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This paper presents a comparative analysis of Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) algorithms in a corner reflector located in Lisbon, Portugal. The reflector was monitored using daily observations from the Global Navigation Satellite System (GNSS) technique with submillimeter precision. The study focuses on comparing the performance and accuracy of different MT-InSAR approaches i) the Persistent Scatterer Interferometry (PSI) method using the open-source software StaMPS, ii) the PSI method using the commercial software SARPROZ, iii) the Quasi-PS method implemented with the SARPROZ software, as well as iv) a hybrid method Persistent scatterer – Distributed Scatterer (PS-DS) obtained from the European Ground Motion Service (EGMS) with SqueeSAR algorithm. The study period assumed was from October 2017 to January 2019, by considering the same initial information (ascending orbit Sentinel images). Statistical analysis of the time series was also performed, and the density of points in the vicinity was evaluated. To provide a comprehensive evaluation of accuracy, the uncertainties associated with both the GNSS and InSAR techniques were assessed. The findings of this comparative analysis offer valuable insights into the strengths and limitations of various MT-InSAR algorithms by using a more precise technique as a benchmark. The results improve the understanding of deformation monitoring in geodetic applications and highlight the potential for enhanced accuracy in such assessments. [ABSTRACT FROM AUTHOR]

The accuracy of microwave remote sensing relies on the calibration of the radar measurement. It is important to estimate the radar cross-section (RCS) using a passive corner reflector (CR) or active transponder to evaluate the quality of imaging radar data. A strong and consistent RCS can be achieved by the acquisition of radar signals concentrated at specific angles during the CR calibration procedure. There are several types of CR depending on the shape and size such as triangular trihedrals, square trihedrals, dihedrals, spheres, or cylinders. In this study, we examine the RCSs using three types of CR with Ku-band ground-based real aperture radar equipment, the Gamma Portable Radar Interferometer-II. It can be easily deployed to acquire fully polarimetric radar observations. The initial experiment was conducted at Busan Sam-nak Auto Camping Site on November 1, 2023. The amplitude images show much higher backscattered radar signals at the CR location, whereas relatively lower power has been captured in the surrounding areas. The attenuation factors in the radar receivers could be useful to prevent saturation around the CR location at the line-of-sight direction. The experiment indicates that the different levels of the RCS measurements from three types of CRs could be utilized for calibration study with fully polarimetric radar observations.

We describe a method to calibrate a Software-Defined Radar (SDRadar) system mounted on an uncrewed aerial vehicle (UAV) with an ultra-wideband (UWB) waveform operated in the near-field region. Radar calibration is a prerequisite for using the full capabilities of the radar system to retrieve geophysical parameters accurately. We introduce a framework and process to calibrate the SDRadar with the UWB waveform in the 675 MHz–3 GHz range in the near-field region. Furthermore, we present the framework for computing the near-field radar cross section (RCS) of an external passive calibration target, a trihedral corner reflector (CR), using HFSS software and with consideration for specific antennas. The calibration performance was evaluated with various distances between the calibration target and radar antennas. The necessity for the knowledge of the near-field RCS to calibrate SDRadar was demonstrated, which sets this work apart from the standard method of using a trihedral CR for backscatter radar calibration. We were able to achieve approximately 0.5 dB accuracy when calibrating the SDRadar in the anechoic chamber using a trihedral CR. In outdoor field conditions, where the ground rough surface scattering effects are present, the calibration performance was lower, approximately 1.5 dB. A solution is proposed to overcome the ground effect by elevating the CR above the ground level, which enables applying time-gating around the CR echo, excluding the reflection from the ground. [ABSTRACT FROM AUTHOR]

ObjectiveIn order to further improve the speed and accuracy of calculating the acoustic scattering fields of underwater concave targets, the acoustic scattering characteristics of underwater corner reflector complexes are studied. MethodBy applying the Kirchhoff approximation and ray tracing methods, and considering the multiple effects of scattering and occlusion by corner reflectors, a simplified acoustic scattering prediction model of an underwater corner reflector complex is established and a rapid prediction method （i.e. modified planar element method, PEM）of acoustic scattering fields is proposed. The acoustic scattering field of a corner reflector complex is calculated by this method and verified via finite element simulation; on this basis, an analysis is made of the characteristics of octahedral corner reflectors, combined polyhedral corner reflectors and cluster-based and space-based strong scattering targets. ResultsThe results show that the modified PEM allows the rapid and accurate calculation of the acoustic fields scattered by diagonal reflectors. The acoustic scattering fields of octahedral corner reflectors and combined polyhedral corner reflectors varies with the incident wave frequency, angle and reflector complex distance. ConclusionThe results of this study can provide important technical support for the design of underwater passive interferer models.

