Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

DOI： 10.1109/tim.2020.3031368

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DOI： 10.1587/comex.2021xbl0157

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

This paper proposes a high-precision fast approximation method for the ℓ2-norm evaluation of 2-tuple arrays by means of a rotated ℓ1-norm evaluation with fixed-point arithmetic. A considerable number of calculations for 2-tuple ℓ2-norm are frequently required in several signal processing applications such as image restoration with isotropic total variation and complex ℓ1-norm regularization. Typical embedded applications prefer parallel processing, constant scaling, and fixed-point arithmetic compared with serial processing, variable multiplication, and floating-point arithmetic. To achieve a hardware-friendly calculation, square and square root operations should be adequately approximated. However, several existing techniques are challenged with respect to approximations with all three preferable features. Thus, in this paper, a hardware-friendly approximation algorithm is proposed. The proposed method uses the fact that the upper bound of the surface of a first-order rotational cone traces a second-order cone, i.e., ℓ2-cone, requests less variable multiplication, and can easily be implemented in parallel with fixed-point arithmetic. To verify the effectiveness of the proposed method, an image restoration performance and software/hardware co-design report are evaluated.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communications Engineers ({IEICE})  

DOI： 10.1587/comex.2020xbl0091

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

DOI： 10.1109/JSTARS.2020.3038980

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Array radar needs enough array length to realize high angular resolution. However, it takes cost to increase elements physically. Recently, Minimum Redundancy Multiple- Input Multiple-Output (MR-MIMO) was proposed to increase the number of virtual elements efficiently. Further improvements by using Khatri-Rao (KR) transformation in the case of incoherent waves were also proposed. In this paper, we show experimental results on indoor human tracking with millimeter-wave MR- MIMO radar to verify the improvements of resolution and tracking performance in comparison with the results by a conventional MIMO radar.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Automatic operating system for vehicle has been widely studied. Especially, automotive millimeter-wave (MMW) radar has been attracting attentions. Synthetic Aperture Radar (SAR) processing by using MMW radar can obtain high-resolution 2-D images. In general, SAR processing is used in straight orbits. However, in the case of automobiles, it is necessary to consider not only straight tracks but also curved tracks. In this paper, we show that the performance of automotive MMW-SAR processing on curved tracks by experimental results.

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© 2019 by the authors. Licensee MDPI, Basel, Switzerland. In a field of polarimetric synthetic aperture radar (SAR) remote sensing, various kinds of polarimetric decomposition techniques have been proposed. However, poor validations prevent them from operational applications. A true composition ratio of scattering mechanisms within a radar backscatter plays a key role. To overcome the issue, a novel comprehensive SAR approach to accurately identify a contribution of each scattering mechanism has been introduced. This is based on multiparametric SAR observation combined with a numerical model simulation. In this article, a comprehensive SAR approach is concisely reviewed to accelerate the research in this field. First, popular model-based polarimetric decompositions are introduced and their limitations are shown. Then, a behavior of scattering mechanisms is analyzed by the discrete scatterer model with some results using real multiparametric SAR data. A comprehensive SAR approach must be essential to realize an operational use of polarimetric SAR data.

DOI： 10.3390/electronics8101098

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/igarss.2019.8900550

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Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

DOI： 10.1109/TGRS.2018.2885550

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Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

DOI： 10.1109/TGRS.2018.2878981

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In this report, we apply the polarimetric entropy (or H/alpha) analysis to 3-D PolSAR dataset, which are reconstructed by the TomoSAR processing, to clarify the polarimetric scattering characteristic on height direction under the layover phenomenon. The H/alpha analysis, where H and alpha denote entropy and angle calculated by the eigen-decomposition of the polarimetric scattering matrix, is widely used for target decomposition and classification. The entropy increases on multiple scattering process such as under the layover phenomenon and decreases on dominant isolated scattering process, so it can be expected the entropy increases by buildings with layover phenomenon. From the experimental results, we show that the H/alpha analysis on height direction is available, and clarify the change of the entropy compared with the conventional 2-D PolSAR and proposed Pol-TomoSAR analysis.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Recently, SAR Tomography (TomoSAR) which exploits multiple SAR datasets to reconstruct three-dimensional target imaging has been attracting attention in microwave remote sensing. The TomoSAR can reconstruct the image without occurring the geometric distortion such as foreshortening and layover which are the problems of conventional 2D-SAR, because it reconstructs the image in three-dimensional space. Especially, the TomoSAR with L-band radar can observe local scatterings inside the vegetation, so it can be applied to biomass estimation and vegetation monitoring. However, the TomoSAR in Pi-SAR-L2, which is the L-band airborne SAR, has not been realized yet. In this paper, we apply the TomoSAR processing to the Pi-SAR-L2 datasets and show that the 3D-imaging is possible. Furthermore, we show that we can discriminate the local scattering mechanisms of three-dimensional target by introducing polarimetric analysis based on the Pauli scattering vector.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

High-resolution property is important for indoor location estimation radars. In order to realize high-resolution location estimation by using array radar, it is necessary to increase the number of elements. However, it is often difficult because of the cost. Therefore, the MIMO radar and the Khatri-Rao (KR) product virtual-array processing, that are techniques to increase the number of elements virtually, have been attracting attentions. We have shown that the number of virtual array elements can be effectively increased by using the MIMO radar with Minimum Redundancy Array (MRA) by the KR product virtual array processing. However, optimum arrangements to realize the largest virtual Uniform Linear Array (ULA) is still unclear. In this paper, we show the optimum element arrangements to have the largest-aperture virtual ULA when we apply the KR product virtual array processing to MIMO radar.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Even though Pulse-Doppler radar estimates velocity by measuring phase shift amount between pulses, the visible Doppler range is limited by Pulse-Repetition-Interval (PRI). In radio wave, Doppler frequency occurs from moving target as well as sound wave and the phase shift information should include slightly in samples of individual pulses. In this study, MUSIC algorithm is applied to measure these minute shift. We show experimental results on Doppler shift amount estimation by using both fast-time and slow-time and show that the shift amount can be measured without depending on PRI.

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/IGARSS.2019.8900071

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communications Engineers (IEICE)  

DOI： 10.1587/transele.E102.C.38

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Other Link： http://dblp.uni-trier.de/db/journals/ieicet/ieicet102b.html#journals/ieicet/YamaguchiMUY19

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TomoSAR is one of the methods which can perform three-dimensional (3-D) imaging with multiple SAR datasets by using Direction-of-Arrival (DOA) estimation techniques to reveal height distribution of scatterers. However, resolution of the TomoSAR is generally insufficient for height estimation of small objects on the ground surface. Also, if we employ a high resolution DOA estimation method for the height estimation, its performance is often degraded due to orbital error. To solve this problem, we employ ESPRIT algorithm and propose a new method named ESPRIT-TomoSAR. The ESPRIT algorithm is one of high resolution DOA estimation techniques using orthogonality between signal and noise subspace, it has not only high resolution performance equivalent to the MUSIC algorithm but also robustness for orbital error. In this paper, to verify effectiveness of the proposed method, we provide experimental results by using actual airborne SAR dataset. The experimental results show that the proposed method realizes high resolution and robustness for orbital error, and it is effective for a precise height estimation such as the structure analysis of buildings.

