Due to the abundant natural resources of the underwater world, autonomous exploration using underwater robots has become an effective technological tool in recent years. Real-time object detection is critical when employing robots for independent underwater exploration. However, when a robot detects underwater, its computing power is usually limited, which makes it challenging to detect objects effectively. To solve this problem, this study presents a novel algorithm for underwater object detection based on YOLOv4-tiny to achieve better performance with less computational cost. First, a symmetrical bottleneck-type structure is introduced into the YOLOv4-tiny’s backbone network based on dilated convolution and 1 × 1 convolution. It captures contextual information in feature maps with reasonable computational cost and improves the mAP score by 8.74% compared to YOLOv4-tiny. Second, inspired by the convolutional block attention module, a symmetric FPN-Attention module is constructed by integrating the channel-attention module and the spatial-attention module. Features extracted by the backbone network can be fused more efficiently by the symmetric FPN-Attention module, achieving a performance improvement of 8.75% as measured by mAP score compared to YOLOv4-tiny. Finally, this work proposed the YOLO-UOD for underwater object detection through the fusion of the YOLOv4-tiny structure, symmetric FPN-Attention module, symmetric bottleneck-type dilated convolutional layers, and label smoothing training strategy. It can efficiently detect underwater objects in an embedded system environment with limited computing power. Experiments show that the proposed YOLO-UOD outperforms the baseline model on the Brackish underwater dataset, with a detection mAP of 87.88%, 10.5% higher than that of YOLOv4-tiny’s 77.38%, and the detection result exceeds YOLOv5s’s 83.05% and YOLOv5m’s 84.34%. YOLO-UOD is deployed on the embedded system Jetson Nano 2 GB with a detection speed of 9.24 FPS, which shows that it can detect effectively in scenarios with limited computing power.

In recent years, to ensure the stable development of the marine economy, the analysis and processing of maritime vessel targets combined with natural light images have played a significant role. However, in scenes such as ports, there are sometimes background noises similar to vessel features, so the classifier based on the convolutional neural network cannot achieve good classification results. To pay more attention to effective information when classifying natural maritime images, we propose an efficient channel attention module (ECAM) and a re-parameterized spatial attention module (RSAM) through one-dimensional convolution and re-parameterization method. This paper combines ECAM and RSAM to present an efficient re-parameterized convolutional block attention module (ER-CBAM) to classify natural maritime images. Besides, in response to the current lack of large-scale natural marine image datasets, we established a natural maritime vessel image (NMVI) dataset. Experiments on NMVI show that by combining the proposed attention module, ResNet50 can achieve a top-1 accuracy score of 85.32% with almost no extra computational consumption and a 3.02% improvement compared to the previous 82.30%, which suggests that the proposed method is suitable for maritime scenarios.