Corner Reflector Array Research Articles

An Identification Method of Corner Reflector Array Based on Mismatched Filter through Changing the Frequency Modulation Slope

The corner reflector is an effective means of interference for radar seekers due to its high jamming intensity, wide frequency band, and combat effectiveness ratio. Properly arranging multiple corner reflectors in an array can form dilution jamming that resembles ships, substantially enhancing the interference effect. This results in a significant decline in the precision attack efficiency of radar seekers. Hence, it is critical to accurately identify corner reflector array. The common recognition methods involve extracting features on the high-resolution range profile (HRRP) and polarization domain. However, the former is constrained by the number of corner reflectors, while the latter is affected by the accuracy of polarization measurement, both of which have limited performance on the identification of corner reflector array. In terms of the evident variations in physical structures, there must be differences in their scattering characteristics. To highlight the differences, this paper proposes a new method based on the concept of mismatched filtering, which involves changing the frequency modulation slope of the chirp signal in the filter. Then, the variance of width and intervals within a specific scope are extracted as features to characterize these differences, and an identification process is designed in combination with the support vector machine. The simulation experiments demonstrate that the proposed method exhibits stable discriminative performance and can effectively combat dilution jamming. Its accuracy rate exceeds 0.86 when the signal-to-noise ratio is greater than 0 dB. Compared to the HRRP methods, the recognition accuracy of the proposed algorithm improves 15% in relation to variations in the quantity of corner reflectors.

Study on design and fabrication method of mirror array for dihedral corner reflector array with height distribution

Study on design and fabrication method of mirror array for dihedral corner reflector array with height distribution

A Method for Solving the Field of View Problem in Dihedral Corner Reflector Arrays

A Method for Solving the Field of View Problem in Dihedral Corner Reflector Arrays

10‐2: Line‐Based Modulation Transfer Function Measurement of Aerial Display by Use of Arrayed Optical Elements

We measured the spatial resolution characteristics of aerial displays using a corner‐cube reflector array and a dihedral corner reflector array, both of which are major arrayed optical elements. In this study, we applied the line‐based MTF measurement method to aerial displays. according to floating distances for prospective applications. The MTF measurement results suggest that the arrayed optical element for the aerial display should be selected based on the desired floating distance.

Development of a magnetic cardan suspension coupled with a single actuated axis for gravity assisted pointing of directional devices: A case study of Moon to Earth alignment for a laser ranging reflector

A new class of Lunar Laser Ranging (LLR) experiments has been recently investigated by the international Space Agencies, in order to deploy a set of Next Generation Lunar Reflector (NGLR) on the Moon surface, funded under NASA's Commercial Lunar Payload Services (CLPS) program (Currie et al., 2020). In principle the Cube Corner Reflector (CCR) arrays deployed by Apollo and Lunokhod missions in the 70’s will be flanked (at different locations) by single bigger reflectors, thus removing the systematic errors in the Time of Flight (TOF) measurement induced by the Moon librations (Turyshev et al., 2012).In this paper we describe a mechanism formed by a passive cardan magnetic suspension, dedicated to the alignment of the CCR toward the mean Earth direction. The suspension is able to compensate for the misalignment due to the slope of the landing site that can be different at each site (Zupp, 2013). If proper control of azimuth angle of the spacecraft at touchdown cannot be guaranteed, an additional motor to rotate the magnetic suspension must be provided by the lander, for the alignment toward the mean Earth direction.Once the landing site is defined, the geometry of the retroreflector housing, together with that of the cardan suspension, will autonomously (without human intervention) and passively (without provision of electrical power by the lander) provide the right elevation angle just by gravity, no matter what the morphology of the site is.The mechanical performances of the magnetic suspension have been preliminarily investigated in (Ancillai et al., 2020). The solution presented can be applied to any directional device, requiring pointing capability, like antennas, and can be adopted with low friction rolling bearings as well.

