Wide Field Of View Research Articles

Optical imaging system for an all-time star sensor based on field of view gated technology.

The wide field of view (FOV) of traditional star sensor optical systems restricts the ability to suppress atmospheric background. An optical imaging system for an all-time star sensor based on FOV gated technology is proposed. In this system, a wide FOV telescope is used to observe a large sky area containing multiple stars. A microlens and microshutter array is employed to subdivide the wide FOV and gate a narrow FOV to suppress atmospheric background radiation. Assisted by a common imaging lens, each set of microlens and microshutter elements corresponds to a FOV gated imaging channel. With the rapid switching of gated FOV, multiple stellar images are obtained on a common detection during daytime. As an example, a FOV gated optical imaging system with 0.4° gated FOV and 61 imaging channels is designed. In addition, a simplified prototype is developed, and a preliminary experiment of FOV gated imaging is performed near the ground. The results verify the capability of multiple stellar detections during daytime. The proposed optical imaging system has a strong capability of suppressing atmospheric background radiation and provides sufficient FOV gated imaging channels to enhance the probability of detecting multiple stars. It provides an effective technical way to develop all-time star sensors based on star pattern recognition and enables a completely autonomous attitude determination possible for platforms inside the atmosphere during daytime.

Dually modulated photonic crystal lasers for wide-range flash illumination.

Flash light sources with a wide field of view (FOV) are indispensable in various fields such as light detection and ranging (LiDAR), optical wireless communication, and adaptive lighting. However, conventional flash light sources, which combine lasers with external optical elements, tend to suffer from high complexity, large size, and high cost. In this study, we investigate a new wide-FOV flash light source which does not require external optical elements, based on a dually modulated photonic crystal surface-emitting laser (PCSEL). First, we propose and design the concept of a photonic crystal into which information of gradually varying diffraction vectors is introduced in order to artificially broaden the divergence angle. We then experimentally demonstrate photonic crystals based on this concept. Finally, by arraying 100 such lasers with mutually different central emission angles and driving all of these lasers simultaneously, we successfully achieve optics-free, 4-W flash illumination over a FOV of 30° × 30° at a wavelength of 940 nm.

Precise position measurement for resident space object with point spread function modeling

Optical survey is a main technique for observing resident space object in state-of-the-art implementations. Wide field of view refracting telescopes are widely used in such applications, they have made great contributions and played significant roles. However due to the inevitable optical defects, the efficiency of data reduction is affected and the precision of astrometry is reduced. To optimize the image processing and data reduction, a technique is proposed to achieve high accuracy position measurement for resident space object based upon precise point spread function modeling. In detail, principal component analysis is adopted to extract the dominated components from large amounts of raw images, then after evaluation the optimal model is constructed and the centering algorithm is developed to estimate the position with the model. A trial observation was performed and three Beidou satellites were observed, based on the raw images acquired the efficiency and reliability of our method are tested. The positions of all objects are measured with our proposed method, Gaussian, modified moment and SExtractor, then they are compared with the reference positions and the measurement accuracy can be derived. The results demonstrate that our proposed technique provides another reliable way on high accuracy position measurement for satellites. As the model reveals the characteristics of the imaging process, the data reduction is improved and a more precise astrometric results can be achieved.

Deep Learning-Based, Misalignment Resilient, Real-Time Fourier Ptychographic Microscopy Reconstruction of Biological Tissue Slides

Fourier ptychographic microscopy probes label-free samples from multiple angles and achieves super resolution phase-contrast imaging according to a synthetic aperture principle. Thus, it is particularly suitable for high-resolution imaging of tissue slides over a wide field of view. Recently, in order to make the optical setup robust against misalignments-induced artefacts, numerical multi-look has been added to the conventional phase retrieval process, thus allowing the elimination of related phase errors but at the cost of a long computational time. Here we train a generative adversarial network to emulate the process of complex amplitude estimation. Once trained, the network can accurately reconstruct in real-time Fourier ptychographic images acquired using a severely misaligned setup. We benchmarked the network by reconstructing images of animal neural tissue slides. Above all, we show that important morphometric information, relevant for diagnosis on neural tissues, are retrieved using the network output. These are in very good agreement with the parameters calculated from the ground-truth, thus speeding up significantly the quantitative phase-contrast analysis of tissue samples.

