Identification of Small Objects in Satellite Image Benchmarks

Recent increases in aerial image access and volume, increases in computational power, and interest in applications have opened the door to scaling up object detection and domain adaptation research to production. Aerial data sets are very large in size, and each frame of the data set contains a huge number of dense and small objects. Deep learning applications for aerial imagery are behind due to a lack of training data, and researchers have recently turned to domain adaptation (DA) from a labeled data set to an unlabeled data set to alleviate the issue. These factors create two major challenges: the high variety between datasets (e.g. object sizes, class distributions, object feature uniformity, image acquisition, distance, weather conditions), and the size of objects in satellite imagery and subsequent failure of state-of-the-art to capture small objects, local features, and region proposals for densely overlapped objects in satellite image. In this paper, we propose two solutions to these problems: a domain discriminator to better align the local feature space between domains; and a novel pipeline that improves the back-end by spatial pyramid pooling, cross-stage partial network, region proposal network via heatmap-based region proposals, and object localization and identification through a novel image difficulty score that adapts the overall focal loss measure based on the image difficulty. Our proposed model outperformed the state-of-the-art method by 7.4%.