54‐3: Reduced Solar‐Loading Using Micro‐Mirror Array in Automotive HUD

Automotive head‐up displays (HUDs) use windshields as part of the display system and are used as partial reflectors for reflecting the images formed inside the dash board towards the driver. The locations of the aerial images are usually at the bumper of the vehicle and beyond, depending on the requirements. One of the major issues with such HUD system is the solar loading created by sunlight shining into the system through the image forming optics with focusing properties especially when the sun is shining into the HUD system in an off‐axis manner. This paper describes a HUD system where the imaging system uses a Micro‐Mirror Array Plate (MMAP) with an optical design that eliminates the issues associated with the off‐axis sunlight. Solar loading is an important design criterion as the HUD optics concentrate the sunlight to levels that can damage the display panel. Based on the aerial imaging properties of MMAP, this design would be applicable to the use of Dihedral Corner Reflector Array (DCRA), and Aerial Imaging by Retro‐Reflection (AIRR). Bench‐top system has been set up using MMAP from ASKA3D, Japan with the expected imaging properties. A complete prototype is being fabricated and will be reported.

Radiometric calibration stability assessment of Sentinel-1B using point targets at Surat Basin, Australia

AbstractThe launch of the Sentinel-1B satellite in April 2016 completed the two-satellite synthetic aperture radar (SAR) constellation of the European Copernicus Sentinel-1 mission. The European Space Agency executed the calibration of this sensor during the commissioning phase and an independent calibration by the German Aerospace Center (DLR) in 2016. The calibration parameters must be monitored to assess the stability of the instrument. This study reports the temporal stability assessment of radiometric calibration and image quality parameters of Sentinel-1B SAR data using the corner reflector (CR) array, Surat Basin, Australia. Impulse response functions generated from the CRs in the satellite images were used to derive the image quality parameters. The average radar cross-section difference between estimated and theoretical values (38.40 dB m2) was 0.53 dB m2 for 1.5 m CRs, which is accordant with the absolute radiometric accuracy specified for the Sentinel-1 SAR system. Derived image quality parameters viz. the mean peak-to-side lobe ratio, mean integrated side lobe ratio, and spatial resolutions in the range and azimuth directions were found to be accordant with the specified value for the Sentinel-1 SAR system. The results indicate the excellent quality of the Sentinel-1B data.

Design of ghost-free aerial display by using prism and dihedral corner reflector array

In a dihedral corner reflector array (DCRA) used as an aerial display, the observer can directly touch aerial images. However, in this optical element, the visibility of the aerial image is reduced by stray light, called a ghost. Although ghost formation can be suppressed using a louver, the viewing angle and brightness of the aerial image also decrease. This paper proposes the design of a ghost-free aerial display using a prism and DCRA. Based on experimental results, the ghost brightness with the proposed method was only about 14% of the DCRA at front. In addition, the aerial image produced by the proposed device was the brightest for 0–20°.

A method for improving the resolving power of edible dihedral corner reflector arrays

A method for improving the resolving power of edible dihedral corner reflector arrays

Novel Corner-Reflector Array Application in Essential Infrastructure Monitoring

High precision monitoring of infrastructure using artificial reflectors is possible with freely available Sentinel-1 data, but large reflectors are needed. We find that a triangular trihedral corner reflector should typically have at least 1 m inner leg length. As such large reflectors are often not feasible for use in urban areas for essential infrastructure monitoring, we designed a multiple corner-reflector array to replace a single corner reflector with an inner leg length of 1 m. In this case, we use four reflectors where each of them is a truncated triangular trihedral with an inner leg length of 0.33 m. We measured InSAR amplitude, phase and coherence of this reflector array with various configurations of alignments of the array. We find that as long as great care is taken in the relative positioning of the four corner reflectors, so that they constructively interfere, each horizontal or vertical configuration provides the expected amplitude, coherence and phase stability. Applications of multiple small corner reflectors in urban areas range from essential infrastructure monitoring (e.g bridges, overpasses, tunnel constructions), through assessment of structural health of buildings, to monitoring highway and railway embankments. We show that the multiple corner array works when placed in a single InSAR resolution cell, but depending on the application, the number and projection of corner reflectors can be varied, as long as sufficient signal-to-clutter ratio is achieved in the area of interest.