DOI： 10.1109/IGARSS.2019.8899878

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Language：Japanese   Publisher：The Institute of Electrical Engineers of Japan  

<p>In recent years, research and development of highly accurate position detection indoors have attracted attention. In this paper, we propose a new scheme to improve accuracy of position detection indoors, identifying the direct wave between BLE transmitter (TX) and BLE receiver (RX), applying RD-CUBA-MUSIC⁽¹⁾ to indoor multi-path environment. In the proposed scheme, the direction of radio wave arrival is estimated in both directions of TX→RX and RX→TX. Estimation accuracy is improved by collating the arrival directions of the pair of two-way direct wave candidates. This Direction-Of-Arrival (DOA) estimation for direct wave is sequentially executed with a plurality of RXs and indoor position of TX is detected using the DOAs and the corresponding RX positions. In RD-CUBA-MUSIC, we select a beam pattern with high correlation with the sinc function beam pattern as a beam pattern of the ESPAR antenna. Computer simulation shows that the proposed scheme can achieve a detection accuracy within 1 m in error at a 91% probability. It also shows within 0.5 m in error at 67% even though it is in an indoor multi-path environment.</p>

DOI： 10.1541/ieejeiss.139.900

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communications Engineers (IEICE)  

DOI： 10.1587/comex.2018xbl0153

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DOI： 10.1587/comex.2018xbl0152

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DOI： 10.1587/comex.2018xbl0131

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/IGARSS.2019.8899878

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Other Link： https://dblp.uni-trier.de/db/conf/igarss/igarss2019.html#GochoYYSKA19

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Insufficient validation for polarimetric decomposition techniques has led to its less perceived popularity for more than 20 years. The true composition ratio of scattering mechanisms within a radar backscatter should be essential to make polarimetric synthetic aperture radar (SAR) operational applications. To achieve this, a novel comprehensive approach to accurately identify the contribution of each scattering mechanism by a multi-incidence angle and multipolarimetric (MIMP) SAR observation combined with a theoretical model simulation is newly applied to L-band SAR data. Rice paddies in Niigata, Japan having a simple vegetation structure without topography were observed by Polarimetric and Interferometric Airborne SAR L-band 2, by gradually varying the flight path in terms of incidence angle. In addition to the MIMP SAR observation, a dominant scattering mechanism is reliably isolated through the theoretical characterization of the data by a discrete scatterer model. Avoiding unnecessary Bragg scattering effect caused by the methodically distributed rice paddies, the volume scattering from grains is identified as a dominant scattering mechanism over incidence angles. In addition, HH and VV are strongly affected by the double-bounce scattering between stalks and the ground surfaces at only small incidence angles, whereas the contribution of the double-bounce scattering for HV is not obvious. The results at the L-band will be compared with another MIMP SAR data at the X-band obtained for the same rice paddies in 2014 so that multifrequency MIMP SAR data analysis shall be conducted for our next step.

DOI： 10.1109/TGRS.2018.2814996

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/igarss.2018.8518947

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DOI： 10.1109/igarss.2018.8517792

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electronics, Information and Communication, Engineers, IEICE  

SAR tomography is one of the methods that can perform 3-dimensional (3-D) imaging with multiple SAR datasets by using the Direction-of-arrival (DOA) estimation technique to estimate the height distribution of scatterers. Several reports on SAR tomography have been issued. However, experimental results of the SAR tomography by the Pi- SAR2-X, Japanese airborne SAR operated by the NICT, have not been reported yet. This paper is the first to report the results of experiments on the Japanese SAR platform. High-resolution 2-dimensional image can be obtained by the X-band SAR. However the image is generated by projecting 3-D objects in to a 2-D image plane, hence the target responses having the same slant-range distance locate at the same image pixel. This is well known as the layover problem. When we employ the X-band SAR tomography, we can obtain 3-D high-resolution images without the layover and also foreshortening problem. It will be useful for disaster damage monitoring, especially in urban areas. The main difficulty of the SAR tomography comes from the phase error caused by inaccurate flight-path data. In many cases, the dataset are preprocessed and compensated so as to parallelize their flight-path to carry out the phase calibration and the DOA estimation easily. However, it is often difficult for common users to obtain such preprocessed datasets. In this paper, we propose a simple calibration method by using a flat-surface area with known altitude. Experiments show that the proposed method is effective for the Pi-SAR2-X standard products without parallelized preprocessing or precise flight-path information.

DOI： 10.1587/transcom.2017ISP0020

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DOI： 10.1587/comex.2018XBL0104

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

We show observation result for snow covered or uncovered urban area using quad-pol ALOS-2/PALSAR-2 data. From the result of the observation for autumn and winter seasons, double bounce scattering contribution decreases and surface scattering contribution increases for the snow covered case, even when radar illumination direction is almost normal to the alignment of urban buildings. To determine the exact cause of the scattering behavior and minutely evaluate the polarimetric features, 'collective' reflected field, which approximately includes all of the multiple reflections inside multi-layered snow, is introduced for additional consideration. By using the collective reflection coefficient, instead of the conventional Fresnel coefficient, one can evaluate the reflection characteristics not only from the surface of the top snow layer but also from all of the internal reflections of each snow layer easily. It is found from the result for the dihedral structure between the three-layered snow plane and vertical concrete wall that the dominant contribution sometimes changes from the double bounce scattering to the surface scattering even when the surface of the top layer of the snow is flat.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

The PolSAR scattering component decomposition is one of powerful tools to extract characteristics of terrain for classification and the other applications. Especially, the model-based scattering decomposition technique becomes popular due to their strong relation to actual scattering mechanism. However, several assumptions are required to derive a unique solution. The authors has proposed the model-based decomposition technique with multi-baseline dataset. However, the technique has a limitation when there exist dominant 3 components. In this report we apply generalized inverse problem with the technique to obtain a sub-optimal solution. Performance of the method is demonstrated numerically, and also experimentally by ALOS2 dataset.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Though SAR remote sensing has been expected as an efficient rice crop monitoring tool, there still exist non-negligible mysteries to extract physical parameters. To solve the problems, it is essential to conduct theoretical characterization of experimentally obtained radar backscatter from rice paddies. In this paper, rice paddies in Niigata city, Japan, were observed by an L-band full polarimetric SAR, by systematically varying the incidence angle and polarization. Bragg scattering was obvious in the SAR imagery at L-band, and it was theoretically modeled. Then, backscatter from the rice paddy suppressing the Bragg scattering effect was obtained by utilizing the model.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

This paper examines the effectiveness of implicit beamforming (IBF), which enables transmission without channel state information (CSI) feedback in multi-user multiple-input multiple-output (MU-MIMO) systems with a large number of antennas. First, we explain why CSI feedback from terminal stations to the base station produces a very large overhead. A calibration technique is then introduced, which compensates for the difference between the complex amplitudes of the transmitters and receivers to facilitate CSI-feedback-free beamforming; this technique is called IBF. The efficacy of this calibration technique is demonstrated by measuring the amplitude and phase errors obtained using a 16-element array testbed and by performing a channel capacity evaluation. Finally, the throughput under IEEE802.11ac-based massive MIMO transmission, both with and without CSI feedback, is obtained in terms of the medium access control efficiency.

