The new SmartSled configuration allows large area GPR surveys, including mapping of agricultural drainage tiles, to be performed quickly and accurately, even in difficult terrain.
Sensors & Software provides more than just GPR hardware; we provide the complete solution that includes practical configurations to deploy the GPR hardware efficiently for the project. For example, the SmartSled configuration was introduced for Noggin & pulseEKKO GPR systems to address the challenges faced by our customers to survey large areas over rough terrain (Figure 1).
The SmartSled configuration is designed for vehicle-towed surveying for NOGGIN® and pulseEKKO 250, 500, and 1000 GPR systems over smooth to rough, open terrain such as agricultural fields, grass, gravel roads or rocky surfaces. The SmartSled attaches to a common trailer hitch on any vehicle such as trucks, ATVs, tractors, golf carts, or snowmobiles. It has built-in straps to secure the GPR sensors and maintain ground-coupling for maximum GPR signal penetration.
The SmartSled can be deployed with or without an odometer wheel (Figure 1). If an odometer wheel is used, the operator sets the distance interval between GPR traces on the surface, also known as the “step size”. Depending on the antenna center frequency and the size of the target, the step size could range from 0.02 to 0.25m.
When deploying a SmartSled without an odometer wheel, the operator collects data in “Free Run” mode and has the choice of collecting data with a specific time interval between GPR traces or, more typically, setting the tow speed, for example, 3 meters per second or 30 km/hr.
The SmartSled has a mounting bracket to attach an external GPS receiver for accurate positioning. The operator can quickly collect large GPR pseudo-grid surveys that can be processed into depth slices using the EKKO_Project post-processing software.
SmartSled Applications
One of the applications perfectly suited for the SmartSled configuration is mapping drainage tiles in agricultural areas. Drainage tiles are typically used in fine-grained, low porosity and compacted soils that don’t drain excess water naturally. Improved water drainage in the area results in plants with stronger root systems and higher crop yields.
Drainage tiles need to be located to prevent damage when excavating, or when adding or replacing sections of tile is required. In addition, with the increase in sustainable energy installations, windfarms and other power infrastructure need to be routed through farm fields, requiring accurate mapping of drainage tiles. Change of farm ownership may require a map of the existing drainage system. Often, there are no maps of the tiles installed decades before by a previous generation of farmers.
Older tiles are clay, precast concrete, or ceramic pipes while newer ones are plastic tubing (Figure 2) . Since drainage tiles are non-metallic, GPR is one of the only methods, and the least labor-intensive, for detecting and mapping them.
In this case study, a 4-hectare (10-acre) field was scanned using a Noggin 250 deployed in a SmartSled configuration in southwestern Ontario, Canada (Figures 3 & 6).
For many applications of GPR, we recommend that data be acquired on closely spaced lines to generate depth slices and detect point and linear objects (for example, see the accompanying story about tree roots). However, in this application, high data density is not typically required; drainage tiles are large scale linear objects that do not typically change paths abruptly.
One 5-kilometer-long survey line was collected by zigzagging across the field with a line spacing of 8 to 12 meters (Figures 3 & 6). The GPR step size was set to 5 cm; this amounted to about 100,000 GPR data traces collected in just over an hour.
A representative section of the data collected is shown in Figure 4. The undulating responses throughout the cross-section are due to the Noggin 250 moving up and down across the furrows in the field. Although having the GPR bouncing across a farmer’s field resulted in some unwanted artifacts in the data, the SmartSled maintained good ground coupling such that hyperbolic responses from drainage tiles and other objects in the subsurface are visible in the data.
Since the main targets of interest are hyperbolas from drainage tiles and not layer boundaries, the data were processed with a Background Subtraction Filter to remove flat-lying responses (Figure 4) and emphasize the hyperbolic responses. This type of filtering was described in an earlier newsletter story here: https://www.sensoft.ca/blog/tips-enhancing-gpr-targets-by-filtering/
Interpretations can be added to the data in the field, during or after data collection, or in the EKKO_Project PC software, after downloading the data. In this case, the interpreter used a simple strategy for interpreting the hyperbolas visible in the data:
Once point interpretations were added to the data, they were plotted in a map using the associated GPS data. The interpretations clearly showed two prominent drainage lines in the field (Figure 5). Other isolated hyperbolas are assumed to be point targets that are not associated with drainage tiles.
One of the benefits of collecting data with an external GPS on board, is the ability to quickly display the GPR survey on Google Earth and show the survey paths and the interpretations in context (Figure 6).
The SmartSled, with its ability to move the Noggin 250 GPR system smoothly across the rough agricultural fields and keep the GPR well-coupled with the surface, simplified the collection of this drainage tile survey without compromising the quality of the data. In less than 2 hours, 4 hectares (10 acres) of land were surveyed, the GPR data were processed, interpreted, and maps generated. The SmartSled allows GPR operators to collect large GPR surveys in traditionally difficult terrains and add more GPR applications to their services.
Our customers have provided positive feedback about the SmartSled, with early adopters saying:
“We have been very happy with the system…. It is easy to deploy and is durable. “
“…it’s worked well for us – in terms of increasing efficiency and surveying large areas.”
If you are interested in learning more about the SmartSled configuration or the drainage tile application, contact us at sensoft_training@spx.com
