The existing unmanned aerial vehicle (UAV) enabled integrated sensing and communications (ISAC) systems primarily focus on the sensing capabilities of the UAV itself, overlooking the fact that the existing ground access points (APs) can receive the reflected signals for passive sensing, which can enhance the overall sensing performance. To address this issue, this paper introduces a UAV empowered air-ground ISAC system, where a UAV serves multiple communication users and performs detection for a potential target simultaneously, with the help of several ground APs. Specifically, the UAV works in active mode by transmitting ISAC signals and extracting information from echoes reflected from the target. In contrast, the ground APs function as sensing receivers, receiving and processing the reflected sensing signals from the target. Considering the limited capacity of the wireless backhaul links, we propose a two-step joint detection method, which contains local detection and result fusion steps. By incorporating the knowledge about the distribution of the reflection coefficient, we propose a maximum a-posteriori ratio test (MAPRT) detector, which is a generalization of earlier approaches such as the generalized likelihood ratio test detectors. Subsequently, the asymptotic distribution of test statistics of the MAPRT detector is derived. Furthermore, to improve the target detection performance, we propose an optimization algorithm that jointly optimizes the placement and transmit beamformer of the UAV, aiming at minimizing the probability of fusion error while guaranteeing the quality of service requirements of the users. Finally, numerical results demonstrate the effectiveness of the proposed algorithm.

The existing unmanned aerial vehicle (UAV) enabled integrated sensing and communications (ISAC) systems primarily focus on the UAV’s own sensing capabilities, overlooking the potential of existing ground access points (APs) in performing passive sensing via the reflected signals—thus limiting the overall performance. To address this issue, this paper introduces a UAV empowered air-ground ISAC system, where a UAV cooperates with several ground APs in detecting a potential target, with the UAV and APs working in active and passive modes, respectively. Different from the conventional generalized likelihood ratio test detectors, we exploit the reflection coefficient’s distribution to design a maximum a-posteriori ratio test (MAPRT) detector and derive its asymptotic test statistic distribution. To break through the capacity limitations of the wireless backhaul links, we introduce a two-step joint detection method involving local detection and result fusion. Further, we propose an optimization algorithm to jointly optimize the UAV’s placement and transmit beamforming, aiming at enhancing the target detection performance. Numerical results demonstrate the effectiveness of the proposed algorithm.

In this paper, we propose an unmanned aerial vehicle (UAV) enabled multi-stage integrated sensing and communications (ISAC) system, where a multi-antenna equipped UAV performs location sensing for a target whose location is initially unknown, while serves the communication users simultaneously, assisted by an existing receive access point. To improve the location sensing accuracy, we propose a multi-stage location sensing scheme, where the beamforming and placement of the UAV are dynamically adjusted in different stages. Specifically, in the first stage, without prior knowledge about the target’s location, the UAV fixes at the initial location and performs wide beam sensing to probe the target. In the following stages, given the coarse estimation result of the target’s location (obtained in the previous stage), the UAV adjusts its location and performs narrow beam sensing to locate the target. Besides, the quality of service requirements of the users are guaranteed in all stages. Based on the proposed sensing scheme, we formulate and solve two optimization problems to improve the sensing accuracy. Finally, numerical results demonstrate the effectiveness of the proposed algorithm.

We propose a Digital Building Analysis (DBA), a digital system for building-scale cloud-based data integration and data analytics. By connecting to cloud mapping platforms such as Google Map Platforms APIs, by leveraging state-of-the-art multi-agent Large Language Models data analysis using ChatGPT(4o) and Deepseek-V3/R1, and by using our Gaussian Splatting-based mesh extraction pipeline, our framework can retrieve a building’s 3D model, visual descriptions, and achieve cloud-based mapping integration with large language model-based data analytics using a building’s address, postal code, or geographic coordinates, and be easily extended to perform data analysis on other cloud-based data streams.

In this paper, we propose an unmanned aerial vehicle (UAV) enabled multi-stage integrated sensing and communications (ISAC) system, where a multi-antenna equipped UAV performs location sensing for a target whose location is initially unknown, while serves the communication users simultaneously, with the aid of an existing receive access point (RAP). By fusing the measurement results of the UAV and RAP, the location of the target is estimated. To improve the location sensing accuracy, we propose a multi-stage location sensing scheme. Specifically, in the first stage, in the absence of prior knowledge about the target’s location, the UAV fixes at the initial location and adjusts the beamformer to perform wide beam sensing to probe the target. In the following stages, with the previous coarse estimation result of the target’s location, the UAV performs narrow beam sensing by jointly adjusting the placement and also transmit beamformer. Besides, the quality of service requirements of the users are guaranteed in all stages. Accordingly, optimization problems are formulated for the first and following stages, respectively. By involving the semidefinite relaxation technique and then solving a quadratic semidefinite programming problem, the solution in the first stage is obtained. In the following stages, we jointly apply the alternating optimization, successive convex approximation, trust region, and also Dinkelbach’s methods to address the intricate coupling between the UAV placement and beamformer. Finally, numerical results demonstrate the effectiveness of the proposed algorithms.

Earth observation satellites can capture optical images under different temporal, climatic conditions, and platforms exhibit substantial differences in color and brightness, leading to poor visual experiences when synthesizing large-area optical satellite images. The related issue of color balancing has attracted considerable attention from researchers, yet challenges such as a lack of research data and sensitivity to model parameters persist. To address these problems, this article publishes a publicly open dataset and presents a semantic segmentation-enhanced color balance network (SECBNet). First, to mitigate the scarcity of research data, we develop a publicly available remote sensing image color balance dataset, Zhu Hai color balance image (ZHCBI), to support related research activities. Second, to improve semantic consistency between the color-balanced images and the target images, we design a dual-branch U-Net architecture guided by segmentation results and propose a novel segmentation feature loss function. Finally, to address issues of seams and unnatural transitions between blocks in segmented processing, we introduce a postprocessing module based on weighted averaging. We conducted comparative experiments and analyses with existing mainstream color balancing algorithms on the ZHCBI dataset. The results demonstrate that our proposed method achieves state-of-the-art color balancing quality, with significant improvement in visual effects and a higher peak signal-to-noise ratio (PSNR) (23.64 dB) compared with other mainstream methods.

Deep learning (DL)-based fully supervised approaches have demonstrated remarkable performance in sea ice classification, showcasing their potential for highly accurate results. However, their reliance on high-resolution labels poses a formidable challenge, as obtaining such data can be a difficult task. In contrast, our method based on weakly supervised learning excels by operating with lower-resolution polygon labels while still achieving outstanding performance. This approach enables precise pixel-level classification of ice stage of development (SOD) by learning from region-based labels embedded within expert-annotated ice charts. During training, region-based loss functions are introduced to quantify the disparity between predicted tensors describing SOD distributions and label tensors derived from ice charts. We leverage the AI4Arctic Sea Ice Challenge Dataset, comprising over 500 Sentinel-1 synthetic aperture radar (SAR) images, ancillary multisource data, and corresponding ice charts, for model training and evaluation. Visual interpretation and numerical analysis reveal that our weakly supervised method outperforms the fully supervised U-Net benchmark. It yields more accurate SOD predictions, significantly enhancing mapping resolution and class-wise accuracy. This methodology marks a critical step forward in the quest for automated operational sea ice mapping.