DOI： 10.3390/electronics6040091

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Various polarimetric decomposition techniques have been proposed and demonstrated for more than 20 years. However, they still have never been operational applications because of insufficient validations. The true composition ratio of scattering mechanisms within a radar backscatter has to be known. To achieve this, a novel comprehensive approach to accurately identify the contribution of each scattering mechanism by a multiincidence angle and multipolarimetric (MIMP) synthetic aperture radar (SAR) observation combined with a theoretical model simulation is introduced. Rice paddies in Niigata City in Japan having a simple vegetation structure without topography were observed by X-band polarimetric and interferometric SAR 2 (Pi-SAR2), by gradually varying the flight path in terms of incidence angle. In addition to the MIMP SAR observation, a dominant scattering mechanism is reliably isolated through the theoretical characterization of the data by a discrete scatterer model. In the case of the rice paddies at a late vegetative stage, a dominant scattering on HH gradually varies from the doublebounce scattering to the volume scattering of rice grains in terms of incidence angle, whereas VV is affected by various volume scatterings of grains, leaves, and stems at the small, medium, and large incidence angles, respectively. HV is simply affected by the volume scattering of grains at the small incidence angle, and then it gradually switches to the volume scattering of the stalks. This brand new approach by the MIMP SAR observation with the theoretical modeling for this specific stage could take forward the polarimetric decomposition studies.

DOI： 10.1109/TGRS.2017.2652447

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The MIMO technique can improve system performance of not only communication system but also of radar systems. In this paper, we apply the MIMO radar with enhanced angular resolution to the indoor location estimation of humans. The Khatri-Rao (KR) matrix product is also adopted for further angular resolution enhancement. We show that the MIMO radar with the KR matrix product processing can increase the number of virtual elements effectively with suitable element arrangement, hence higher angular resolution can be realized. In general, the KR matrix product processing is not suitable for coherent radar because of signal correlation. However, when targets signals have enough Doppler frequency differential against each other, this approach works well because the signals are decorrelated. In addition, Doppler filtering is introduced to remove unwanted responses of stationary objects which make human detection difficult with conventional methods. Computer simulation and experimental results are provided to show performance of the proposed method.

DOI： 10.1587/transcom.2015ISP0029

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This paper addresses the local incidence angle dependence of several polarimetric indices corresponding to landslides in forested areas. Landslide is deeply related to the loss of human lives and their property. Various kinds of remote sensing techniques, including aerial photography, high-resolution optical satellite imagery, LiDAR and SAR interferometry (InSAR), have been available for landslide investigations. SAR polarimetry is potentially an effective measure to investigate landslides because fully-polarimetric SAR (PolSAR) data contain more information compared to conventional single- or dual-polarization SAR data. However, research on landslide recognition utilizing polarimetric SAR (PolSAR) is quite limited. Polarimetric properties of landslides have not been examined quantitatively so far. Accordingly, we examined the polarimetric scattering properties of landslides by an assessment of how the decomposed scattering power components and the polarimetric correlation coefficient change with the local incidence angle. In the assessment, PolSAR data acquired from different directions with both spaceborne and airborne SARs were utilized. It was found that the surface scattering power and the polarimetric correlation coefficient of landslides significantly decrease with the local incidence angle, while these indices of surrounding forest do not. This fact leads to establishing a method of effective detection of landslide area by polarimetric information.

DOI： 10.3390/rs71115424

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we address the theoretical aspects of coherence region modeling and its inversion methods for polarimetric interferometric synthetic aperture radar (PolInSAR). Instead of only considering the geometrical shape of the coherence region, we focus on directly modeling the whitened interferometric cross-correlation matrix of the PolInSAR data. In particular, we consider three classes of generic scattering models that respectively contain single, double, and triple phase centers within one resolution cell. We then demonstrate, for each class, that the modeled whitened interferometric cross-correlation matrix is normal. Based on this property, we propose, for each case, efficient algorithms to obtain the best normal matrix approximation solution for model inversion from the observed whitened interferometric cross-correlation matrix. In addition, we show how a simple and effective criterion can be designed from the derived solutions for model validation. Finally, we verify the solutions with both simulated and real data. The results prove the proposed method to be a very promising tool for PolInSAR applications.

DOI： 10.1109/TGRS.2014.2332553

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

Circular synthetic aperture radar (CSAR) is an imaging technique of which the radar trajectory takes a circular form, and the antenna beam illuminates the center of the circular path to acquire the backscattering of targets. Comparing to the SAR systems which have a linear trajectory such as stripmap SAR or spotlight SAR, CSAR has an advantage of being able to image the radar cross section (RCS) of the targets from various azimuthal angles to obtain the high-resolution image. In this report, a simple preprocessing scheme for CSAR received data, called the wire structure intensifier (WSI), is proposed to enhance the scattering from a wire-like target. To demonstrate the proposed method, CSAR experiments are carried out in an anechoic chamber.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Massive MIMO enables the improvement on the transmission rate without increasing the burden on the signal processing by employing a large number of antennas at a base station (BS). Channel state information (CSI) feedback scheme from terminal stations to BS gives a very large overhead when considering massive MIMO and implicit beamforming (IBF) with the calibration technique as the countermeasures are introduced. However, it is reported that CSI estimation itself has a large overhead when considering massive MIMO. In this paper, we propose analog-digital hybrid configuration using analog multi-beams with dielectric line array and lens and blind algorithm called Constant Modulus Algorithm (CMA) which does not need the CSI estimation. Via a computer simulation, the effectiveness of proposed configuration is verified.

