Wide Field Of View Research Articles

Leveraging CNNs for Panoramic Image Matching Based on Improved Cube Projection Model

Three-dimensional (3D) scene reconstruction plays an important role in digital cities, virtual reality, and simultaneous localization and mapping (SLAM). In contrast to perspective images, a single panoramic image can contain the complete scene information because of the wide field of view. The extraction and matching of image feature points is a critical and difficult part of 3D scene reconstruction using panoramic images. We attempted to solve this problem using convolutional neural networks (CNNs). Compared with traditional feature extraction and matching algorithms, the SuperPoint (SP) and SuperGlue (SG) algorithms have advantages for handling images with distortions. However, the rich content of panoramic images leads to a significant disadvantage of these algorithms with regard to time loss. To address this problem, we introduce the Improved Cube Projection Model: First, the panoramic image is projected into split-frame perspective images with significant overlap in six directions. Second, the SP and SG algorithms are used to process the six split-frame images in parallel for feature extraction and matching. Finally, matching points are mapped back to the panoramic image through coordinate inverse mapping. Experimental results in multiple environments indicated that the algorithm can not only guarantee the number of feature points extracted and the accuracy of feature point extraction but can also significantly reduce the computation time compared to other commonly used algorithms.

Front-End Electronics of CXPD for Measuring Transient X-Ray Sources

The Low Energy Polarization Detector (LPD), a payload of the POLAR-2 mission, is a soft X-ray polarization detector with a wide field of view and a large array aimed at measuring X-ray transients. These transients exhibit rapid intensity changes of several orders of magnitude, making it crucial for polarization detectors to have front-end electronics with low dead time, fast readout capabilities, high time resolution, and good energy resolution. In this paper, we present the design of the front-end electronics, which consist of a rolling shutter CMOS pixel charge sensor - Topmetal- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">II</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> , and a gas microchannel plate (GMCP) bottom amplifier circuit. Topmetal- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">II</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ’s rolling shutter readout provides fast scanning of large pixel arrays without dead time and acquires two-dimensional images of photoelectron tracks. Meanwhile, the GMCP’s bottom amplifier circuit measures the energy and time of the X-ray. The front-end electronics are employed by the CubeSat CXPD (Cosmic X-ray Polarimeter Detector), a proto-flight model of the LPD, achieving a timing resolution of 19 ns, and an energy resolution of 16.5% for linearly polarized X-rays at 8 keV.

Enhancing process efficiency through improved temperature measurement: the EMPRESS projects

EMPRESS 2 is a European project to enhance the efficiency of high value manufacturing processes by improving temperature measurement and control capability. This project seeks to address four contemporary thermometry challenges in this sector, and new developments from this and its predecessor project, EMPRESS, will be described:• Below 1000°C many industrial processes require reliable surface thermometry e.g. welding, coating, forging and forming. Conventional non-contact surface thermometry techniques e.g. thermal imaging are prone to large errors (tens of degrees) due to reflected thermal radiation and unknown emissivity. Contact thermometry approaches are prone to similarly large errors. Traceable imaging phosphor thermometry is being developed to overcome these difficulties, and is being combined with quantitative thermography to determine emissivity for thermometry over wide fields of view.• Above 1300°C sensor drift is a significant unaddressed issue for casting, forging and heat treatment, causing large errors. There is a need for more stable sensors and standardisation of at least one new thermocouple type to fill the gap from 1300°C to 1800°C. This is being addressed through improved Pt-Rh thermocouples and optimisation of double-walled mineral insulated, metal sheathed thermocouples by mitigating insulation breakdown and drift effects.• Combustion temperature measurement is very challenging and traceability is almost non-existent; for example, thermocouple measurements of flame temperatures can be in error by hundreds of degrees. A ‘standard flame’ that can be transported to users’ sites has been developed, and is being deployed in several high value manufacturing and industrial applications to a) demonstrate the possibility of reducing flame temperature uncertainties by at least an order of magnitude and b) for the first time to demonstrate in-situ traceability to the International Temperature Scale of 1990 (ITS-90).• Many processes are not amenable to any conventional thermometry techniques due to inaccessibility, ionising radiation, electromagnetic interference, and contamination; here methods based on optical fibres are ideal but there are no traceable calibration techniques for such sensors currently available. A suite of different fibre-optic thermometers and calibration techniques is being developed to address this. In some cases (ionising radiation) darkening of the fibre is a problem, and this is being overcome by the development of novel thermometry approaches based on practical ‘hollow core’ fibres.

