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Cross-domain ground-based cloud classification is a challenging issue as the appearance of cloud images from different cloud databases possesses extreme variations. Two fundamental problems which are essential for cross-domain ground-based cloud classification are feature representation and similarity measurement. In this paper, we propose an effective feature representation called transfer of local features (TLF), and measurement method called discriminative metric learning (DML). The TLF is a generalized representation framework that can integrate various kinds of local features, e.g., local binary patterns (LBP), local ternary patterns (LTP) and completed LBP (CLBP). In order to handle domain shift, such as variations of illumination, image resolution, capturing location, occlusion and so on, the TLF mines the maximum response in regions to make a stable representation for domain variations. We also propose to learn a discriminant metric, simultaneously. We make use of sample pairs and the relationship among cloud classes to learn the distancemetric. Furthermore, in order to improve the practicability of the proposedmethod,we replace the original cloud images with the convolutional activation maps which are then applied to TLF and DML. The proposed method has been validated on three cloud databases which are collected in China alone, provided by Chinese Academy ofMeteorological Sciences (CAMS),Meteorological Observation Centre (MOC), and Institute of Atmospheric Physics (IAP). The classification accuracies outperform the state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Ground-based cloud detection plays an essential role in meteorological research, and object segmentation techniques have recently been introduced to solve this issue. As a kind of object segmentation technique, interactive graph cut has emerged as a very powerful tool due to its effective segmentation ability. However, it requires users to provide labels for certain pixels as “object” or “background,” which inevitably prohibits automatic cloud detection in large-scale applications. In this letter, we focus on the issue of automatic cloud detection and propose a novel algorithm named as automatic graph cut. We treat clouds as a special kind of object and eliminate human labeling by two procedures. First, we adaptively compute the thresholds for each cloud image which automatically label some pixels as “cloud” or “clear sky” with high confidence. Then, those labeled pixels serve as hard constraint seeds for the following graph cut algorithm. The experimental results show that the proposed algorithm not only achieves better results than the state-of-the-art cloud detection algorithms but also achieves comparable results with the interactive segmentation algorithm. [ABSTRACT FROM PUBLISHER]

Since clouds are one of the most important meteorological phenomena related to the hydrological cycle and affect Earth radiation balance and climate changes, cloud analysis is a crucial issue in meteorological research. Most researchers only consider the classification task of cloud images while less attention has been paid to the synthesis one. In addition, all the existing research on cloud identification from sky images is based on single cloud images. However, the cloud-measuring devices on the ground actually take one image of the clouds every few minutes and collect a series of cloud images. Thus, the existing methods neglect the temporal information exhibited by contiguous cloud images. To overcome this drawback, in this letter we treat ground-based cloud sequences (GCSs) as dynamic texture. We then propose the Tensor Ensemble of Ground-based Cloud Sequences (eTGCS) model which represents the ensemble of GCSs in a tensor manner. In the eTGCS model, all GCSs form a single tensor, and each GCS is a subtensor of the single tensor. There are two main characteristics of the eTGCS model: 1) All GCSs share an identical mode subspace, which makes the classification convenient, and 2) a new GCS can be synthesized as long as the parameters of the eTGCS model are used. Therefore, less storage space is required. Comprehensive experiments are conducted to prove the superiority of our eTGCS model. The classification accuracy achieves 92.31%, and the synthesized GCSs are similar to the original ones in visual appearance. [ABSTRACT FROM PUBLISHER]