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This paper proposes a simple algorithm for detecting largely oriented man-made object by using angular index (beta) over bar, in addition to the conventional angular index (alpha) over bar. The angular indices are derived by the eigenvalues/eigenvectors analysis to the rotated coherency matrix of fully polarimetric SAR data. Here the orientation angle compensation (OAC) is carried out to the coherency matrix before doing the eigenvalues/eigenvectors analysis. In the proposed algorithm, thresholds Th-1,Th-2 for (alpha) over bar, (beta) over bar are included and must be determined for accurate detection of the objects. In order to determine them, we carry out the Finite -Difference Time -Domain (FDTD) polarimetric scattering analysis for relatively large scale man-made objects models. The dependency of the polarimetric scattering feature on the variation of squint angle is in detail investigated. Resultantly, it is found from the FDTD analysis that the candidates of appropriate thresholds for (alpha) over bar and (beta) over bar are obtained for largely -oriented man-made objects detection.

DOI： 10.1109/IGARSS.2015.7326654

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MIMO technique can improve system performance not only communication system but also radar system. In this paper, we propose a quasi-MIMO Doppler radar for indoor human detection. In the indoor measurements, multipath reflections by wall, floor, and furniture, often make human detection difficult. Doppler filtering is introduced to remove these undesired response and extract radar echoes by human in motion before target detection. Also virtual array technique based on the Khatri-Rao matrix product is introduced in the MIMO radar detection. Experimental results are reported to shown performance improvement especially in angular resolution.

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In this paper, the results of polarimetric scattering measurement is presented to verify the efficiency of proposed man-made object detection algorithm. The polarimetric angular indices (alpha) over bar and (beta) over bar are known to be effective for identification of well-regulated structures. However, the validity for detecting deformed structures is not clear. So the feature of (alpha) over bar and (beta) over bar for the squint angle variation of deformed man- made objects was investigated in detail.

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This paper presents the scattering power decomposition images over Singapore using 3 fully polarimetric SAR data acquired with ALOS-PALSAR. The land cover are precisely imaged with RGB color-coding indicating R: the double bounce scattering, G: the volume scattering, and B: the surface scattering. It is seen the image is useful for identifying various objects including urban area, forest, agricultural area, in addition to numerous ships around Singapore sea area.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Recently, microwave remote sensing has been used for observation of the global environment extensively. There are many techniques in the microwave remote sensing. Among them, SAR (Synthetic Aperture Radar) Tomography is one of the emerging technique that can realize three dimensional imaging, by using multiple flight paths. The data pixels in each SAR image obtained at the slightly different paths may be regarded as the observed data with an array antenna. Thus, it is applying the Direction of Arrival (DOA) estimation technique to the array data, we estimate angle of dominant scatterers, or height of the targets.
In this report, we provide preliminary results of the multi-baseline SAR Tomography observed by the PiSAR2-X, airborne X-band SAR of NICT, Japan.

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Soil moisture retrieval from polarimetric synthetic aperture radar (SAR) imagery over forested terrain is quite a challenging problem, because the radar backscatter is affected by not only the moisture content, but also by large vegetation structures such as the trunks and branches. Although a large number of algorithms which exploit radar backscatter to infer soil moisture have been developed, most of them are limited to the case of bare soil or little vegetation cover that an incident wave can easily reach the soil surface without serious disturbance. However, natural land surfaces are rarely free from vegetation, and the disturbance in radar backscatter must be properly compensated to achieve accurate soil moisture measurement in a diversity of terrain surfaces. In this paper, a simple polarimetric parameter, co-polarized backscattering ratio, is shown to be a criterion to infer moisture content of forested terrain, from both a theoretical forest scattering simulation and an appropriate experimental validation under well-controlled condition. Though modeling of forested terrain requires a number of scattering mechanisms to be taken into account, it is essential to isolate them one by one to better understand how soil moisture affects a specific and principal scattering component. For this purpose, we consider a simplified microwave scattering model for forested terrain, which consists of a cloud of dielectric cylinders as a representative of trunks, vertically stood on a flat dielectric soil surface. This simplified model can be considered a simple boreal forest model, and it is revealed that the co-polarization ratio in the ground-trunk double-bounce backscattering can be an useful index to monitor the relative variation in the moisture content of the boreal forest.

DOI： 10.1587/transcom.E97.B.2074

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Much attention has recently been paid to direction of arrival (DOA) estimation using compressed sensing (CS) techniques, which are sparse signal reconstruction methods. In our previous study, we developed a method for estimating the DOAs of multi-band signals that uses CS processing and that is based on the assumption that incident signals have the same complex amplitudes in all the bands. That method has a higher probability of correct estimation than a single-band DOA estimation method using CS. In this paper, we propose novel DOA estimation methods for multi-band signals with frequency characteristics using the Khatri-Rao product. First, we formulate a method that can estimate DOAs of multiband signals whose phases alone have frequency dependence. Second, we extend the scheme in such a way that we can estimate DOAs of multi-band signals whose amplitudes and phases both depend on frequency. Finally, we evaluate the performance of the proposed methods through computer simulations and reveal the improvement in estimation performance.

DOI： 10.1587/transcom.E97.B.2110

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In PolSAR data utilization, it is important to precisely detect urban areas, not only for monitoring the effect of urbanization but also for detecting the stricken residential buildings immediately after a big disaster. In order to improve the accuracy of the detection, it is required to reveal scattering characteristics of urban areas in detail. This paper reports empirical findings from polarimetric scattering measurement for simplified man-made structure models. It is found from the measurement data analysis that both squint and incident angles have strong effect on some polarimetric indices. We also discuss the relationship between the size of the model and its polarization features.

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This paper describes the effectiveness of calibration technique for implicit beamforming which enables the transmission without the channel state information (CSI) feedback in massive MIMO system. First, we address the calibration technique using the circulation of self transmit signal. The effectiveness of calibration method is next verified by using 16-element testbed for the massive MIMO system. Finally, the throughput performance by the IEEE802.11ac based massive MIMO transmission with and without CSI feedback is verified when considering calibration errors which are obtained by the testbed.

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In massive MIMO transmission, implicit beam forming was studied to eliminate channel state information (CSI) feedback. However, it is essential to introduce the calibration circuit which compensates the difference of complex amplitudes between the transmitters and receivers. This paper presents the effectiveness of calibration circuit for massive MIMO transmission by the testbed which implements the calibration circuit, when considering the interference signal.

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Recently, researches on the wideband wireless system becomes important increasingly due to growth of the requirements on the high-speed broadband communications. Direction of arrival estimation of such a wideband sources with array also important for radio propagation estimation and/or surveillance. DOA estimation of wideband sources is one of the difficult problem because suitable element separation of the array essentially determined by the wavelength of the wave(s). In this report, we propose a new wideband DOA estimation technique that is available depending on the signal correlations.

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Ocean surface current radar has attracted attention as a system which can be observed ocean phenomenon effectively. In this report, we evaluate the aperture enhancement effect by applying the Khatri-Rao (KR) product array to the Doppler frequency and angular resolution. Since Doppler frequency represents surface current velocity, resolution enhancement leads to estimation accuracy improvement of the velocity. In this paper, we apply the KR product to actual data set of the ocean surface current radar, and estimated surface current velocity.