ДВУХПОЗИЦИОННЫЙ ГЕОРАДИОЛОКАТОР НА БПЛА ДЛЯ ОПЕРАТИВНОГО МОНИТОРИНГА ПОДПОВЕРХНОСТНЫХ ВОДНЫХ РЕСУРСОВ

This paper considers the implementation of a two-position ground penetrating radar (GPR) located on board unmanned aerial vehicles (UAVs) and designed for the operational search for groundwater in arid and desert regions of Mongolia, which is an extremely urgent task. With the help of synthesizing the GPR antenna aperture on the UAV, a significant increase in information content is achieved compared to existing GPRs, since it becomes possible to obtain a panoramic radar image of the subsurface layers of the probed medium with the required resolution with a sufficiently wide swath. On the other hand, the necessary efficiency (required, for example, when monitoring vast desert areas) can only be achieved with a sufficiently wide field of view created on the basis of the two-position sounding principle, where the emitting and receiving signals are formed and processed on UAVs of different or equal heights flying with the same speed and spaced orthogonally to the direction of their movement, which makes it possible to use quasi-mirror reflection. In this case, the swath will be noticeably larger than in the case of nadir sounding. In a condensed form, the article considers the following issues: the model of a subsurface aquifer, the geometry of a two-position GPR in the quasi-mirror sounding mode, up to the features of synthesizing the aperture (Doppler narrowing of the radiation pattern) of the receiving antenna, resolution, the required potential of a two-position GPR for reliable detection of an aquifer subsurface horizon, accuracy measurements of its depth, as well as the need for experimental work to test the theoretical provisions.

ASPHERIC TWO-MIRROR TELESCOPES OF NANOSATELLITES FOR REMOTE EARTH SENSING AND SEARCH OF MINERALS

The optical system is one of the important components of any space satellite used to observe the Earth's surface or astronomical objects. Due to the small overall size of nanosatellites, lens objectives with the relatively short focal length are often used. The latter provides the sufficiently wide field of view, but limits the spatial resolution of obtained images. In addition, to address various problems in agriculture and geodesy, it is important to obtain images of the earth's surface in different spectral ranges. This fact prevents the application of widespread commercial photographic lenses corrected for the visible spectral range. The article presents the results of the automated parametric synthesis of centered and decentered aspheric optical systems of mirror telescopes based on the Ritchie-Chretien scheme. The obtained optical systems have the focal length of 547 mm, the square entrance aperture of 80×80 mm, and the axial length that does not exceed the size of two CubeSat units. The angular field of view of the telescopes, which is equal to 0.7° in diagonal, enables to apply modern matrix image sensors having a diagonal of the sensitive area up to 6.7 mm. For an axial beam, 90% of the radiation energy falls into a square area of the image with a side of 2.5 μm. The maximum value of relative distortion does not exceed 0.4 %. The considered mirror systems do not have chromatic aberrations, which makes it possible to obtain high-quality images not only in the visible spectral range, but also in several infrared sub-bands. The given results of the aberration analysis testify to the high image quality achieved in both variants. The presented optical systems can observe a rectangular area of the Earth's surface with the diagonal size of about 7.9 km from the satellite’s track height of 650 km. When using a multi-element image detectors with the pixel size of 3 μm, the geometric projection of one pixel on the Earth's surface will be equal to 3.6 m.

Frequency-angular resolving LiDAR using chip-scale acousto-optic beam steering.