Using the tunderwater corner reflector (CR) to simulate the acoustic scattering characteristics of the military target is a new technology to counter active sonar detection. Existing underwater CRs only have the ability to interfere with the acoustic field, but have limitations in acoustic wave modulation. Therefore, acoustic metasurfaces applied on CRs to enhance the ability of acoustic wave modulation has a great application prospect. A fast prediction method based on the Kirchhoff approximation (KA) and the ray tracing theory is proposed to calculate the acoustic scattering characteristics of CR with acoustic metasurfaces in grooves array type. The accuracy of the method is verified by the finite element method (FEM) simulation. The modulation effect of CR with grooves array in different gradient combinations on the structural scattering acoustic field is analyzed. The research shows that the CR with different combinations of the acoustic metasurface has an obvious modulation effect on the amplitude of the acoustic waves and the deflection of acoustic field. In particular, the grooves array in combination with positive and negative gradients has an obvious deflection impact on the scattering acoustic field. [ABSTRACT FROM AUTHOR]

This paper proposes a corner reflector and Luneburg ball reflector group. The omnidirectional radar cross-sectional (RCS) distribution characteristics of a fighter are simulated using the sharp and smooth RCS distribution features of the corner and the Luneburg ball reflectors, respectively. A new type of Doppler signal generation principle is proposed to design a Doppler frequency simulator to transmit frequency signals by connecting in parallel with the metal layer of the corner reflector and the Luneburg sphere ball, and then transmit through their other end. The existing radar target aircraft cannot simulate the RCS and speed of the targets that are less than 0.005 m2 by enhancing the echo intensity of the target location, which makes it impossible for the military to conduct practice drills and evaluate the effectiveness of the air defense systems. The experimental results show that the Doppler frequency simulator successfully simulates the target speed of 0-80 km/h and when the speed is greater than 20 km/h, the error of the simulation frequency is less than 1.5%. The proposed method can provide guidance and a theoretical basis for simulating the speed of various types of aircraft in future work.

This paper proposes a corner reflector and Luneburg ball reflector group. The omnidirectional radar cross-sectional (RCS) distribution characteristics of a fighter are simulated using the sharp and smooth RCS distribution features of the corner and the Luneburg ball reflectors, respectively. A new type of Doppler signal generation principle is proposed to design a Doppler frequency simulator to transmit frequency signals by connecting in parallel with the metal layer of the corner reflector and the Luneburg sphere ball, and then transmit through their other end. The existing radar target aircraft cannot simulate the RCS and speed of the targets that are less than 0.005 m² by enhancing the echo intensity of the target location, which makes it impossible for the military to conduct practice drills and evaluate the effectiveness of the air defense systems. The experimental results show that the Doppler frequency simulator successfully simulates the target speed of 0-80 km/h and when the speed is greater than 20 km/h, the error of the simulation frequency is less than 1.5%. The proposed method can provide guidance and a theoretical basis for simulating the speed of various types of aircraft in future work. [ABSTRACT FROM AUTHOR]

We describe a method to calibrate a Software-Defined Radar (SDRadar) system mounted on an uncrewed aerial vehicle (UAV) with an ultra-wideband (UWB) waveform operated in the near-field region. Radar calibration is a prerequisite for using the full capabilities of the radar system to retrieve geophysical parameters accurately. We introduce a framework and process to calibrate the SDRadar with the UWB waveform in the 675 MHz–3 GHz range in the near-field region. Furthermore, we present the framework for computing the near-field radar cross section (RCS) of an external passive calibration target, a trihedral corner reflector (CR), using HFSS software and with consideration for specific antennas. The calibration performance was evaluated with various distances between the calibration target and radar antennas. The necessity for the knowledge of the near-field RCS to calibrate SDRadar was demonstrated, which sets this work apart from the standard method of using a trihedral CR for backscatter radar calibration. We were able to achieve approximately 0.5 dB accuracy when calibrating the SDRadar in the anechoic chamber using a trihedral CR. In outdoor field conditions, where the ground rough surface scattering effects are present, the calibration performance was lower, approximately 1.5 dB. A solution is proposed to overcome the ground effect by elevating the CR above the ground level, which enables applying time-gating around the CR echo, excluding the reflection from the ground.