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Soil moisture content is an essential parameter in agriculture and hydrological processes. Using remote sensing, we can measure soil moisture content in real time over wide area. Oh model is one of the important models that characterize the scattering properties of the soil, and it can be reliably used to estimate the soil moisture content and surface roughness of the bare soil. However, the estimation accuracy of the Oh model decreases under the influence of vegetation. Therefore, in this paper, we propose a modified method which first extracts the scattering component of the soil surface by using scattering power decomposition, and then applies Oh model for soil moisture and roughness estimation. In the experiment, we report the results on the measured data over a field and demonstrate the effectiveness of the proposed approach.

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MIMO radar and Khatri-Rao (KR) product virtual array are the methods for increasing angular resolution of the array radar. The KR product is not suited to radar because KR product needs data property of uncorrelated wave incidence. However, when we extract responses of moving targets having different Doppler frequencies by Doppler filtering, the KR product array works almost properly because their correlation become low. In this report, we show the availability of the MIMO radar with the KR product virtual array for indoor location estimation by experiment.

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This paper describes the effectiveness of implicit beamforming which enables the transmission without the channel state information (CSI) feedback in massive MIMO system. First, we explain the CSI feedback scheme from the terminal stations to base station gives a very large overhead. The calibration technique, which compensate the difference of complex amplitudes between transmitters and receivers for the implicit beamforming, is next introduced. Finally, the throughput by the IEEE802.11ac based massive MIMO transmission with and without CSI feedback is clarified when considering Medium Access Control efficiency.

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Several techniques for detecting the temporal changes in satellite polarimetric synthetic aperture radar (POLSAR) imagery, called as the polarimetric change detector (PCD), are developed. The PCD would be able to detect areas in the scene for which the observed polarimetric characteristics noticed a change between the two acquisitions. So these techniques have one of the most important applications to understand the evolution of our planet. The X-band very high-resolution polarimetric and interferometric airborne synthetic aperture radar (PiSAR-2) system has been developed by National Institute of Information and Communications Technology (NICT). The more accurate land monitoring is possible from this system. This paper introduces the result of several PCD using multi-temporal Pi-SAR2 polarimetric data with the reference of ground truth data.

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Recently, the direction-of-arrival (DOA) estimation using an array antenna has been studied extensively. Accordingly, array calibration method has also become an important topic. Conventional data acquisition methods often require a positioner or an azimuth table to make sources of known DOAs for premeasurement of array calibration in a radio anechoic chamber. However, such a measurement is both time-consuming and expensive. In this paper, we propose a simple data acquisition method for array calibration using a Web camera and show its effectiveness by experiments. Additionally, we also report a simulation study to confirm the relationship between the distance from transmitter (Tx) to receiver (Rx) and the array length.

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Sensing technology using radio wave has been attracting attention for various applications such as office/home security and surveillance. Classification of human motion has been extensively studied in these applications. They often utilize Doppler frequency characteristic occurred by human motion. In this paper, range-Doppler distributions by human motion are studied. We show range-Doppler signatures of six motions in this paper, and evaluate the difference of the motions by correlation. We demonstrated experimentally that the motion difference can be discriminated by the range-Doppler correlation and can be enhanced by the elimination filter of DC Doppler components.

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Much attention has been paid to direction of arrival (DOA) estimation using a compressed sensing technique. In our previous study, we have proposed a method to estimate DOAs of multi-band signals using an array antenna at a receiver. As a result, we have produced an improvement of the probability of correct estimation. Moreover, the method can deal with waves exceeding the degrees of freedom of the array. However, we have assumed that incident waves have multi-bands where complex amplitudes are the same. First, in this paper, we propose a method that allows the estimation of DOAs when only the phases at the bands are different using not the complex amplitudes but powers of the signals. Second, we extend the technique in such a way that it can estimate DOAs of the signals having different amplitudes among bands.

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This paper presents very high resolution (30 cm) and fully polarimetric images acquired with a new airborne Polarimetric Interferometric Synthetic Aperture Radar 2 (Pi-SAR2) system operating at the X-band. Pi-SAR2 is a successive version of the former X-band Pi-SAR aiming at exploring the possibility of fully polarimetric SAR. In collaborative works among NICT and research institutions in Japan, data acquisition flights over Niigata have been carried out on August 25 and November 17, 2013. Some imaging results with interesting phenomena are shown using polarimetric scattering power decomposition.

DOI： 10.1109/IGARSS.2014.6946350

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This paper shows efficacy of an algorithm detecting man-made objects area by measuring and analyzing wave scattering from its models. The algorithm uses the co-polarized correlation coefficient in LR circularization basis and its normalized one, and switch these coefficients for detecting the man-made objects not only normally but also obliquely alignment to the radar illumination direction. For setting parameters in the algorithm appropriately, we carry out a polarimetric scattering measurement for man-made objects models in anechoic chamber.

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Recently, researches on the wideband wireless system becomes important increasingly due to growth of the requirements on the high-speed broadband communications. Direction of arrival estimation of such a wideband sources with array also important for radio propagation estimation and/or surveillance. DOA estimation of wideband sources is one of the difficult problem because suitable element separation of the array essentially determined by the wavelength of the wave(s). In this report, we propose a new wideband DOA estimation technique that is available depending on the signal correlations.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Recently, researches on wideband wireless communications have been investigated intensively. With the progress of wideband wireless communications, DOA estimation technique for wideband incident waves has been also required. The history of high-resolution wideband DOA estimation started several decades ago. However its standard technique is not developed yet. In this report, we have proposed a new wideband DOA estimation technique using the Khatri-Rao matrix product. This method enables a wideband DOA estimation by using a simple conversion of sub-frequency band signals. In addition this technique realizes enhancement of the degrees-of-freedom of the array as well as high DOA resolution property. In this paper, performance of the proposed technique is reported by computer simulations.

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Sensing technology using radio wave has been attracting attention for various applications such as office/home security and surveillance. Classification of human motion has been extensively studied in these applications. They often utilize micro-Doppler signature, or Doppler frequency signature occurred by human motion. In this paper, 4 type of range-Doppler signatures in human motion at a certain range are studied, and difference of the motions is confirmed experimentally. Moreover, extraction technique for range-Doppler signature with several moving humans are studied. Experimental results show that we can easily suppress the undesired target responses and extract the desired target response by using range-Doppler filtering scheme.

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Ocean surface current radar is a Doppler radar to observe oceanographic information using the Bragg scattering resonance mechanism. In this paper, we consider angular resolution improvement of the radar. The radar employs an antenna array with FMICW operation, then it can resolve angular distribution by Digital Beam Forming (DBF) and distance by Fourier transform of the beat signal obtained by the FMICW radar. In order to obtain sufficient angular resolution, large array length or aperture with increasing the number of elements is needed, that is often difficult to realize in the HF/VHF ocean surface current radar. In this paper we propose to apply the Khatri-Rao (KR) product array processing to the radar. To verify effectiveness of the KR product array processing in angular resolution enhancement for the ocean surface current radar, we apply the KR product array to actual experimental data set of the radar, and show that the method is available to angular resolution enhancement and Doppler spectrum improvement.