Binocular dynamic holographic floating image display.

This paper proposes a binocular holographic floating display. The device consists of two phase-modulation spatial light modulators (SLM) and a dihedral corner reflector array (DCRA) element. The conjugate images of the SLMs generated by the DCRA become the system's exit pupils. Exit pupils that are larger than the pupils of human eyes are arranged to locate at the position of observer's eyes. Therefore, the dimension of the SLM will not limit the viewing angle, although the pixel pitch of the SLM still limits the maximum field of view. For the laser light source, the resolution of the images can achieve 3 arc minutes when the distance between images and DCRA is less than 20 cm. The full-color display function is also performed in the proposed device.

See-through aerial display using a dihedral corner reflector array and hologram mirrors.

In this study, we reveal a novel aerial display system, to the best of our knowledge, that combines volume hologram mirrors with a dihedral corner reflector array (DCRA). The suggested aerial display has a see-through capability, which allows for a new design of aerial displays by combining with other types of displays. Furthermore, the virtual image, which frequently disrupts the observation of aerial images, can be suppressed by the Bragg condition of the volume hologram. The color dispersion in the holograms is efficiently compensated by employing features of the DCRA. The findings of preliminary experiments are demonstrated using a DCRA device and full-color hologram mirrors.

Compact in-line floating display system using a dihedral corner reflector array

We propose a compact type floating display system using a dihedral corner reflector array. Conventional floating displays using the dihedral corner reflector array usually have a folded configuration which makes the system bulky. The proposed technique achieves the compact in-line configuration using a pair of decentered lenses. The decentered lenses make the effective incident angle to the dihedral corner reflector array be tilted while maintaining the display panel and the dihedral corner reflector array in parallel. The ghost images are also refracted largely by the decentered lenses, being separated from the desired floating images. The proposed technique is verified by optical experiments.

Time-Domain Scattering Characteristics and Jamming Effectiveness in Corner Reflectors

The outboard corner reflectors are widely used as a countermeasure to radar tracking and detection. Therefore, it is essential to determine the composite time-domain scattering characteristics of the corner reflector and ship against the sea background and the jamming effectiveness of the corner reflector array. In this paper, the composite electromagnetic scattering characteristics of ship target, corner reflector, and the sea surface are studied based on the time-domain bouncing ray method (TDSBR). The radar echo and broadband radar cross section (RCS) results for the time domain pulse incident are also obtained and the high-resolution range profile (HRRP) is calculated. We then devise an evaluation system based on centroid jamming intensity and range profile similarity to determine the jamming characteristics of passive jamming. We further propose an array composing of three sizes of corner reflectors. Finally, the centroid jamming effectiveness is analyzed by comparing the RCS of the corner reflector array and the ship, and the deception jamming effectiveness is measured by calculating the range profile similarity based on the cosine similarity method and the range profile peak envelope overlap. Simulation results show that the reflector array can achieve a good performance both for centroid and range profile deception. The simulation results given and the evaluation method proposed in this paper provides significant practical insights into the design and analysis of the passive jamming systems.

Design and Evaluation of Optical See-Through Head-Mounted Display With Wide FOV Based on Dihedral Corner Reflector Array

Existing optical see-through (OST) head-mounted displays (HMDs) generally utilize plane mirrors with partial transmission to merge the virtual and real-world scenes, which inducing the vignetting effect to result in small field of view (FOV). Accordingly, this paper proposes an OST-HMD system in which a rotationally-symmetric eyepiece with a wide FOV of ±30 degrees is coupled with a dihedral corner reflector array (DCRA) to achieve a sufficient relief distance to project all of the exit rays of the eyepiece into the pupil. The feasibility of the proposed system is evaluated by means of numerical simulations based on optical models of the HMD lens, DCRA and human eye. The simulation results show that the eye can receive the display information in the wide FOV with a sufficient relief distance through this kind of the OST-HMD development.

