## 2 Methods and Tools  
### Components and Integration  
Ground-based and drone-based GPR systems comprise several essential components, each playing a pivotal role in ensuring the accuracy and functionality of the technology. First and foremost, the core of this system is the GPR unit itself. The single-unit GPR includes the radar transmitter and receiver antennas, which emit electromagnetic waves  
Figure 1: The location of the GPR survey. (**a**) The site’s location under study is marked by the red arrow (zoom-out map). (**b**) The detailed orthophoto map of the surveyed area provides a high-resolution visual representation to complement the ground-penetrating radar (GPR) data for enhanced interpretation of the subsurface archaeological features.  
into the ground and capture the reflected signals. These antennas are crucial for collecting subsurface data and are typically chosen based on the specific application, considering factors like the desired penetration depth and resolution. The drone-based GPR is produced by Radar Systems Inc. (Radsys, Riga, Latvia), and the ground-based GPR is produced by Sensors & Software Inc. (from Radiodetection, Bristol, UK).  
Integrating GPR technology with drones for archaeological surveys represents a synergistic union between aerial platforms and subsurface sensing capabilities. As seen in Figure 2a, the GPR unit is securely mounted onto the drone, situated underneath the drone, with the radar antennas facing downwards.  
Several key specifications must be considered to achieve optimal performance in such integration. The choice of GPR frequency is paramount, as it directly affects the penetration depth and the subsurface data resolution. Lower frequencies offer greater depth penetration but may sacrifice resolution, while higher frequencies provide finer details at shallower depths. The selection of the appropriate frequency band depends on the specific research objectives and the characteristics of the archaeological site. In the case of the Hulata archeological site, previous exploratory excavations performed by the Israel Antiquities Authority (IAA) [41] in the area brought up findings that indicated that the antiquities in the region are found up to a maximum depth of 2 m from the surface. Therefore, the chosen GPR central frequency was set to 500 MHz, with a built-in 500A antenna, 100 ns time range, and 512 samples per scan.  
Figure 2: Two types of GPR instruments at the site under study. (**a**) A DJI M-300 drone with a GPR 500 MHz shielded dipole antenna is attached below. The SkyHub computer, which is positioned on the right side, is responsible for controlling the automatic flight operations. At the front of the drone, an altimeter measures the distance from the ground, maintaining a constant flight altitude. (**b**) An intelligent cart with a GPR 500 MHz shielded dipole antenna is attached in the middle. Both GPRs provide similar subsurface sensing capabilities up to 5 m below the surface.  
Furthermore, the drone's payload capacity and flight time are critical factors determining the system's overall usability. A well-balanced drone with sufficient payload capacity ensures the GPR unit can be mounted securely without compromising the flight stability, and longer flight times allow for extended data collection periods, which is essential for comprehensively covering large archaeological areas. Additionally, the data-processing capabilities of the drone, or the capacity to transmit data to a ground station for processing, influence the real-time utility of the system and the speed at which results can be obtained during an archaeological survey.  
The ground-based GPR's (Figure 2b) central frequency is the same as for the drone-based GPR (500 MHz), with a 100 ns time range and the dynamic option for the number of scans that ensures the optimal sample number per scan (usually between 8 and 16 stacks). The instrument was equipped with a GPS antenna with a license for the RTK technology integrated to provide accurate georeferencing.