Thanks to its superior imaging resolution and range, light detection and ranging (LiDAR) is fast becoming an indispensable optical perception technology for intelligent automation systems including autonomous vehicles and robotics1-3. The development of next-generation LiDAR systems critically needs a non-mechanical beam-steering system that scans the laser beam in space. Various beam-steering technologies4 have been developed, including optical phased array5-8, spatial light modulation9-11, focal plane switch array12,13, dispersive frequency comb14,15 and spectro-temporal modulation16. However, many of these systems continue to be bulky, fragile and expensive. Here we report an on-chip, acousto-optic beam-steering technique that uses only a single gigahertz acoustic transducer to steer light beams into free space. Exploiting the physics of Brillouin scattering17,18, in which beams steered at different angles are labelled with unique frequency shifts, this technique uses a single coherent receiver to resolve the angular position of an object in the frequency domain, and enables frequency-angular resolving LiDAR. We demonstrate a simple device construction, control system for beam steering and frequency domain detection scheme. The system achieves frequency-modulated continuous-wave ranging with an 18° field of view, 0.12° angular resolution and a ranging distance up to115 m. The demonstration can be scaled up to an array realizing miniature, low-cost frequency-angular resolving LiDAR imaging systems with a wide two-dimensional field of view. This development represents a step towards the widespread use of LiDAR in automation, navigation and robotics.

Optical Alignment Method for the PRIME Telescope

In this paper, we describe the optical alignment method for the Prime-focus-Infrared Microlensing Experiment (PRIME) telescope which is a prime-focus near-infrared (NIR) telescope with a wide field of view for the microlensing planet survey toward the Galactic center that is the major task for the PRIME project. There are three steps for the optical alignment: preliminary alignment by a laser tracker, fine alignment by intra- and extra-focal (IFEF) image analysis technique, and complementary and fine alignment by the Hartmann test. We demonstrated that the first two steps work well by the test conducted in the laboratory in Japan. The telescope was installed at the Sutherland Observatory of South African Astronomical Observatory in August, 2022. At the final stage of the installation, we demonstrated that the third method works well and the optical system satisfies the operational requirement.

Diagnosis of Proximal Dental Caries Using Intraoral and Extraoral Bitewing Radiographs: A Narrative Review

Radiographic examination using intraoral bitewing (IOBW) radiography is an ideal examination to detect proximal carious lesions. Besides the risk of triggering gag reflex, the IOBW technique is susceptible to SARS-CoV-2 virus transmission through saliva-contaminated film or digital sensor. Examination using intraoral techniques during the COVID-19 pandemic should be avoided to minimize cross-contamination of the SARS-CoV-2 virus. The alteration from using IOBW to extraoral bitewing (EOBW) radiography can be a promising alternative to overcome these problems. This review article aims to describe the advantages of the EOBW technique and compares diagnostic performance of IOBW and EOBW radiographs in detecting proximal dental caries. The databases used for literature searching in the review include Google Scholar, PubMed, and Science Direct. The inclusion criteria were original articles, case reports, and English and Indonesian scientific textbooks published from 2010 to 2021. The exclusion criteria were article reviews and original articles that did not contain research methods. A total of 29 literatures were discussed in this narrative review. The EOBW technique is recommended during the COVID-19 pandemic to reduce the risk of cross-contamination in dental radiography. This technique ensures the patient for a more comfortable procedure, with shorter time needed and a wider field of view that allows it to be used to detect bone loss in the alveolar crest. Sensitivity, specificity, and area-under-curve in the IOBW technique were higher than in the EOBW. Nevertheless, EOBW shows good accuracy, so it can be used as an alternative technique for patients who find it difficult to undergo the IOBW technique, especially during the COVID-19 pandemic.

New Approach for Superthin Anterolateral Thigh Flap Elevation.

