Polarimetric Detection Research Articles

Polarimetric imaging detection using a convolutional neural network with three-dimensional and two-dimensional convolutional layers.

Polarimetric imaging detection is a relatively new and largely undeveloped field. Although convolutional neural networks (CNNs) have achieved great success in two-dimensional (2D) normal intensity images in the field of target detection, traditional CNN methods have not been widely applied to optical polarimetric images, and they cannot take full advantage of the connection between different polarimetric images. To solve this problem, three-dimensional (3D) convolutions are adopted to consider the relationship between S0, S1, and S2 images as a third dimension. Based on the 3D convolutions, a CNN with 3D and 2D convolutional layers is introduced to further improve the success rate of target detection with limited polarimetric images. The evaluations in different natural backgrounds reveal that the proposed method achieves higher detection accuracy than that of two traditional methods for comparison.

A 220-GHz InP HEMT Direct Detection Polarimeter

In this article, a 220-GHz direct detection polarimetric receiver is reported. This polarimetric receiver is intended for sensing of the microphysical properties of cloud ice in the earth’s upper atmosphere. In the article, we report the measured RF performance, including RF gain of approximately 35 dB per channel and integrated noise figure of the receiver. The noise figure is measured to be 5.1 dB for the horizontally polarized channel and 5.4 dB for the vertically polarized channel. The receiver measures only 1.8 cm $\times3.0$ cm $\times6.4$ cm and has a total regulated dc power consumption of 520 mW. This article represents the first 220-GHz polarimetric direct detection receiver and is enabled by an advanced 25-nm indium phosphide (InP) HEMT monolithic microwave integrated circuit (MMIC) technology.

Optical Polarimetric Detection for Dental Hard Tissue Diseases Characterization.

Dental enamel constitutes the outer layer of a crown of teeth and grows nearly parallel. This unique nanostructure makes enamel possess birefringence properties. Currently, there is still no appropriate clinical solution to examine dental hard tissue diseases. Therefore, we developed an optical polarization imaging system for diagnosing dental calculus, caries, and cracked tooth syndrome. By obtaining Stokes signals reflected from samples, Mueller images were constructed and analyzed using Lu-Chipman decomposition. The results showed that diattenuation and linear retardance images can distinguish abnormal tissues. Our result also aligns with previous studies assessed by other methods. Polarimetric imaging is promising for real-time diagnosing.

TRANSFORMATION BASED ALGORITHMS FOR CHANGE DETECTION IN FULL POLARIMETRIC REMOTE SENSING IMAGES

Abstract. Thanks to the recent advances in the development of polarimetric synthetic aperture radar (SAR) sensors, this remote sensing field attracts many applications. Among the different applications of these data, change detection is one of the most important applications. PolSAR images, due to interactions between electromagnetic waves and the target, could be used to study changes in the Earth's surface. This paper is a type of transformation-based method for polarimetric change detection (CD) purpose. For this purpose, we use full polarimetry imaging radar and extracted 138 features based on decomposition. The CD methods are the principal component analysis (PCA), the Multivariate Alteration Detection (MAD), the Iteratively Reweighted Multivariate Alteration Detection (IR-MAD), the Covariance Equalization (CE), and the Cross-Covariance (CRC). Assessment of the incorporated methods performed using most common criteria as quantity and quality assessment, such as overall accuracy (OA), kappa coefficient, and as visual analysis. The results of the experiments show that CC has better performance compared with other algorithms.

Moving target detection with polarimetric distributed MIMO radar in heterogeneous clutter

In this study, the authors consider the problem of moving target detection in the presence of heterogeneous clutter. The knowledge-aided method has been extended to derive the polarimetric multiple-input multiple-output (MIMO) radar detector. And the polarimetric clutter covariance matrix was modelled as a complex inverse Wishart distribution. More precisely, the clutter covariance matrices between different transmitter–receiver (Tx–Rx) pairs are assumed to follow the distribution which shares a prior clutter covariance matrix structure while with different values of the power levels. Under this assumption, the generalised likelihood ratio test (GLRT) approach has been adopted to develop the polarimetric knowledge-aided detector without secondary data. Numerical results are shown to illustrate the effectiveness of the polarimetric knowledge-aided GLRT detector in heterogeneous clutter.

