HMSM-Net: Hierarchical multi-scale matching network for disparity estimation of high-resolution satellite stereo images

Disparity estimation of satellite stereo images is an essential and challenging task in photogrammetry and remote sensing. Recent researches have greatly promoted the development of disparity estimation algorithms by using CNN (Convolutional Neural Networks) based deep learning techniques. However, it is still difficult to handle intractable regions that are mainly caused by occlusions, disparity discontinuities, texture-less areas, and re-petitive patterns. Besides, the lack of training datasets for satellite stereo images remains another major issue that blocks the usage of CNN techniques due to the difficulty of obtaining ground-truth disparities. In this paper, we propose an end-to-end disparity learning model, termed hierarchical multi-scale matching network (HMSM-Net), for the disparity estimation of high-resolution satellite stereo images. First, multi-scale cost volumes are con-structed by using pyramidal features that capture spatial information of multiple levels, which learn corre-spondences at multiple scales and enable HMSM-Net to be more robust in intractable regions. Second, stereo matching is executed in a hierarchical coarse-to-fine manner by applying supervision to each scale, which allows a lower scale to act as prior knowledge and guides a higher scale to attain finer matching results. Third, a refinement module that incorporates the intensity and gradient information of the input left image is designed to regress a detailed full-resolution disparity map for local structure preservation. For network training and testing, a dense stereo matching dataset is created and published by using GaoFen-7 satellite stereo images. Finally, the proposed network is evaluated on the Urban Semantic 3D and GaoFen-7 datasets. Experimental results demonstrate that HMSM-Net achieves superior accuracy compared with state-of-the-art methods, and the improvement on intractable regions is noteworthy. Additionally, results and comparisons of different methods on the GaoFen-7 dataset show that it can severs as a challenging benchmark for performance assessment of methods applied to disparity estimation of satellite stereo images. The source codes and evaluation dataset are made publicly available at https://github.com/Sheng029/HMSM-Net.