О проекте евразийских субмиллиметровых телескопов (ESMT) и возможности применения адаптивной оптики для улучшения качества субмм изображений

Actual problems in submillimeter astronomy require the creation of instruments, which combine high sensitivity, angular resolution, wide field of view, and multi-wavelength (multicolor) spectral range. Currently, new single mm/submm telescopes are in great demand in Eurasia, as well as their inclusion in the Event Horizon Telescope (EHT) VLBI network. The concept of the Eurasian Submillimeter Teselscopes (ESMT) project involves the construction of three structurally identical mm/submm radio telescopes of the 15-21 m class on the Suffa Plateau, Uzbekistan (2400 m or higher), in the Russian Federation (3000 m or higher) and in Tibet, China (higher than 5000 m). The ESMT concept is considered, where the design of the European ALMA antennas is taken as a starting point. The antenna diameter should be increased from 12 m to 21 m, the optical layout and the structure of the truss frame will be changed accordingly, tertiary optics and an “active surface” have been added, and tools for its operational diagnostics have been proposed. The article presents variants of the ESMT optical scheme and tertiary optics, which make it possible to hold a compact cryostat with a KID-matrix in a vertical position to ensure its operability when the telescope is tilted. Comparison of ESMT capabilities with other mm/submm tools and projects is provided. The necessary astroclimatic conditions and characteristics of ESMT sites are considered, estimates of the precipitated water PWV, dPWV and the share of total cloudiness TCC for a number of practically interesting sites obtained using the ERA-Interim and ERA-5 reanalysis databases are presented. The influence of atmospheric turbulence on a radio telescope, radio astronomy methods for suppressing atmospheric fluctuations and possibilities of using adaptive optics, in particular, tip-tilt correction for improving the quality of submm images, are considered.

Dynamic imaging comparison of 18F-FDG tracers with Compton imaging and PET coincidence imaging

In the clinical situation of positron emission tomography (PET) scans, an activity of an approximately few hundred megabecquerels (3.7 MBq/kg) is used for injection. Monitoring and imaging of moving radioisotopes is useful in clinical applications, such as tracer injection and leakage monitoring in PET scan protocols. We have developed a Compton imaging and PET coincidence system to monitor a moving radioisotope using 8 × 8 GAGG crystal arrays coupled to SiPM arrays with dynamic time-over-threshold-based individual readout circuits, and its imaging performance is considered. The measured resolution of PET and Compton imaging is 3.2 mm and approximately 17 degrees for a 22Na point source. In the experiment, radiotracers with activities from 11.2 MBq to 93.3 MBq moving with speeds from 1 mm/s to 10 mm/s were used for mimicking the blood flow. Both reconstructed images of PET and Compton imaging successfully visualized the movement, except for Compton imaging in the 93.3 MBq case. PET shows better activity-tracking capability and radio-tracer speeds up to 100 MBq. In contrast, Compton imaging has a wider field of view (FOV) to monitor a larger area than the limited FOV in a PET system. We believe that this work can contribute to solutions of various medical problems such as blood flow measurement and extravasation detection.