The results of the interferometric processing and analysis of European spaceborne synthetic aperture radar (SAR) Sentinel-1 acquired over the territory of Norilsk thermal power plant TPP-3 between July 2017 and August 2020 are presented. Twelve-day differential interferograms allow the estimation of the stability of the position of all TPP-3 oil reservoirs with respect to reference known stable targets. The strong distorting influence of meteorological precipitation, as well as of the freeze–thaw processes of snow cover on the TPP-3 territory, on the quality of interferometric phase measurements is noted. It is found that on all of the twelve-day interferometric observation intervals from July 2019 to August 2020 made in warm seasons, the relative position of all four reservoirs and the adjacent territory is stable within the accuracy of about 1.3 mm. According to observations of the reservoirs between July 2017 and August 2020 using summer interferograms with a one-year interval between image acquisitions, the long-term stability of the position is about 4 mm. We can conclude that the reservoir damage was not caused by areal displacements of the scattering surfaces in the study area, supposedly due to the melting of permafrost in the area of the reservoirs. [ABSTRACT FROM AUTHOR]

With the growing availability of accurate and long-term measurements of displacements of technical infrastructure elements, there is a growing interest in the automated processing of acquired data. Various methods can be used for monitoring; however, radar interferometry and Global Navigation Satellite Systems (GNSS) measurements are among the best for long-term monitoring. GNSS allows for continuous monitoring of individual points, while radar interferometry allows only periodic data collection but with an areal coverage. Radar interferometry can also reach a better precision under certain conditions; therefore, it appears to be more appropriate. Automated systems are being developed that allow not only to process radar data but also to detect anomalies in vertical displacement. It is advisable to have a testing polygon for their verification, enabling the comparison of the automated processing of radar interferometry with an independent GNSS measurement. In autumn 2019, a testing polygon was built at the Department of Geoinformatics, HGF VSB – Technical University of Ostrava, consisting of three corner reflectors. Two are fixed, but one, complemented by a GNSS receiver, has an adjustable height. The article describes its construction and presents the first results of comparing automated radar interferometry processing with GNSS measurements.

Ship target detection using radar has important applications in the military and civilian fields. As a decoy, the corner reflector (CR) can successfully deceive a radar by its strong radar cross-section (RCS) to protect a ship. In order to discriminate between a CR and ship, this paper proposes a discrimination method based on three-dimensional characteristics. First, we deduce the basic scattering of CR by the high-frequency electromagnetic theory, and propose a CR decomposition which can solve the problem that the Krogager decomposition has terrible errors in clutter. Then, we introduce the definition of the main scattering polarization and give the multi-dimensional characteristic of CR. Subsequently, we analyze the spatial-time characteristic of radar based on the three-dimensional proportional guidance. With the CR mean square error (MSE), a CR discrimination method is proposed based on the time-spatial-polarization (TSP) joint domains. Finally, the proposed method is analyzed and compared using the fully polarimetric data of Feko software, which can achieve 95% discrimination probability and 4.1% false alarm probability. [ABSTRACT FROM AUTHOR]

The emergence and popularization of various fifth-generation fighter jets with supersonic cruise, super maneuverability, and stealth functionalities have raised higher and more comprehensive challenges for the tactical performance and operational indicators of air defense weapon systems. The training of air defense systems requires simulated targets; however, the traditional targets cannot simulate the radar cross-section (RCS) distribution characteristics of fifth-generation fighter aircrafts. In addition, the existing target aircrafts are expensive and cannot be mass-produced. Therefore, in this paper, a corner reflector and a Luneburg ball reflector with RCS distribution characteristics of a fifth-generation fighter in a certain spatial area are designed for target simulation. Several corner reflectors and Luneburg balls are used to form an array to realize the simulations. The RCS value and distribution characteristics of the target can be combined with fuzzy clustering and a single-chip microcomputer to design an intelligent switching system, which improves the practicability of the intelligent target design proposed in this paper. [ABSTRACT FROM AUTHOR]