Anterolateral thigh (ALT) flaps are widely used for soft tissue reconstructions. They have several advantages, most notably a long pedicle, an appropriate pedicle caliber, low donor site morbidity, and the possibility of 2 teams working simultaneously. However, conventional, thick ALT flaps used for reconstructions of head and neck and lower extremity defects may cause postoperative range of motion limitations and cosmetic problems. The aim of this study was to develop and propose strategies to facilitate the harvest of superthin ALT flaps and minimize technical difficulties. This article provides step-by-step instructions for simple, quick, and reliable dissections of superthin ALT flaps. This study retrospectively analyzed data from 60 free superthin ALT flaps used for soft tissue reconstructions in 56 patients between January 2018 and February 2019. Superthin flaps were elevated just above the superficial Scarpa's fascia using a vertical approach. Thirty-eight of the patients were operated on for lower extremity wounds, 16 were for head and neck defects, and 6 were for upper extremity wounds. The mean follow-up period was 7 months. The median hospital stay was 10 days. Total flap loss was observed in 4 cases (6.6%), and partial flap loss was observed in another 4 cases (6.6%). The superthin elevated ALT flap is a reliable and effective option for the reconstruction of soft tissue defects. In our vertical approach, the wide field of view of the flap perforator provides easy dissection, making it easier to elevate the superthin ALT flap.

Inverse-Designed Multi-Level Diffractive Doublet for Wide Field-of-View Imaging

Wide field-of-view (WFOV) imaging is extensively used in fields as diverse as macro photography, virtual reality, machine vision, and microscopy. Conventional WFOV cameras are bulky since they require multiple refractive lenses. Here, we design, fabricate, and characterize a 100° FOV camera with a total-track length of ∼2 mm, composed of an inverse-designed multi-level diffractive doublet with an input-aperture diameter of 0.204 mm, a back-focal length of 1 mm, and operating at λ = 850 nm (bandwidth ∼ 34 nm). Using careful experiments, we characterize the focusing and imaging performance as well as demonstrate de-vignetting based on experimental calibration. The spatial frequency at 10% modulation-transfer-function contrast was measured at 150 and 38 lp/mm for 0 and 50° incident angles, respectively. Our approach can be scaled to larger aperture sizes and smaller f/#s, potentially leading to thin, lightweight WFOV cameras for portable applications.

Thermal aerial culling for the control of vertebrate pest populations

Helicopter-based shooting is an effective management tool for large vertebrate pest animals. However, animals in low-density populations and/or dense habitat can be difficult to locate visually. Thermal-imaging technology can increase detections in these conditions. We used thermal-imaging equipment with a specific helicopter crew configuration to assist in aerial culling for feral pigs (Sus scrofa) and fallow deer (Dama dama) in South Australia in 2021. Seventy-two percent of pigs and 53% of deer were first detected in dense canopy/tall forest habitat. Median time from the first impact shot to incapacitation was < 12 s. The culling rate (animals hour−1) doubled compared to visual shoots over the same populations and the wounding rate was zero resulting in a incapacitation efficiency of 100%. The crew configuration gave the shooter a wide field of view and the thermal operator behind the shooter provided essential support to find new and escaping animals, and to confirm species identification and successful removal. The crew configuration allowed for successful target acquisition and tracking, with reduced target escape. The approach can increase the efficiency of aerial culling, has the potential to increase the success of programs where eradication is a viable option, and can improve animal welfare outcomes by reducing wounding rates and the escape of target animals.

Compact structured light generation based on meta-hologram PCSEL integration

Metasurfaces, a catalog of optical components, offer numerous novel functions on demand. They have been integrated with vertical cavity surface-emitting lasers (VCSELs) in previous studies. However, the performance has been limited by the features of the VCSELs such as low output power and large divergence angle. Although the solution of the module of VCSEL array could solve these issues, the practical application is limited by extra lens and large size. In this study, we experimentally demonstrate reconstruction of a holographic images using a compact integration of a photonic crystal surface-emitting laser and metasurface holograms designed for structured light generation. This research showcases the flexible design capabilities of metasurfaces, high output power (on the order of milliwatts), and the ability to produce well-uniformed images with a wide field of view without the need for a collection lens, making it suitable for 3D imaging and sensing.

