Abstract: Aiming at the problem that the deep-learning-based model for road information extraction can only output single-task results and the inadequate use of correlation between multiple tasks,a combined road segmentation and contour extraction method based on cascaded U-Net is proposed,which extracts the road contour after fusing the feature map of road semantic segmentation with the original image.Firstly,the U-Net network structure is used to extract the hierarchical features of optical remote sensing images,and the cascaded U-Net structure is introduced to concatenate the features to extract the pixel-level label and contours of roads respectively.Secondly,the attention mechanism module is added to each stage of U-Net to extract spatial context information and deep level features to improve the detection sensitivity of details.Finally,the joint loss function composed of dice coefficient and cross-entropy error is used for the overall training to extract simultaneously the road semantic segmentation and contour results.On the optical remote sensing dataset of the urban area of Ottawa,Canada,the joint extraction method of road information based on cascaded U-Net achieves 42% precision,58% recall,48.2% F1 score and 71.6% mIoU in the segmentation index,and achieves a global optimal threshold(ODS) of 0.896 in the road detection index.The results show that,the model can meet the requirements of joint extraction of road multi-task information and has better detection accuracy.

Key words: Remote sensing image, Road segmentation, Contour extraction, Cascaded U-Net, Attention mechanism