Orthorectification of High-resolution SAR Images in Island Regions Based on Fast Multimodal Registration
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摘要: 随着高分辨率合成孔径雷达(SAR)卫星的陆续发射,对天气条件多变的海岛区域进行全天候、全时段的高精度观测已变得可行。作为多种遥感应用的关键前置步骤正射校正,依赖于高精度控制点来纠正SAR影像的几何定位误差。然而,在海岛区域获取符合SAR校正要求的人工控制点不仅成本高,且风险大。为了应对这一挑战,该文首先提出了一种光学与SAR异源影像的快速配准算法,然后基于光学参考底图自动提取控制点,实现了海岛区域SAR影像的正射校正。所提出的配准算法分为两个阶段:首先构建异源影像的共性密集特征,然后在降采样后的特征上进行逐像素匹配,避免了异源影像特征点重复性低的问题。为了降低匹配复杂度,引入了海陆分割掩模以限定搜索范围。接着,对初步匹配点进行局部精细匹配,以减少降采样带来的不准确性。同时,引入海岸线均匀采样点以提升匹配结果的均匀性,并通过分段线性变换模型生成正射影像,确保了稀疏岛屿区域的整体校正精度。该算法在多景海岛区域的高分辨率SAR影像上表现出色,平均定位误差为3.2 m,整景校正时间仅需17.3 s,均优于现有多种先进的异源配准与校正算法,显示出其在工程应用中的巨大潜力。Abstract: With the successive launch of high-resolution Synthetic Aperture Radar (SAR) satellites, conducting all-weather, all-time high-precision observation of island regions with variable weather conditions has become feasible. As a key preprocessing step in various remote sensing applications, orthorectification relies on high-precision control points to correct the geometric positioning errors of SAR images. However, obtaining artificial control points that meet SAR correction requirements in island areas is costly and risky. To address this challenge, this study first proposes a rapid registration algorithm for optical and SAR heterogeneous images, and then automatically extracts control points based on an optical reference base map, achieving orthorectification of SAR images in island regions. The proposed registration algorithm consists of two stages: constructing dense common features of heterogeneous images; performing pixel-by-pixel matching on the down-sampled features, to avoid the issue of low repeatability of feature points in heterogeneous images. To reduce the matching complexity, a land sea segmentation mask is introduced to limit the search range. Subsequently, local fine matching is applied to the preliminary matched points to reduce inaccuracies introduced by down-sampling. Meanwhile, uniformly sampled coastline points are introduced to enhance the uniformity of the matching results, and orthorectified images are generated through a piecewise linear transformation model, ensuring the overall correction accuracy in sparse island areas. This algorithm performs excellently on the high-resolution SAR images of multiple scenes in island regions, with an average positioning error of 3.2 m and a complete scene correction time of only 17.3 s, both these values are superior to various existing advanced heterogeneous registration and correction algorithms, demonstrating the great potential of the proposed algorithm in engineering applications.
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表 1 待校正的SAR影像成像参数信息
Table 1. The imaging parameter information of the SAR image to be rectified
测试区域 卫星型号 成像模式 成像视角(°) 波段 采样间隔(m) 影像尺寸(像素) A1 高分三号 滑动聚束 41.2 C 0.56/0.36 15616 ×29344 A2 高分三号 滑动聚束 21.4 C 0.56/0.31 8635 ×33560 B 高分三号 滑动聚束 39.3 C 0.56/0.34 13660 ×32208 C 高分三号 滑动聚束 29.7 C 0.56/0.33 10946 ×32032 D1 海丝一号 滑动聚束 28.0 C 0.31/0.17 9188 ×45875 D2 海丝一号 滑动聚束 28.8 C 0.31/0.32 12748 ×22937 表 2 所有算法在6组测试影像上的定位误差(m)
Table 2. The positioning errors of all algorithms on six sets of test images (m)
方法 A1 A2 B C D1 D2 平均处理时间(s) 本文算法 1.82 2.98 3.65 5.50 2.81 2.45 17.3 SFOC 2.10 / / 15.20 3.88 3.43 139.8 RIFT 2.93 3.87 7.09 6.54 5.90 4.33 194.3 3MRS 2.02 4.15 5.51 12.68 6.15 3.59 160.7 海岸线匹配 8.71 / / 9.44 12.15 6.04 172.1 注:/代表校正失败。 表 3 消融实验方法设置
Table 3. Setting of the ablation study
方法 基于海陆分割掩模的
逐像素匹配结合海岸线采样点的
分段线性变换GPU加速 T0(本文算法) √ √ √ T1 × √ √ T2 √ × √ T3 √ √ × 表 4 消融实验对比结果,包括定位误差(m)和平均处理时间(s)
Table 4. The comparison results of ablation study, including positioning error (m) and average processing time (s)
方法 A1 A2 B C D1 D2 平均处理时间(s) T0 1.82 2.98 3.65 5.50 2.81 2.45 17.3 T1 2.28 4.14 5.29 8.32 4.67 3.71 205.6 T2 2.24 3.71 7.31 5.63 3.95 3.38 16.9 T3 1.89 3.18 4.42 5.58 2.82 3.02 158.8 表 5 开源海岸线矢量与海陆分割的对比结果,包括定位误差(m)、平均处理时间(s)和采样点数量(个)
Table 5. The comparison results between open-source coastline vectors and land-sea segmentation, including positioning error (m), average processing time (s), and the number of sampling points (count)
测试区域 定位误差(m) 平均处理时间(s) 采样点数量(个) 开源海岸线矢量 海陆分割 开源海岸线矢量 海陆分割 开源海岸线矢量 海陆分割 A1 1.82 1.92 14.2 22.2 269 1451 A2 2.98 3.15 12.3 18.4 269 1451 B 3.65 4.67 15.0 20.25 783 1253 C 5.50 4.53 24.1 51.4 1119 3464 D1 2.81 3.28 15.5 20.91 157 824 D2 2.45 2.69 16.8 21.49 157 824 -
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