헤드 마운티드 디스플레이를 위한 시간 제약 렌더링을 이용한 적응적 포비티드 광선 추적법

Ray tracing-based rendering creates by far more realistic images than the traditional rasterization-based rendering. However, it is still burdensome when implemented for a Head-Mounted Display (HMD) system that demands a wide field of view and a high display refresh rate. Furthermore, for presenting high-quality images on the HMD screen, a sufficient number of ray sampling should be carried out per pixel to alleviate visually annoying spatial and temporal aliases. In this paper, we extend the recent selective foveated ray tracing technique by Kim et al. [<xref ref-type="bibr" rid="B1">1</xref>], and propose an improved real-time rendering technique that realizes the rendering effect of the classic Whitted-style ray tracing on the HMD system. In particular, by combining the ray tracing hardware-based acceleration technique and time-constrained rendering scheme, we show that fast HMD ray tracing is possible that is well suited to human visual systems.

Wide field-of-view Fourier Ptychography microscopy based on Fresnel propagation scheme

Fourier ptychographic microscopy (FPM) is a computational imaging method that gives a significantly increased space-bandwidth product, in practice high resolution combined with a wide field of view. In this article, we propose an improved Fourier Ptychography algorithm based on Fresnel wave propagation integral for wide field-of-view coherent imaging while correcting for the misalignment of the illuminating LED board and calibration of system parameters. In addition, the wave emanating from the LEDs is taken to be parabolic instead of plane wave as done by others. The advantage of this scheme is that it enables to simulate the transition regions between bright and dark field in wide image patches, and hence this feature can be used to estimate the LED misalignment as well as the distortion of the imaging lens. Experimental results are presented for a USAF resolution target and a biological sample for on-axis and off-axis image patches over a wide sample area showing excellent performance of this scheme when compared to the traditional Fraunhofer-model based Fourier Ptychography algorithm. The article summarizes with high technical detail our experiences with developing and implementing improved FPM methods and will hopefully assist other scientists entering this scientific field.

Galactic observatory science with the ASTRI Mini-Array at the Observatorio del Teide

The ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) Mini-Array will be composed of nine imaging atmospheric Cherenkov telescopes at the Observatorio del Teide site. The array will be best suited for astrophysical observations in the 0.3–200 TeV range with an angular resolution of few arc-minutes and an energy resolution of 10-15%. A core-science programme in the first four years will be devoted to a limited number of key targets, addressing the most important open scientific questions in the very-high energy domain. At the same time, thanks to a wide field of view of about 10∘, ASTRI Mini-Array will observe many additional field sources, which will constitute the basis for the long-term observatory programme that will eventually cover all the accessible sky. In this paper, we review different astrophysical Galactic environments, e.g. pulsar wind nebulae, supernova remnants, and gamma-ray binaries, and show the results from a set of ASTRI Mini-Array simulations of some of these field sources made to highlight the expected performance of the array (even at large offset angles) and the important additional observatory science that will complement the core-science program.

FisheyeHDK: Hyperbolic Deformable Kernel Learning for Ultra-Wide Field-of-View Image Recognition

Conventional convolution neural networks (CNNs) trained on narrow Field-of-View (FoV) images are the state-of-the art approaches for object recognition tasks. Some methods proposed the adaptation of CNNs to ultra-wide FoV images by learning deformable kernels. However, they are limited by the Euclidean geometry and their accuracy degrades under strong distortions caused by fisheye projections. In this work, we demonstrate that learning the shape of convolution kernels in non-Euclidean spaces is better than existing deformable kernel methods. In particular, we propose a new approach that learns deformable kernel parameters (positions) in hyperbolic space. FisheyeHDK is a hybrid CNN architecture combining hyperbolic and Euclidean convolution layers for positions and features learning. First, we provide intuition of hyperbolic space for wide FoV images. Using synthetic distortion profiles, we demonstrate the effectiveness of our approach. We select two datasets - Cityscapes and BDD100K 2020 - of perspective images which we transform to fisheye equivalents at different scaling factors (analogue to focal lengths). Finally, we provide an experiment on data collected by a real fisheye camera. Validations and experiments show that our approach improves existing deformable kernel methods for CNN adaptation on fisheye images.