DOI： 10.1587/transcom.E96.B.2469

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, we study on direction-of-arrival (DOA) estimation error reduction by Khatri-Rao (KR) product extended array in the presence of correlated waves. Recently, a simple array signal processing technique called KR product extended array has been proposed. By using the technique, degrees-of-freedom of an array can be easily increased. However, DOA estimation accuracy deteriorates when correlated or coherent waves arrive. Such highly correlated waves often arrive for radar application, hence error reduction technique has been desired. Therefore, in this paper, we propose a new method for error reduction preprocessing scheme by using N-th root of matrix. The N-th root of matrix has a similar effect to the spatial smoothing preprocessing for highly correlated signals. As a result, DOA estimation error due to signal correlation will be reduced. The optimal order of N depends on the data itself. In this paper, a simple iterative method to obtain adaptive N is also proposed. Computer simulation results are provided to show performance of the proposed method.

DOI： 10.1587/transcom.E96.B.2475

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This paper investigates the parameter estimation of compound Wishart distribution for statistical modeling of polarimetric synthetic aperture radar data. We show that the recently proposed method of matrix log-cumulant may lead to non-invertible equations and cause unstable performances. In order to overcome such difficulty, we proposed a Bayesian-based method to re-estimate the log-cumulants. Simulation experiment demonstrates that the proposed algorithm provides both improved and stabler results. Finally, we present an application of the new method for texture analysis of the Germany F-SAR polarimetric data.

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Recently, researches on radio wave security sensors by using array antenna or MIMO(Multiple-Input Multiple Output) system have been attracting attention. These sensors utilize the property that MIMO channel matrix is sensitive to the propagation environment change in indoor multipath environment. Now the property is used for event detection, such as intrusion, by calculating correlation of MIMO channel matrices. Fundamental study has been performed, however, statistical property, or quantitative detection performance analysis, of the sensor was still remain to be clarified. So, our objective is to derive a probability density function (PDF) of the correlation coefficient and to demonstrate them experimentally. The PDF is a key function to derive detection rate and so on. In the conventional MIMO sensor, correlation coefficient of the channel matrix between with and without an event is used as a measure of events. Therefore, in this report we will derive the PDF of the channel correlation used in the conventional MIMO sensor theoretically and also show the validity by experimental results.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electronics, Information and Communication, Engineers, IEICE  

Ocean surface current radar is a Doppler radar to observe oceanographic information using the Bragg scattering resonance mechanism. In this paper, we consider angular resolution improvement of the radar. The radar employs an antenna array with FMICW operation, then it can resolve angular distribution by Digital Beam Forming (DBF) and distance by Fourier transform of the beat signal obtained by the FMICW radar. In order to obtain sufficient angular resolution, large array length or aperture with increasing the number of elements is needed, that is often difficult to realize in the HF/VHF ocean surface current radar. In this paper we propose to apply the Khatri-Rao (KR) product array processing to the radar. To verify effectiveness of the KR product array processing in angular resolution enhancement for the ocean surface current radar, we apply the KR product array to actual experimental data set of the radar, and show that the method is available to angular resolution enhancement and Doppler spectrum improvement. Copyright © 2013 The Institute of Electronics, Information and Communication Engineers.

DOI： 10.1587/transcom.E96.B.2469

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Recently, many model-based decomposition algorithms, which are based on several scattering models, have been proposed to extract physical parameters of the Earth's surface [1]-[4]. Those algorithms decompose the received power into several scattering components, and some assumptions are necessary to find the scattering contribution. By the assumption( s) and scattering models in a used algorithm, decomposed scattering power of each component becomes often different with each other. Therefore, it is difficult to judge which algorithm is the best for a certain observation area. It can be useful to compare the algorithms and to clarify which one is suitable to detect a particular scattering mechanism. As a first step of the research, we compared several model-based polarimetric decomposition algorithms qualitatively from a viewpoint of "a visual difference in decomposition images", "negative power", and "ratio of scattering power". In this paper, forested and urban area are selected for discussion.

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This paper reviews the model-based scattering power decomposition methods of fully polarimetric SAR data. Starting from Freeman & Durden 3-component decomposition, comparison of 4-component decompositions are given in terms of available information included in the coherency matrix. The final general 4-component decomposition method with unitary transformation (G4U) employs 100% polarimetric information.

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Polarimetric radar has a potential ability to retrieve forest parameters such as the moisture content and the biomass. Accurate retrieval of those parameters is the key to understand forest ecosystem and to prevent global climate change. For those purposes, this research aims to establish a quantitative approach to the forest parameter retrieval using polarimetric radar. To achieve this, we need a scattering model which describes scattering from forested terrain. The scattering mechanism has been extensively investigated, and several scattering models have been proposed. Although those models are validated with a field experiment, difficulties arise because those models require many input parameters which are difficult to measure accurately over widespread area. Therefore, a relatively simple scattering model is necessary, and carefully controlled experiment is essential to validate the model. In this research, we employ the discrete scatterer model (DSM) described in [1] as the forest scattering model. Using this model, we pointed out that fully polarimetric observation has the potential ability to retrieve the moisture content of forested terrain [2]. This paper aims to prove this theoretical result through an indoor fully polarimetric measurement.

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This paper proposes a simple algorithm to precisely detect man-made objects with any alignment to radar illumination direction. Here, a couple of polarimetric indices, i.e. the co-pol. correlation coefficient in LR circular polarization basis, and its normalized one are utilized in the algorithm, since the former is emphasized in reflection symmetry (RS) as normally aligned man-made objects area, whereas the latter is enhanced in Non-RS as obliquely aligned man-made objects area. The appropriate thresholds for switching the polarimetric indices are determined by considering the result of polarimetric scattering analysis for simplified man-made objects model. The Finite-Difference Time-Domain (FDTD) method is utilized for the analysis. It is finally confirmed from the result of the PolSAR image analysis that the proposed algorithm is very effective for detecting the man-made objects not only normally but also obliquely alignment to the radar illumination direction.

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Speckle noise makes the synthetic aperture radar (SAR) image interpretation difficult and reduces the accuracy of the rapid disaster assessment. This paper introduces the influence of speckle filtering methods on the polarimetric SAR data interpretation of damages. Four types of speckle filtering methods, such as boxcar filter, refined Lee filter, Lee sigma filter, and sequential filter, are investigated to determine the best filtering options for detection of damaged areas. As a result, Lee sigma filter exhibits the best performance in the analysis of the damaged areas. The sequential filtering approach also shows a good performance, which is comparable with that of Lee sigma filter, with minimum computational cost.