The traditional corner reflector is a type of classical passive jamming equipment but with several shortcomings, such as fixed electromagnetic characteristics and a poor response to radar polarization. In this paper, an eight-quadrant corner reflector equipped with an electronically controlled miniaturized active frequency-selective surface (MAFSS) for X band is proposed to obtain better radar characteristics controllability and polarization adaptability. The scattering characteristics of the new eight-quadrant corner reflector for different switchable scattering states (penetration/reflection), frequency and polarization are simulated and analyzed. Results show that the RCS modulation depth, which is jointly affected by the electromagnetic wave frequency and incident directions, can be maintained above 10 dB in the majority of directions, and even larger than 30 dB at the resonant frequency. Moreover, the RCS adjustable bandwidth can be as wide as 1 GHz in different incident directions. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The polarimetric distortions present in the polarimetric SAR (PolSAR) data sets leads to unexpected results from the polarimetric decomposition and classification models, which in turn result in the ground target misinterpretation. The most important polarimetric distortions in airborne PolSAR data sets are the channel imbalance and crosstalk. The minimization of these polarimetric distortions using polarimetric calibration techniques is very important to carry out the quantitative analysis using PolSAR data and time series analysis and to compare results between different sensors. In the current state of the art, the spatial variability of the polarimetric distortions at different slant‐range positions in the data set was not completely analyzed and also the temporal variability of the polarimetric distortions using multiple data sets needs to be more investigated. Therefore, the main objectives of this study were to develop an operational processor to perform the external polarimetric calibration of the L‐band Uninhibited Aerial Vehicle Synthetic Aperture Radar system and to analyze the spatio‐temporal behavior of the polarimetric distortions. The polarimetric distortion matrix (PDM) was formulated after considering the crosstalk and channel imbalance polarimetric distortions to derive the scattering matrix free from all kinds of polarimetric distortions from the observed scattering matrix. The Quegan, improved Quegan, and Ainsworth methods for polarimetric calibration were implemented to solve the PDM. The residual channel imbalance and crosstalk after polarimetric calibration were estimated to compare the calibration efficiency of these methods. After that, a spatio‐temporal analysis was carried out with several data sets to assess the spatio‐temporal behavior of these polarimetric distortions. The polarimetric signatures and the coherency matrix behavior of the trihedral corner reflectors were used to analyze the ground target characterization improvement after polarimetric calibration. The results obtained from this study revealed that the crosstalk is the major cause for the polarimetric distortions and the channel imbalance and phase bias present in the data sets were not high. From the spatio‐temporal analysis, it was found that the variability of these polarimetric distortions both in spatial and temporal domains was minimum and can be discarded without causing any considerable error in the polarimetric calibration process. Key Points: The major cause for the polarimetric distortions in the UAVSAR data sets was due to the crosstalkThe channel imbalance and phase bias distortions were not high for all the data setsPolSAR calibration involves the use of Quegan, Improved Quegan, and Ainsworth methods in this study [ABSTRACT FROM AUTHOR]

In this article, we devise a polarimetric calibration method utilizing only three types of calibration targets, i.e., trihedral, dihedral, and a 22.5°-rotated dihedral corner reflectors and requiring no assumptions on the scene statistics. The influence of the roll angle in a 22.5°-rotated dihedral corner reflector is assessed by a full-wave numerical simulation. The effectiveness and accuracy of the method are verified with a ground-based synthetic aperture radar system and an airborne L-band Pi-SAR data. We demonstrate that an amplitude error as low as 0.5 dB and a phase error within 3° can be achieved, showing an excellent agreement between the theoretical and calibrated polarimetric signatures for the reference targets. We further exploit the calibration on the Pauli decomposition, Yamaguchi four-component decomposition, and the estimation of the polarimetric parameters derived from target scattering vector method decomposition to show the superior performance of the devised calibration method.