Compact athermalized LWIR objective lens

A new compact optical passive athermalized objective lens is designed with a focal length 120 mm and F-number 1.1. Its full field of view is 12.2°. The geometrical aberrations due to the large aperture and the wide field of view are well corrected as well as the chromatic aberration. Hence, the maximum RMS radius of the spot diagram over the full field of view is less than 17 µm and the Strehl ratio is 0.95 at 20 °C. The MTF is nearly limited in diffraction over the full F.O.V. This good correction of aberrations makes the optical system gain high resolution and suitable to work with a focal plane array detector with 17-µm pixel pitch. This performance is stable over a long temperature range from − 40 °C to + 65 °C. Moreover, the optical system is relatively compact “140 mm.” The total transmittance (after absorption consideration) of the optical system is enhanced from 6.6 to 94.07% at λ = 10 µm along the optical axis upon applying an anti-reflection coating.

Extraction of Water Body Information from Remote Sensing Imagery While Considering Greenness and Wetness Based on Tasseled Cap Transformation

Water, as an important part of ecosystems, is also an important topic in the field of remote sensing. Shadows and dense vegetation negatively affect most traditional methods used to extract water body information from remotely sensed images. As a result, extracting water body information with high precision from a wide range of remote sensing images which contain complex ground-based objects has proved difficult. In the present study, a method used for extracting water body information from remote sensing imagery considers the greenness and wetness of ground-based objects. Ground objects with varied water content and vegetation coverage have different characteristics in their greenness and wetness components obtained by the Tasseled Cap transformation (TCT). Multispectral information can be output as brightness, greenness, and wetness by Tasseled Cap transformation, which is widely used in satellite remote sensing images. Hence, a model used to extract water body information was constructed to weaken the influence of shadows and dense vegetation. Jiangsu and Anhui provinces are located along the Yangtze River, China, and were selected as the research area. The experiment used the wide-field-of-view (WFV) sensor onboard the Gaofen-1 satellite to acquire remotely sensed photos. The results showed that the contours and spatial extent of the water bodies extracted by the proposed method are highly consistent, and the influence of shadow and buildings is minimized; the method has a high Kappa coefficient (0.89), overall accuracy (92.72%), and user accuracy (88.04%). Thus, the method is useful in updating a geographical database of water bodies and in water resource management.

Freeform wide-angle camera lens enabling mitigable distortion.

Allowing natural scenes as well as maximizing field of view (FoV) can benefit from the minimization of distortion for the wide-angle camera. The wide-angle camera utilizing freeform surfaces for mitigating distortions, either barrel distortion or pincushion distortion, is therefore of interest. In this paper, the designs of using all-aspherical surfaces and aspherical surfaces combined with freeform surfaces are investigated. To minimize the deviation before and after converting from aspherical surfaces to freeform surfaces, a mathematical conversion scheme is derived. By applying it to the design example, the methodology is shown to be effective in the case of an optical system with a large number of aspherical/freeform surfaces. Additionally, custom freeform analysis tools are developed for quantitative analysis and visualization of the critical characteristics of optical performance, namely, a 2D lateral color field map, 2D relative illumination field map, 2D spot radius field map, and 2D average modulation transfer function (MTF) field map. Compared to classical all-aspherical design, simulation results show that freeform design has the capability to reduce distortion, and other performances such as relative illumination, spot size, and MTF can also be improved, even though there are some compromises on the peripheral FoV. The design approach will have potential important research and application values for lens systems utilized in miniature camera lenses, especially the wide FoV capability.

Nanoscale Antiferromagnetic Domain Imaging using Full-Field Resonant X-ray Magnetic Diffraction Microscopy.

