Full Polarimetric Information Research Articles

Polarimetric Decomposition-Based Unified Manmade Target Scattering Characterization With Mathematical Programming Strategies

Due to the orientation variation and structural complexity, designing generalized and unified features to highlight manmade target scattering from polarimetric synthetic aperture radar (PolSAR) data is challenging. Inspired by the thought of mathematical programming (MP) and coupled with the model-based decomposition, this article proposes two polarimetric features: scattering contribution combiner (SCC) and scattering contribution angle (SCA) for unified scattering characterization of manmade targets. To this end, a rotated dihedral scattering model is first constructed concerning the analogous difference reciprocal and sigmoid function transformations, which adequately reflects the transition of co- and cross-pol responses caused by the orientation variation. Along with the dipole-like compound scattering models and through designing a discriminant-based model solution method, a fine eight-component decomposition using full polarimetric information is proposed. Through skillfully employing the MP strategies, the proposed decomposition achieves the physical optimization of scattering modeling and reasonable inversion of model parameters. Thus, it can accurately describe the local structure scattering and remarkably improve the overestimation of volume scattering. Subsequently, by analyzing the significance distribution on targets of different scattering mechanisms, the SCC is constructed via the linear/nonlinear combination of scattering contributions on the one hand. On the other hand, by further mining the information implied in the scattering contributions, the SCA is proposed with the strategy of trigonometric function transformation. Experimental results conducted on real PolSAR data not only demonstrate the effectiveness and superiority of the constructed features but also exhibit a clear advantage of fine polarimetric decomposition in scattering understanding, which encourages the use of them for further applications.

Mueller micropolarimeter for color imaging of aluminum metasurfaces

Many anticounterfeiting tags rely on images intricate in different color and/or different polarization states to create optical effects invisible in conventional observation conditions. We build here an imaging micropolarimeter based on the dual-rotating compensator system and using the color capabilities of cameras to yield the full polarimetric information for any color coordinates in one acquisition step. After correction for the camera response, the full color image reconstructed from the polarimetric response is validated by comparison with images obtained in an optical microscope fitted with polarizers.

Sensitivity of PolSAR decomposition to forest disturbance and regrowth dynamics in a managed forest

Managed forests, dynamic with activities of harvest and afforestation, have become an area of imminent research opportunity to understand the effects of these disturbances and regrowth dynamics. As low frequency polarized radar signals have the ability to penetrate forest canopies, the fully polarized Synthetic Aperture Radar (SAR) data gives an ideal representation of conditions in the forest. However, this valuable information has not been optimally utilized in understanding the forest disturbances and regrowth dynamics. Several forest change monitoring studies have been performed using single or dual polarization SAR data, whereas limited studies utilized full polarimetric information. In this study, L-band ALOS/PALSAR and ALOS-2/PALSAR-2 fully polarimetric data is used to study and understand the behavioural dynamics of homogeneous and heterogeneous forest compartments having single and multiple species composition, respectively. Radar scattering pattern of different species, and its variation with respect to phenology, disturbances, harvesting and plantation regrowth are analysed to understand the trend in scattering components with respect to above said forest changes. Based on the scattering properties and their analyses, a two stage rule based classifier has been developed to categorize the forest based on its disturbance and regrowth status into disturbed, re-growth, stable/no change and non forest classes. The classifier performed with, considerably, high accuracy having an overall accuracy of 85.39% and a kappa coefficient of 0.8. The classifier developed in this work presents the potential of fully polarimetric data in understanding the level and extent of disturbances and regrowth dynamics of a forest.

Investigation of C-Band SAR Polarimetry for Mapping a High-Tidal Coastal Environment in Northern Canada