Rain Monitoring with Polarimetric GNSS Signals: Ground-Based Experimental Research

In recent years, there has been a preliminary research on monitoring rainfall information based on polarimetric Global Navigation Satellite System (GNSS) signals, which is a quite novel concept. After previous theoretical research on monitoring rain based on polarimetric phase shift of GNSS signals, the paper aims to detect rain using polarimetric GNSS signals from a ground-based experiment. Firstly, a conical horn antenna specially designed for receiving dual-polarized (H, horizontal, and V, vertical) GNSS signals was developed, and an experimental system for polarimetric GNSS rain detection was built. Then, taking Global Positioning System (GPS) satellites as signal source, a ground-based experiment was carried out at a mountain in Nanjing, where heavy rain tends to occur frequently in rainy season. Additionally, a data processing algorithm mainly following Padullés et al. (2016) to solve the problems of quality control, unlocking, hardware effect, phase ambiguity, multipath effect was applied independently to this ground-based data from the polarimetric GNSS rain detection system. Also, the multi-source data from nearby weather radar and weather stations was used for verification. Results from 14 GPS satellites show that the obtained phase shift is zero in all no-rain days while it is not zero during rainy days, which is in accordance with the actual situation. Compared with weather radar and rain gauges’ data, the results verify that the phase shift is caused by rain. Besides, when individual cases are examined, many show that their tendencies of accumulated phase shift are quite similar to that of a weather station’s rainfall data, even some correlation coefficients are up to 0.99. These demonstrate the reliability of our experimental system and the feasibility of the data processing algorithm. This study will provide technical support for future spaceborne experiment, which has promising applications in global rain monitoring.

CFAR Ship Detection Methods Using Compact Polarimetric SAR in a K-Wishart Distribution

Compact polarimetric target detection is currently attracting increasing interest due to the generation of synthetic aperture radar (SAR) systems. Recently, the polarimetric notch filter (PNF) has been demonstrated to be effective for ship detection in both full-polarization and compact polarization-mode SAR images. In this paper, the probability density function (PDF) and the probability of false alarms (PFA) of the PNF are derived in the K -Wishart case (where the texture obeys the gamma distribution) since K distributions are suitable for many scenes including sea clutter. The PDF and PFA are also derived in closed forms for the polarimetric whitening filter (PWF) in the K -Wishart distribution case, the performance of which is close to that of the optimal polarimetric detector. The constant false alarm rate threshold for ship detection can be obtained from the PFA via the bisection method, which allows for the automatic and adaptive implementation of ship detection in complicated sea backgrounds in practical applications. The performances of the two detectors are compared via simulated data and measured data from AIRSAR in the compact polarimetric SAR case. The results show that the detectors given are accurate, while the PWF detector is generally better than the PNF detector in the K -Wishart case of the CP SAR model.

Elimination of Unwanted Modes in Wavelength-Selective Uncooled Infrared Sensors with Plasmonic Metamaterial Absorbers using a Subtraction Operation.

Wavelength- or polarization-selective uncooled infrared (IR) sensors have various applications, such as in fire detection, gas analysis, hazardous material recognition, biological analysis, and polarimetric imaging. The unwanted modes originating due to the absorption by the materials used in these sensors, other than plasmonic metamaterial absorbers (PMAs), cause serious issues by degenerating the wavelength or polarization selectivity. In this study, we demonstrate a method for eliminating these unwanted modes in wavelength- or polarization-selective uncooled IR sensors with various PMAs, using a subtraction operation and a reference pixel. The aforementioned sensors and the reference pixels were fabricated using a complementary metal oxide semiconductor and micromachining techniques. We fabricated the reference pixel with the same structure as the PMA sensors, except a flat mirror was formed on the absorber surface instead of PMAs. The spectral responsivity measurements demonstrated that single-mode detection can be achieved through the subtraction operation with the reference pixel. The method demonstrated in this study can be applied to any type of uncooled IR sensors to create high-performance wavelength- or polarization-selective absorbers capable of multispectral or polarimetric detection.

