# Underwater Excavation Records Using Underwater Acoustic Survey: A Case Study in South Korea
## 3 Dangampo Site: Equipment Testing
### Results and Discussion
#### 3.2.4 Performance Evaluation  
The wide swath of the SiSS proved advantageous for the geophysical survey as it enabled the rapid surveying and real-time monitoring of the scanned objects, which was useful for detecting anomalous objects (Figure 3). However, the images acquired showed distorted aspect ratios because of the irregular twing speeds, which were reflected in the vertical axis of the acquired images. As a result, the SiSS was not effective in mapping the overall seafloor topography.  
In contrast, the MBES plotted the results as 3D maps displaying the underwater topography (Figure 4). The eastern part of the site had a water depth of 9-10 m, which decreased from around the midpoint onwards to a final depth of 4-5 m in the southern part. Accurate topographic features were distinguishable due to the post-correction of the raw data based on information about the side- and lengthwise shaking of the vessel, navigation speed, depth-dependent speed of a sound wave, and tidal change during surveying. However, this process was time-consuming, and great care was taken to avoid the accidental removal of important information during data cleaning. These inconveniences lowered the efficacy of the MBES for detecting anomalous objects compared with the SiSS system.  
Figure 2: Map codes indicating the geophysical survey sediment removal section at the Dangampo site (§: sediment removal section after the operation).  
The main disadvantage of the SS method is the length of time required to survey a large area, which requires moving between scan positions by repeatedly placing the transducer on different areas of the seafloor. For this reason, the surveying could not be completed as scheduled, although only a partial area of the site was selected for the survey.  
Overall, the SiSS was effective for rapidly obtaining information about the seafloor over a large area, but it was difficult to obtain accurate images. The MBES exhibited disadvantages in terms of its limited survey conditions and the considerable time required to process the data and obtain results. However, it effectively mapped the overall topography of the area. The SS was not efficient for surveying a large area because of the time required to set up the equipment.  
Our results indicated that the SiSS obtained high-resolution images when operated at a 1250 kHz frequency. However, repeated surveying was necessary to obtain high-quality images, and it was difficult to correct distortions incurred during the survey. Despite the advantage of no or little distortion owing to post-correction, the MBES did not efficiently record the SRA because of its low resolution. Conversely, the SS was straightforward to operate and yielded excellent images, even without post-correction.  
Therefore, through the comparative testing of the three survey devices conducted at the first UE at the Dangampo site, the SS was identified as the best-suited instrument for recording the sediment removal survey site.  
Figure 4: Surveying range of the multibeam echo sounder at the site (\(\square\): the site, Google Earth).  
Figure 3: Surveying range of the side scan sonar system at the site (\(\square\): the site, Google Earth).