## 4 Material and Methods
### Ground Penetrating Radar  
Ground penetrating radar (GPR) is an electromagnetic approach that archaeologists can use in the 21 st century to undertake excavations. Its purpose is to investigate the earth's shallow subsurface, as well as bridges, canals, ancient quarries, railroads, urban structures, building supplies, cave structures, and archaeological features with considerable deeply stratified masonry relics. This will offer precise exploration depth for various subsurface structures [68]. The GPR method necessitates the transmission of electromagnetic radio (radar) signal in the form of an elliptical cone from the transmitting antenna to the ground, as well as the estimation of the time among transmission and reflections of the buried discontinuity, and reception back to the surface radar antenna (receiving antenna). Ground penetrating radar is commonly used in archaeological evidence. It's rapid, and it allows an archaeologist to cover a large area of buried archaeological sites with high accuracy while avoiding harm to the surface. One advantage of radar scans over other archaeology approaches is that they can map the subsurface stratigraphy and archaeological aspects of a site at a true depth according to the antenna's frequency [69].  
The GPR data was collected utilizing Geophysical Survey Systems Incorporation (GSSI) type SIR 4000 equipment with a central frequency antenna of 200 MHz. Sensors, control units, and connections are the critical elements of this instrument. The control system produces a high-voltage electrical signal that is delivered via cables to the transmitter, boosting the voltage and form of the pulse before it is transmitted by the antenna, maintains the system during the scan, and keeps track of the transmitter-receiver relationship [69]. The Topcon GPS receiver is used to precisely locate the coordinates of the observed sections. The data from the output is filtered, enlarged, and stored (Figure 4). This survey was carried out in two stages at the study site: reconnaissance and details surveys. A detailed survey was carried out over the prospective locations based on the results of the reconnaissance phase. As a result, the research site was divided into four grids, each measuring 50 \(\times\) 51 m, where successive inline profiles were surveyed with 1.5 m spacing, yielding 35 profiles in each grid for a total of 140 profiles (Figure 5).  
Figure 4: (**a**) is GPR field survey operation, and (**b**) is GSSI-SIR 4000 instrument attached with a central frequency antenna of 200 MHZ.  
Figure 5: Locations of the GPR profiles in the study region, where the main site was categorized into four grids for implementation of the radar field survey. Every grid was surveyed with 35 parallel profiles with a length of 50 m conducing 140 profiles for the total work.  
According to the historical background of the pre-explored tombs, the expected depth of the undiscovered archaeological features is not likely to surpass 5 m. Accordingly, the central frequency antenna of 200 MHz was used for producing high resolution images of the main potential targets. Figure 5 shows the four surveyed grids in the study site. Careful inspection of the results of all radiograms which produced from 140 profiles in all grids indicate that there are some places exhibited potential archaeological features and other placed do not exhibit any archaeological features. As a result, the areas that may have indicated archaeological features were re-surveyed using more precise grids of 11 inline and 11 crossline profiles each of them is 15 m length.