## 1 Introduction
By combining GPR with geospatial analysis, they comprehensively characterized moisture distribution. However, a few of these examples directly relate to construction engineering [37]. They are applicable only with limited measurement lines in relatively flat and accessible areas convenient for traditional land GPR measurement. On the other hand, airborne-based GPR emerges as a cutting-edge technology, utilizing electromagnetic waves to penetrate the subsurface and capture detailed geological information [39]. In contrast to traditional ground-based GPR, drone-based GPR offers several advantages over conventional ground-based methods [40]. Uncrewed aerial vehicles (UAVs) equipped with GPR sensors can rapidly and non-invasively cover large and inaccessible areas, offering a three-dimensional perspective of the subsurface boundaries with their geotechnical properties and achieving heightened spatial resolution [41]. Applying real-time kinematic (RTK) GPS positioning enables precise survey paths to be repeated and opens new opportunities for 4D data acquisition [42]. The UAV-mounted GPR system, equipped with advanced signal processing techniques such as cross-correlation-based background subtraction and interference suppression [43; 44], ensures accurate detection of underground targets. [PERSON] and [PERSON] [45], for example, demonstrate a good fit between the results by comparing land-based GPR and drone-based GPR, both operating with a 500 MHz antenna, to map archaeological artifacts at a clayey soil site in Northern Israel. Despite the potential advantages, it also addressed how to overcome specific physical challenges related to drone-based GPR, such as increased above-ground interference, signal decay in air, and drone stability issues, by presenting analytical formulations [45]. A drone-based GPR application helps examine areas with limited accessibility, e.g., the regions with sharply changed topography, rough, stony, muddy soil/rock surfaces, etc. For example, [PERSON] et al. [46] demonstrated the effectiveness of drone-borne controlled-source electromagnetic (CSEM) systems in capturing detailed 3D datasets over alpine glaciers. [PERSON] et al. [47] used drone-borne GPR with a 900 MHz antenna to map snow cover depth in the Alps, proving the readiness of drone technology for high-altitude GPR applications. [PERSON] et al. [48] showed how drone-mounted GPR with 120 MHz antennas can optimize mining operations by mapping geological structures in a quarry in Falconara Albanese, Italy. [PERSON] et al. [49] highlighted using airborne GPR in clay soils, identifying subsurface objects despite challenges with electromagnetic wave decay, an issue also managed by [PERSON] et al. [32] using land GPR in agricultural fields. This study addresses the critical challenge of accurately identifying subsurface boundaries, such as soil-to-rock interfaces and groundwater levels, in areas with complex topography and limited accessibility. These features are crucial for structural engineering analyses, especially in foundation engineering applications [13; 14; 15] and site-specific response evaluations [18; 19; 20]. Hence, it is essential to identify them accurately. Traditional geophysical methods, including ground-based GPR and borehole drilling, often face coverage, cost, and efficiency limitations, particularly in challenging terrains [50; 51; 52; 4; 6; 7]. This research introduces an innovative approach by utilizing drone-based GPR technology, which offers a non-invasive, rapid, and precise method for mapping subsurface features, even in densely obstructed urban environments. The study's significance lies in its potential to revolutionize structural engineering analyses and site-specific response evaluations by offering a more accurate and practical solution for assessing subsurface conditions in environments where conventional methods fall short.