Three-dimensional urban scene reconstruction and modeling is a crucial research area. From a technical perspective, it is an interdisciplinary research area spanning computer vision, computer graphics, and photogrammetry. Its applications span across multiple disciplines including autonomous navigation with 3-D scene understanding, remote sensing/photogrammetry for the creation of 3-D maps from aerial/drone/satellite images, geographic information systems with urban digital twins, augmented and virtual reality with photorealistic scene reconstructions. Using Google Earth imagery, we create a 3-D Gaussian splatting (3DGS) model of the Waterloo region centered on the University of Waterloo, and are able to achieve view-synthesis results far exceeding previous 3-D view-synthesis results based on neural radiance fields (NeRFs)which we demonstrate in our benchmark. We also retrieve the 3-D geometry of the scene using the 3-D point cloud extracted from the 3DGS model, thereby reconstructing both the 3-D geometry and photorealistic lighting of the large-scale urban scene.

LiDAR point cloud segmentation has increasingly benefited from the application of Mamba-based models. However, unordered and irregular natures of point clouds necessitates serialization, which significantly impacts the performance of Mamba-based methods. This paper explores the critical role of token serialization in Mamba-based point cloud processing, using the pure Mamba network, PointMamba, as the baseline. We systematically investigated existing point cloud serialization methods, evaluating their performance on two challenging LiDAR datasets: the airborne MultiSpectral LiDAR (MS-LiDAR) dataset and the aerial DALES dataset. To explore the inherent factors of serialization contributing to Mamba’s performance, we design novel indicators for serialization quality, focusing on spatial and semantic proximity. These indicators are validated across all datasets, offering a valuable reference and guidance for advancing token serialization in Mamba-based point cloud processing. Guided by these indicators, we proposed a new point cloud serialization method that integrates spatial and semantic features through a weighted comprehensive distance matrix. The proposed method achieves superior accuracy on both LiDAR datasets, surpassing existing approaches, and establishes a strong foundation for advancing Mamba-based point cloud processing.

Although efficient extraction of discriminative spatial-spectral features is critical for hyperspectral images classification (HSIC), it is difficult to achieve these features due to factors such as the spatial-spectral heterogeneity and noise effect. This paper presents a Spatial-Spectral Diffusion Contrastive Representation Network (DiffCRN), based on denoising diffusion probabilistic model (DDPM) combined with contrastive learning (CL) for HSIC, with the following characteristics. First, to improve spatial-spectral feature representation, instead of adopting the UNets-like structure which is widely used for DDPM, we design a novel staged architecture with spatial self-attention denoising module (SSAD) and spectral group self-attention denoising module (SGSAD) in DiffCRN with improved efficiency for spectral-spatial feature learning. Second, to improve unsupervised feature learning efficiency, we design new DDPM model with logarithmic absolute error (LAE) loss and CL that improve the loss function effectiveness and increase the instance-level and inter-class discriminability. Third, to improve feature selection, we design a learnable approach based on pixel-level spectral angle mapping (SAM) for the selection of timesteps in the proposed DDPM model in an adaptive and automatic manner. Last, to improve feature integration and classification, we design an Adaptive weighted addition modul (AWAM) and Cross timestep Spectral-Spatial Fusion Module (CTSSFM) to fuse time-step-wise features and perform classification. Experiments conducted on widely used four HSI datasets demonstrate the improved performance of the proposed DiffCRN over the classical backbone models and state-of-the-art GAN, transformer models and other pretrained methods. The source code and pre-trained model will be made available publicly.

Fully supervised deep learning approaches have demonstrated impressive accuracy in sea ice classification, but their dependence on high-resolution labels presents a significant challenge due to the difficulty of obtaining such data. In response, our weakly supervised learning method provides a compelling alternative by utilizing lower-resolution regional labels from expert-annotated ice charts. This approach achieves exceptional pixel-level classification accuracy by introducing regional loss representations during training to measure the disparity between predicted and ice chart-derived sea ice type distributions. Leveraging the AI4Arctic Sea Ice Challenge Dataset, our method outperforms the fully supervised U-Net benchmark in mapping resolution and class-wise accuracy, marking a significant advancement in automated operational sea ice mapping.

Although transformer models are main network architectures for the delineation of roads from remote sensing imagery, they have critical limitations due to their regular patch mechanism and inefficiency in local information learning. To address these limitations for enhanced road extraction, this letter presents a novel double-branch architecture and random block coding transformer (DBARCT), with the following contributions. First, to improve local spatial details’ learning, we integrate transformer with convolutional neural network (CNN) into a novel dual-branch encoder-decoder architecture, such that the resulting model is efficient at learning both the local edge information and the global context information that are highly complementary for accurate road extraction. Second, to additionally augment the learning of global contextual information, we integrate the regular patching approach in traditional transformer models with a new irregular patching approach, such that it can better capture the global spatial information correlations that might be ignored by the regular patching approach. Third, an array of tests was carried out to meticulously scrutinize the efficacy of the fundamental elements of the suggested model. The empirical findings reveal that the intersection over union (IoU) metric attained by the proposed methodology on the LRSNY dataset stands at 88.53%, thereby corroborating the efficacy and preeminence of our approach in tasks related to road extraction.

High-resolution sea ice concentration (SIC) maps are critical to support various applications, e.g., climate modeling, ship navigation, and activities in Northern communities. However, operational mapping of SIC based on expert annotations is coarse in spatial resolution and time-consuming to prepare. Although many convolutional neural network (CNN)-based methods have been proposed for automated sea ice mapping from synthetic aperture radar (SAR) imagery in recent years, the lack of pixel-based labels for model training hinders them from producing high-resolution reliable mapping results. To overcome this challenge, this letter presents a novel weakly supervised learning approach that generates pixel-level SIC prediction using coarse region/polygon-level SIC ground truth. Specifically, a novel region-level loss function is designed to enable direct use of regional/polygon SIC values in ice charts for the training of a U-Net-based model. This avoids the errors in transferring region-level SIC values to pixel-level ground-truth SIC values effectively and allows the generation of pixel-level SIC and sea ice extent (SIE) estimates. The proposed approach is evaluated on the recently published AI4Arctic Sea Ice Challenge Dataset with over 500 Sentinel-1 SAR scenes, ancillary data, and associated ice charts. The results demonstrate the effectiveness of the weakly supervised model in producing pixel-level high-resolution SIC maps that are consistent with ice charts and visual interpretation.

