Anchor-Free One-Stage Detector for Unmanned Aerial Vehicle

With the popularity of commercial unmanned aerial vehicles (UAVs), people have easy access to UAV. However, people's privacy and safety can be threatened if UAV flies at airports, private yards, etc. It is important to be able to detect the illegal UAV accurately and promptly on these vulnerable sites. However, motion blur, occlusion and truncation occur frequently due to fast movement of UAV. It is hard to make correct predictions because of the small size of UAV in images. In this paper, we propose an anchor-free one-stage method for UAV detection. The method eliminates the anchor boxes that are used in most existing detectors, which makes our method simpler and more efficient. We improve the detection accuracy in the following two ways. First, a new multi-scale feature fusion method is proposed to enhance the semantic information exchange between different scales. Second, a reasonable loss function is adopted to increase the proportion of small UAV's loss. Experimental results validate the effectiveness of our improvements and our proposed detector achieve a superior performance.