Chiroptical fingerprints to characterize lavender and lavandin essential oils

Polarimetric HPLC detector was used to acquire chromatograms for lavender/lavandin essentials oils (EOs) on different chiral stationary phases. Amylose tris-(3,5-dichloro-phenylcarbamate) immobilized on silica allowed the best separation of the numerous chiral phytomarkers and was thus used to obtain a chiroptical fingerprint for 158 samples of French lavender/lavandin EOs. Samples from different varieties (Abrial, Fine, Grosso, Maillette, Matherone, Sumian and Super) were collected over three crop years (2012, 2013 and 2014), from four different locations in France (``Alpes-de-Haute-Provence'', ``Ardèche'', ``Drôme'' and ``Vaucluse'') to take into account seasonal and geographic origin variations. The combination of the polarimetric fingerprints and chemometrics was tested for varietal discrimination. We assessed the ability to discriminate the EOs samples and their variety by partial least squares-discriminant analysis (PLS-DA). This case study showed that liquid chromatography with polarimetric detector in tandem with chemometric analysis was efficient to differentiate the varietal origins of French lavender/lavandin EOs.

Generalised RAO test for polarimetric target detection

Here, a generalised Rao test method is presented for polarimetric multichannel adaptive signal detection. By introducing several tunable parameters into the Rao test detection statistics, the proposed polarimetric detector is quite general with the modified Rao test detector, the adaptive-matched filter detector, and the adaptive subspace detector being its special cases. The performance of the proposed polarimetric detector has been demonstrated with synthetic and real data. The results show that the new detector provides more flexibility of being adjustable than the current modified Rao test detector, against target steering vector mismatch.

Polarimetric Detection of Chemotherapy-Induced Cancer Cell Death

Imaging polarimetry is a focus of increasing interest in diagnostic medicine because of its non-destructive nature and its potential to distinguish normal from tumor tissue. However, handling and understanding polarimetric images is not an easy task, and different intermediate steps have been proposed in order to introduce helpful physical magnitudes. In this research, we look for a sensitive polarimetric parameter that allows us to detect cell death when cancer cells are treated with chemotherapy drugs. Experiments in two different myelomonocytic leukemia cell lines, U937 and THP1, are performed in triplicate, finding a highly-significant positive correlation between total diattenuation of samples in transmission configuration, D T , and chemotherapy-induced cell death. The location of the diattenuation enhancement gives some insight into the cell death process. The proposed method can be an objective complement to conventional methodologies based on pure observational microscopy and can be easily implemented in regular microscopes.

Robust Polarimetric Adaptive Detector Against Target Steering Matrix Mismatch

A polarimetric scheme is presented for the detection of a range-spread target when the presumed target steering matrix is deviated from the actual one. Following the adaptive beamformer orthogonal rejection test model, the decision statistic of the proposed detector involves the polarimetric clutter-plus-noise covariance matrix, the target component after noise whitening and rotation, as well as the sidelobe interference vectors of multiple range cells. In the practical realization of the detector, the polarimetric clutter-plus-noise covariance matrix is estimated by using the minimum mean-square-error regularized secondary data sample averaging. Taking into account the mismatch involved in the presumed target steering matrix, the target component is obtained by least square fitting subject to multiple separate conic uncertainty set constraints. The estimation of the sidelobe interference vectors is also based on the Bayesian statistics, and the involved polarimetric clutter-plus-noise covariance matrix is ultimately replaced by its Bayesian estimate previously obtained. The performance of the proposed detector has been evaluated and compared with the existing popular polarimetric detectors using both synthetic and real data. The results show that in the presence of target steering matrix mismatch caused by pointing errors, sensor position errors, channel calibration errors, multipath propagation, and random errors, the proposed detector has a superior performance to the current detectors in terms of the probability of detection.

