What is Noise-Modulated GPR?
Noise-Modulated GPR is a form of GPR technology that uses noise-like coded signals to perform subsurface imaging. Like more common pulsed and stepped-frequency technologies, Noise-Modulated GPR systems produce measurements of signal reflection strength versus travel time. This is achieved by emitting a special coded signal, measuring the reflected response and cross-correlating it with the emitted code to produce the familiar GPR A-scan (‘trace’) profile.
Is NM-GPR the same thing?
Partially. ‘NM-GPR’ refers to a particular type of 3D GPR technology developed by CodedRADAR. As the name implies, it uses a form of noise-modulation. Importantly, however, it implements this approach using multiple simultaneous receivers that employ a unique ultra-rapid low-fidelity sampling technique.
Sampling GPR return signals in low fidelity may at first seem counter-intuitive. This approach, however, enables the use of simple hardware that can measure much more quickly and efficiently than conventional methods. The measurement capacity benefits achieved are significant and they vastly outweigh any drawbacks, considering that high quality GPR data can be produced from low-fidelity measurements through the use of dithering and stacking techniques.
The use of simplified hardware is also highly advantageous, as it enables multiple dedicated transmitter and receiver circuits to be integrated into the same GPR digitiser, without it becoming overly complex and unreliable.
An analogy to this are the cores within a modern computer’s Central Processing Unit (CPU). A CPU with more dedicated cores has greater capacity to perform calculations as it distribute the task across more resources. Likewise, having multiple dedicated radar circuits within the NM-GPR digitiser means it can transmit and receive on multiple antennas at the same time, significantly increasing the overall system collection capacity.
Why do we need a different approach?
As 3D GPRs must gather data at regular intervals on so many simultaneous channels, this places significant demand on the radar system’s collection capacity. At times conventional GPR technologies struggle to keep up with this demand, requiring lower collection speeds or compromises in penetration depth, measurement spacing or data quality to keep within operational limits.
The NM-GPR signal and sampling approach is unique within the field of GPR. NM-GPR receivers measure the return signal fast. Really fast. And there are many receivers (4 or 8) operating simultaneously within each NM-GPR digitiser unit. This superior sampling speed, use of multiple receivers and the large improvement in collection capacity that results are needed to enable much faster 3D GPR data collection that does not compromise data spacing, depth or quality.
The NM-GPR approach enables more of the reflected signal to be measured after each transmission. While conventional technologies can only sample one point or a handful of points per return signal, NM-GPR receivers sample each return signal sequentially at 0.1 nanosecond intervals.
As it is the only GPR technology capable of sampling GPR returns at anywhere near this rate, thus NM-GPR is arguably the only true real-time sampling GPR technology available today.
Its lightning-fast sampling capabilities, superior receiver efficiency, simplified radar architecture, and use of multiple simultaneous radars makes NM-GPR-equipped systems blisteringly quick, reliable and capacious. As a result, NM-GPR systems are unmatched for rapid 3D subsurface imaging applications.