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This paper investigates polarimetric scattering characteristics for accurately detecting stricken man-made objects. In order to understand the polarimetric scattering features generated from various damaged man-made buildings, we carry out the Finite-Difference Time-Domain (FDTD) polarimetric scattering analysis for deformed and/or collapsed man-made target models. The dependency of the polarimetric scattering feature on the variation of squint angle is in detail investigated. It is confirmed from the estimation based on various polarimetric analyses that the double-bounce scattering, the co-pol correlation coefficient in LR circular porlarization basis, and its normalized one are useful markers for stricken man-made objects detection/identification.

DOI： 10.1109/IGARSS.2013.6723286

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In this study, the usability of the co-polarization correlation coefficients of polarimetric SAR data for characterization of terrain types in the natural and urban areas has been investigated. The co-polarization coherence signature plot and the co-polarization phase correlation plot, which display the correlation coefficients as a function of the polarization state, are introduced with the unitary basis transformation of the polarimetric covariance matrix. Experimental results indicate that the co-polarization coherence signatures can be an effective way to characterize terrain scatter types.

DOI： 10.1109/IGARSS.2013.6723288

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In this paper, we study on DOA estimation error reduction by nested array in the presence of correlated waves. In recent years, at simple array signal processing technique called nested array has been proposed. By using the technique, degrees-of-freedom of the array can be easily increased. However, accuracy of DOA estimation deteriorates when correlated or coherent waves arrived. Therefore, in this report, we propose a new method for error reduction by using N-th root of matrix. The optimal order N depends on the data. In this study, we also provide an iterative method to determine a sub-optimal N by using estimated correlation coefficients. Availability of the proposed method is verified by computer simulation. © 2013 IEEE.

DOI： 10.1109/APS.2013.6711091

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We propose modeling method for the wall through radar by using near-field GTD as a near-region target model and delayed path-length for multi-layered dielectric sheets. Radar image can be constructed by AF (array-factor), which is a kind of synthetic aperture imaging. For near-region target, we apply focusing procedure of optical ray to the AF summation and the wall through pass. Refraction coefficient of N-layered dielectric sheets is exactly derived as boundary wave problem and applied to the wall through radar imaging. Theoretical near-field AF images are compared with far-field model, traditional SAR (synthetic aperture radar) image, and measured data. © 2013 IEICE.

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There exist 9 independent polarization parameters in the coherency or covariance matrix as the second order statistics. Various decomposition methods have been presented based on the physical scattering model using these parameters. However, none of them accounts for all polarimetric information, typically leaving T-13 element un-accounted in the coherency matrix. This paper presents a complete four-component scattering power decomposition method using all polarimetric information. Using double unitary transformation of measured coherency matrix, it is possible to eliminate T-23 element, which results in a reduction of polraization parameters from 9 to 7. Then by unitary transformation of expansion matrices, it becomes possible to account for T-13 term, which has never been accounted for in the physical model-based decomposition. By the double unitary transformations to minimize the T-33 component, all polarimetric parameters are accounted. This methodology also reduces the negative power problem significantly. This method is a further extension of the existing four-component decomposition. The four scattering powers (surface, double bounce, volume, helix) are assigned to blue, red, green, and yellow to compose full-color image. An example image of San Francisco area acquired with ALOS-PALSAR is shown to validate the decomposed result.

DOI： 10.1109/IGARSS.2012.6351629

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The moisture content of terrain or forest, which is highly related to the permittivity, is a key parameter to understand global water cycle. This study is focused on retrieving permittivity from radar backscattering measurements. The basic concept of the proposal is to utilize Brewster's angle effect of double-bounce backscattering. If the Brewster's angle is known, it is possible to estimate the permittivity of medium directly. In order to demonstrate the Brewster's angle effects on the backscattering of forested area, the authors have carried out a simple laboratory experiment and the results are shown in this paper.

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This paper proposes a simple man-made object detection method by utilizing the nonnegative eigenvalue decomposition (NNED) [1] and a unitary rotation [2] to the covariance matrix. It is observed from the result of the PolSAR image analysis using the proposed method that the double-bounce scattering contribution P-d becomes stronger than that by the conventional scattering power decomposition even when the stricken residential houses are built on rough and slope ground surface. Furthermore, in order to analytically verify the improved effect for the stricken man-made object detection, the Finite-Difference Time-Domain (FDTD) polarimetric scattering analysis is also carried out for a simplified man-made objects model, which consists of quad dielectric rectangular parallelepipeds on finite circular plate with rough surface. The rectangular parallelepipeds are considered as a simplified man-made buildings model. It is cleared from the FDTD result that the enhancement of P-d can be realized by doing the C-22 rotation, in addition to the NNED procedure.

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Polarimetric SAR decomposition has been expected to be a potential candidate of a tool to measure physical parameters of vegetated fields For this context, it is important to validate theoretical model quantitatively with well controlled experiment. In this paper, simple boreal forest was modeled based on discrete scatterer model. Through sensitivity study by using the model, we propose several useful indexes to infer vegetation parameters such as soil moisture. This study will be validated by X-band indoor full polarimetric SAR in Niigata University.

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The improvement of position estimation accuracy is a very important factor in various radar applications. This paper focuses on two-dimensional (2-D) location estimation in radar surveillance using leaky coaxial cables. A leaky coaxial cable is a kind of antenna and has recently attracted attention as a powerful tool for vehicle detection and as an intrusion detection sensor for perimeter security. We derive the Cramer-Rao bound (CRB) for a leaky coaxial cable sensing application and introduce the CRB ellipsoid to evaluate the accuracy of the 2-D location estimation of an object. The diameter and angle of a CRB ellipsoid indicates its error distribution. A leaky coaxial cable has an outer conductor with periodic slots. Its slot pattern determines the radiation characteristics such as the beam angle and harmonic radiation. We focus on the slot pattern to improve the estimation accuracy. Numerical analyses show that a slot pattern generating multi-beams improves the accuracy while single radiation is preferred for general use in communication applications.

DOI： 10.1109/TAP.2011.2143661

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper presents an improvement to a decomposition scheme for the accurate classification of polarimetric synthetic aperture radar (POLSAR) images. Using a rotation of the coherency matrix to minimize the cross-polarized component, the four-component scattering power decomposition is applied to fully polarimetric SAR images. It is known that oriented urban area and vegetation signatures are decomposed into the same volume scattering mechanism in the previous decompositions and that it is difficult to distinguish vegetation from oblique urban areas with respect to the radar direction of illumination within the volume scattering mechanism. It is desirable to distinguish these two scattering mechanisms for accurate classification although they exhibit similar polarimetric responses. The new decomposition scheme by implementing a rotation of the coherency matrix first and, subsequently, the four-component decomposition yields considerably improved accurate results that oriented urban areas are recognized as double bounce objects from volume scattering.