The physical properties of magnetic materials frequently depend not only on the microscopic spin and electronic structures, but also on the structures of mesoscopic length scales that emerge, for instance, from domain formations, or chemical and/or electronic phase separations. However, experimental access to such mesoscopic structures is currently limited, especially for antiferromagnets with net zero magnetization. Here, full-field microscopy and resonant magnetic X-ray diffraction are combined to visualize antiferromagnetic (AF) domains of the spin-orbit Mott insulator Sr2 IrO4 with area over ≈0.1 mm2 and with spatial resolution as high as ≈150nm. With the unprecedented wide field of views and high spatial resolution, an intertwining of two AF domains on a length comparable to the measured average AF domain wall width of 545nm is revealed. This mesoscopic structure comprises a substantial portion of the sample surface, and thus can result in a macroscopic response unexpected from its microscopic magnetic structure. In particular, the symmetry analysis presented in this work shows that the inversion symmetry, which is preserved by the microscopic AF order, becomes ill-defined at the mesoscopic length scale. This result underscores the importance of this novel technique for a thorough understanding of the physical properties of antiferromagnets.

TiEMPO: open-source time-dependent end-to-end model for simulating ground-based submillimeter astronomical observations

The next technological breakthrough in millimeter–submillimeter astronomy is three-dimensional imaging spectrometry with wide instantaneous spectral bandwidths and wide fields of view. The total optimization of the focal-plane instrument, the telescope, the observing strategy, and the signal-processing software must enable efficient removal of foreground emission from the Earth’s atmosphere, which is time-dependent and highly nonlinear in frequency. Here, we present Time-dependent End-to-end Model for Post-process Optimization (TiEMPO) of the DEep Spectroscopic HIgh-redshift MApper (DESHIMA) spectrometer. TiEMPO utilizes a dynamical model of the atmosphere and parameterized models of the astronomical source, the telescope, the instrument, and the detector. The output of TiEMPO is a time stream of sky brightness temperature and detected power, which can be analyzed by standard signal-processing software. We first compare TiEMPO simulations with an on-sky measurement by the wideband DESHIMA spectrometer, and find good agreement in the noise and sensitivity. We then use TiEMPO to simulate the detection of the line emission spectrum of a high-redshift galaxy using the DESHIMA 2.0 spectrometer in development. The TiEMPO model is open source. Its modular and parametrized design enables users to adapt it to optimize the end-to-end performance of spectroscopic and photometric instruments on existing and future telescopes.

Non-uniformity correction of wide field of view imaging system.

Requirements for wide field of view (FOV) imaging system reflect the need for both uniform illumination as well as excellent image quality across the entire FOV. As the monocentric lens combined with a parallel array of relay imagers achieves a wide-FOV while maintaining a high resolution, we studied the monocentric cascade imaging system (MCIS). However, the imaging experiment of the prototype shows two issues, including vignetting and non-uniform image quality over the full FOV. They affect the image stitching which is necessary for wide-FOV image acquisition. This paper studies how the position of the aperture stop affects the vignetting and the local aberrations in MCIS. Moving laws of the aperture stop and its relationship with the local aberrations are presented. Moreover, aspheric surfaces on proper surfaces are introduced and studied to balance the local aberrations. Accordingly, an MCIS with uniform illumination and good image quality is presented. The MCIS achieves a wide-FOV of 116.4° and an instantaneous FOV of 0.0021°. It keeps a relative illumination exceeding 97% during the full FOV. The modulation transfer function (MTF) is over 0.285 at the Nyquist frequency of 270 lp/mm. This paper provides a profound theorical reference for further applications and developments of MCIS.