Synthetic Aperture Radar (SAR) has been used in characterizing intertidal zones along northern Canadian coastlines. RADARSAT-2, with its full polarimetric information, has been considered for monitoring these vulnerable ecosystems and helping enhance the navigational safety of these waters. The RADARSAT Constellation Mission (RCM) will ensure data continuity with three identical SAR satellites orbiting together, providing superior revisit capabilities. The three satellites are equipped with multiple configurations, including single-polarization (HH, HV, VV), conventional (HH-HV, VV-VH, and HH-VV), hybrid (i.e., compact) dual polarization, and fully polarimetric (FP) modes. This study investigates the potential of the compact polarimetric (CP) mode for mapping an intertidal zone located at Tasiujaq village on the southwest shore of Ungava Bay, Quebec. Simulated RCM data were generated using FP RADARSAT-2 images collected over the study site in 2016. Commonly used tools for CP analysis include Raney m-delta classification and the hybrid dual polarizations RH-RV (where the transmitter is right-circular and the receivers are horizontal and vertical linear polarizations) and RR-RL (where the transmitter is right circular and the receivers are right-circular and left-circular polarizations). The potential of CP is compared with single, conventional dual-pol, and FP. The Freeman–Durden and Touzi discriminators are used for FP analysis. The random forest classifier is used as a classification approach due to its well-documented performance compared to other classifiers. The results suggest that the hybrid compact (RR-RL and RH-RV) dual polarizations provide encouraging separability capacities with overall accuracies of 61% and 60.7%, respectively, although they do not perform as well as conventional dual-pol HH-HV (64.4%). On the other hand, the CP polarimetric m-delta decomposition generated slightly less accurate classification results with an overall accuracy of approximately 62% compared to the FP Freeman–Durden (67.08%) and Touzi discriminators (71.1%).

Spectropolarimetric Analysis of FRB 181112 at Microsecond Resolution: Implications for Fast Radio Burst Emission Mechanism

Abstract We have developed a new coherent dedispersion mode to study the emission of fast radio bursts (FRBs) that trigger the voltage capture capability of the Australian SKA Pathfinder (ASKAP) interferometer. In principle the mode can probe emission timescales down to 3 ns with full polarimetric information preserved. Enabled by the new capability, here we present a spectropolarimetric analysis of FRB 181112 detected by ASKAP, localized to a galaxy at redshift 0.47. At microsecond time resolution the burst is resolved into four narrow pulses with a rise time of just 15 μs for the brightest. The pulses have a diversity of morphology, but do not show evidence for temporal broadening by turbulent plasma along the line of sight, nor is there any evidence for periodicity in their arrival times. The pulses are highly polarized (up to 95%), with the polarization position angle varying both between and within pulses. The pulses have apparent rotation measures that vary by and apparent dispersion measures that vary by . Conversion between linear and circular polarization is observed across the brightest pulse. We conclude that the FRB 181112 pulses are most consistent with being a direct manifestation of the emission process or the result of propagation through a relativistic plasma close to the source. This demonstrates that our method, which facilitates high-time-resolution polarimetric observations of FRBs, can be used to study not only burst emission processes, but also a diversity of propagation effects present on the gigaparsec paths they traverse.

Analysis of Azimuthal Variations Using Multi-Aperture Polarimetric Entropy with Circular SAR Images

In conventional synthetic aperture radar (SAR), sensors with a fixed look angle are assumed, and the scattering properties are considered as invariant in the azimuth. In some new SAR modes such as wide-angle SAR and circular SAR (CSAR), the azimuthal angle of view is much larger. Anisotropic targets which have different physical shapes from different angles of view are difficult to interpret in the traditional observation model if variations remain unconsidered. Meanwhile, SAR polarimetry is a powerful tool to analyze and interpret targets’ scattering properties. Anisotropic targets can be precisely described with polarimetric signatures from different angles of view. In this paper, polarimetric data is separated into sub-apertures to provide polarimetric properties from different angles of view. A multi-aperture observation model which contains full polarimetric information from all angles of view is then established. Based on the multi-aperture observation model, multi-aperture polarimetric entropy (MAPE) is defined and is suggested as an extension of polarimetric entropy in multi-aperture situations. MAPE describes both targets’ polarimetric properties and variations across sub-apertures. Variations across the azimuth are analyzed and anisotropic and isotropic targets are identified by MAPE. MAPE can be used in many polarimetric wide angle and CSAR applications. Potential applications in target discrimination and classification are discussed. The effectiveness and advantages of MAPE are demonstrated with polarimetric CSAR data acquired from the Institute of Electronics, Chinese Academy of Sciences airborne CSAR system at P-band.

