Range Of Viewing Angles Research Articles

Pattern search algorithm-aided structural color Sb2S3-based dynamic hybrid all-dielectric metasurface

The versatility and dynamic tunability of reconfigurable photonic devices hold paramount significance in optics. Nevertheless, most such dynamically adjustable all-dielectric metasurfaces, particularly those utilized in structural color applications, are usually resonators made exclusively of phase-change materials. The elevated absorption coefficients exhibited by phase-change materials in the short-wavelength band (particularly within the blue light range) often culminate in suboptimal performance for generating colors. To address this challenge, we designed a hybrid all-dielectric metasurface that achieved reflectivities of 60%, 75%, and 96% across blue, green, and red-light bands, respectively and achieved dynamic tunability of the metasurface by generating chromatic aberrations of 19.626, 3.341, and 17.354 via the reversible phase transition of Sb2S3. The device exhibits good angular robustness, maintaining nearly constant color within a viewing angle range of ±20°. Meanwhile, we employ a pattern search algorithm to accelerate the inverse design process of metasurfaces. The algorithm can reduce the design time by a factor of at least two orders of magnitude relative to the genetic algorithm, substantially improving design efficiency. The algorithm applies to high degree-of-freedom inverse design problems for intricate physical systems with similar design relationships. It offers a promising avenue for rapid and dependable optical device design.

An applied framework to unlocking multi-angular UAV reflectance data: a case study for classification of plant parameters in maize (Zea mays)

AbstractOptical sensors, mounted on uncrewed aerial vehicles (UAVs), are typically pointed straight downward to simplify structure-from-motion and image processing. High horizontal and vertical image overlap during UAV missions effectively leads to each object being measured from a range of different view angles, resulting in a rich multi-angular reflectance dataset. We propose a method to extract reflectance data, and their associated distinct view zenith angles (VZA) and view azimuth angles (VAA), from UAV-mounted optical cameras; enhancing plant parameter classification compared to standard orthomosaic reflectance retrieval. A standard (nadir) and a multi-angular, 10-band multispectral dataset was collected for maize using a UAV on two different days. Reflectance data was grouped by VZA and VAA (on average 2594 spectra/plot/day for the multi-angular data and 890 spectra/plot/day for nadir flights only, 13 spectra/plot/day for a standard orthomosaic), serving as predictor variables for leaf chlorophyll content (LCC), leaf area index (LAI), green leaf area index (GLAI), and nitrogen balanced index (NBI) classification. Results consistently showed higher accuracy using grouped VZA/VAA reflectance compared to the standard orthomosaic data. Pooling all reflectance values across viewing directions did not yield satisfactory results. Performing multiple flights to obtain a multi-angular dataset did not improve performance over a multi-angular dataset obtained from a single nadir flight, highlighting its sufficiency. Our openly shared code (https://github.com/ReneHeim/proj_on_uav) facilitates access to reflectance data from pre-defined VZA/VAA groups, benefiting cross-disciplinary and agriculture scientists in harnessing the potential of multi-angular datasets. Graphical abstract

Large-field Gesture Tracking and Recognition for Augmented Reality Interaction

In recent years, with the continuous development of computer vision and artificial intelligence technology, gesture recognition is widely used in many fields, such as virtual reality, augmented reality and so on. However, the traditional binocular camera architecture is limited by its limited field of view Angle and depth perception range. Fisheye camera is gradually applied in gesture recognition field because of its advantage of larger field of view Angle. Fisheye cameras offer a wider field of vision than previous binocular cameras, allowing for a greater range of gesture recognition. This gives fisheye cameras a distinct advantage in situations that require a wide field of view. However, because the imaging mode of fisheye camera is different from traditional camera, the image of fisheye camera has a certain degree of distortion, which makes the calculation of gesture recognition more complicated. Our goal is to design a distortion correction processing strategy suitable for fisheye cameras in order to extend the range of gesture recognition and achieve large field of view gesture recognition. Combined with binocular technology, we can use the acquired hand depth information to enrich the means of interaction. By taking advantage of the large viewing Angle of the fisheye camera to expand the range of gesture recognition, make it more extensive and accurate. This will help improve the real-time and precision of gesture recognition, which has important implications for artificial intelligence, virtual reality and augmented reality.

Integral imaging reconstruction system based on the human eye viewing mechanism.

For integral stereo imaging systems based on lens arrays, the cross-mixing of erroneous light rays between adjacent lenses seriously affects the quality of the reconstructed light field. In this paper, we proposed a light field reconstruction method based on the human eye viewing mechanism, which incorporates simplified human eye imaging into the integral imaging system. First, the light field model for specified viewpoint is established, and the distribution of the light source for each viewpoint is accurately calculated for the EIA generation algorithm of fixed viewpoint. Second, according to the ray tracing algorithm in this paper, non-overlapping EIA based on the human eye viewing mechanism is designed to suppress the amount of crosstalk rays fundamentally. The actual viewing clarity is improved with the same reconstructed resolution. Experimental results verify the effectiveness of the proposed method. The SSIM value is higher than 0.93, which verifies that the viewing angle range is increased to 62°.

