Dual-polarization Technique Research Articles

Error Structure Analysis for Multiple Dual-polarization Radar using Ensemble Learning

Accurate quantitative precipitation estimation (QPE) was essential for the prediction and prevention of natural disasters. Recently, radar has been attracting attention as a technique for performing QPE with high spatiotemporal resolution. In particular, the QPE was improved by introducing a dual-polarization technique that observed several hydrometeorological variables at various scales compared to the single polarization radar that utilized only the existing reflectivity-precipitation relationship. This study aimed to analyze the error structure of dual-polarization radar by predicting gauged rainfall using ensemble models. The location of the radar was Gwanaksan, Garisan, and Gwangdeoksan which belonged to the Bukhan river basin. The Pearson correlation coefficients between reflectance-precipitation and gauged rainfall were examined initially. After that, each gauged rainfall was predicted using ensemble learning, which included random forest (RF), gradient boost, and XGboost. Mean absolute error, root mean squared error, and R squared were evaluated as the predictive performance. Hyper-parameters were optimized by 5-fold cross-validation, and the reliability of the research results was obtained by 10 iterations. The result showed that RF had better predictive performance than other models. Gauged stations that operated at high altitudes were not good enough for the QPE because of the mountain effect. Due to the mountain range effect, the importance of the Gwanaksan radar at an altitude of 3 km was very high.

A Refined Model for Quad-Polarimetric Reconstruction from Compact Polarimetric Data

As a special dual-polarization technique, compact polarimetric (CP) synthetic aperture radar (SAR) has already been widely studied and installed on some spaceborne systems due to its superiority to quad-polarization; moreover, quad-pol information can be explored and reconstructed from the CP SAR data. In this paper, a refined model is proposed to estimate the quad-pol information for the CP mode. This model involves CP decomposition, wherein the polarization degree is introduced as the volume scattering model parameter. Moreover, a power-weighted model for the co-polarized coherence coefficient is proposed to avoid the iterative approach in pseudo-quad-pol information reconstruction. Experiments were implemented on the simulated Gaofen-3 and ALOS-2 data collected over San Francisco. Compared with typical reconstruction models, the proposed refined model shows its superiority in estimating the quad-pol information. Furthermore, terrain classification experiments using a complex-value convolutional neural network (CV-CNN) were performed on AIRSAR Flevoland data to validate the reconstruction effectiveness for classification applications.

Wearable Antennas: A Review of Materials, Structures, and Innovative Features for Autonomous Communication and Sensing

Wearable antennas have gained much attention in recent years due to their attractive features and possibilities in enabling lightweight, flexible, low cost, and portable wireless communication and sensing. Such antennas need to be conformal when used on different parts of the human body, thus need to be implemented using flexible materials and designed in a low profile structure. Ultimately, these antennas need to be capable of operating with minimum degradation in proximity to the human body. Such requirements render the design of wearable antennas challenging, especially when considering aspects such as their size compactness, effects of structural deformation and coupling to the body, and fabrication complexity and accuracy. Despite slight variations in severity according to applications, most of these issues exist in the context of body-worn implementation. This review aims to present different challenges and issues in designing wearable antennas, their material selection, and fabrication techniques. More importantly, recent innovative methods in back radiations reduction techniques, circular polarization (CP) generation methods, dual polarization techniques, and providing additional robustness against environmental effects are first presented. This is followed by a discussion of innovative features and their respective methods in alleviating these issues recently proposed by the scientific community researching in this field.

Improving the detection limit of conformational analysis by utilizing a dual polarization Vernier cascade.

The dual polarization microring technique enables the simultaneous and accurate detection of thickness and refractive index of a bound molecular layer. By using three microring resonators in a double Vernier cascade configuration, the dual polarization technique is improved on three distinct levels: an increase of the sensitivity, a suppression of common noise due to self-referencing and the ability to migrate from a standard tunable laser to a cheap broadband LED and an on-chip arrayed waveguide grating as read-out system, allowing for a system which is orders of magnitude faster and cheaper. A dual polarization Vernier cascade proof-of-concept is fabricated and characterized, a read-out computational framework is constructed and it is shown on a theoretical basis that the limit of detection is improved.

