Nearly daily, we receive questions regarding the use of long-range GPR in specific environments with the assumption that radar will or won’t work due to water, clays or salt. Often, these assumptions by customers are entirely wrong or misguided.
GPR does not work below the water table
This is partially correct. All radar technologies work through the water table, assuming the groundwater is non-saline. However, radar signals are attenuated in saturated sediments more than they are in dry sediments, particularly with consumer-grade GPR systems. UltraGPR operates in the 10 – 50 MHz and 40 – 100 MHz bandwidths, and is not significantly impacted by the presence of ground water. In fact, UltraGPR would be entirely ineffective at mapping ground water tables for this reason.
GPR does not work in clays
This is partially correct. The suitability of clays to radar penetration is a function of their formation history. Clays which are transported (sedimentary) and their lithified derivatives (claystone, mudstone, shale etc) are generally very poor radar environments with an average of 3 m penetration possible with UltraGPR. However, tropical clays which are formed in situ by weathering are excellent UltraGPR environments, with over 50 m penetration possible.
GPR won’t work on steep slopes or in rough terrain
Consumer-grade GPR systems indeed are not designed for the extreme conditions of mineral exploration and most geotechnical projects. However, UltraGPR has been designed specifically to overcome the limitation of these systems. UltraGPR’s total weight of less than 4 kgs and it’s streamlined antenna design allows it to be towed by hand or vehicle up the steepest of terrains with ease, over extremely rough ground. UltraGPR uses not one cable of fibre optic line – the sources of constant equipment failures with consumer-grade GPR systems. Rather, every communication is handled by WiFi and Bluetooth wireless modules. Tracking is accomplished by differential (SBAS, OmniStar or RTK) GPS, built into UltraGPR.
GPR has been used at a certain project in the past and it didn’t work
We are often faced with the issue where a GPR technology has been applied to a project or a region in the past with little success, or ambiguous results. Certainly the laws of physics apply to all radar technologies. However, it is not simply the use of a certain instrument which yields the most useful data, but also the knowledge and experience of processing and interpreting the data. In some cases the sites are indeed unsuitable for GPR, whilst in many others, the wrong type/frequency/processing was used.
GPR is easy and anyone can do it
This is concept promoted by GPR manufacturers to sell their “cart” mounted GPR systems for pipe, rebar or land mine mapping systems, and it is entirely correct for those systems. Cart and handheld systems are designed for laypeople to produce useable data for shallow targets, and over 90% of GPR system sales are aimed at the lucrative civil infrastructure sectors. However, deep radar applications are far more complex and require specialised systems and experience.
GPR produces wiggly lines that no one can understand
Generally, this is true for deep-radar applications. However, Groundradar firmly believes that if radar data requires an expert to understand it, the technology did not work and should not be used further. Groundradar’s editing, processing and interpretation steps serve to position and enhance the data interpretability. If the basic targets are not evident in the raw data in the field, they cannot be teased out later.
There is this company from Scotland/Russia/Zimbabwe/etc that has a new type of radar that can image 200 m into the ground.
Groundradar encourages potential users of long-range GPR to acquaint themselves with the laws of physics which govern GPR. More information may be found here. Briefly, penetration is not increased by simply increasing transmitter power. If this was the case, it would be trivial to use 1940’s “spark-gap” transmitters to extend the range of radar. In the case of “technologies” such as ADR, Groundradar suggests that this paper be first reviewed by any interested parties. As previously stated, GPR is perhaps the most over-sold geophysical technique in the world, simply because it is not well understood.