This study proposes an approach to unsupervised change detection in which two different change maps are fused using different trade-off parameters of an active contour model. First, the change vector analysis method is conducted to produce a difference image from multitemporal and multispectral remotely sensed images. Second, two change maps are obtained based on the difference image using an active contour model using two different values of the trade-off parameter. Finally, an advantage fusion strategy is proposed to yield a final change map by fusing the two change maps, thereby reducing false alarms and preserving the accurate outlines of the changed regions. Two experiments are conducted with Landsat-7 Enhanced Thematic Mapper Plus and Landsat-5 Thematic Mapper data sets to evaluate the performance of the proposed method. Results confirm the effectiveness of the proposed approach vis-à-vis some of the state-of-the-art methods. This work contributes to the reduction of the effect of the trade-off parameter on the accuracy of the change map.
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This paper presents a fuzzy local double neighborhood information c-means (FLDNICM) clustering algorithm for remotely sensed imagery classification, which incorporates flexible and accurate local spatial and spectral information. First, a tradeoff weighted fuzzy factor is established based on a pixel spatial attraction model that considers spatial distance and class membership differences between the central pixel and its neighbor simultaneously. This factor can adaptively and accurately estimate the spatial constraints from neighboring pixels. To further enhance robustness to noise and outliers, another fuzzy prior probability function is also defined, which integrates the mutual dependence information from a pixel and its neighbor in a fuzzy logical way for obtaining accurate spatial contextual information. The FLDNICM enhances the conventional fuzzy c-means algorithm by producing homogeneous segmentation while reducing the edge blurring artifacts. The new trade-off weighted fuzzy factor and prior probability function are both parameter free and fully adaptive to the image content. Experimental results demonstrate the superiority of FLDNICM over competing methodologies, considering a series of synthetic and real-world images classification applications.
This article proposes an unsupervised change-detection method using spectral and texture information for very-high-resolution (VHR) remote-sensing images. First, a new local-similarity-based texture difference measure (LSTDM) is defined using a grey-level co-occurrence matrix. A mathematical analysis shows that LSTDM is robust with respect to noise and spectral similarity. Second, the difference image is generated by integrating the spectral and texture features. Then, the unsupervised change-detection problem in VHR remote-sensing images is formulated as minimizing an energy function related with changed and unchanged classes in the difference image. A modified expectation-maximization-based active contour model (EMCVM) is applied to the difference image to separate the changed and unchanged regions. Finally, two different experiments are performed with SPOT-5 images and compared with state-of-the-art unsupervised change-detection methods to evaluate the effectiveness of the proposed method. The results indicate that the proposed method can sufficiently increase the robustness with respect to noise and spectral similarity and obtain the highest accuracy among the methods addressed in this article.
This letter presents a long-range contextual dependency enhanced network (LCDE-Net) for semantic segmentation of large-scale point cloud, which employs a U-shaped framework. Firstly, point clouds are subsampled with grid sampling and fed into convolutional layers to learn more representative local features of points. Then global and local encoders (GLE) are designed to exploit long-range contextual dependencies and local features simultaneously. The core of GLE consists of two parts: global feature enhancement (GFE) module and feature channel modulation (FCM) module. Secondly, through decoder layers, the encoded features are upsampled through the nearest-neighbour interpolation and aggregated with the intermediate encoded features by skip connections to capture multi-scale discriminative features for semantic segmentation of point cloud. Finally, via Fully Connection layer and Softmax classifier, each point's label is assigned. Two different benchmark datasets are conducted to evaluate the performance of the proposed method, Experimental results report that the proposed LCDE-Net achieves 78.6% in terms of mean intersection over union (mIoU) on Semantic3D, and 68.2% on S3DIS, which is the highest among the comparison methods. The code of LCDE-Net is available at https://github.com/xrzmyz/LCDE-Net.
The emergence of very high resolution (VHR) images contributes to big challenges in change detection. It is hard for traditional pixel-level approaches to achieve satisfying performance due to radiometric difference. This work proposes a novel feature descriptor that is based on spectrum-trend and shape context for VHR remote sensing images. The proposed method is mainly composed of two aspects. The spectrum-trend graph is generated first, and then the shape context is applied in order to describe the shape of spectrum-trend. By constructing spectrum-trend graph, spatial and spectral information is integrated effectively. The approach is performed and assessed by QuickBird and SPOT-5 satellite images. The quantitative analysis of comparative experiments proves the effectiveness of the proposed technique in dealing with the radiometric difference and improving the accuracy of change detection. The results indicate that the overall accuracy and robustness are both boosted. Moreover, this work provides a novel viewpoint for discriminating changed and unchanged pixels by comparing the shape similarity of local spectrum-trend.
In change detection (CD) of medium-resolution remote sensing images, the threshold and clustering methods are two kinds of the most popular ones. It is found that the threshold method of the expectation maximization (EM) algorithm usually generates a CD map including many false alarms but almost detecting all changes, and the fuzzy local information c-means algorithm (FLICM) obtains a homogenous CD map but with some missed detections. Therefore, a framework is designed to improve CD results by fusing the advantages of the threshold and clustering methods. The CD map generated by the clustering method of FLICM is used to remove false alarms in the CD map obtained by EM threshold method by an overlap fusion. Then, the local Markov random field model is implemented to verify the potentially missed detections. Finally, a fused CD map with less false alarms and missed detections is achieved. Two experiments were carried out on two Landsat ETM+ data sets. The proposed method obtained the least errors (1.11% and 3.51%) and the highest kappa coefficient (0.9366 and 0.8834), respectively, when compared with five popular CD methods.
Underground coal fires can increase surface temperature, cause surface cracks and collapse, and release poisonous and harmful gases, which significantly harm the ecological environment and humans. Traditional methods of extracting coal fires, such as global threshold, K-mean and active contour model, usually produce many false alarms. Therefore, this paper proposes an improved active contour model by introducing the distinguishing energies of coal fires and others into the traditional active contour model. Taking Urumqi, Xinjiang, China as the research area, coal fires are detected from Landsat-8 satellite and unmanned aerial vehicle (UAV) data. The results show that the proposed method can eliminate many false alarms compared with some traditional methods, and achieve detection of small-area coal fires by referring field survey data. More importantly, the results obtained from UAV data can help identify not only burning coal fires but also potential underground coal fires. This paper provides an efficient method for high-precision coal fire detection and strong technical support for reducing environmental pollution and coal energy use.
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