Polarimetric imaging method for target enhancement in haze based on polarimetric retrieval

ABSTRACTPolarimetric imaging has been proven to be an effective way in detecting the targets of interest in complicated surroundings by analyzing the polarization property, instead of the intensity, of the light emanating from the objects. Unfortunately, polarimetric imaging encounters difficulty when the surroundings are very scattered, where on the one hand the polarization property of the object light usually becomes very faint after a strong depolarized scattering process; on the other hand, the object light will be blended with the atmospheric light scattered by haze particles (airlight). In this paper, we propose a polarimetric imaging retrieval method that can be used for such challenging conditions. Firstly, the airlight radiance is estimated precisely. Then, the airlight is removed from the hazy images. Finally, the residual polarization property of the object light is regained, which ensures the validity of the polarimetric imaging method in these conditions. The experiments confirm that the proposed method is useful in enhancing polarimetric imaging detection in haze.

On-Orbit Polarization Calibration for Multichannel Polarimetric Camera

In this paper, a new on-orbit polarization calibration method for the multichannel polarimetric camera is presented. A polarization calibration model for the polarimetric camera is proposed by taking analysis of the polarization radiation transmission process. In order to get the polarization parameters in the calibration model, an on-orbit measurement scheme is reported, which uses a solar diffuser and a built-in rotatable linear analyzer. The advantages of this scheme are sharing the same calibration assembly with the radiometric calibration and acquiring sufficient polarization accuracy. The influence of the diffuser for the measurement is analyzed. By using a verification experiment, the proposed method can achieve on-orbit polarization calibration. The experimental results show that the relative deviation for the measured degree of linear polarization is 0.8% at 670 nm, which provides a foundation for the accurate application of polarimetric imaging detection.

SAR Compact Polarimetry for Change Detection and Characterization

Coherent and incoherent exploitation of complex-valued, synthetic aperture radar imagery separated by temporal and/or spatial baselines can provide significant information for change detection. The majority of the existing techniques, however, deal with the single-channel coherency or correlation for change analysis. We develop change detection/change techniques by incorporating the target polarimetric response. The formalism allows straightforward application to quad-pol, dual-pol, and hybrid-pol (compact-pol) imagery. Our aim is to develop polarimetric change detection and change characterization methodologies utilizing a general polarimetric framework that is suitable for quad, dual, and compact polarimetry.

A polarimetric CFAR ship detector based on the joint probability function of simulated first-order Markov chains

ABSTRACTIn this work, a novel ship detection procedure is presented for radar signals whose backscattering power is of the same order while their polarimetric characteristics differ greatly. The stochastic nature of the polarimetric characteristics of the background (clutter) and the target signal (ship) can be adequately described by first-order Markov chains (FMCs). The proposed feature corresponds to the joint probability of sequential states of variable finite sequential segments of the FMCs. The classic Constant False Alarm Rate (CFAR) detection theory is adapted to the discrete space of the Markov experimental distributions of the proposed feature while the adaptive thresholding technique is overcome by considering a global model for describing the clutter. Performance assessment of the proposed detection procedure is carried out by means of three sets of FMCs each one corresponding to a clutter-target pair for different lengths of the finite FMC segments. The experimental results present high detection scores making the proposed detection procedure ideal for signals characterized by the Markov property. A comparative study of previous detection approaches has been implemented that shows the superiority of the proposed detection procedure.

