Abstract
The edge detection plays an important role in post-processing of PolSAR images. It is still a great challenge for extracting all the edge features and suppress speckle noises, especially when weak/strong edges appear simultaneously outside and within heterogenous areas. In this paper, a novel hybrid edge detection framework is proposed to address this problem. The proposed method is designed by fusing two initial edge detectors, which can detect complementary edge information. One is an improved polarimetric constant false alarm rate (IP_CFAR) edge detector, which can detect weak edges well, but fail to detect the edges in the heterogeneous regions. The other is the proposed weighted gradient-based (WG) detector which can detect edges in heterogeneous areas well, but loses some weak edges and produces some false edges due to the speckle noises. Secondly, based on the two detectors above, a wavelet-based hybrid edge detection method is proposed by combining their merits and suppress their shortcomings. To fuse them effectively, wavelet transformation is utilized and semantic rules are defined to extract their advantages. Moreover, a despeckling scheme is designed to suppress the false edges in the wavelet domain. Experimental results demonstrate that the proposed method outperforms the state-of-art methods in extracting both weak edges and strong edges within heterogeneous regions.
Highlights
Polarimetric synthetic aperture radar (PolSAR) images [1] have been paid much attention by researchers in recent years, since they can provide more information than singlepolarimetric synthetic aperture radar (SAR) images
The urban area and the forest are considered as the heterogenous areas, since there are obvious intensity changes within them
The improved polarimetric constant false alarm rate (IP_CFAR) and weighted gradient-based (WG) edge detectors are proposed to detect the weak edges in the homogenous areas and strong edges within the heterogenous areas respectively
Summary
Polarimetric synthetic aperture radar (PolSAR) images [1] have been paid much attention by researchers in recent years, since they can provide more information than singlepolarimetric synthetic aperture radar (SAR) images. A complex PolSAR scene usually includes both heterogenous and homogenous terrain types such as the urban areas, forests, farmlands, waters and so on. As shown in Fig., in the PolSAR image of Oberpfaffenhofen area, the road and the farmland are homogenous areas and the buildings are heterogenous areas. It can be seen the road edge in the red rectangle is weak edge, and the internal changes of urban areas in the yellow rectangle is the strong edge. The target of edge detection is to detect the boundary between different ground objects in homogenous areas, and the internal changes of heterogeneous areas. A higher threshold will lose some weak edges, while a lower threshold will produce false edges by speckle noises
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