(2) There exists a nonlinear intensity difference (NID) between the two images. The main difficulties encountered in realizing high-performance co-registration of optical and SAR images are: (1) The imaging modes of the two are quite different.
#Templates for pages order form registration
Image registration is the process of aligning two or more images corresponding to the same scene acquired at different times, different sensors, or under different conditions. The co-registration of optical and SAR images is mainly used in image fusion, image segmentation, change detection, 3D reconstruction, and so on. The high-efficiency and high-precision automatic co-registration of optical and SAR images is a prerequisite for the fusion of their advantages. However, compared to optical images, the imaging properties of SAR images make them not easy to interpret. Compared with optical sensors, it can realize all-weather earth observation without being affected by weather changes. Synthetic aperture radar (SAR) is an active microwave sensor. The registration results obtained on seven pairs of test images show that the proposed method has significant advantages over state-of-the-art methods in terms of comprehensive registration accuracy and efficiency. Aiming at the repeated feature description in the overlapping template and the multi-peak problem on the search surface, this paper adopts the template search strategy of overlapping template merging and non-maximum suppression. On this basis, the 3 × 3 neighborhood angle-weighted gradients of each pixel are fused to form a pixel-wise 3D dense feature description. In order to more accurately describe the structural features of the image, the single-scale Sobel and ROEWA operators are used to calculate the gradients of optical and SAR images, respectively. This paper proposes a fast co-registration method including 3D dense feature description based on a single-scale Sobel and the ratio of exponentially weighted averages (ROEWA) combined with the angle-weighted gradient (SRAWG), overlapping template merging, and non-maxima suppressed template search. However, due to the inaccuracy of sensor parameters, the relative positioning accuracy is still as high as tens or even hundreds of pixels.
With the development of remote sensing technology, both optical and SAR images equipped with sensor positioning parameters can be roughly registered according to geographic coordinates in advance. These phenomena lead to what is known as a challenging task to register optical and SAR images.
The SAR image is also accompanied by strong multiplicative speckle noise. Due to differences in synthetic aperture radar (SAR) and optical imaging modes, there is a considerable degree of nonlinear intensity difference (NID) and geometric difference between the two images.
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