DOI： 10.1109/TGRS.2010.2099124

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

High resolution direction-of-arrival (DOA) estimation algorithm for array antennas becomes popular in these days. However, there are several error factors such as mutual coupling among the elements in actual array. Hence array calibration is indispensable to realize intrinsic performance of the algorithm. In the many applications, it is preferable that the calibration can be done in the practical environment in operation. In such a case, the incident wave becomes coherent multipath wave. Calibration of array in the multipath environment is a hard problem, even when DOA of elementary waves is known. To realize array calibration in the multipath environment will be useful for some applications even if reference signals are required. In this report, we consider property of reference waves in the multipath environment and derive a new calibration technique by using the multipath coherent reference waves. The reference wave depends on not only the DOA but also complex amplitude of each elementary wave. However, the proposed technique depends on the DOA only. This is the main advantage of the technique. Simulation results confirm the effectiveness of the proposed technique.

DOI： 10.1587/transcom.E94.B.1201

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In recent years, high-resolution Direction of Arrival (DOA) estimation with an array antenna has become indispensable for various applications such as microwave-power transmission and reception. In actual measurement, however, DOA estimation accuracy is deteriorated by many error factors. Furthermore, almost all the computationally efficient DOA estimation algorithm can apply to the uniform arrays. In this report, we proposed the calibration method for Root-MUSIC which is low computationally efficient method with an arbitrary array. © 2011 IEEE.

DOI： 10.1109/IMWS.2011.5877119

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This paper investigates polarimetric scattering characteristics from boundary region between the water area and the surrounding emerged plants in wetland, and proposes a simple true water area estimation method, by using both phi(HH)-phi(VV) and P-d in polarimetric synthetic aperture radar (PolSAR) image analysis. The true water area includes not only the body of water but also the water area under emerged-plants and/or floating-leave plants in wetland.
To verify the generating mechanism of the specific polarimetric scattering features, the Finite-Difference Time-Domain (FDTD) polarimetric scattering analysis is also carried out for a simplified boundary model, which simulates the local boundary region around the wetland and consists of lots of vertical thin dielectric pillars on a dielectric plate.
Taking into account the polarimetric feature obtained by both the FDTD and PolSAR image analyses, one can distinguish the actual water area from the emerged-plants around a wetland, even when the water area is concealed by emerged-plants and/or floating-leave plants. Resultantly, it is found that by using the proposed simple classification markers, one can estimate the true water area boundary for wetland and the surrounding emerged-plants.

DOI： 10.1109/IGARSS.2011.6048915

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this tutorial presentation, model-based scattering power decompositions for fully polarimetric SAR data analysis are reviewed, and a relevant four-component scattering power decomposition scheme is presented. Although the method is still not perfect, it provides us with intuitive imaging results by RGB color-coding based on the physical scattering mechanisms. By using a rotation of the coherency matrix to minimize the cross-polarized component, the result of the four-component decomposition becomes more significant with simple and easy calculation. It is shown that oriented urban areas or man-made structures are clearly distinguished from volume scattering as double bounce objects.

DOI： 10.1109/IGARSS.2011.6049374

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Vegetation monitoring is one of the major applications of polarimetric synthetic aperture radar (PolSAR). In this paper, permittivity estimation method for vegetation by using multi-angle polarimetric radar is proposed. The method utilizes Brewster's angle of double-bounce scattering component. We demonstrate validity of the proposed method by indoor model experiments. We use a dihedral reflector and dipole cloud to obtain double-bounce scattering and volume scattering, respectively. The experimental results show that the proposed method works properly when volume scatterer exists. © 2011 KIEES.

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In recent years, several indoor intrusion/event detection methods using radio propagation change caused by intruder have been proposed. One of the indoor intrusion/event detection methods with an array antenna can detect intrusion/event using receiving signal eigenvector change. In addition, the method intrusion/event detection method using MIMO channel change also has been proposed. However, these reports have not discussed intruder location detection. In this report, we consider possibility of indoor intrusion/location detection by the computer simulations.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In the MIMO system, transmitted streams are multiplexed spatially at the same frequency. This causes inter-stream interference at the receiver. Therefore, equalization/decoding method is necessary. Least Squares Channel Estimation (LSCE) is often used as the method. However, overhead of throughput due to training symbols is a problem for effective transmission. In this report, we employ on Independent Component Analysis (ICA) as a blind method without the training symbols. We have reported effectiveness of the ICA with a small number of training symbols compared with that of the LSCE. However, since the ICA is statistical channel estimation method, many data symbols are often needed. In this report, we propose to apply a pre-filtering processing to the transmitting signals to obtain better performance compared with the conventional ICA. Computer simulation results are shown to demonstrate availability of the method. Furthermore we provide some experimental results to show the effectiveness of proposed method in the real environment.

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This paper investigates polarimetric scattering features generated from man-made targets for accurately observing stricken residential area by making full use of quad. polarimetric SAR data set. First, we propose a simple improvement of the scattering power decomposition method by introducing a unitary rotation of the coherency matrix. It is found from the results of the POLSAR image analysis for a mountainous region including some stricken residential areas that by carrying out the rotation procedure, double-bounce scattering contribution can be enhanced even when the targets are oriented and/or set on small inclined ground plane. This peculiar scattering feature is utilized as a useful marker for precisely detecting man-made targets.
To verify the generating and enhancing mechanism of the double-bounce scattering, we also carry out the Finite-Difference Time-Domain (FDTD) polarimetric scattering analysis for a simplified man-made target model. The dependency of the polarimetric scattering feature on the variation of squint angle is investigated. It is confirmed from the FDTD analysis for oblique squint angular range that by applying the rotation procedure before the scattering power decomposition, the double-bounce scattering contribution tends to be enhanced, and the volume scattering becomes small.

DOI： 10.1109/IGARSS.2010.5650043

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The scattering power decomposition for POLSAR data is one of the powerful tools in the radar polarimetry. There are several model-based decomposition techniques. However, since the number of independent observables in POLSAR images is limited, these techniques require several assumptions to obtain unique solution. The authors have proposed an alternative technique with POL-InSAR dataset. By using the POL-InSAR dataset, we can increase the number of observables. However, selection of volume scattering component was still a problem. Recently, Dr. Arii et. al., proposed a generalized volume scattering model, and applied it to the POLSAR dataset with the adaptive non-negative eigenvalue decomposition technique. In this report, we appy the model to the ESPRIT-based POL-InSAR decomposition technique and verify the estimation performance experimentally.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this presentation, a new decomposition scheme of first using a rotation of the coherency matrix followed by the four-component decomposition is presented. It is shown using airborne Pi-SAR data sets that oriented urban areas are clearly distinguished from volume scattering as double bounce objects by the rotation of coherency matrix.

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