Multiple-aperture interferometric synthetic aperture radar (MAI) technology can obtain the deformation of the surface along the azimuth direction, which makes up for the limitations of traditional interferometric synthetic aperture radar (InSAR) technology. However, the MAI measurement is vulnerable to the ionosphere, which makes the ionospheric delay mixed with the surface deformation, resulting in a serious reduction of the accuracy of the azimuth measurement. In this article, a method for correcting the azimuth ionospheric delay phase is proposed based on the relationship between the ionospheric delay phase and the group phase delay offset, termed by the azimuth group phase delay (AGPD) method. This approach accommodates large-scale deformation fields, facilitating a more comprehensive acquisition of ionospheric information. This method is first employed to reconstruct the coseismic deformation field associated with the 2021 Maduo earthquake. After ionospheric correction, the root mean square errors (RMSEs) between GNSS and MAI measurements decrease from 0.08 to 0.04 m. Then, the results from the Alaska case demonstrate the method’s ability in the identification of intricate ionospheric stripe patterns. Comparative analysis against the existing azimuth ionospheric error correction methods indicates a significant improvement of above 50%.

Change detection (CD) based on time-series PolSAR images is an effective way to analyze land use change in the process of urban change. The deep learning method can extract representative deep features from PolSAR images, but the precise construction of commonly used deep learning models often depends on a large number of training samples. This paper proposes a weak supervised deep learning CD method based on small-scale labeled samples. Using the Unet++ structure and combining semantic information to detect changes, experiments were conducted on two sets of UAVSAR datasets. The results show that the proposed limited labeled samples based Unet++ PolSAR-CD method can effectively detect changes in SAR images under the condition of 40% training samples, which has the best Overall Accuracy (OA), Kappa Coefficient (KC), Precision(Pre), Recall (Rec), and F1-Score, exceeding 0.96, 0.85, 0.89, 0.86, and 0.88 respectively.

Limited labels and increasing multisource data promote domain adaptation (DA) problem as a challenging study for polarimetric synthetic aperture radar (PolSAR) interpretation. Existing DAs for optical images cannot generalize over PolSAR imagery due to its special side-imaging characteristics and complex distribution shifts. In this letter, a general feature paradigm (GFP) is proposed for unsupervised cross-domain PolSAR image classification. The GFP is based on a key observation that interclass aggregation is optimized after four-step feature transformations. This key observation leads to GFP that not only reduces the domain shifts but also compatible with typical DA methods. The GFPs are conducted on both source and target domain by unsupervised manner, including polarimetric basis extraction, the Wishart clustering, histogram statistics, and dimensionality reduction. After these transformations, the unlabeled target PolSAR image can be classified based on obtained GFP, DA, and limited labeled samples only from the source domain. Extensive unsupervised cross-domain experiments on 27 scenarios verified that GFP leads to at most 93.76% accuracy for full- and dual-polarized synthetic aperture radar (SAR) images’ classification. Moreover, the GFP shed light on extensive cross-domain PolSAR applications about built-up areas, vegetation, and bare land analysis.

Isolating the orbital error from the interferometric synthetic aperture radar (InSAR) observations is a great challenge, especially in the presence of tectonic deformation due to their similar spatial patterns. The influence of orbital error is systematic, which can reduce the reliability of deformation monitoring. In this letter, we propose a method to isolate the orbital error from the multitemporal InSAR (MTInSAR) derived tectonic deformation based on the wavelet multiresolution analysis and independent component analysis (ICA). Starting from the sequential interferometric phase of unwrapping, the tectonic deformation and orbital error are firstly extracted from the interferometric phase by wavelet analysis based on their longwavelength spatial patterns, and ICA is then used to isolate the orbital error from the tectonic deformation according to the different temporal characteristics of the two types of signals. In the simulation experiment, the root-mean-square error (RMSE) of the isolated orbital error is 2.6 mm. Experiments with real data in Southern California show that the proposed method can successfully separate the orbital error from the tectonic deformation, and the InSAR deformation rates are in good agreement with the GPS observations.

