A comprehensive analysis of modern object detection methods for maritime vessel detection
Object detection is the basis for several computer vision applications and autonomous functionalities. The task has been studied extensively and since the onset of deep learning detection accuracy have increased significantly. Every year several new models based on convolutional neural networks (CNNs) are developed and released. However, the development is driven by large research datasets, such as ImageNet and MS COCO, which aim to cover a large range of classes and contain very strong biases with respect to object size and position. Thus existing models and design choices are biased towards such situations. More specialized domains, such as that of maritime vessel detection, can have very different requirements and not all mainstream models are equally suited towards this task. Specific challenges of maritime vessel detection in surface-to-surface view are a large variety of object sizes due to distances from the camera but also the large range in different vessel types, atmospheric effects, and strong overlap between objects. Furthermore, the lack of of large training datasets in such specialized domains is a limitation that needs to be considered. Finally, the existing smaller datasets often contain strong biases themselves, as they were usually recorded in a single location with unique visual characteristics and vessel types that may be very distinct from those in other datasets. In this work we analyze the performance of several of the latest state-of-the-art object detectors in the context of maritime vessel detection. We evaluate the detectors on the limited existing public datasets, including the specialized Singapore Maritime Dataset and the SeaShips dataset but also ship images included in general object detection datasets, such as MS COCO. We specifically analyze how well existing dataset biases impact the ability of the resulting detectors to generalize. In addition to this, we create our own maritime vessel training data from online sources and investigate the impact of adding such data to the training process. Our evaluation results in a set of models which achieve strong vessel detection accuracy on all datasets. In summary, this work does not aim at methodological novelty but rather seeks to provide an empirical basis for choice of object detector and composition of training data for future work on the subject of maritime vessel detection.