| dc.description.abstract | Synthetic Aperture Radar (SAR) data are often used in environmental and disaster observations and monitoring. Using the Differential SAR Interferometry (D-InSAR) technique, the displacement of the surface can be obtained. However, in mountainous and urban areas, there may be serious problems such as foreshortening, layover effect and shadow. This will lead to errors in calculating coordinates and removing terrain effects. Combining synthetic aperture radar imagery and digital surface model (DSM) is a potential solution to reduce these artifacts.
The objective of this study is to solve the problem of incorrect coordinates of SAR images. The idea is to use the DSM with ray tracing method to simulate the SAR image of the terrain scanned by a satellite to generate a simulated SAR image. Then, combining the simulated SAR image with the radar image, so that the simulated SAR image provides the three-dimensional coordinates of each pixel in the real SAR image.
The developed method is applied to examples of correcting the coordinates of dams, bridges or tall building in SAR images. Layover effect will cause continuous high-intensity radar signals to be located at wrong positions. These signals should come from the structural reflection of the dam body, bridges, and buildings. The correctly derived positions should be on the wall or top of these artificial structures, but SAR images have only two-dimensional coordinates and cannot correctly represent the positions of the signals. After applying the method developed in this study, converting the two-dimensional coordinates into three-dimensional coordinates can solve these problems. In most cases of this study, the radar signal at the wrong position can be corrected by 20~40 meters in the horizontal direction, and it can improve the accuracy of the image coordinates. However, the radar signals in other areas, such as plains, the coordinate offsets of these positions are less substantial. However, after applying the developed method, the radar signal can still be corrected by 0~10 meters in the horizontal direction and mapped onto 3D surfaces correctly. The outcome of this research can help the subsequent processing and analysis of SAR data, and the results can be correctly overlaid with other spatial datasets. | en_US |