Cell-free massive multiple-input-multiple-out (CF-mMIMO) systems provide limited coverage because of expensive wired fronthaul between access points (APs) and central processing unit (CPU). To address this challenge, we propose a novel framework where an unmanned aerial vehicle (UAV), acting as an aerial AP, works coherently with the ground APs to expand the coverage of conventional CF-mMIMO system. To fully utilize the spectrum resource, the wireless fronthaul between the CPU and UAV shares the total bandwidth with the radio access networks. Considering limited power supply of the UAV and for the goal of green communications, we formulate a weighted sum power minimization problem to jointly optimize downlink beamforming and fronthaul compression, as well as UAV placement. The formulated problem is a mixed timescale problem, thus we propose a two-timescale optimization framework in which the UAV placement is optimized in each long timescale based on statistical channel state information (CSI), then the downlink beamforming and fronthaul compression are optimized in each short timescale based on instantaneous CSI. Specifically, uplink-downlink duality and semidefinite relaxation (SDR) based alternating optimization techniques are introduced to find solutions to the short timescale issue, while successive convex approximation and SDR methods are invoked to find solutions to the long timescale issue. Finally, simulation results corroborate the performance of the proposed algorithm.

Although the application of Transformers to 3-D point cloud processing has achieved significant progress and success, it is still challenging for existing 3-D Transformer methods to efficiently and accurately learn both valuable global and local features for improved applications. This article presents a novel point cloud representational learning network, called 3-D Dual Self-attention global local (GLocal) Transformer Network (3DGTN), for improved feature learning in both classification and segmentation tasks, with the following key contributions. First, a GLocal feature learning (GFL) block with the dual self-attention mechanism [i.e., a novel point-patch self-attention, called PPSA, and a channel-wise self-attention (CSA)] is designed to efficiently learn the global and local context information. Second, the GFL block is integrated with a multiscale Graph Convolution-based local feature aggregation (LFA) block, leading to a GLocal information extraction module that can efficiently capture critical information. Third, a series of GLocal modules are used to construct a new hierarchical encoder–decoder structure to enable the learning of information in different scales in a hierarchical manner. The proposed framework is evaluated on both classification and segmentation datasets, demonstrating that the proposed method is capable of outperforming many state-of-the-art methods on both synthetic and LiDAR data. Our code has been released athttps://github.com/d62lu/3DGTN.

One critical challenge in 6D object pose estimation from a single RGBD image is efficient integration of two different modalities, i.e., color and depth. In this work, we tackle this problem by a novel Deep Fusion Transformer (DFTr) block that can aggregate cross-modality features for improving pose estimation. Unlike existing fusion methods, the proposed DFTr can better model cross-modality semantic correlation by leveraging their semantic similarity, such that globally enhanced features from different modalities can be better integrated for improved information extraction. Moreover, to further improve robustness and efficiency, we introduce a novel weighted vector-wise voting algorithm that employs a non-iterative global optimization strategy for precise 3D keypoint localization while achieving near real-time inference. Extensive experiments show the effectiveness and strong generalization capability of our proposed 3D keypoint voting algorithm. Results on four widely used benchmarks also demonstrate that our method outperforms the state-of-the-art methods by large margins. Code is available at https://github.com/junzastar/DFTr_Voting.

This study investigates the relationship between gray-level co-occurrence matrix (GLCM) texture features and synthetic aperture radar (SAR) incidence angle (IA) for sea ice classification. We analyzed dual polarization RADARSAT-2 C-band SAR data comprising 29 scenes. GLCM features were extracted from the radar cross-section (σo) in dB and categorized by sea ice class. To assess IA dependence per sea ice class, we used linear interpolation and the coefficient of determination (R2). We evaluated separability among ice classes using the Jeffries–Matusita distance and confirmed the improved separability with a Bayesian classifier. The results reveal a significant IA dependence of GLCM features. Notably, GLCM features from the HV band display stronger IA dependence and higher separability among ice classes compared to those from the HH band. These findings emphasize the significance of considering IA in the utilization of GLCM features for sea ice classification.

This paper investigates the influence of input image scale on deep learning-based Beluga whale detection from aerial remote sensing imagery. Beluga whales in the Arctic are jeopardized due to increased coastal activities and climate change. Aerial survey is a common population counting method, and it can be laborious and exhausting to count the number of whales manually. Convolutional neural networks (CNNs) have greatly improved the performance of detecting and counting whales. Since most remote sensing images are very high in resolution, it is a common practice to slice the image into small patches. In this work, we input the full image (after resizing) into an object detection model and compare its performance with the sliding window approach. Experimental results suggest that increasing the input image size helps improve the model’s performance, and the model is able to learn the contextual information.

Although light-weighted explainable deep learning techniques are critical for operational hyperspectral image (HSI) classification, it is very challenging to achieve these techniques due to difficulties to deal with the spatial-spectral complexity and coupling effect in HSI. Leveraging the excellent feature learning capability of the attention mechanism, this paper presents a spatial-spectral dual transformer (SSDT) network that decomposes the conventional spatial-spectral transformer operation into a spatial transformer and a spectral transformer, which not only reduce the model complexity, but also allows the use of self-attention to explain feature relevance. The proposed approach is tested on some benchmark HSI scenes and the results demonstrate that the proposed dual transformer network not only achieves new state-of-the-art performance due to its excellent feature extraction capability, but also enables the analysis and visualization of feature importance and decision making process.

Bayesian neural networks (BNNs) have been demonstrated to be effective in accurate retrieval of sea ice concentration (SIC) from multi-source data, while providing estimates of uncertainty, which are essential for downstream services. However, uncertainty obtained by BNNs are intrinsically uncalibrated, which indicates that it may not correlate well with model error. To address this issue, we investigate a new approach that combines an auxiliary prediction interval (PI) estimator with the BNN-based SIC mean estimator to develop a well-calibrated SIC retrieval model that is both accurate and reliable. We adopt a training strategy called “uncertainty matching" to train the model, which ensures that the estimated uncertainties match the estimated PIs. We use a subset of AMSR2 brightness temperature data and ERA5 atmospheric data collected from 2014 to 2015 in the Baffin Bay area as input features of the model. Comparison between model inference and SIC labels obtained from the enhanced NASA Team (NT2) algorithm shows that the proposed approach is able to produce well-calibrated uncertainty with more accurate predictions in marginal ice zones.

