of high productivity GPR and has not been satisfied with the performance when compared to the grid survey method for small areas at this time, given that in most cases we use high productivity GPR for large area surveys, we do not consider the time saving on small areas to be worth the performance reduction. For these reasons we currently do not recommend the ‘mini-Stream’ approach.
GPR Pro will continue to experiment with new technologies as they reach the market.
Advantages of a grid method GPR survey
The principle points about a gridded GPR survey method / system can be summarised as follows:
- Grid survey method
– Optimal coverage
– Reliable positioning
- Both high and low frequency antennas are used in all scans
– Excellent detection capability
– Ability to see through some rebar
– Can operate in smaller spaces and around obstructions
– Limited ‘Off road’ capability
The principle consideration when specifying a gridded GPR survey is speed, a typical gridded GPR survey is 450% slower on-site than our Stream EM vehicle towed high productivity GPR system. Leading to higher costs and slower delivery times.
The gridded GPR survey method also requires personal to be working in the road at all times and often requires traffic management.
The combination of additional time on site and traffic management lead directly to higher costs and reduced safety.