How do you interpret the data from ground penetrating radar scans?

1 GPR Basics

Ground penetrating radar operates by sending high-frequency radio waves into the ground and recording the time it takes for a signal to return after bouncing off subsurface structures. You'll see this data represented as a series of hyperbolas or lines on a radargram, which is the visual output of GPR data. The strength and timing of these reflections help determine the depth and density of the materials below. It's important to calibrate the radar system according to the specific soil conditions to get accurate readings.

2 Data Patterns

When analyzing a radargram, you'll notice distinct patterns that represent different subsurface anomalies. Continuous horizontal lines may indicate layers of soil or rock, while hyperbolic shapes suggest the presence of discrete objects or voids. The challenge lies in distinguishing between these patterns and noise—irrelevant signals that can clutter the data. With experience, you can learn to recognize typical reflections from materials like water, metal, or rock and differentiate them from less significant signals.

3 Material Identification

To interpret what materials are beneath the surface, you need to understand signal velocity. Different materials have unique dielectric properties that affect how fast the radar wave travels. By comparing the velocity of the signal return to known values for different materials, you can make educated guesses about the composition of the subsurface features. This is where your knowledge of local geology can be particularly useful, as it provides a reference for what to expect in the given area.

4 Depth Estimation

Estimating the depth of an object or layer is a crucial part of GPR data interpretation. The time it takes for the radar signal to hit an object and bounce back is directly related to its depth. However, because different materials affect the speed of the signal, you must use the correct wave velocity for your calculations. This often requires some on-site testing or background research to establish an accurate velocity model for the area being scanned.

5 Anomaly Analysis

Once you've identified potential subsurface anomalies, the next step is to analyze their shape, size, and depth to determine their significance. For instance, a small, rounded reflection might indicate a boulder or an underground utility, while a linear pattern could suggest a buried pipe or trench. By considering the context of the location, such as known historical sites or utility maps, you can make more informed interpretations of these anomalies.

6 Advanced Techniques

For complex sites or more detailed analysis, advanced techniques like 3D GPR imaging or integrating GPR data with other geophysical methods can provide a clearer picture. Creating a 3D model involves collecting data from multiple angles and using software to construct a volumetric representation of the subsurface. This can help in visualizing the spatial relationships between different structures or objects, providing a more comprehensive understanding of the scanned area.