Ground deformation in the coal mining area of Northwestern China is usually featured by large and inconsistent subsidence. Large subsidence brings great challenge to Differential Interferometric Synthetic Aperture Radar (DInSAR) and Permanent Scatterer Interferometry (PSI) technology due to the pixel-level offset in the range direction after co-registration, which could directly result in complete coherence loss even for the artificial Corner Reflectors (CRs). Offset tracking provides an alternative to capture the large deformation although the results could be biased due to the large deformation gradient and use of fixed correlation window size. In this paper, the point-like target (PT) offset tracking method is introduced to deformation monitoring in coal mining area with a levelly decreasing correlation window size. For each PT-centered SLC patch in the reference SAR image, the estimate from the larger correlation window will serve as a guide for the smaller one to locate the matching SLC patch in the slave SAR image, thus providing a guarantee that the residual offsets to be estimated remain to be a small fraction of the decreasing patch size. The offset estimates were evaluated by ground surveying results at 34 CRs obtained using single reference real-time kinematic (RTK) GPS technique, with a RMS error of 1/13-1/14 SLC pixel in both the range and azimuth directions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Remote Sensing is the property of Editorial Office of Journal of Remote Sensing & Science Publishing Co. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the growing availability of accurate and long-term measurements of displacements of technical infrastructure elements, there is a growing interest in the automated processing of acquired data. Various methods can be used for monitoring; however, radar interferometry and Global Navigation Satellite Systems (GNSS) measurements are among the best for long-term monitoring. GNSS allows for continuous monitoring of individual points, while radar interferometry allows only periodic data collection but with an areal coverage. Radar interferometry can also reach a better precision under certain conditions; therefore, it appears to be more appropriate. Automated systems are being developed that allow not only to process radar data but also to detect anomalies in vertical displacement. It is advisable to have a testing polygon for their verification, enabling the comparison of the automated processing of radar interferometry with an independent GNSS measurement. In autumn 2019, a testing polygon was built at the Department of Geoinformatics, HGF VSB – Technical University of Ostrava, consisting of three corner reflectors. Two are fixed, but one, complemented by a GNSS receiver, has an adjustable height. The article describes its construction and presents the first results of comparing automated radar interferometry processing with GNSS measurements. [ABSTRACT FROM AUTHOR]

The emergence and popularization of various fifth-generation fighter jets with supersonic cruise, super maneuverability, and stealth functionalities have raised higher and more comprehensive challenges for the tactical performance and operational indicators of air defense weapon systems. The training of air defense systems requires simulated targets; however, the traditional targets cannot simulate the radar cross-section (RCS) distribution characteristics of fifth-generation fighter aircrafts. In addition, the existing target aircrafts are expensive and cannot be mass-produced. Therefore, in this paper, a corner reflector and a Luneburg ball reflector with RCS distribution characteristics of a fifth-generation fighter in a certain spatial area are designed for target simulation. Several corner reflectors and Luneburg balls are used to form an array to realize the simulations. The RCS value and distribution characteristics of the target can be combined with fuzzy clustering and a single-chip microcomputer to design an intelligent switching system, which improves the practicability of the intelligent target design proposed in this paper.

Ship target detection using radar has important applications in the military and civilian fields. As a decoy, the corner reflector (CR) can successfully deceive a radar by its strong radar cross-section (RCS) to protect a ship. In order to discriminate between a CR and ship, this paper proposes a discrimination method based on three-dimensional characteristics. First, we deduce the basic scattering of CR by the high-frequency electromagnetic theory, and propose a CR decomposition which can solve the problem that the Krogager decomposition has terrible errors in clutter. Then, we introduce the definition of the main scattering polarization and give the multi-dimensional characteristic of CR. Subsequently, we analyze the spatial-time characteristic of radar based on the three-dimensional proportional guidance. With the CR mean square error (MSE), a CR discrimination method is proposed based on the time-spatial-polarization (TSP) joint domains. Finally, the proposed method is analyzed and compared using the fully polarimetric data of Feko software, which can achieve 95% discrimination probability and 4.1% false alarm probability.

The traditional corner reflector is a type of classical passive jamming equipment but with several shortcomings, such as fixed electromagnetic characteristics and a poor response to radar polarization. In this paper, an eight-quadrant corner reflector equipped with an electronically controlled miniaturized active frequency-selective surface (MAFSS) for X band is proposed to obtain better radar characteristics controllability and polarization adaptability. The scattering characteristics of the new eight-quadrant corner reflector for different switchable scattering states (penetration/reflection), frequency and polarization are simulated and analyzed. Results show that the RCS modulation depth, which is jointly affected by the electromagnetic wave frequency and incident directions, can be maintained above 10 dB in the majority of directions, and even larger than 30 dB at the resonant frequency. Moreover, the RCS adjustable bandwidth can be as wide as 1 GHz in different incident directions.

In this article, we devise a polarimetric calibration method utilizing only three types of calibration targets, i.e., trihedral, dihedral, and a 22.5°-rotated dihedral corner reflectors and requiring no assumptions on the scene statistics. The influence of the roll angle in a 22.5°-rotated dihedral corner reflector is assessed by a full-wave numerical simulation. The effectiveness and accuracy of the method are verified with a ground-based synthetic aperture radar system and an airborne L-band Pi-SAR data. We demonstrate that an amplitude error as low as 0.5 dB and a phase error within 3° can be achieved, showing an excellent agreement between the theoretical and calibrated polarimetric signatures for the reference targets. We further exploit the calibration on the Pauli decomposition, Yamaguchi four-component decomposition, and the estimation of the polarimetric parameters derived from target scattering vector method decomposition to show the superior performance of the devised calibration method. [ABSTRACT FROM AUTHOR]