The extraction of building outline vectors is an essential task in supporting various applications. Although the recent development of deep-learning-based techniques has made advancements in the automation of this task, the accuracy and precision are insufficient due to errors caused by abundant noise and obstruction around buildings in aerial images. To better address this issue, this letter presents a new approach called multi-task edge detection (MTED) for building vectorization with the following characteristics. First, instead of detecting building corner points that are very sensitive to noise effects, a deep-learning-based rotated bounding box (RBB) detector is introduced for building edge detection to increase robustness to interference. Second, a multi-task learning strategy is designed to integrate building segmentation inside the METD framework to closely guide edge detection using spatial context. Third, a simple yet effective geometry-guided postprocessing method is designed to reconstruct vectorized building outlines based on the detected edges and learned building shape prior knowledge. The comparative experiments conducted on benchmark very-high-resolution optical aerial images indicate that the proposed approach can significantly outperform the state-of-the-art in terms of vertex-based building outline accuracy metrics. With a test time of 58 ms per building, this method enables efficient building polygon labeling in interactive mapping applications for building surveying and mapping. Code is available athttps://github.com/yifanthomaswu/MTED_framework.

Algorithms designed for ice–water classification of synthetic aperture radar (SAR) sea ice imagery produce only binary (ice and water) output typically using manually labeled samples for assessment. This is limiting because only a small subset of labeled samples are used, which, given the nonstationary nature of the ice and water classes, will likely not reflect the full scene. To address this, we implement a binary ice–water classification in a more informative manner considering the uncertainty associated with each pixel in the scene. To accomplish this, we have implemented a Bayesian convolutional neural network (CNN) with variational inference to produce both aleatoric (data-based) and epistemic (model-based) uncertainty. This valuable information provides feedback as to regions that have pixels more likely to be misclassified and provides improved scene interpretation. Testing was performed on a set of 21 RADARSAT-2 dual-polarization SAR scenes covering a region in the Beaufort Sea captured regularly from April to December. The model is validated by demonstrating: 1) a positive correlation between misclassification rate and model uncertainty and 2) a higher uncertainty during the melt and freeze-up transition periods, which are more challenging to classify. By incorporating the iterative region growing with semantics (IRGS) segmentation algorithm and an uncertainty value-based thresholding algorithm, the Bayesian CNN classification outputs are improved significantly via both numerical analysis and visual inspection.

Unsupervised subpixel mapping (SPM) of hyperspectral image (HSI) is a challenging task due to the difficulties to integrate different prior information and model constraints into a coherent framework. This paper presents a Bayesian neural network for unsupervised HSI SPM, which has the following characteristics. First, the deep image prior (DIP) achieved by a fully convolutional neural network (FCNN) is used to model the spatial correlation efficiently and adaptively in the subpixel label domain. Second, a discrete spectral mixture model (DSMM) is designed to leverage the forward model for enhanced SPM. Third, an auto-encoder architecture is designed to integrate the FCNN and the DSMM to allow efficient unsupervised representational learning using both data and knowledge. Fourth, an expectation-maximization approach is designed to solve the resulting maximum a posteriori problem, where a purified means approach extracts endmembers, and the gradient descent approach updates FCNN parameters for subpixel label estimation. Comparative experiments on both real and simulated HSIs demonstrate that the proposed method outperforms other state-of-the-art methods in terms of both numerical accuracies and visual subpixel mapping results.

Electric vehicle (EV) is the core part of future automobile technology, and safe and reliable wireless power transfer (WPT) technology is the key link to improve the intelligent driving technology of EV. In this paper, the uncertainty quantification method is proposed to guide the optimization design of WPT structure, so as to improve the efficiency of WPT. First this paper establishes a surrogate model of WPT efficiency based on the adaptive sparse polynomial chaos expansion, and the uncertainty of EVs WPT transmission efficiency is quantified, the computational efficiency is improved by about 8.4 times. Then the surrogate model is combined with the global sensitivity analysis method to quantify the impact of different variables in WPT on efficiency and screen out the variables with greater impact. Finally, this paper uses the improved marine predators algorithm to optimize the selected WPT system structure parameters. Considering the uncertainty, the average efficiency of the optimized WPT system is increased from 73.43% to 94.64%. Compared with other optimization methods, it proves that the method in this paper can optimize WPT more efficiently, and significantly improve the transmission efficiency.

Monitoring sea ice in polar regions is essential for environmental modeling and ship navigation. National ice agencies expect robust sea ice classification methods for operational use. However, fully supervised machine learning models require large training datasets, which are usually limited to the sea ice classification domain. Therefore, a semi-supervised sea ice classification model is proposed to address this challenge. First, the IRGS segmentation is applied to generate superpixels that construct the graph. Then, two graph convolutional layers are utilized to learn the features of each node. Finally, a softmax layer assigns labels to the nodes in the graph. The proposed model is named IRGS-GCN and tested on four RADARSAR-2 dual-polarized scenes. The experimental results show that the IRGS-GCN achieves an overall accuracy of 95.17% and outperforms fully-supervised random foreset and ResNet trained on limited data. Most of the sea ice boundary and leads are successfully preserved in the results.

To build small and efficient neural networks for hyperspectral image (HSI) classification, this letter presents a depthwise separable residual neural network (ResNet). This approach, motivated by the popular MobileNet architecture, decomposes the traditional spatial-spectral convolution operation into a spatial-independent pointwise spectral convolution and a spectral-independent depthwise spatial convolution. It allows the separation of spectral and spatial information in HSI and also greatly reduces the network size to prevent the overfitting issue. To better preserve the class boundaries and edges, the proposed ResNet is integrated into a maximum a posteriori (MAP) framework to allow the use of the conditional random field (CRF) model. The experiment results on benchmark HSI scene demonstrate that the proposed ResNet compares favorably with several popular deep learning HSI classifiers and that the ResNet-CRF approach achieves higher accuracy and better boundaries among neighboring classes.

Automatic building footprint extraction from remote sensing imagery is a challenging task with important applications in geomatics and environmental science. Significant advances have been made in this field as a result of the emergence of deep convolutional neural networks (CNNs) designed for semantic segmentation. Although CNNs have demonstrated state-of-the-art performance in coarse annotation and identification of buildings, the accuracy of extracted building footprints is still insufficient for high-precision applications such as mapping and navigation. We propose the topography-aware multi-resolution fusion learning strategy tailored to the problem of enhanced building footprint extraction. More specifically, we introduce a topography-aware loss (TAL) for enhancing a deep CNN’s ability to learn heterogeneous building features for better boundary preservation during segmentation. We then incorporate the proposed TAL loss within a multi-resolution fusion architecture to boost high-resolution segmentation performance. Finally, we introduce a novel metric named average thresholded contour accuracy (tCA) which specifically measures the accuracy of segmentation boundaries. The experimental results on the SpaceNet buildings dataset show significant improvements in boundary integrity of extracted building footprints when compared with previously proposed methods. Hence, this method enables accurate boundary annotation toward automatic production of building footprint maps for high-precision applications.