Homogeneous pixel selection (HPS) plays an important role in the application of multitemporal SAR interferometry. The statistical goodness-of-fit testing of the temporal samples has been widely used for HPS. However, the detection rates of the existing methods are unsatisfactory under small datasets. In this paper, a stacked auto-encoder (SAE) network based method is proposed for the selection of homogeneous pixels under the idea of deep learning image classification, as termed by SAEHPS. The SAE network is used to learn the spatial distribution behavior of the average intensity image. The deep network is trained and tested on different high-resolution SAR datasets of the Hong Kong Airport and the Fuzhou City, and three pixel-wise labels (i.e., high, medium, and low reflections) are regarded as outputs of model learning. The unsupervised training and supervised fine-tuning realize the class prediction. The results show that the SAE can achieve robust accuracies above 90% based on empirically labeled samples, especially in non-architectural areas where the distributed scatterers exist. The SAE results are devoted to the multitemporal PS/DS InSAR approach to identify homogeneous pixels. Both qualitative and quantitative experiments in HPS, phase optimization, and deformation monitoring have demonstrated the superiority of the novel method.

The scattering response of polarimetric synthetic aperture radar (PolSAR) data is strongly target orientation-dependent. Formulating the polarimetric matrix as sequential data by rotating the polarimetric matrix along the radar line of sight would provide rich information about land-cover properties. In this work, we propose a composite sequential network (CSN) with polarization orientation angle (POA) attention to model the polarimetric coherency matrix sequence and explore target scattering orientation diversity features. Three major factors strengthen the proposed method for PolSAR image analysis. First, CSN improves the feature comprehensiveness by extending the interpretation mode of PolSAR data from spatial polarization to spatial polarization orientation. In this way, CSN could describe polarimetric response dynamics at different orientations. Second, a two-stream composite network with both real- and complex-valued convolutional long short-term memory (ConvLSTM) network is proposed to process the diagonal and off-diagonal elements of the coherency matrix sequence, respectively. Compared to existing real-/complex-valued networks, the CSN explores the significant phase information of the off-diagonal elements by operations in the complex domain. Meanwhile, CSN prevents padding 0 meaninglessly in the imaginary part of the real-valued diagonal elements. Third, during the sequential modeling of the polarimetric matrix, a POA attention mechanism is proposed. Equipped with POA-sensitive decomposition loss, the CSN attends to substantial POA range derived by targets’ physical scattering mechanism and learns features closely related to the scattering mechanism. Extensive experiments and analysis on land-cover classification demonstrate the proposed method’s robustness and excellence.

Accurate labeled samples for polarimetric synthetic aperture radar (PolSAR) images are usually difficult to obtain. So unsupervised learning is meaningful for PolSAR land cover classification tasks. In this paper, we proposed an unsupervised spontaneous clustering network named deep graph cluster. Spatial information and polarimetric coherency matrix are combined to represent and cluster the data. Firstly, an accurate and efficient clustering algorithm based on approximate nearest neighbor search is proposed. Then, we proposed the deep graph cluster based on spatial aggregation propensity of the same class and spatial dispersion of different classes. Two groups of experiments on PolSAR images shows that the accuracy of proposed method reaches 90-96%, 7-12% higher than classical unsupervised method and close to the some supervised models.

Increasing amounts of polarimetric synthetic aperture radar (PolSAR) images from different sensors covering different scenes are available, but limited labeled samples and trained models can hardly work well in these cross-domain data interpretations. Fortunately, domain adaptation (DA) can transfer knowledge in existing images to new yet related images. DA shows attractive potential for PolSAR classification, and it is still challenging due to more complex domain shifts caused by different sensors, imaging conditions, and distributions. Inspired by the widely applicable polarimetric scattering mechanisms and DA ability of subspace alignment (SA), this article is devoted to constructing a robust unsupervised cross-domain PolSAR classification framework, by exploring scattering and statistical characteristics mapping between the source and target domains. First, classical scattering components of both source and target data were extracted, and Wishart clustering was adopted to derive the statistical information of scattering components at patch level. Second, the intrinsic polarimetric scattering components were estimated and extracted, which were called statistical scattering components (SSCs). Third, by applying SA, the source SSC was aligned with target SSC, and domain shift was further reduced. Finally, the target PolSAR image was classified based on labeled samples from source domain, and unsupervised cross-domain classification was achieved by SSC-based SA (SSC-SA). The unsupervised cross-domain experiments are conducted on 49 units among 11 data sets, including Radarsat-2, Gaofen-3, AIRSAR, and Pi-SAR images. With randomly selected labeled samples (about 2%–10%) from source domain, the accuracies of the proposed cross-domain classifications range between 80.20% and 95.64%. Also, the proposed SSC feature pattern is proved extensible for other polarimetric basis and decompositions.