Over the past few decades, the global population and the built environment’s vulnerability to natural hazards have risen dramatically. As a result, decisive actions, such as the SENDAI framework, have emerged to foster a global culture of successful disaster risk reduction policies, including actions to mitigate the social and economic impact of geohazards. The effective study of natural disasters requires meticulous and precise monitoring of their triggering factors, with ground- and space-based techniques. The integration of GNSS and SAR observations through the establishment of permanent infrastructures, i.e., Continuously Operating Reference Stations (CORS) networks and arrays of Corner Reflectors (CRs), may form a seamless ground displacement monitoring system. The current research literature provides fragmented guidelines, regarding the co-location of SAR and GNSS permanent infrastructures. Furthermore, there exist no guidelines for the determination of the most suitable locations using a holistic approach, in terms of criteria and required data. The purpose of this paper is to present a semi-automatic multicriteria site suitability analysis and evaluation of candidate sites for the installation of a permanent CORS and two CRs; one for each pass, taking into account various parameters and criteria. The first results demonstrate that the collocation of SAR and GNSS permanent infrastructures, utilizing a holistic criteria-based approach, is successful and complies with all the literature’s requirements.

To verify the performance of the high-resolution fully polarimetric synthetic aperture radar (SAR) sensor carried by the Xinzhou 60 remote-sensing aircraft, we used corner reflectors to calibrate the acquired data. The target mechanism in high-resolution SAR images is more complex than it is in low-resolution SAR images, the impact of the point target pointing error on the calibration results is more obvious, and the target echo signal of high-resolution images is more easily affected by speckle noise; thus, more accurate extraction of the point target position and the response energy is required. To solve this problem, this paper introduces image context information and proposes a method to precisely determine the integration region of the corner reflector using sliding windows based on the integral method. The validation indicates that the fully polarimetric SAR sensor on the Xinzhou 60 remote-sensing aircraft can accurately reflect the radiometric characteristics of the ground features and that the integral method can obtain more stable results than the peak method. The sliding window allows the position of the point target to be determined more accurately, and the response energy extracted from the image via the integral method is closer to the theoretical value, which means that the high-resolution SAR system can achieve a higher radiometric calibration accuracy. Additionally, cross-validation reveals that the airborne SAR images have similar quality levels to Sentinel-1A and Gaofen-3 images.

The paper describes the development of passive, chipless tags for a novel indoor self-localization system operating at high mm-wave frequencies. One tag concept is based on the low-Q fundamental mode of dielectric resonators (DR) which exhibits peak scattering at its resonance frequency. As the radar cross-section (RCS) of DRs at mm-wave frequencies is far too low for the intended application, arrays of DRs and combinations with dielectric lens and corner reflectors are investigated to boost the RCS while keeping the scattering retro-directive over wide-angle incidence. Satisfactory results are demonstrated experimentally in W-band with metal corner reflectors combined with planar arrays of DRs; the tags produce a high RCS level over a moderately broad angular range and a wide frequency range where they exhibit a notch at the resonance frequency of the dielectric resonators. These designs suffer from low coding range of 3 to 6 bit, degradations of RCS in angular range, and a difficult separation of the tag response from strong clutter. Both the suppression of large clutter interference by using time gating of the tag response and a larger coding range are promised by a chipless tag concept based on multiple high-Q resonators in photonic crystal (PhC) technology. Experimental samples are characterized as transmission resonators and as retro-directive tags at the 230 GHz band. As a concept to boost the retro-directive RCS with a truly wide-angle response, the integration of PhC resonators with a Luneburg lens is discussed. [ABSTRACT FROM AUTHOR]

In this letter, a three-dimensionally printed one-sixteenth fractional spherical homogeneous dielectric lens antenna on a metallic corner reflector is designed. This lens antenna is fed by an open-ended rectangular waveguide for high-gain radiation. The main design concept is to produce an equivalent spherical dielectric lens that is excited by multiple virtual sources arising from the multiple images of the original feed by the corner reflector's walls. Thus, the antenna can retain a compact size with a sufficiently effective aperture to produce a higher radiation gain. In particular, a ray-tracing method of geometrical optics is introduced for easily determining the proper sizes of the corner reflector's walls, which leads the proposed work to be more efficient than using a full-wave simulation. The superiority of the antenna is validated by examining a practical design for a radar system at 9 GHz band. It is found that the optimum dielectric constant (ϵr), ground plane size, and effective aperture area, relatively speaking, depend on the radius of the lens's sphere. This proposed antenna well suits multifeed satellite communication antennas, radar, and other high-gain antennas applications. [ABSTRACT FROM AUTHOR]

