# Quality Analysis of Unmanned Aerial Vehicle Images Using a Resolution Target
## 5 Conclusions  
In this study, we acquired images from four types of UAVs and one type of manned aircraft to investigate the need for MTF analysis in UAV image quality assessment. We also examined the impact of shooting altitude and sensor performance on the quality of unmanned aerial images. An MTF analysis was conducted using a slanted edge target, while the GSD analysis was performed using a bar target. First, the trend in \(\sigma_{MTF}\) indicated that the image quality worsened as the flight height increased in both the MTF and GSD analyses. However, the \(\sigma_{MTF}\) values were low for the FC 6520 and FC 6310 sensors, resulting in a slight blurring of the white object. The MTF analysis evaluates both image resolution and contrast; hence, slight blurring has a considerable effect on \(\sigma_{MTF}\). However, the MTF analysis of the corresponding bar was not possible owing to contrast reduction of the bar target for which the visual resolution analysis was possible. The smallest bar that can be recognized as the bar target, which can be analyzed by visual resolution, determines the GSD of the corresponding image. For example, the FC 6310 sensor, at a shooting altitude of 150m, can analyze up to Bar 5, which is 6.3 cm in size due to reduced contrast ratio. However, the GSD results analyzed using Bars 1-5 showed a 5 cm result. Similarly, the iXM-100 sensor, at a 400m shooting altitude, can analyze up to Bar 6, which is 5.6 cm in size due to reduced contrast ratio. However, the analyzed GSD result was 4.5 cm. Therefore, the MTF, which can analyze both the degree of contrast and resolution of the image, was required to verify the quality of the unmanned aerial image, which experienced a deterioration in its quality owing to various factors, such as weather conditions, the use of non-surveying cameras, and low-cost navigation devices. Thus, the MTF analysis was proven to be a more objective and reliable method of analysis than the GSD analysis. Secondly, we observed a decline in image quality for both the FC 6310 and iXM-100 sensors as shooting altitude increased. Furthermore, when comparing images captured by these sensors at the same altitude of 150 m, it was evident that the GSD and MTF values varied based on the sensor's performance. Consequently, we confirmed that both shooting altitude and sensor performance significantly impact the image quality of UAV images. Third, despite the UltraCAM Eagle M2 manned aircraft sensor exhibiting the poorest image quality, the results from the FC 6310 sensor were nearly identical at a height of 150 m compared to those from the UltraCAM Eagle M2 sensor. These observations suggest that obtaining high-quality UAV images during UAV photogrammetry is contingent upon the operator accurately determining appropriate camera-sensor parameters, overlapping, and UAV performance before capturing the images, regardless of the number of UAV sensors used. Figure 12: Comparison of the MTF curves obtained from cameras using slanted edge target. In this study, we confirmed the necessity of both MTF analysis and GSD analysis for assessing image quality. This was achieved by conducting analyses at various research sites, adjusting the flight height, and using different mounted sensors, which exert the most significant influence on image quality. In future studies, if a test bed with a permanent UAV photogrammetry resolution target can be constructed to analyze the quality of the image under the same conditions, it will be possible to analyze it more quantitatively and objectively, and to accumulate data. As a result of the analysis, it was determined that MTF analysis, which can analyze the resolution and contrast of images simultaneously, rather than GSD analysis, was a more objective and reliable method. It was found that high-quality unmanned aerial images could be obtained only when workers properly judge the performance of camera sensors, redundancy, and the aircraft's performance. Investigation, S.-M.S. and J.-H.K. ; Methodology, S.-M.S. and J.-H.K. ; Supervision, J.-H.K.