Remote Sensing (RS)
Fateme Amjadipour; Hamid Dehghani; Mojtaba Behzad Fallahpour
Abstract
Extended AbstractIntroductionThe complexity of interpreting SAR radar images makes target recognition difficult despite many studies performed in this regard. Various factors including material and dimensions of the target, radar frequency, polarization, target shape, and vision geometry affect the response ...
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Extended AbstractIntroductionThe complexity of interpreting SAR radar images makes target recognition difficult despite many studies performed in this regard. Various factors including material and dimensions of the target, radar frequency, polarization, target shape, and vision geometry affect the response received from SAR radar. Investigating these characteristics facilitate target recognition.Synthetic Aperture Radar sensors are widely used in both airborne and space-borne systems. Space-borne systems equipped with Synthetic Aperture Radar sensors are side-looking and because of their nature as a radar, many parameters such as vision geometry will affect their ability (or disability) in seeing the target and change the resulting images. Therefore, it is very important to study the effect of this parameter to identify the target and interpret these images. The visibility geometry includes incidence angle, look angle, and the direction of the imaging. Materials & MethodsThe present study investigates visibility geometry in revision images and ascending and descending scenes. To reach this aim, a single scene captured by Sentinel-1 from a residential area is examined in different images with different directions, incidence angles, and imaging time. Results indicate that incidence angle changed slightly (4 degrees) and thus, left a negligible effect on the image. Moreover, there was a 5-day time interval between the captured images and therefore, this factor had the least effect on Synthetic Aperture Radar images. Unlike optical images, the direction of imaging had the greatest effect on SAR images. For an instance, a single ramp behaves differently in two images captured from different directions. Therefore, direction of imaging and its effects on seeing (or not seeing) the target are analyzed in ascending and descending images. Results & DiscussionThe effect of vision geometry on radar images has been rarely investigated in similar studies, and the present paper has taken a step forward in this regard. Fallahpour et al., (2016) have simulated the effect of incidence angle, which is a parameter of visibility geometry and the shape of the targets in SAR images. Shapes such as cones, cylinders, and cubes were used in this simulation representing real buildings, niches, tree trunks, etc. which are very common in SAR images. Moreover, behavioral pattern of the aforementioned geometric shapes were simulated at different landing angles (30, 40, 45, 50, and 60 degrees) from the viewpoint of SAR imaging systems to reach a more comprehensive result.Then, various studies investigating the effects of incidence angle and direction on radar images have been reviewed. Some of these studies have dealt with the effect of these parameters on the classification of radar images. Dumitru et al. have examined the effects of resolution, pixel spacing, patch size, path direction, and incidence angle on the classification of TerraSAR-X images. To reach this aim, they have selected an optimal TerraSAR-X product and then specified the number of classes. They have finally investigated the effects of incidence angle and path direction on the classification results. Results indicated that images captured in ascending direction were 80% better than the descending images. Moreover, images captured from an incidence angle near the upper wing showed better results. ConclusionThe present study has investigated the effect of usually neglected parameter of visibility geometry on SAR images. Images were captured by Sentinel-1 in both ascending and descending directions. Following speckle noise reduction and geometric correction, incidence angle and its effects on the detected changes were investigated. The slight 4-degree changes of this parameter have not caused the resulting changes. Moreover, there was a 5 day time interval between these two images and thus, time could not be an effective parameter too. Results indicate that detected changes in the residential area were due to a change in the direction of imaging. Changes of this parameter can result in seeing (or not seeing) the target, and therefore, it is very important to investigate the effects of this parameter and correct it.
Mojtaba Behzad Fallahpour; Hamid Dehghani; Ali Jabbar Rashidi; Abbas Sheikhi
Abstract
Abstract
Effective factors in SAR images can be divided into five general categories of radar, radar-carrying platform, channel, imaging domain and raw data processing section. In each of these factors, various physical, structural, hardware and software parameters are influential, in such a way that ...
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Abstract
Effective factors in SAR images can be divided into five general categories of radar, radar-carrying platform, channel, imaging domain and raw data processing section. In each of these factors, various physical, structural, hardware and software parameters are influential, in such a way that one can see the role of each of them in the final formed image.
Modeling, Analyzing and, in general, knowing the effect of each of these parameters, will provide a better understanding of how SAR imaging systems operate, and from this point of view, it will not only be an important step in designing and manufacturing these types of systems, but also it will provide the possibility of interpreting and analyzing these types of images. For this purpose, in the present paper, the effect of the angle of incidence and the shape of the targets which are parts of the radar and the imaging domain parameters, are simulated in SAR images. The shapes used in this simulation are cylinders, cones and cubes, which represent buildings, silos, tree trunks, etc., in the real world, so they are very abundant in SAR images. Also, for more comprehensive results, different angles of incidence of 30, 40, 45, 50 and 60 degrees have been selected for simulation. With this simulation and analysis of the results, the behavioral pattern of the above geometric shapes is extracted at different angles of incidence from the perspective of SAR imaging systems. Thus, an important step in identifying and recognizing various shapes, which is one of the most important issues in the interpretation of SAR images will be taken.