Spectral unmixing (SU) plays a fundamental role in hyperspectral image (HSI) processing. Effective SU relies on the accurate and efficient characterization of the noise effect, the endmembers, and the spatial correlation effect in abundances, as well as efficient optimization techniques to estimate these effects. To address these issues, this article presents a Bayesian fully convolutional hyperspectral unmixing network (BCUN) with the following key characteristics. First, a fully convolutional neural network (FCNN)-based deep image prior (DIP) is designed for enhanced characterization and estimation of the spatial context information in abundance maps, leading to more efficient and accurate abundance modeling than the traditional nonnegative least squares (NNLS) approaches. Second, a multivariate Gaussian distribution with an anisotropic covariance matrix is designed to characterize the conditional distribution of the spectral observations, leading to a novel Mahalanobis distance-based loss for FCNN training that is better capable of addressing the noise heterogeneous effect in HSI than the Euclidean distance-based mean squared error (MSE) loss in traditional deep neural networks. Third, the designed conditional distribution of spectral observations also enables the incorporation of the spectral mixture model (SMM) into the FCNN training process for effectively leveraging the knowledge in the forward spectral model. Fourth, the endmembers are modeled and estimated by a “purified means” approach that is capable of better characterizing endmembers. Finally, the above key components are coherently integrated into a Bayesian framework, and the resulting maximuma posteriori(MAP) problem is solved by a designed expectation–maximization (EM) algorithm. Experimental results on both simulated and real HSIs demonstrate that the proposed BCUN approach outperforms the other classical and state-of-the-art methods on both endmember estimation and abundance estimation.

Sentinel-1 is a synthetic aperture radar platform that provides free and open-source images of the Earth. A product type of Sentinel-1 is ground range detected (GRD), which records intensity while discarding phase information from the radar backscatter. Especially in cross-polarized GRD images, there are noticeable intensity changes throughout the image that are caused by amplifying the noise floor of the signal, which varies due to the nonuniform radiation pattern of the satellite’s antenna. While Sentinel-1 has instrument processing facility (IPF) software to estimate the noise floor, even in the newer versions (3.1 or above) of the IPF software there are still instances where the estimates provided do not fit the actual noise floor in the image, which is particularly noticeable in transitions between adjacent subswaths. In this work, we propose a method that reduces the impact of the varying noise-floor throughout the image. The method models the intensity of the noise floor to be a power function of the radiation pattern power. The method divides the swath into several sections depending on the location of the local minimum and maximum of the radiation pattern power with respect to the range. The parameter estimation is portrayed as a geometric programming problem that is transformed into a linear programming problem by logarithmic transformation. Affine offsets are computed for each subswath by a weighted least squares approach. Vast improvement is found on extra-wide (EW) and interferometric wide (IW) Sentinel-1 modes over cross-polarized images. Code implementation is available athttps://github.com/PeterQLee/sentinel1_denoise_rs.

Point cloud classification is a fundamental task in 3D applications. However, it is challenging to achieve effective feature learning due to the irregularity and unordered nature of point clouds. Lately, 3D Transformers have been adopted to improve point cloud processing. Nevertheless, massive Transformer layers tend to incur huge computational and memory costs. This paper presented a novel hierarchical framework that incorporated convolutions with Transformers for point cloud classification, named 3D Convolution-Transformer Network (3DCTN). It combined the strong local feature learning ability of convolutions with the remarkable global context modeling capability of Transformers. Our method had two main modules operating on the downsampling point sets. Each module consisted of a multi-scale local feature aggregating (LFA) block and a global feature learning (GFL) block, which were implemented by using the Graph Convolution and Transformer respectively. We also conducted a detailed investigation on a series of self-attention variants to explore better performance for our network. Various experiments on ModelNet40 and ScanObjectNN datasets demonstrated that our method achieves state-of-the-art classification performance with a lightweight design. The code is publicly available athttps://github.com/d62lu/3DCTN.

Building rooftop data are of importance in several urban applications and in natural disaster management. In contrast to traditional surveying and mapping, by using high spatial resolution aerial images, deep learning-based building rooftops extraction methods are efficient and accurate. Although more training data is preferred in deep learning-based tasks, the effect of data volume on building extraction models is underexplored. Therefore, the paper explores the impact of data volume on the performance of building rooftop extraction from very-high-spatial-resolution (VHSR) images using deep learning-based methods. To do so, we manually labelled 0.12m spatial resolution aerial images and perform a comparative analysis of models trained on datasets of different sizes using popular deep learning architectures for segmentation tasks, including Fully Convolutional Networks (FCN)-8s, U-Net and DeepLabv3+. The experiments showed that with more training data, algorithms converged faster and achieved higher accuracy, while better algorithms were able to better mitigate the lack of training data.

Although accurate training and initialization information is difficult to acquire, unsupervised hyperspectral subpixel mapping (SPM) without relying on this predefined information is an insufficiently addressed research issue. This letter presents a novel Bayesian approach for unsupervised SPM of hyperspectral imagery (HSI) based on the Markov random field (MRF) and a band-weighted discrete spectral mixture model (BDSMM), with the following key characteristics. First, this is an unsupervised approach that allows adjustment of abundance and endmember information adaptively for less relying on algorithm initialization. Second, this approach consists of the BDSMM for accommodating the noise heterogeneity and the hidden label field of subpixels in HSI. The BDSMM also integrates SPM into the spectral mixture analysis and allows enhanced SPM by fully exploring the endmember-abundance patterns in HSI. Third, the MRF and BDSMM are integrated into a Bayesian framework to use both the spatial and spectral information efficiently, and an expectation-maximization (EM) approach is designed to solve the model by iteratively estimating the endmembers and the label field. Experiments on both simulated and real HSI demonstrate that the proposed algorithm can yield better performance than traditional methods.

Building footprint extraction in remote sensing data benefits many important applications, such as urban planning and population estimation. Recently, rapid development of convolutional neural networks (CNNs) and open-sourced high resolution satellite building image datasets have pushed the performance boundary further for automated building extractions. However, CNN approaches often generate imprecise building morphologies including noisy edges and round corners. In this paper, we leverage the performance of CNNs, and propose a module that uses prior knowledge of building corners to create angular and concise building polygons from CNN segmentation outputs. We describe a new transform, Relative Gradient Angle Transform (RGA Transform) that converts object contours from time vs. space to time vs. angle. We propose a new shape descriptor, Boundary Orientation Relation Set (BORS), to describe angle relationship between edges in RGA domain, such as orthogonality and parallelism. Finally, we develop an energy minimization framework that makes use of the angle relationship in BORS to straighten edges and reconstruct sharp corners, and the resulting corners create a polygon. Experimental results demonstrate that our method refines CNN output from a rounded approximation to a more clear-cut angular shape of the building footprint.