Transmission Efficiency Limit for Nonlocal Metalenses

AbstractThe rapidly advancing capabilities in nanophotonic design are enabling complex functionalities limited mainly by physical bounds. The efficiency of transmission is a major consideration, but its ultimate limit remains unknown for most systems. This study introduces a matrix formalism that puts a fundamental bound on the channel‐averaged transmission efficiency of any passive multi‐channel optical system based only on energy conservation and the desired functionality, independent of the interior structure and material composition. Applying this formalism to diffraction‐limited nonlocal metalenses with a wide field of view shows that the transmission efficiency must decrease with the numerical aperture for the commonly adopted designs with equal entrance and output aperture diameters. It also shows that reducing the size of the entrance aperture can raise the efficiency bound. This study reveals a fundamental limit on the transmission efficiency as well as provides guidance for the design of high‐efficiency multi‐channel optical systems.

The Study of Helium Variations in Star Clusters Using China Space Station Telescope

The China Space Station Telescope (CSST) is a 2 m space-based optical-UV telescope. Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Survey Camera. With its wide field of view (1.1 square degrees) and a mosaic imager containing 640 million pixels, studying the different populations of stars within star clusters is highly feasible. The aim of this study is to assess the CSST’s ability to distinguish between stellar populations with varying helium abundance levels, with the help of Modules for Experiments in Stellar Astrophysics. The results of the CSST’s photometry for these different populations are presented by transferring the models into the CSST Survey Camera photometric system. The findings confirm that helium-enriched stellar populations will have unique patterns in the color–magnitude diagrams under the CSST photometric system, compared to normal stellar populations. The CSST, with its filters and wide field of view of the Survey Camera, provides a new avenue for the study of multiple populations in star clusters.

Neural-network-based wavefront solution algorithm for a wide field survey telescope.

The wide field survey telescope (WFST) is a 2.5m optical survey telescope currently under construction in China. The telescope employs a primary-focus optical design to achieve a wide field of view of 3deg, and its focal plane is equipped with four pairs of curvature sensors to perform wavefront sensing and active optics. Currently, there are several wavefront solution algorithms available for curvature sensors, including the iterative fast Fourier transform method, orthogonal series expansion method, Green's function method, and sensitivity matrix method. However, each of these methods has limitations in practical use. This study proposes a solution method based on a convolutional neural network model with a U-Net structure for the curvature wavefront sensing of the WFST. Numerical simulations show that the model, when properly trained, has a high accuracy and performs a curvature wavefront solution effectively. Upon a comparison with the sensitivity matrix method, this new method demonstrates its superiority. Finally, the study is summarized, and the drawbacks of the proposed method are discussed, which leads to direction for future optimizations.

Spaceborne Relative Radiometer: Instrument Design and Pre-Flight Test

In order to simultaneously determine the values of total solar irradiance (TSI) and the Earth’s radiation at the top of the atmosphere (TOA) on board the Fengyun-3F satellite, a spaceborne relative radiometer (SRR) was developed. It adopts a dual-channel structure, including a solar radiometer channel (SR) with an unobstructed field of view (FOV) of 1.5° and an Earth radiometer channel (ER) with a wide field of view (WFOV) of 95.3° and a diameter of about 1900 km on the ground. Before the launch, both the SR and ER were calibrated. The SR, installed on the inner frame of the solar tracker of the SIM-II (solar irradiance monitor-II), is used to observe rapid changes in solar radiance with the SIAR (solar irradiance absolute radiometer), an electrical-substitution radiometer, on orbit. The ER is mounted on the U-shaped frame of the solar tracker, directly pointing in the nadir direction. Additionally, a dark space observation mode is used to determine the on-orbit background noise and lunar observation mode for on-orbit calibration. In this article, the instrument design and working principle of the SRR is first introduced, and an analysis of the measurement model of the ER, the WFOV channel of the SRR, is focused on. Finally, ground test results of the SRR are introduced.