Limits on the mass, velocity and orbit of PSR J1933−6211

We present a high-precision timing analysis of PSR J1933$-$6211, a millisecond pulsar (MSP) with a 3.5-ms spin period and a white dwarf (WD) companion, using data from the Parkes radio telescope. Since we have accurately measured the polarization properties of this pulsar we have applied the matrix template matching approach in which the times of arrival are measured using full polarimetric information. We achieved a weighted root-mean-square timing residuals (rms) of the timing residuals of 1.23 $\rm \mu s$, 15.5$\%$ improvement compared to the total intensity timing analysis. After studying the scintillation properties of this pulsar we put constraints on the inclination angle of the system. Based on these measurements and on $\chi^2$ mapping we put a 2-$\sigma$ upper limit on the companion mass (0.44 M$_\odot$). Since this mass limit cannot reveal the nature of the companion we further investigate the possibility of the companion to be a He WD. Applying the orbital period-mass relation for such WDs, we conclude that the mass of a He WD companion would be about 0.26$\pm$0.01 M$_\odot$ which, combined with the measured mass function and orbital inclination limits, would lead to a light pulsar mass $\leqslant$ 1.0 M$_\odot$. This result seems unlikely based on current neutron star formation models and we therefore conclude that PSR J1933$-$6211 most likely has a CO WD companion, which allows for a solution with a more massive pulsar.

Polarimetric Analysis of Compact-Polarimetry SAR Architectures for Sea Oil Slick Observation

In this paper, a theoretical and experimental analysis of polarimetric synthetic aperture radar (SAR) architectures is undertaken for sea oil slick observation purposes. Reference is made to the conventional full-polarimetric (FP) SAR that is here contrasted with new-generation polarimetric SAR architectures, known as compact-polarimetric (CP) SAR. Two CP modes are considered, i.e., the hybrid-polarity and π/4 modes, whose measurements are emulated from actual L- and C-band FP SAR data. Polarimetric sea surface scattering is predicted according to an extended version of the Bragg scattering model (X-Bragg) in order to point out the differences exhibited between FP and CP SAR architectures and among CP SAR modes. Theoretical predictions are then contrasted with experiments undertaken on actual polarimetric SAR data collected over well-known oil slicks and weak-damping surfactants. Results confirm model prediction, showing that differences mainly apply when polarimetric features are estimated over slick-free sea surface using different SAR architectures, with the π/4 mode behaving closer to FP SAR. Although CP SAR architectures measure only a subset of the FP information content, they represent an interesting operational alternative for both detecting oil slicks and discriminating them from weak-damping surfactants.

Assessment of C-band compact polarimetry SAR for sea ice classification

The C-band synthetic aperture radar (SAR) data from the Bohai Sea of China, the Labrador Sea in the Arctic and the Weddell Sea in the Antarctic are used to analyze and discuss the sea ice full polarimetric information reconstruction ability under compact polarimetric modes. The type of compact polarimetric mode which has the highest reconstructed accuracy is analyzed, along with the performance impact of the reconstructed pseudo quad-pol SAR data on the sea ice detection and sea ice classification. According to the assessment and analysis, it is recommended to adopt the CTLR mode for reconstructing the polarimetric parameters σHH0, σVV0, H and α, while for reconstructing the polarimetric parameters σHV0, ρH-V, λ1 and λ2, it is recommended to use the π/4 mode. Moreover, it is recommended to use the π/4 mode in studying the action effects between the electromagnetic waves and sea ice, but it is recommended to use the CTLR mode for studying the sea ice classification.

Parallel Implementation of Polarimetric Synthetic Aperture Radar Data Processing for Unsupervised Classification Using the Complex Wishart Classifier

This work investigates the parallel implementation of target decomposition and unsupervised classification algorithms for polarimetric synthetic aperture radar (POLSAR) data processing. The algorithms are implemented using two different parallel programming models: 1) clusters of CPUs, using message passing interface (MPI), and 2) commodity graphic processing units (GPUs), using the compute device unified architecture (CUDA). POLSAR data processing generally involves a large amount of computations as the full polarimetric information needs to be decomposed and analyzed. Our experiments reveal that GPU architectures provide a good framework for massive parallelization of POLSAR data processing. For instance, it is found that a single GPU can be more efficient than a cluster of 128 nodes with speedups of more than $100 \times $ in comparison with the single processor times. The proposed implementation makes the best use of low-level features in the GPU architecture such as shared memories, while also providing coalesced accesses to memory in order to achieve maximum performance.

Adaptive Anisotropic Diffusion Method for Polarimetric SAR Speckle Filtering

In this paper, we present an adaptive anisotropic diffusion (AD) method for the speckle filtering of polarimetric synthetic aperture radar (PolSAR) images. One of the main innovations of our work is that we employ a likelihood-ratio test method to measure the equality of two polarimetric covariance matrices to control the diffusivity, and thus consider the full polarimetric information and the statistical traits of PolSAR data in the diffusion process. Meanwhile, to overcome the drawback of the conventional AD methods, we integrate the local homogeneity information into the diffusion model to adaptively control the generosity of the filtering. Experiments were conducted on a simulated image and two airborne PolSAR images to illustrate the filtering performance, and the results show that the proposed method effectively reduces speckle, retains edges, and targets, and preserves the polarimetric scattering mechanisms.

