Floating-algae detection plays an important role in marine-pollution monitoring. The surveillance cameras on ships and shores provide a powerful way of monitoring floating macroalgae. However, the previous methods cannot effectively solve the challenging problem of detecting Ulva prolifera and Sargassum, due to many factors, such as strong interference with the marine environment and the drastic change of scale. Recently, the instance-segmentation methods based on deep learning have been successfully applied to many image-recognition tasks. In this paper, a novel instance-segmentation network named AlgaeFiner is proposed for high-quality floating-algae detection using RGB images from surveillance cameras. For improving the robustness of the model in complex ocean scenes, the CA-ResNet is firstly proposed by integrating coordinate attention into the ResNet structure to model both the channel- and position-dependencies. Meanwhile, the Ms-BiFPN is proposed by embedding the multi-scale module into the architecture of BiFPN to strengthen the ability of feature fusion at different levels. To improve the quality of floating-algae segmentation, the Mask Transfiner network is introduced into the AlgaeFiner to obtain the high-quality segmentation results. Experimental results demonstrate that the AlgaeFiner can achieve better performance on floating-algae segmentation than other state-of-the-art instance-segmentation methods, and has high application-value in the field of floating-macroalgae monitoring.

Video surveillance on the offshore booster station and around the coast is a effective way to monitor floating macroalgae. Previous studies on floating algae detection are mainly based on traditional image segmentation methods. However, these algorithms cannot effectively solve the problem of extracting Ulva prolifra and Sargassum at different sizes and views. Recently, instance segmentation methods have achieved great success in computer vision applications. In this paper, based on the CenterMask network, a novel instance segmentation architecture named AlgaeMask is proposed for floating algae detection from the surveillance videos. To address the feature extraction ability of the network in the inter-dependencies for position and channel, we introduce a new OSA-V3 module with the dual-attention block, which consists of a position attention mechanism and channel attention mechanism. Meanwhile, scale-equalizing pyramid convolution is introduced to solve the problem of scale difference. Finally, we introduce the feature decoder module based on FCOS head and segmentation head to obtain the segmentation area of floating algae in each bounding box. The extensive experiment results show that the average precision of our AlgaeMask in the tasks of mask segmentation and box detection can reach 44.22% and 48.13%, respectively, which has 15.09% and 8.24% improvement over CenterMask. In addition, the AlgaeMask can meet the real-time requirements of floating algae detection.