The creation of space technology in the Soviet Union in 1957 initiated flights of automated interplanetary stations to the Moon, Venus, and Mars and provided an opportunity for scientists and specialists to begin comprehensive studies of these celestial bodies. Outstanding roles were played in organizing the program by Acads. S.P. Korolev, M.V. Keldysh, A.P. Vinogradov, G.I. Petrov, and R.Z. Sagdeev, among other people. In January 1958, they turned to the Soviet Government with a proposal to carry out work on creating an automated interplanetary station and landing it on the Moon and obtaining photographs of the lunar far side. On December 10, 1959, the Resolution of the Central Committee of the Communist Party of the Soviet Union and the Council of Ministers "On Space Research Development" was issued, which was of great importance for performing scientific experiments to study the Moon and the Solar System planets. In the Resolution, among the main areas in which outer space could be studied, work on the creation of an automated scientific station on the Moon (or in its region) for studying the physical properties of the Earth's satellite and the possible presence of life on it, as well as on the data transmission to the Earth, was distinguished as being of paramount importance. In the period of 1958–1976 in the Soviet Union, a series of landing and orbital automated interplanetary stations was developed to study the lunar surface and near-lunar space. The self-propelled vehicles Lunokhod 1 and 2 were delivered to the Moon for studying the lunar surface in detail and taking samples of lunar soil. [ABSTRACT FROM AUTHOR]

To correctly interpret the estimated displacements in InSAR point clouds, especially in the built environment, these need to be linked to real-world structures. This requires the accurate and precise 3D positioning of each point. Artificial ground control points (GCPs), such as corner reflectors, serve this purpose, but since they require efforts and resources, there is a need for criteria to assess their usefulness. Here we evaluate the value and necessity of using GCPs for different scenarios, concerning the required efforts, and compare this to alternatives such as digital surface models (DSM) and advanced (geo) physical corrections. We consider single-epoch as well as multi-epoch GCP deployment, reflect on the number of GCPs required in relation to the number of SAR data acquisitions, and compare this with digital surface models of different quality levels. Analyzing the geolocation performance using TerraSAR-X and Sentinel-1 data, we evaluate the pros and cons of various deployment options and show that the multi-epoch deployment of a GCP yields optimal geolocalization results in terms of precision, accuracy, and reliability. [ABSTRACT FROM AUTHOR]

In accordance with the weakness of low target strength and obvious frequency characteristics of underwater elastic metal plate corner reflectors,a new air-filled cavity elastic corner reflector is designed.The scattering acoustic fields of underwater air-filled cavity corner reflector and single layer metal sheet corner reflector are simulated and compared by using the structural finite element coupled fluid boundary element method(IBEM). The influences of thickness and incident angle on the target strengths and scattering mechanisms of different corner reflectors within 5-15 kHz frequency of incident wave are analyzed and verified through experiment. The research results show that the air-filled cavity corner reflector has great scattering intensity and no obvious frequency characteristics,and the decoupling effect is obvious.The simulated results are in basic agreement with the experimental results. Compared with the cumbersome single layer metal corner reflector with weak reflection intensity,the air-filled cavity corner reflector has better acoustic reflection performance and lighter weight,and is an ideal underwater acoustic reflection device. [ABSTRACT FROM AUTHOR]

This letter presents a thermally reconfigurable antenna with beam-direction- and beamwidth-switching capability using origami reflectors with smart shape memory polymer (SMP) hinges. The proposed antenna consists of a single monopole antenna with four origami reflectors. We employ SMP hinges to actuate the origami reflectors. When all origami reflectors are unfolded on the ground plane (Mode I), the monopole antenna exhibits omnidirectional radiation because the reflectors operate as dummies. When two origami reflectors are folded perpendicular to the ground plane, forming a corner reflector (Mode II), the proposed antenna operates as a directional antenna. Beam direction can be switched to 45°, 135°, 225°, and 315° by actuating various origami reflector pairs, with increased peak gain from 4.5 dBi (Mode I) to 11 dBi (Mode II). When one origami reflector is folded perpendicular to the ground plane (Mode III), the 3 dB beamwidth increases from 52° (Mode II) to 140° (Mode III). Beam direction of Mode III can also be switched through 0°, 90°, 180°, and 270° by actuating each origami reflector. The proposed antenna performance was successfully demonstrated from electromagnetic simulation and measurement. [ABSTRACT FROM AUTHOR]