Deep-learning-based blood pressure estimation using multi channel photoplethysmogram and finger pressure with attention mechanism

Recently, several studies have proposed methods for measuring cuffless blood pressure (BP) using finger photoplethysmogram (PPG) signals. This study presents a new BP estimation system that measures PPG signals under progressive finger pressure, making the system relatively robust to errors caused by finger position when using the cuffless oscillometric method. To reduce errors caused by finger position, we developed a sensor that can simultaneously measure multi-channel PPG and force signals in a wide field of view (FOV). We propose a deep-learning-based algorithm that can learn to focus on the optimal PPG channel from multi channel PPG using an attention mechanism. The errors (ME ± STD) of the proposed multi channel system were 0.43±9.35 mmHg and 0.21 ± 7.72 mmHg for SBP and DBP, respectively. Through extensive experiments, we found a significant performance difference depending on the location of the PPG measurement in the BP estimation system using finger pressure.

A Review of Advanced Transceiver Technologies in Visible Light Communications

Visible Light Communication (VLC) is an emerging technology that utilizes light-emitting diodes (LEDs) for both indoor illumination and wireless communications. It has the potential to enhance the existing WiFi network and connect a large number of high-speed internet users in future smart home environments. Over the past two decades, VLC techniques have made significant strides, resulting in transmission data rates increasing from just a few Mbps to several tens of Gbps. These achievements can be attributed to the development of various transceiver technologies. At the transmitter, LEDs should provide high-quality light for illumination and support wide modulation bandwidths. Meanwhile, at the receiver, optics systems should have functions such as optical filtering, light concentration, and, ideally, a wide field of view (FOV). The photodetector must efficiently convert the optical signal into an electrical signal. Different VLC systems typically consider various transceiver designs. In this paper, we provide a survey of some important emerging technologies used to create advanced optical transceivers in VLC.

60‐1: Invited Paper: Emerging microdisplay technologies for AR/VR applications

LCD and OLED are presently the two dominating microdisplays for VR headsets. How to achieve high resolution density for wide field of view and eliminating the screen‐door effect, while keeping low power consumption remains a major challenge. For ultracompact and lightweight AR displays, micro‐LED, OLED‐on‐silicon, MEMS, laser beam scan, and front‐lit LCoS are strong contenders. To reduce the required display brightness for low power consumption, and to enable occlusion effect, a segmented smart dimmer is a viable approach. The pros and cons of each approach will be analyzed.

UNCOVERing the extended strong lensing structures of Abell 2744 with the deepest JWST imaging

ABSTRACT We present a new parametric lens model for the massive galaxy cluster Abell 2744 based on new ultra-deep JWST imaging taken in the framework of the UNCOVER program. These observations constitute the deepest JWST images of a lensing cluster to date, adding to existing deep Hubble Space Telescope (HST) images and the recent JWST Early Release Science and Director’s Discretionary Time data taken for this field. The wide field of view of UNCOVER (∼45 arcmin2) extends beyond the cluster’s well-studied central core and reveals a spectacular wealth of prominent lensed features around two massive cluster sub-structures in the north and north-west, where no multiple images were previously known. We identify 75 new multiple images and candidates of 17 sources, 43 of which allow us, for the first time, to constrain the lensing properties and total mass distribution around these extended cluster structures using strong lensing (SL). Our model yields an effective Einstein radius of θE, main = 23.2 ± 2.3 arcsec for the main cluster core (for zs = 2), enclosing a mass of M(&amp;lt; θE, main) = (7.7 ± 1.1) × 1013 M⊙, and θE, NW = 13.1 ± 1.3 arcsec for the newly discovered north-western SL structure enclosing M(&amp;lt; θE, NW) = (2.2 ± 0.3) × 1013 M⊙. The northern clump is somewhat less massive with θE, N = 7.4 ± 0.7 arcsec enclosing M(&amp;lt; θE, N) = (0.8 ± 0.1) × 1013 M⊙. We find the northern sub-structures of Abell 2744 to broadly agree with the findings from weak lensing analyses and align with the filamentary structure found by these previous studies. Our model in particular reveals a large area of high magnification values between the various cluster structures, which will be paramount for lensed galaxy studies in the UNCOVER field. The model is made publicly available to accompany the first UNCOVER data release.