Accurate built-up area (BA) information plays crucial role for many applications. PolSAR imagery can provide important source for BAs information analysis. However, the BAs with large orientation angles are usually misdetected as vegetation, and labeled BA samples with special orientations are diffi-cult to obtain. In this paper, a PolSAR BA extraction method based on eigenvalue statistical information and PU-Learning is proposed to overcome abovementioned problems. Firstly, the roll invariance of coherency-matrix eigenvalues and the building orientations have been analyzed. Then, by adopting eigenvalue-Wishart unsupervised classification, regional statistical information and rotation invariant property are comprehensively utilized. Finally, the BAs are extracted by combining PU-Learning classifier with only positive samples at same distinguishable orientation. Six experiments on PolSAR imageries show the accuracy of proposed method can reach 92-99% with only a few positive samples, 8-20% higher than classical model decomposition-based PU-Learning method, and the requirement for labeled samples is less than 0.65%.

Polarimetric response is strongly target orientation dependent. The observed polarimetric matrices from the same target with different orientations can be quite different. The existence of target scattering orientation diversity contains rich information, and leveraging information of target scattering orientation diversity may help to reveal polarimetric properties of different land cover types. In this work, a robust land cover feature descriptor, dynamic fractal texture, is introduced to capture the stochastic self-similarities of land cover scattering responses in both spatial and rotation domains. We extend the polarimetric matrix to the rotation domain by polarimetric basis transformation. Varying polarization orientation angle (POA) or ellipticity angle (EA), polarimetric responses of land cover under a series of orientations can be obtained. Then, the dynamic fractal texture is formulated by serializing received responses as a polarimetric synthetic-aperture radar (PolSAR) image sequence. Finally, the proposed features are combined with random forest (RF)/support vector machine (SVM) classifier to produce the classification maps on real PolSAR data. Experiment results show that dynamic fractal texture has an advantage in indicating rotation domain information. The proposed method has superior performance in land cover classification and yields accurate classification results.

Polarimetric synthetic aperture radar (PolSAR) image classification is one of the most important applications in Pol-SAR image processing. More and more deep learning methods are applied to PolSAR image classification. As we know, the polarimetric response of a target is related to the orientation of the target, but the features in rotation domain are not fully used in deep learning. We use a convolutional LSTM (ConvLSTM) along with a sequence of polarization coherent matrices in rotation domain for PolSAR image classification. First, nine different polarization orientation angles (POA) are used to generate nine polarization coherent matrices in rotation domain. Second, a deep learning model that stacked with multiple ConvLSTM layers and fully connected layers is proposed for classification. Finally, the sequence of polarization coherent matrices is fed into the ConvLSTM to classify Pol-SAR images. Experiments show that the classification results of ConvLSTM are better than the LeNet-5.

BACKGROUND: As one of the most successful knowledge-based energy functions, the distance-dependent atom-pair potential is widely used in all aspects of protein structure prediction, including conformational search, model refinement, and model assessment. During the last two decades, great efforts have been made to improve the reference state of the potential, while other factors that also strongly affect the performance of the potential have been relatively less investigated. RESULTS: Based on different distance cutoffs (from 5 to 22 Å) and residue intervals (from 0 to 15) as well as six different reference states, we constructed a series of distance-dependent atom-pair potentials and tested them on several groups of structural decoy sets collected from diverse sources. A comprehensive investigation has been performed to clarify the effects of distance cutoff and residue interval on the potential's performance. Our results provide a new perspective as well as a practical guidance for optimizing distance-dependent statistical potentials. CONCLUSIONS: The optimal distance cutoff and residue interval are highly related with the reference state that the potential is based on, the measurements of the potential's performance, and the decoy sets that the potential is applied to. The performance of distance-dependent statistical potential can be significantly improved when the best statistical parameters for the specific application environment are adopted.

In this paper we proposed a metric learning-based method to extract collapsed buildings from post-earthquake PolSAR imagery. In this method, eight building and orientation related features, including entropy H, the average scattering angle α, anisotropy A, the circular polarization correlation coefficient ρ and the four scattering powers of Yamaguchi 4 component decomposition with a rotation of the coherency matrix, are considered and analyzed. Then a transformation matrix is learned from collapsed and intact building samples via an improved informational-theoretic metric learning(ITML). With such a transformation matrix, the features are projected into a low-dimension space to mitigate the impact of topography and building's aspect angle. Finally a k − NN classifier is utilized to distinguish collapsed and intact buildings. The proposed method is tested on one RadarSAT-2 PolSAR image acquired after 2010 Yushu Earthquake in the Qinghai Province of China. Results are validated by the manually interpretation map of a very high resolution (VHR) optical image. It shows that, the method is efficient to extract collapsed building areas using limited samples and only one post-earthquake PolSAR image.