The Canadian RADARSAT Constellation Mission (RCM) proposes a new synthetic aperture radar (SAR) data mode called compact (hybrid or partial) polarimetry (CP) in a wide swath. Compact polarimetry maximizes the measurement potential if the multilook complex (MLC) coherence matrix of the SAR backscattered field is used. The MLC CP coherence matrix follows the Wishart distribution. In this paper, an unsupervised region-based semantic segmentation of the MLC CP coherence matrix data using the complex Wishart distribution is presented. The segmentation method is an extension of the iterative region growing with semantics (IRGS) to complex CP data. The proposed algorithm is called CP-IRGS and is formulated based on conditional random fields (CRFs) incorporating edge strength over the image. Applications of the algorithm are demonstrated using a simulated MLC CP data set and a real single-look complex (SLC) quadrature polarimetric (QP) SAR data set which is used to derive the MLC CP data.

Synthetic aperture radar images from the Sentinel-1 program are obtained by interpreting signals from a non-uniform radiation pattern. Cross-polarized images in extra-wide mode show significant additive noise patterns that take the form of varying intensity and are independent of the ground targets. While Sentinel-1 provides a method for removing these noise patterns via noise-calibration files, there still remain significant issues in the transformed products, particularly from discontinuous changes among adjacent subswaths. In this work, we consider recalibration by assuming the noise-gain to be a power function of the platform's radiation pattern. We propose a method that estimates the scaling and exponent parameters of the power-function by applying linear programming to the log transform of the data and the radiation pattern intensity, alone with affine rescaling with least-squares estimation. Our method is able to rescale Sentinel-1 scenes to have a more consistent intensity profile among the subswaths of the image.

Shipping traffic has grown steadily in the Arctic in recent years. One of the reasons for this increased traffic is the lengthening of open water season, which is accompanied by increases in the area covered by intermediate ice concentrations' or marginal ice zones (MIZs). These regions are difficult to detect using passive microwave data. In this paper, we propose the use of deep learning for automatic detection of MIZs in the RADARSAT-2 satellite images. A synthetic aperture radar (SAR) dataset is manually annotated to train, test and refine the method. Various convolutional neural network (CNN) models are evaluated as fixed feature extractors for the task of classification. To aid the classification accuracy we use a weighted binary cross-entropy loss criterion. Finally, to refine the segmentation process, we used a multi-scale patch technique. The analysis of the results demonstrates that CNN model predictions obtained with multiple sizes of spatial windows is able to detect MIZs in SAR images.

The global leaf area index (LAI) and fraction of photosynthetically active radiation absorbed by vegetation (FPAR) product-VNP15A2H, generated from the first VIIRS sensor, has inherited the scientific role of MODIS data and provides 8-year time-series dataset from 2012 to present. Compared to MODIS products, the VNP15A2H still lacks intensive evaluation and validation efforts, which arises the priority to study its quality and stability in the context of the upcoming retirement of MODIS and launching of a series of VIIRS. This paper documents the trend of product quality as well as LAI/FPAR magnitude using a multi-year (2013-2018) and multi-site (445 sites) dataset. We analyze 46 composites in each year and 7 biome types respectively and find that both LAI/FPAR and its accuracy do not show significant trends during the studied period, which guarantees our confidence to continue the long-term data record using VIIRS observations.

Unmixing is a key but difficult issue in hyperspectral image (HSI) processing, and many unmixing methods have been proposed. However, an effective introduction of the spatial context in unmixing remains a challenge but is a necessary condition for many real scene applications. In this letter, a new nonnegative matrix factorization (NMF) method that combines nonlocal spatial information with spatial group sparsity (NLNMF) is proposed. Each superpixel generated by the simple linear iterative clustering (SLIC) segmentation method was used as a group. The search region of the nonlocal means method was adaptively set using a superpixel label from each spectrum to find the similar spectra to reestimate the reference spectrum. Additionally, the sparsity of spectra in the same superpixel was considered to be the same. Experiment results for synthetic and real HSI showed that the proposed method not only can more accurately estimate the endmember and abundance compared with other unmixing methods but also has good performance regarding antinoise.

With a small number of labeled samples for training, it can save considerable manpower and material resources, especially when the amount of high spatial resolution remote sensing images (HSR-RSIs) increases considerably. However, many deep models face the problem of overfitting when using a small number of labeled samples. This might degrade HSR-RSI retrieval accuracy. Aiming at obtaining more accurate HSR-RSI retrieval performance with small training samples, we develop a deep metric learning approach with generative adversarial network regularization (DML-GANR) for HSR-RSI retrieval. The DML-GANR starts from a high-level feature extraction (HFE) to extract high-level features, which includes convolutional layers and fully connected (FC) layers. Each of the FC layers is constructed by deep metric learning (DML) to maximize the interclass variations and minimize the intraclass variations. The generative adversarial network (GAN) is adopted to mitigate the overfitting problem and validate the qualities of extracted high-level features. DML-GANR is optimized through a customized approach, and the optimal parameters are obtained. The experimental results on the three data sets demonstrate the superior performance of DML-GANR over state-of-the-art techniques in HSR-RSI retrieval.

Although efficient hyperspectral image (HSI) denoising relies on complete and accurate description and modeling the spatial-spectral signal in HSI, the current approaches do not fully account for key characteristics of HSI, i.e., the mixed spectra effect, the spatial nonstationarity effect, and noise variance heterogeneity effect. To address this issue, this article presents a linear spectral mixture model with nonlocal means constraint (LSMM-NLMC), with the following advantages. First, LSMM-NLMC can effectively learn the signal in mixed pixels in HSI by estimating clean endmembers and abundances for image restoration. Second, LSMM-NLMC can efficiently address nonstationary spatial correlation effect by imposing NLMC on the latent scene signal. Last, LSMM-NLMC provides accurate noise characterization by accounting for noise variance heterogeneity effect using a band-dependent noise model and a band-weighted Mahalanobis distance for similarity measurement. A novel optimization method based on the expectation-maximization (EM) algorithm and the purified means approach is used to efficiently solve the resulting maximum a posterior (MAP) problem. The experiments on both simulated and real HSI data sets demonstrate that the visual quality and denoising accuracy are significantly improved by the proposed LSMM-NLMC compared with previous methods.

Despeckling of synthetic aperture radar (SAR) is a known research challenge. A novel solution to this problem has been developed and evaluated via an iterative maximum a posterior estimation incorporating a Bayesian joint decorrelation and despeckling based on a correlation model. This model realistically explores the physical correlation process of SAR speckle noise and is determined automatically via Bayesian estimation in the log-Fourier domain. A patchwise computation is used to account for the spatial nonstationarity associated with SAR image data. The proposed approach is compared to the existing despeckling techniques using both simulated and real SAR data, and the experimental results demonstrate the improvement in preserving the structural details while suppressing speckle noise.