Improved Building Extraction With Integrated Decomposition of Time-Frequency and Entropy-Alpha Using Polarimetric SAR Data

Building extraction is one of the primary applications of urban remote sensing. Polarimetric synthetic aperture radar (POLSAR), with its all-weather day and night imaging, canopy penetration and full polarimetric information, provides a unique way to detecting and characterizing urban areas. In this study, the time-frequency decomposition technique and the entropy/alpha-Wishart classifier were integrated to improve building extraction. The entropy/alpha-Wishart classifier was able to extract ortho-oriented buildings. After time-frequency transformation, the variation of entropy, alpha, anisotropy differs for objects with different scattering mechanisms, and the alpha angle of subaperture images was optimal in delineating slant-oriented buildings. A comparison between the integrated approach and the conventional entropy/alpha-Wishart classifier was performed on both C- and L-band NASA/JPL AIRSAR datasets. The overall accuracy and kappa value of the integrated approach was about 20% higher than that of the entropy/alpha-Wishart classifier. The C-band output tends to show more detailed scattering properties whereas the extracted buildings from the L-band image reveal better overall visual results.

SAR images analysis based on polarimetric signatures

In the presented paper a new method of identification of canonical coherent scatterers in the quad-polarimetric SAR data are presented. The proposed method is based on the analysis of polarimetric signatures. The observed signatures are compared with the polarimetric signatures of four canonical objects: trihedral, dihedral and helix – right and left which represent basic scattering mechanisms: single bounce, double bounce and helix scattering. The polarimetric matrices are treated as vectors in a unitary space with a scalar product that generates the norm. A recognized object is classified to one of the four coherent classes by a Kohonen network. It is not trained in an iteration process but its weights are adjusted according to the given patterns. The network classification is supported by rules. The obtained maps of pixels that represent canonical objects are compared with a map of coherent scatterers which was obtained by using the polarimetric entropy approach. The developed method of canonical coherent scatterers identification based on the polarimetric signatures analysis allows us not only to identify precisely the canonical coherent scatterers but also to determine the type of scattering mechanism characteristic for each of them. Since the proposed method works on a single-look (non-averaged) SAR data, it does not cause any spatial nor spectral decrease of amount of information because averaging is not conducted. Moreover, the proposed method will enable us the identification of a type of scattering mechanism in the canonical coherent pixels. This is an improvement in comparison to the existing methods. The obtained results should be more precise because the full polarimetric information about the scatterers is used in the identification procedure.

A New Automatic Ship Detection Method Using $L$-Band Polarimetric SAR Imagery

Ship-sea contrast can be improved significantly when the full polarimetric information is used, compared with the information provided by a single polarization channel. Therefore, a new automatic ship detection method, termed SPAN Wishart (SPWH), is proposed in this paper based on an unsupervised classification concept, which combines the SPAN of a polarimetric SAR (POLSAR) data with the complex Wishart classifier. The significant improvement of this technique is to utilize the SPAN of ship cluster center as an iterative termination criterion to realize the automatic ship detection. Then, another method based on multifrequency is proposed to discriminate between ships and their ambiguities to provide a substitute for the ground truth for the subsequent validation of the SPWH algorithm by using an AIRSAR polarimetric dataset, which consists of C- and L-band data covering Kojimawan in Tamano of Japan. After that, the SPWH is validated only using the L-band data with the defined ships by comparing the performance of the SPWH with a traditional CFAR detector. By contrast, the SPWH algorithm is more effective, robust, and completely automatic.

Polarimetric mode of full polarization interferometric radiometer

全极化综合孔径辐射计（Full Polarization Interferometric Radiometer，FPIR）是一套高分辨率、轻量化、低功耗的X波段一维综合孔径微波辐射计.分析了FPIR的极化理论，推导出FPIR的极化可视度函数.为了获取全极化信息，FPIR系统采用两种不同的天线阵列设计方案.对于每种稀疏天线阵列，设计了最优极化切换序列.设计的最优极化序列不仅使灵敏度的损失达到最小，还使得水平极化、垂直极化和交叉极化亮温的灵敏度达到相同水平.