A new approach: LYSO based polarimetry for the EDM measurements

One of the fundamental questions of modern particle physics is the existence of finite electric dipole moments (EDM) of the hadrons. In case of charged particles, like protons and deuterons, the proposed method is the precise determination of the precession of the beam polarization vector in a storage ring. For that purpose, the JEDI (Jülich Electric Dipole moment Investigations) collaboration is developing a precise polarimeter detector based on LYSO scintillator coupled to SiPM modules. They are capable of stopping 300 MeV elastically scattered deuterons and protons. Precise measuring of the kinetic energy of the scattered projectiles ensures the accurate reaction identification leading to a precise polarization determination. To create the long-term reliable detector system, we have performed four iterations of the detector development. Currently, we are operating 52 LYSO modules with a dedicated dead-time less sampling ADC readout system. The modules are very compact, due to modern high pixel density SiPM readout.

Extended Geometrical Perturbation Based Detectors for PolSAR Image Target Detection in Heterogeneously Patched Regions

Target detection in synthetic aperture radar image utilizing polarimetric information has attracted considerable attention. Single-target detector (STD), partial-target detector (PTD), and geometrical perturbation-polarimetric notch filter (GP-PNF) are three traditional polarimetric detectors based on polarimetric information. STD aims at detecting single targets, whereas PTD is suitable for partial targets. GP-PNF focuses on detecting targets with features, which are different from the homogeneous background. Both STD and PTD need a prior knowledge of the target, whereas GP-PNF needs to estimate the local clutter automatically. All these three methods use a feature vector to describe the character of the target or clutter. In fact, the feature vectors of the clutter and target may distribute in a subspace. Especially for the heterogeneous background, a feature vector cannot accurately describe the clutter. Motivated by this, this paper extends the clutter model from a complex feature vector to a complex feature subspace, which is suitable for a heterogeneously patched region and derives extended PTD and extended GP-PNF. Experimental results show the extended detectors’ validation and superiority to traditional detectors for target detection in heterogeneous regions.

Cavity Attenuated Phase Shift Faraday Rotation Spectroscopy

Cavity attenuated phase shift Faraday rotation spectroscopy has been developed and demonstrated by oxygen detection near 762 nm. The system incorporates a high-finesse cavity together with phase-sensitive balanced polarimetric detection for sensitivity enhancement and achieves a minimum detectable polarization rotation angle (1σ) of 5.6 × 10-9 rad/√Hz, which corresponds to an absorption sensitivity of 4.5 × 10-10 cm-1/√Hz without the need for high sampling rate data acquisition. The technique is insusceptible to spectral interferences, which makes it highly suitable for chemical trace gas detection of paramagnetic molecules such as nitric oxide, nitrogen dioxide, oxygen, and the hydroxyl/hydroperoxyl radicals.

Integrating subwavelength polarizers onto InP-InxGa1−xAs sensors for polarimetric detection at short infrared wavelength

There are growing needs for polarimetric detection at infrared wavelengths for broad applications in bioscience, communications, ocean detection, agriculture, etc. Subwavelength metallic gratings are capable of separating the transverse magnetic mode from the transverse electric mode to form polarized light, offering a promising approach for realizing polarimetric detection. The conventional method is to assemble a commercially supplied polarizer in the form of a chip in a standard detector. This article describes our recent advances in integrating a subwavelength grating with an independent InP-InxGa1−xAs sensor by nanofabrication based on electron-beam lithography. A technical issue encountered in the fabrication is the strong backscattering of primary electrons from InP-InxGa1−xAs, causing significant extra exposure on the resist such that the standard copolymer/poly(methyl methacrylate) bilayer is not applicable. Instead, a single layer of poly(methyl methacrylate) is applied, and the necessary undercut profile for the lift-off process is created by use of the beam spread condition in the lithography. The fabricated detector with pixelated polarizers demonstrates uniform polarimetric detection at a wavelength of 1320 nm with an extinction ratio of 18:1. The reduction of the ratio in the fabricated detector is theoretically interpreted by a finite-difference time-domain method on the basis of the actual grating structures. Finally, the enhancement of the extinction ratio is discussed.