Automatic classification methods using satellite imagery are beneficial in the sea-ice-type mapping of the Arctic regions. In the near future, the RADARSAT Constellation Mission (RCM) will be launched, providing unique compact polarimetric (CP) synthetic aperture radar (SAR) data, expected to be an improvement over the current RADARSAT-2 dual-polarimetric SAR imagery. This motivates the implementation of a CP-dedicated automatic scene classification approach. First, an existing unsupervised segmentation algorithm called iterative region growing using semantics (IRGS) is used to segment ice-class homogeneous regions to reduce the impact of speckle noise. Second, a support vector machine (SVM) is used to classify the ice-type labels for each homogeneous region. Two complex quad-polarimetric RADARSAT-2 scenes are used to mathematically simulate the corresponding CP scenes for algorithm testing. Classification accuracy shows that using only the two CP intensity images leads to improved results compared with standard dual-polarimetric scenes. Using the CP data, the best classification results are obtained with the reconstructed QP data for the IRGS segmentation and all derived CP features for the SVM labeling. The results support the expected potential that CP scenes will provide improved sea-ice classification than the current operational dual-pol scenes.

The problem of limited labeled training samples is challenging for the classification of remote sensing imagery. We develop a joint classification and segmentation algorithm to address this problem. Our algorithm combines semisupervised learning and conditional random fields (CRFs) into a single framework. The multimodal Gaussian maximum-likelihood classifier is used to estimate the probabilities for the unary potentials of the CRF. Unlike traditional methods based on random fields, region merging is concatenated with the CRF inference to reduce the number of nodes iteratively. Moreover, a semisupervised technique called self-training is used, which iteratively enlarges the training sample set and retrains the classifier. The selection of training samples is based on the region information, so that the risk of assigning wrong labels is largely reduced. The proposed algorithm is applied to hyperspectral image classification, and results on benchmark data sets show that the proposed algorithm significantly improves classification performance after using self-training, and outperforms state-of-the-art spectral-spatial methods for limited labeled training samples.

Although the synthesis of the synthetic aperture radar (SAR) imagery with both sea ice and oil spills can significantly benefit in improving the consistency and comprehensiveness of testing and evaluating algorithms that are designed for mapping cold ocean regions, creating such imagery is difficult due to the heterogeneity and complexity of the source images. This letter presents an enhanced region-based probabilistic posterior sampling approach to effectively synthesize SAR imagery with different ocean features. In the proposed approach, instead of relying entirely on the SAR intensity values, the posterior sampling is performed based on a number of quantitative factors, such as intensity, label field, and the prior class probability of sampling candidates, constituting a complete probabilistic framework that addresses key aspects in the synthesis of SAR imagery from heterogeneous sources. The experiments demonstrate that the proposed approach can better address the difficulties caused by the heterogeneity in the source images compared with the existing state-of-the-art ice synthesis method, and it will improve the consistency, comprehensiveness, and fairness of the evaluation of the remote sensing classification and segmentation algorithms.

The classification of pixels in remotely sensed imagery (RSI) into land cover classes typically requires knowing the labels of some image pixels for model training. However, accurate pixel-level label information is usually difficult and expensive to acquire, which restricts the applicability of supervised image classification methods. In contrast, the region labels information that specifies which classes are contained in a region of the image that is easier to acquire and less susceptible to identification errors. To utilize the region label information for remotely sensed image classification, this paper presents a weakly supervised image classification approach using label constraint and edge penalty (ILCEP), which has the following key characteristics. First, the predefined region labels are used as constraints in ILCEP to guide the inference of pixel labels in the image. Second, the edges between neighboring pixels are used as penalties to address the spatial contextual information in the image. Third, the label constraint and edge penalty are incorporated into the conditional random field framework, and simultaneous model learning and label inference are achieved by solving the maximum a posteriori problem through an enhanced simulated annealing algorithm. Experiments on both simulated and real RSIs demonstrate that the proposed approach can achieve high classification accuracy by knowing only the region-level label information.

With the fast advancement of remote sensing platforms and sensors, remotely sensed imagery (RSI) is increasingly being characterized by both high spatial resolution and high temporal resolution. How to efficiently use the rich spatial and temporal information in RSI for highly accurate object detection and classification is an important research question. Nevertheless, there is still a lack of a probabilistic framework that is capable of fully accounting for the spatial-temporal information in RSI for improved applications. In this paper, we present a Bayesian spatial-temporal random field model that constitutes a complete probabilistic framework for fully explaining the spatial-temporal correlation in RSI, leading to an enhanced object detection approach that is used for cloud detection from RSI. Under the Bayesian theorem, the posterior distribution of a label field is decomposed into the label prior, the data likelihood, the temporal label likelihood, and the temporal data likelihood. To address the difficulties in modeling the complex spatial-temporal correlation effect in the temporal data likelihood, a stochastic sampling approach is presented. Based on the maximum a posteriori approach, the posterior distribution is seamlessly integrated into the graph-cut optimization framework, and, therefore, the model optimization can be efficiently solved. The proposed algorithm is tested for cloud detection on both simulated and real RSIs and the results demonstrate that the proposed algorithm can effectively exploit the spatial-temporal information for achieving higher detection accuracy.

The potential of active learning (AL) methods for improving the marine oil spills identification system is exploited using 10-year (2004-2013) RADARSAT data. Six basic AL methods are proposed according to the uncertainty criteria and coupled with the support vector machine (SVM) classifier. As many as 56 commonly used features are used for the classification. The AUC measures are estimated using the 6-fold cross validation technique to achieve bias-reduced evaluation of performance of the AL-based classifiers. The experiment results show that 22 to 74 percent of samples could be reduced for training SVM classifiers with certain destination performance, if the proper AL method such as AL-6 is selected and the criteria of exploitation and exploration could further improve the performance.

Unsupervised classification of hyperspectral imagery (HSI) relies on a data generative model, based on which the labels of pixels and the model parameters are iteratively estimated. Traditionally, the generative model is based on the Gaussian mixture model (GMM) that describes the data generation process from a statistical perspective. However, considering the fact that a semantic class is always dominated by a particular endmember, classifying the spectral pixels based on the associated endmember-abundance pattern as described by the spectral mixture model (SMM) is more meaningful from a physical perspective. In this paper, we explore the potential of spectral mixture model for assisting unsupervised classification of HSI based on a recently proposed K-P-Means unmixing algorithm. Moreover, we investigate modeling the spatial information using Markov random field in this new context. We incorporate SMM and MRF into the Bayesiam framework and solve it via the maximum a posterior (MAP) approach. The results on both simulated and real hyperspectral images demonstrate that this new approach can effectively exploit the spatial-spectral information of HSI for improved unsupervised classification of HSI.