Determining the Spectral Content of MOSES Images

The Multi-Order Solar Extreme Ultraviolet Spectrograph (MOSES) sounding rocket was launched from White Sands Missile Range on 2006 February 8th, to capture images of the Sun in the He ii 303.8 Å emission line. MOSES is a slitless spectrograph that forms images in multiple spectral orders simultaneously using a concave diffraction grating in an effort to measure line profiles over a wide field of view from a single exposure. Early work on MOSES data showed evidence of solar features composed of neither He ii 303.8 Å nor the nearby Si xi 303.3 Å spectral lines. We have built a forward model that uses cotemporal EIT images and the Chianti atomic database to fit synthetic images with known spectra to the MOSES data in order to quantify this additional spectral content. Our fit reveals a host of dim lines that alone are insignificant but combined contribute a comparable intensity to MOSES images as Si xi 303.3 Å. In total, lines other than He ii 303.8 Å and Si xi 303.3 Å contribute approximately 10% of the total intensity in the MOSES zero order image. This additional content, if not properly accounted for, could significantly impact the analysis of MOSES and similar slitless spectrograph data, especially those using a zero-order (undispersed) image. More broadly, this serves as a reminder that multilayer EUV imagers are sensitive to a host of weak contaminant lines.

Combined Optical and Radio‐Frequency Perspectives on the Time Evolution of Lightning Measured by the FORTE Satellite

AbstractWe use a cluster feature data set for the Fast On‐orbit Recording of Transient Events (FORTE) satellite that combines detections from its pixelated Lightning Locating System (LLS), photodiode detector (PDD) and Radio‐Frequency (RF) instrumentation to generate statistics describing the frequency and timing of lightning events detected by each instrument during lightning flashes. Coincident observations from the same vantage point allow us to directly compare flash details that can be resolved by the wide Field of View (FOV) instruments relative to the pixelated LLS—whose design is based on NASA's Lightning Imaging Sensor. We find that both the PDD and RF system typically generate more detections than the lightning imager (mean: 1.5 PDD events per LLS group, 2 RF events per LLS group) from pulses that are either not sufficiently bright in the optical band (in the case of RF) or that lack the optical energy density (in the case of the PDD) required to trigger one of the pixels on the LLS imaging array. This includes additional activity before the first LLS group or after the final LLS group. These FORTE results demonstrate that certain lightning processes would be better resolved by wide‐FOV optical and RF instruments than lightning imagers. Current/future space‐based missions that use/plan to use similar instruments will improve our understanding of flash evolution by resolving details missed by lightning imagers.

Design and Fabrication of a High-Frequency Microconvex Array Transducer for Small Animals Imaging.

High-frequency convex array transducer, featuring both high spatial resolution and wide field of view, has been successfully developed for ophthalmic imaging. To further expand its application range to small animals' imaging, this work develops a high-frequency microconvex array transducer possessing smaller aperture size and wider scanning angle. This transducer featured 128 array elements arranged in a curvilinear 2-2 piezoelectric composite configuration, yielding a maximum view angle of 97.8°. The array was composed of two front matching layers, a nonconductive backing layer, and a customized flexible circuit that electrically connected array elements to coaxial cables. The center frequency and the -6-dB fractional bandwidth were about 18.14 MHz and 69.15%, respectively. The image of a tungsten wire phantom resulted in approximately 62.9- [Formula: see text] axial resolution and 121.3- [Formula: see text] lateral resolution. The image of the whole kidney of a rat as well as its internal arteries was acquired in vivo, demonstrating the imaging capability of the proposed high-frequency microconvex array transducers for small animals' imaging applications.

In Search of Short Gamma-Ray Burst Optical Counterparts with the Zwicky Transient Facility

The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to ∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10 Fermi-GBM SGRBs during 2018 and 2020–2021. Bridging the large sky areas with small field-of-view optical telescopes in order to track the evolution of potential candidates, we look for the elusive SGRB afterglows and kilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, even though more than 10 ground-based telescopes, part of the Global Relay of Observatories Watching Transients Happen (GROWTH) network, have taken part in these efforts. The candidate selection procedure and the follow-up strategy have shown that ZTF is an efficient instrument for searching for poorly localized SGRBs, retrieving a reasonable number of candidates to follow up and showing promising capabilities as the community approaches the multi-messenger era. Based on the median limiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event up to ∼200 Mpc and SGRB afterglows to z = 0.16 or 0.4, depending on the assumed underlying energy model. Future ToOs will expand the horizon to z = 0.2 and 0.7, respectively.