Tsunami Damage Investigation of Built-Up Areas Using Multitemporal Spaceborne Full Polarimetric SAR Images

This paper explores the use of full polarimetric synthetic aperture radar (PolSAR) images for tsunami damage investigation from the polarimetric viewpoint. The great tsunami induced by the earthquake of March 11th, 2011, which occurred beneath the Pacific off the northeastern coast of Japan, is adopted as the study case using the Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar multitemporal PolSAR images. The polarimetric scattering mechanism changes were quantitatively examined with model-based decomposition. It is clear that the observed reduction in the double-bounce scattering was due to a change into odd-bounce scattering, since a number of buildings were completely washed away, leaving relatively a rough surface. Polarization orientation (PO) angles in built-up areas are also investigated. After the tsunami, PO angle distributions from damaged areas spread to a wider range and fluctuated more strongly than those from the before-tsunami period. Two polarimetric indicators are proposed for damage level discrimination at the city block scale. One is the ratio of the dominant double-bounce scattering mechanism observed after-tsunami to that observed before-tsunami, which can directly reflect the amount of destroyed ground-wall structures in built-up areas. The second indicator is the standard deviation of the PO angle differences, which is used to interpret the homogeneity reduction of PO angles. Experimental results from after- and before-tsunami comparisons validate the efficiency of these indexes, since the built-up areas with different damage levels can be well discriminated. In addition, comparisons between before-tsunami pairs further confirm the stability of the two polarimetric indexes over a long temporal duration. These interesting results also demonstrate the importance of full polarimetric information for natural disaster assessment.

Compact and robust method for full Stokes spectropolarimetry

We present an approach to spectropolarimetry that requires neither moving parts nor time dependent modulation, and that offers the prospect of achieving high sensitivity. The technique applies equally well, in principle, in the optical, UV, or IR. The concept, which is one of those generically known as channeled polarimetry, is to encode the polarization information at each wavelength along the spatial dimension of a two-dimensional data array using static, robust optical components. A single 2D data frame contains the full polarization information and can be configured to measure either two or all of the Stokes polarization parameters. By acquiring full polarimetric information in a single observation, we simplify polarimetry of transient sources and in situations where the instrument and target are in relative motion. The robustness and simplicity of the approach, coupled with its potential for high sensitivity, and applicability over a wide wavelength range, is likely to prove useful for applications in challenging environments such as space.

Fluctuation polarimetry

We examine the relationship between the strength of the intensity fluctuations and the polarimetric properties of a random electromagnetic field composed of a Gaussian, random field, and nonrandom field, and we present a method for determining the state of polarization of the Gaussian random field. The approach relies on incoherently mixing a Gaussian random field with a controllable reference field and measuring the intensity fluctuations of their superposition. We demonstrate that by controlling the reference field, the full polarimetric information about the Gaussian random field can be uniquely determined.

Automated Non-Gaussian Clustering of Polarimetric Synthetic Aperture Radar Images

This paper presents an automatic image segmentation method for polarimetric synthetic aperture radar data. It utilizes the full polarimetric information and incorporates texture by modeling with a non-Gaussian distribution for the complex scattering coefficients. The modeling is based upon the well-known product model, with a Gamma-distributed texture parameter leading to the K-Wishart model for the covariance matrix. The automatic clustering is achieved through a finite mixture model estimated with a modified expectation maximization algorithm. We include an additional goodness-of-fit test stage that allows for splitting and merging of clusters. This not only improves the model fit of the clusters, but also dynamically selects the appropriate number of clusters. The resulting image segmentation depicts the statistically significant clusters within the image. A key feature is that the degree of sub-sampling of the input image will affect the detail level of the clustering, revealing only the major classes or a variable level of detail. Real-world examples are shown to demonstrate the technique.

Full Stokes polarimetric imaging using a single ferroelectric liquid crystal device

This paper reports the design and the implementation of a Stokes imaging polarimeter able to provide full polarimetric information at 200 fps. This portable implementation is based on a division-of-time architecture and uses a single ferroelectric liquid crystal device as the polarization modulating element. Our system is designed to work at 532 nm with natural light or with controlled illumination, without temperature control. We propose an optimized driving scheme of the modulator such that the liquid crystal device can produce four polarization states which makes it possible to retrieve the full polarimetric information. The modulator characterization is reported and experimental results are provided.