Efficient super-resolution of hyperspectral images (HSI) relies on the representational model (RM) that is capable of capturing the spatial and spectral correlation in hyperspectral images. In this paper, the spectral information in hyperspectral images is explained by linear spectral mixture model (LSMM), which expressed the observed pixels as a linear combination of endmembers, and the spatial information is captured by a spatial auto-regression model. The two component is combined in the maximum likelihood estimation (MLE) framework and solved by the expectation and maximization (EM) algorithm. Experiments on both simulated and real hyperspectral images demonstrate that the proposed method is not only capable of providing an accurate and effective super-resolution reconstruction of the image, but also capable of resisting the influence of noise.

Efficient denoising of hyperspectral imagery (HSI) relies on an representational model that is capable of capturing the spatial and spectral correlation in HSI. Recently, an intrinsic representation (IR) approach based on the linear spectral mixture model (LSMM) was proposed for unsupervised feature extraction. The IR model constitutes a sound representational model due to its ability to account for the physical data generation process of HSI, the spatial correlation effect, and the noise variance heterogeneity effect. In this paper, we explore the potential of IR for the denoising of HSI. A noisy pixel in HSI is expressed as a nonnegative linear combination of several endmembers, plus some Gaussian noise with heterogeneous noise variances. In order to perform denoising, the IR approach is used to adaptively estimate both the endmembers and the nonnegative coefficients (i.e., the abundances), which are finally used to reconstruct the clean image. The experiments on both simulated and real hyperspectral images demonstrate that the IR approach not only can resist the influence of noise, but also can preserve the image details.

High-resolution ice concentration maps are of great interest for ship navigation and ice hazard forecasting. In this case study, a convolutional neural network (CNN) has been used to estimate ice concentration using synthetic aperture radar (SAR) scenes captured during the melt season. These dual-pol RADARSAT-2 satellite images are used as input, and the ice concentration is the direct output from the CNN. With no feature extraction or segmentation postprocessing, the absolute mean errors of the generated ice concentration maps are less than 10% on average when compared with manual interpretation of the ice state by ice experts. The CNN is demonstrated to produce ice concentration maps with more detail than produced operationally. Reasonable ice concentration estimations are made in melt regions and in regions of low ice concentration.

Unsupervised feature extraction from hyperspectral images (HSIs) relies on efficient data representation. However, classical data representation techniques, e.g., principal component analysis and independent component analysis, do not reflect the intrinsic characteristics of HSI, and as such, they are less efficient for producing discriminative features. To address this issue, we have developed an intrinsic representation (IR) approach to support HSI classification. Based on the linear spectral mixture model, the IR approach explains the underlying physical factors that are responsible for generating HSI. Moreover, it addresses other important characteristics of HSI, i.e., the noise variance heterogeneity effect in the spectral domain and the spatial correlation effect in image domain. The IR model is solved iteratively by alternating the estimation of IR coefficients given IR bases and the update of IR bases given the coefficients. The resulting IR coefficients are discriminative, compact, and noise resistant, thereby constituting powerful features for improved HSI classification. The experiments on both simulated and real HSI demonstrate that the features extracted by the IR model are more capable of boosting the classification performance than the other referenced techniques.

Despeckling of complex polarimetric synthetic aperture radar (SAR) images is more difficult than denoising of general images due to the low signal-to-noise ratio and the complex signals. A novel stochastic polarimetric SAR despeckling technique based on quasi Monte Carlo sampling (QMCS) and region-based probabilistic similarity likelihood has been developed. The despeckling of complex polarimetric SAR images is formulated as a Bayesian least squares optimization problem, where the posterior distribution is estimated by QMCS in a nonparametric manner. The QMCS approach allows the incorporation of the statistical description of local texture pattern similarity. Experiments on two benchmark quad-pol SAR images demonstrate that the proposed QMC texture likelihood sampling (QMCTLS) filter outperforms referenced methods in terms of both noise removal and detail preservation.

A feature extraction approach for hyperspectral image classification has been developed. Multiple linear manifolds are learned to characterize the original data based on their locations in the feature space, and an ensemble of classifier is then trained using all these manifolds. Such manifolds are localized in the feature space (which we will refer to as “localized manifolds”) and can overcome the difficulty of learning a single global manifold due to the complexity and nonlinearity of hyperspectral data. Two state-of-the-art feature extraction methods are used to implement localized manifolds. Experimental results show that classification accuracy is improved using both localized manifold learning methods on standard hyperspectral data sets.

This letter presents a Bayesian method for hyperspectral image classification based on the sparse representation (SR) of spectral information and the Markov random field modeling of spatial information. We introduce a probabilistic SR approach to estimate the class conditional distribution, which proved to be a powerful feature extraction technique to be combined with the label prior distribution in a Bayesian framework. The resulting maximum a priori problem is estimated by a graph-cut-based α-expansion technique. The capabilities of the proposed method are proven in several benchmark hyperspectral images of both agricultural and urban areas.

This letter presents K-P-Means, a novel approach for hyperspectral endmember estimation. Spectral unmixing is formulated as a clustering problem, with the goal of K-P-Means to obtain a set of “purified” hyperspectral pixels to estimate endmembers. The K-P-Means algorithm alternates iteratively between two main steps (abundance estimation and endmember update) until convergence to yield final endmember estimates. Experiments using both simulated and real hyperspectral images show that the proposed K-P-Means method provides strong endmember and abundance estimation results compared with existing approaches.

The combination of nonlocal grouping and transformed domain filtering has led to the state-of-the-art denoising techniques. In this paper, we extend this line of study to the denoising of synthetic aperture radar (SAR) images based on clustering the noisy image into disjoint local regions with similar spatial structure and denoising each region by the linear minimum mean-square error (LMMSE) filtering in principal component analysis (PCA) domain. Both clustering and denoising are performed on image patches. For clustering, to reduce dimensionality and resist the influence of noise, several leading principal components identified by the minimum description length criterion are used to feed the K-means clustering algorithm. For denoising, to avoid the limitations of the homomorphic approach, we build our denoising scheme on additive signal-dependent noise model and derive a PCA-based LMMSE denoising model for multiplicative noise. Denoised patches of all clusters are finally used to reconstruct the noise-free image. The experiments demonstrate that the proposed algorithm achieved better performance than the referenced state-of-the-art methods in terms of both noise reduction and image detail preservation.

Abstract Modeling 3D objects is difficult, especially for the user who lacks the knowledge on 3D geometry or even on 2D sketching. In this paper, we present a novel sketch‐based modeling system which allows novice users to create 3D custom models by assembling parts based on a database of pre‐segmented 3D models. Different from previous systems, our system supports the user with visualized and meaningfulshadow guidanceunder his strokes dynamically to guide the user to convey his design concept easily and quickly. Our system interprets the user's strokes as similarity queries into database to generate the shadow image for guiding the user's further drawing and returns the 3D candidate parts for modeling simultaneously. Moreover, our system preserves the high‐level structure in generated models based on prior knowledge pre‐analyzed from the database, and allows the user to create custom parts with geometric variations. We demonstrate the applicability and effectiveness of our modeling system with human subjects and present various models designed using our system.