Suppression of floating image degradation using a mechanical vibration of a dihedral corner reflector array.

Dihedral corner reflector arrays (DCRAs) are imaging devices that form real images and are used in a variety of applications, including floating virtual touchscreens and image presentation around physical objects. However, they induce several types of degradations to floating images. It is desirable to suppress these degradations to provide better viewing experiences. This paper proposes a method of suppressing degradations which appear as high-frequency noise by using mechanical vibration. The effects of vibrating the DCRA were confirmed through an analysis of the floating image quality in the frequency domain.

POLARIMETRIC CALIBRATION OF L-BAND AIRBORNE SAR DATA

Abstract. The PolSAR calibration ensures that the relationship between the SAR observations and the target characteristics on the ground are consistent and resembles the theoretical estimation which in turn improves the overall data quality. Essentially, calibration prevents the propagation of uncertainty into further analysis to characterise the target. In this study, the UAVSAR L-Band data of Rosamond dry lake bed has been calibrated. The calibration of amplitude and phase are carried out with the help of the corner reflector array present in the Rosamond site. The dataset is further calibrated for the crosstalk and channel imbalance using the Quegan’s distortion model. Since the crosstalk distortion model requires an accurate estimation of the covariance matrix, the optimal kernel size for the its computation is selected based on the distortion model behaviour with varying window sizes. Furthermore, the effectiveness of the calibration process has been studied using polarimetric signatures and other statistical measures.

In-Depth Verification of Sentinel-1 and TerraSAR-X Geolocation Accuracy Using the Australian Corner Reflector Array

This article shows how the array of corner reflectors (CRs) in Queensland, Australia, together with highly accurate geodetic synthetic aperture radar (SAR) techniques-also called imaging geodesy-can be used to measure the absolute and relative geometric fidelity of SAR missions. We describe, in detail, the end-to-end methodology and apply it to TerraSAR-X Stripmap (SM) and ScanSAR (SC) data and to Sentinel-1 interferometric wide swath (IW) data. Geometric distortions within images that are caused by commonly used SAR processor approximations are explained, and we show how to correct them during postprocessing. Our results, supported by the analysis of 140 images across the different SAR modes and using the 40 reflectors of the array, confirm our methodology and achieve the limits predicted by theory for both Sentinel-1 and TerraSAR-X. After our corrections, the Sentinel-1 residual errors are 6 cm in range and 26 cm in azimuth, including all error sources. The findings are confirmed by the mutual independent processing carried out at University of Zurich (UZH) and German Aerospace Center (DLR). This represents an improvement of the geolocation accuracy by approximately a factor of four in range and a factor of two in azimuth compared with the standard Sentinel-1 products. The TerraSAR-X results are even better. The achieved geolocation accuracy now approaches that of the global navigation satellite system (GNSS)-based survey of the CRs positions, which highlights the potential of the end-to-end SAR methodology for imaging geodesy.

Design of ghost-free floating 3D display with narrow thickness using offset lens and dihedral corner reflector arrays.

A floating 3D display with a dihedral corner reflector array (DCRA) is presented to improve space efficiency and eliminate ghost images. Floating displays using a DCRA have the space efficiency problem of having a system thickness equal to the height of the floating image and the problem of a ghost image interrupting the visibility of the floating display. The DCRA is analyzed to find the ghost image region. Based on the analysis, an off-axis integral floating display is placed outside the ghost image region to avoid the ghost image. To increase space efficiency, the optical path is folded using a mirror. In addition, the off-axis integral floating display is used to create a tilt angle for projecting the input image onto the DCRA in a proposed confined and narrow system to observe the complete 3D image. The effectiveness of the system was verified through simulations and experiments.

Air Floating Image based on a Dihedral Corner Reflector Array

Air Floating Image based on a Dihedral Corner Reflector Array