For the previously proposed model of the corner reflector with a convex cylindrical surface at the base, intended for simulating crack-like corrosion–mechanical defects, formulas for high-resolution acoustic in-line inspection tool (ILI) have been derived in the geometrical acoustics approximation. Based on simulation results, it is demonstrated that the geometrical characteristics of the proposed model of the corner reflector affect the amplitude of angled incident transverse waves reflected from its surface in comparison with the model of a corner reflector coming to a flat surface prescribed by technical regulations. [ABSTRACT FROM AUTHOR]

This study presents the results obtained from image quality assessment of Radar Imaging SATellite (RISAT-1). Image quality parameters such as spatial resolution, peak to sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) are calculated by the analysis of impulse response function (IRF) of the point target. The study is carried out to assess temporal stability and consistency of image quality parameters obtained from analysis of IRF of 44 point targets. The results obtained from this study show that the mean values of the range and azimuth resolution are 2.048 ± 0.081 m and 3.383 ± 0.097 m for RH and 1.981 ± 0.081 m and 3.348 ± 0.076 m for RV, respectively. PSLR/ISLR values for RH channel are obtained as −26.492 dB/−26.823 dB for azimuth and −19.209 dB/−19.921 dB for the range. For RV channel, PSLR/ISLR values are −26.300 dB/−27.572 dB for azimuth and −19.146 dB/−19.827 dB for range. [ABSTRACT FROM AUTHOR]

Ground-based interferometric radar can realize small regional-scale continuous deformation monitoring with high-accuracy. To investigate the deformation detection capability and accuracy, a set of accuracy verification platform and system are established in this paper. The corner reflectors are arranged at different positions on the roof and the stepping platforms are used to control the corner reflectors and simulate deformation in different values. The deformation corner reflectors, stable points and the surface of the roof constitute a small two-dimensional deformation field. We use the IBIS-L system to finish the deformation detection and analysis. The experimental results show that when the millimeter level deformation occurs in the corner reflectors, the average accuracy of deformation detection of the ground-based interferometric radar IBIS-L system is 0.27 mm, while the sub millimeter level deformation occurs the corner reflectors, its average accuracy is 0.11 mm. This system can realize the sub millimeter level deformation detection in small regional-scale. For the small and slow change, this system has better deformation detection ability and reliability. [ABSTRACT FROM AUTHOR]

Abstract It is already been testified that, with the help of corrugations, depolarizing trihedral corner reflectors can be applied in polarization stimulation of targets. However, how to choose the size of the reflector to stimulate a target is still indistinct. A method of choosing size of depolarizing trihedral corner reflector based on the target data is presented in this article, helping to find the suitable reflectors to realize the polarization stimulation of the target. [ABSTRACT FROM AUTHOR]

Abstract Polarimetric calibration is a critical step to suppress the potential system distortion before implementing any applications for polarimetric synthetic aperture radar (PolSAR). Among all the distortion elements, the crosstalk and cross-pol channel imbalance are generally estimated by the use of natural media, and the co-pol channel imbalance is traditionally solved by the use of corner reflectors (CRs). However, the deployment of ground CRs is costly and may even be impossible in some areas. Many bright point targets, such as poles, lamps, and corner points of structures, are commonly found in manmade regions. In particular, if the object orientation is parallel or perpendicular to the radar flight direction, some points will present similar polarimetric responses to trihedral or dihedral CRs. These points, which are referred to here as "CR-like targets", can be treated as a supplement to approximately solve the system distortion elements when CRs are unavailable. In this paper, we propose a novel step-by-step algorithm to determine the CR-like targets and estimate the co-pol channel imbalance phase in uncalibrated PolSAR imagery. Chinese X-band airborne and C-band satellite PolSAR data were used to test the proposed method. Compared with the CR-derived co-pol channel imbalance phase, the solution errors of the CR-like targets were 1.305° and 0.03° for the X- and C-band experiments, respectively. The results of the experiments confirm that the solutions of the CR-like targets are very close to those of ground-deployed CRs, and the proposed method can be considered as an effective way to calibrate PolSAR images when sufficient CR-like point targets are detected in manmade regions. [ABSTRACT FROM AUTHOR]