## 2 Materials and Methods
### Establishment of the Performance Test Site  
Since 2010, the Sungkyunkwan University Geospatial Technology Center has operated a certified test site dedicated to the evaluation of underground utility detection systems. The facility serves as a standardized environment for validating the depth range, positional accuracy, and detection reliability of various sensing technologies. The 25 m \(\times\) 25 m testbed is systematically organized into two zones: one comprising metallic conduits and the other composed of non-metallic lines such as PVC and PE pipelines.  
Although no globally standardized depth is universally enforced, underground utilities are typically installed at approximately 3 m. To simulate a range of real-world field conditions, additional test lines were installed at a depth of 2 m for research and calibration purposes. The conduits were constructed in accordance with national specifications regarding diameter, wall thickness, and material classification.  
The backfill consisted of a 30 cm thick layer of compacted decomposed granite soil, selected for its favorable wave transmission characteristics. This layer was then covered with 5 cm of asphalt to replicate typical urban pavement conditions. To ensure accurate spatial referencing, a total station was used to measure and record the three-dimensional coordinates of each buried conduit. The resulting dataset enables the precise assessment of detection accuracy, allowing for consistent comparisons between different types of utility detection equipment.  
In addition, the testbed includes features such as conductive tracer wires along metallic pipelines and high-contrast positioning for non-metallic lines. These components enhance the reproducibility and repeatability of detection scenarios, providing a standardized environment for validating the performance of GPR, AML, and other smart locator technologies.  
According to [44] well-defined test environments are essential for evaluating the positional accuracy and detection reliability of underground utility sensing systems using GPR and similar technologies. Similarly, ref. [45] emphasized the importance of structured testing environments in assessing the performance of underground utility detection equipment. Furthermore, ref. [46] highlighted that integrating AR and GIS technologies can  
Figure 4: Determination of depth with AML equipment.  
significantly enhance the visualization and mapping of underground utilities, facilitating real-time data sharing and improving communication among stakeholders. The testbed was constructed with various underground utilities, including metallic and non-metallic pipes, as shown in Figure 5.  
To ensure procedural consistency across the two-year testing period, all 32 AML measurements were conducted by the same operator under dry environmental conditions, with no rainfall occurring for at least three days prior to each trial. Pre-calibration of the AML device was performed before each measurement session, and no drift or recalibration adjustments were necessary throughout the experimental timeline. This methodological consistency helped mitigate operator-induced variability and environmental influences, thereby enhancing the reliability and reproducibility of the recorded results.