Effect of Fiber Nonlinearity on the Performance of WDM Dual-Polarization Coherent Optical OFDM Systems

In recent years, there is increasing interest in using dual-polarization (DP) technique to enable future systems with at least 100 Gb/s rate per channel to operate over existing optical networks. The performance of these advanced systems can be enhanced further by using coherent optical orthogonal multiplexing (CO-OFDM) technique which offers high spectral efficiency and outstanding tolerance of fiber dispersion. This paper addresses the effect of fiber nonlinear optics on the performance of dual-polarization wavelength-division multiplexing (WDM) CO-OFDM systems operating with 100 Gb/s per channel. Different modulation formats, namely BPSK, QPSK and 16-QAM, are used. First, the performance of a single-channel system is investigated in the absence and presence of fiber nonlinearity. The results are compared with a conventional (single-polarization) system to identify the key role played by the DP technique. The investigation is then extended to WDM systems incorporating DP-OFDM technique. The results reveal that the effect of fiber nonlinearity can be reduced by using optimum transmitter laser power Popt. Further, the value of Popt is a function of transmission distance, number of multiplexed channels, and modulation formats. Popt of -11, -12, and -5 dBm is needed for a ten-channel DP system operating with BPSK, QPSK, and 16-QAM formats, respectively. Simulation results presented in this work are obtained using Opti System (version 11.1) which is a commercial software package

High-resolution dual-polarization frequency modulated reflectometer density profile measurements on DIII-D

A novel dual-polarization technique has been applied to the frequency-modulated electron density profile reflectometer on DIII-D. In this application, both O- and X-mode waves are simultaneously launched from a common high-performance solid-state source, and simultaneous measurements of both O- and X-mode reflections from corresponding cutoffs serve to expand the density coverage. The system consists of both Q-band (33–50 GHz) and V-band (50–72 GHz) subsystems, their combination covers a density range from 0 to 6.4×1019 m−3, with a time resolution of ⩾10 μs and spatial resolution of ⩾4 mm. The dual-polarization technique was implemented successfully in the Q-band subsystem during 2003 and detailed information for H-mode pedestal physics studies was provided. It has also recently been applied to the V-band subsystem, and extended contributions to H-mode pedestal physics and particle transport studies are expected during the 2004 DIII-D campaign.

Soil moisture inversion at L-band using a dual-polarization technique: A model-based sensitivity analysis

The inverse problem of estimating soil moisture from vegetated and non-vegetated terrain is investigated using a passive microwave technique. The radiometer response at L-band is modelled by the Peake's approach that involves the integration of bistatic scattering coefficients to calculate surface emissivity. For vegetated terrain, a discrete scatter model employing the distorted Born approximation is used to obtain bistatic scattering coefficients. For non-vegetated rough surface, the Kirchhoff 's rough surface approximation is used to calculate bistatic scattering coefficients. A series of vegetated and non-vegetated surfaces are simulated for this study by changing vegetation densities and ground roughness conditions. The forward model is simplified so that it can be inverted with a minimum of auxiliary information about the vegetation and the ground. An inversion procedure is set up such that the ratio of horizontal to vertical Fresnel reflectivity is expressed in terms of dual-polarized microwave brightness temperatures (available from the forward model or a radiometer). The reflectivity ratio expression is then solved to obtain soil moisture. In the case of weak vegetation such as soybean canopy, no information regarding vegetation is necessary in the inversion procedure because the difference between horizontal and vertical optical depth is assumed to be negligibly small at low to medium viewing angles. The consequence of this assumption on the soil moisture estimation from canopies of higher Leaf Area Index (LAI) is analysed. Similarly, in the case of non-vegetated rough terrain, inversion is carried out without information about rough surface because the rms surface roughness height cancels out in ratioing of the Fresnel reflectivity. To account for instrument and other errors in experimental data, a random noise is added to model data and the rms error in soil moisture inversion is calculated for vegetated and non-vegetated terrain. A comparison of the dual polarization with single (horizontal) polarization technique reveals that the dual polarization is a better technique for soil moisture estimation. The sensitivities and implications of a priori information are discussed in the context of developing a soil moisture estimation algorithm from satellites to be launched in the forthcoming space missions.

Reduction of intermodulation distortion in interferometric optical modulators

A dual-polarization technique for reducing intermodulatíon distortion in integrated-optic interferometric modulators is described. While this technique results in a decrease in modulator sensitivity, the intermodulation distortion can be significantly reduced for a given depth of optical modulation by adjusting the relative amounts of TE and TM optical power. Reductions in intermodulation distortion as high as 21 dB were demonstrated by means of this technique with a Ti:LiNbO(3) device.

Statistical Reference Envelopes for Rain Crosspolarization At Hicher Frequencies for Use In Satellite System Design

Dual polarization techniques are becoming more attractive in satellite communications because they permit more efficient utilization of the frequency spectrum. It is essential in designing such systems to reasonably estimate the level of rain crosspolarization, especially when higher frequencies are to be used to avoid crowding in the lower band. The correlation between rain crosspolarization and rain attenuation has received extensive study. Some of the results are collected in this paper, and statistical reference envelopes for rain crosspolarization at higher frefrencies are proposed. They are developed by considering ing both analytical derivations and experimental observations. These envelopes give the worst-case rain crosspolarization estimation at 11 to 30 GHz when the rain attenuation is known, or assumed, from the weather statistics; they can be used in satellite system design.