Hyperspectral anomaly detection (HAD) aims to identify anomalous objects that deviate from surrounding backgrounds in an unlabeled hyperspectral image (HSI). Most available neural networks that make use of the reconstruction error to perform HAD tend to fit both backgrounds and anomalies, resulting in small reconstruction errors for both and not being effective in separating targets from background. To address this issue, we develop Dual-window-inspired reconstruction Network (DirectNet), a new background reconstruction network for HAD that seamlessly integrates a sliding dual-window model into a blind-block architecture. Concretely, DirectNet establishes an inner window within the network’s receptive field by erasing the center block information so that the content of the inner window remains invisible during the reconstruction of the central pixel. In addition, the depth of our reconstruction network is adaptive to the size of the input image patch, ensuring that the network’s receptive field aligns with the dimensions of the input patch. The receptive field outside the inner window is considered an outer window. This weakens the impact of anomalies on the reconstruction process, causing the reconstructed pixels to converge toward the background distribution in the outer window region. Consequently, the reconstructed HSI can be regarded as a pure background HSI, leading to further amplification of reconstruction errors for anomalous targets. This enhancement improves the discriminatory ability of DirectNet. Specifically, DirectNet solely utilizes the outer window information to predict/reconstruct the central pixel. As a result, when reconstructing pixels inside anomalous targets of different sizes, the targets primarily fall within the inner window. Comprehensive experiments (conducted on four datasets) demonstrate that DirectNet achieves competitive performance compared to other state-of-the-art detectors.

Hyperspectral anomaly detection (HAD) poses the challenge of distinguishing anomalous targets from the majority of background objects without prior knowledge. Most existing deep learning models struggle to account for both local and global spatial-spectral features in the image, limiting their performance. In this letter, we introduce PUNNet, which integrates the patch-shuffle downsampling technique and nonlinear activation free network (NAFNet) block with dilated convolution into an advanced blind-spot network for HAD. Specifically, PUNNet utilizes the patch-shuffle downsampling operation to extend its receptive field and exploits channel attention in the NAFNet block with dilated convolution to capture global contextual information in the image. Meanwhile, PUNNet satisfies the blind-spot requirement, meaning its receptive field excludes the center pixel’s information. This allows for reliable and precise background reconstruction in a self-supervised learning paradigm, further weakening anomalous feature expression and increasing the reconstruction error of anomalies. Experimental results demonstrate that PUNNet achieves a leading position in HAD performance. The code will be available at https://github.com/DegangWang97.

The detection of camouflaged targets in the complex background is a hot topic of current research. Existing hyperspectral target detection algorithms do not take advantage of spatial information and rarely use temporal information. It is difficult to obtain the required targets, and the detection performance in hyperspectral sequences with complex background will be low. Therefore, a hyperspectral time-series target detection method based on spectral perception and spatial-temporal tensor decomposition (SPSTT) is proposed. Firstly, a sparse target perception strategy based on spectral matching is proposed. To initially acquire the sparse targets, the matching results are adjusted by using the correlation mean of the prior spectrum, the pixel to be measured and the four-neighborhood pixel spectra. The separation of target and background is enhanced by making full use of local spatial structure information through local topology graph representation of the pixel to be measured. Secondly, in order to obtain a more accurate rank and make full use of temporal continuity and spatial correlation, a spatial-temporal tensor model based on the Gamma norm and L _2,1 norm is constructed. Furthermore, an excellent alternating direction method of multipliers is proposed to solve this model. Finally, spectral matching is fused with spatial-temporal tensor decomposition in order to reduce false alarms and retain more right targets. A 176-band hyperspectral image sequence (BIT-HSIS-I) dataset is collected for the hyperspectral target detection task. It is found by testing on the collected dataset that the proposed SPSTT has superior performance over the state-of-the-art algorithms.

Synthetic aperture radar (SAR) change detection provides a powerful tool for continuous, reliable, and objective observation of the Earth, supporting a wide range of applications that require regular monitoring and assessment of changes in the natural and built environment. In this paper, we introduce a novel SAR image change detection method based on principal component analysis and two-level clustering. First, two difference images of the log-ratio and mean-ratio operators are computed, then the principal component analysis fusion model is used to fuse the two difference images, and a new difference image is generated. To incorporate contextual information during the feature extraction phase, Gabor wavelets are used to obtain the representation of the difference image across multiple scales and orientations. The maximum magnitude across all orientations at each scale is then concatenated to form the Gabor feature vector. Following this, a cascading clustering algorithm is developed within this discriminative feature space by merging the first-level fuzzy c-means clustering with the second-level neighbor rule. Ultimately, the two-level combination of the changed and unchanged results produces the final change map. Five SAR datasets are used for the experiment, and the results show that our algorithm has significant advantages in SAR change detection.

Hyperspectral target detection technology is becoming more and more important in remote sensing. Most of the traditional methods of target sensing using spectral information treat hyperspectral image as 2-D matrix regardless of the structure information of hyperspectral image, resulting in insufficient separation of target and background and limited detection accuracy. In order to better utilize the hyperspectral intrinsic structural information, this article proposes a hyperspectral target sensing approach based on tensor adaptive reconstruction cascaded with global and local feature fusion (TRGLF). First, the Tucker decomposition and reconstruction method is utilized to alleviate the influence of noise and other elements in the complex background hyperspectral, which can maintain the intrinsic structural features of the data and improve the background and target separation. The principal components of the factor matrix are determined by a logarithmic singular value summation strategy, and then the energy difference between the spectra to be measured and the previous spectra is calculated to fine-tune the principal components and obtain more appropriate principal component values. Second, on the basis of reconstructed data, a global and local spatial spectral fusion method is adopted to obtain the target of interest. This includes using globally constrained energy minimization to obtain the target of interest and using local differential sensing to further obtain the target boundary. The detection performed on four realistically acquired hyperspectral water surface datasets demonstrate the excellent detection performance of the proposed target detection method.