The influence of Sentinel-1 SAR sub-swath on the recorded backscatter time-series over managed hemiboreal forests

Abstract The view angle range of Sentinel-1 SAR in the Interferometric Wide swath (IW) measurement mode is 29.1° – 46.0°. The dependence of backscatter on the arbitrary local incidence angle is usually corrected using a linear regression model where the incidence angle is a predictor variable. We analysed the whole time series of Sentinel-1 SAR VV-polarised backscatter over the flat 15×15 km test site in Laeva, Estonia (26° 26′ 43″ E; 58° 31′ 56″ N). Time series containing measurements from three different orbits were constructed for 3,159 stands from nighttime data and for 1,105 stands from daytime data. We can confirm that daytime backscatter is systematically greater than nighttime backscatter. We found a significant deviation from linearity in the backscatter dependence on local incidence angle. The empirical finding may be caused by the microwave scattering dependence on local incidence angle or by the influence of Sentinel-1 SAR sub-swath configuration in the Terrain Observation with Progressive Scans SAR (TOPSAR) method that is used for the measurements.

NaGAN: Nadir-like Generative Adversarial Network for Off-Nadir Object Detection of Multi-View Remote Sensing Imagery

Detecting off-nadir objects is a well-known challenge in remote sensing due to the distortion and mutable representation. Existing methods mainly focus on a narrow range of view angles, and they ignore broad-view pantoscopic remote sensing imagery. To address the off-nadir object detection problem in remote sensing, a new nadir-like generative adversarial network (NaGAN) is proposed in this paper by narrowing the representation differences between the off-nadir and nadir object. NaGAN consists of a generator and a discriminator, in which the generator learns to transform the off-nadir object to a nadir-like one so that they are difficult to discriminate by the discriminator, and the discriminator competes with the generator to learn more nadir-like features. With the progressive competition between the generator and discriminator, the performances of off-nadir object detection are improved significantly. Extensive evaluations on the challenging SpaceNet benchmark for remote sensing demonstrate the superiority of NaGAN to the well-established state-of-the-art in detecting off-nadir objects.

Experimental study of fire plume temperature and radiant heat flux of a horizontal jet flame impinging a wall

Jet fire usually appears in natural gas fuel production and transportation due to uncontrolled fuel leakage. Jet fire can impinge on equipment surface or a passive firewall to make the fire plume temperature and the radiant heat flux complex. Experiments of a horizontal jet flame impinging a wall under various fuel initial velocity and nozzle-wall spacing were carried out. Results show the changing relationship between the amount of oxygen required and the actual amount of oxygen results in the different temperature distribution of fire plume on the wall surface. A new dimensionless number is proposed to determine the maximum rising temperature of fire plume on the wall surface. The fire plume volume and the distance between a certain position and fire plume within the viewing angle range of the radiometer, as two important factors, can explain the trend of radiant heat flux well. A virtual total radiant heat flux Qv,tr received by a core area of the horizontal jet fire impinging the wall is estimated. Qv,tr firstly increases, and then decreases with Zn-w increasing. Increasing fire plume volume and increasing distance between the wall and the fire plume have the opposite effect on controlling Qv,tr together.

Exact reconstruction condition for angle-limited computed tomography of chemiluminescence.

Computed tomography of chemiluminescence (CTC) is an effective technique for three-dimensional (3D) combustion diagnostics. It reconstructs the 3D concentrations of intermediate species or 3D images of flame topology by multiple chemiluminescence projections captured from different perspectives. In the previous studies of CTC systems, it was assumed that projections from arbitrary perspectives are available. However, for some practical applications, the range of view angles and the number of projections might be restricted due to the optical access limitation, greatly affecting the reconstruction quality. In this paper, the exact reconstruction condition for angle-limited computed tomography of chemiluminescence was studied based on Mojette transform theories, and it was demonstrated by numerical simulations and experiments. The studies indicate that the object tested within limited angles can be well reconstructed when the number of grids, the number of projections, and the sampling rate of projections satisfy the exact reconstruction condition. By increasing the sampling rate of projections, high-quality tomographic reconstruction can be achieved by a few projections in a small angle range. Although this technique is discussed under combustion diagnostics, it can also be used and adapted for other tomography methods.

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Computerised Tomography Analysis of Pelvic Inlet and Outlet Fluoroscopic View Angles.

Pelvic inlet and outlet fluoroscopy views are routinely used in operative treatment of posterior pelvic ring injuries. In this study, we aimed to evaluate the angles of pelvic inlet and outlet fluoroscopic view, their differences with hip flexion and the correlation of these differences with sacral slope changes. Sagittal reconstructions of 100 lumbopelvic CT were used to measure sacral slope, pelvic inlet and outlet view angles. The range of pelvic inlet-outlet view angles and their relation with age, sex and sacral slope were analyzed. In ten of these 100 patients, who were undergone a second CT imaging, hips were passively flexed to 60° to change pelvic tilt. The difference in sacral slope and pelvic inlet-outlet view angles in different positions were compared. Mean angles for inlet view, outlet view and sacral slope were 28.9, 41.4 and 37.0, respectively. There was no difference between males and females (p > 0.05). Pelvic outlet angles had a negative correlation with age (p < 0.05). Sacral slope changes with hip flexion showed a negative correlation with inlet angles and positive correlation with outlet angles (p < 0.05). The differences in sacral slope, pelvic inlet and outlet view angles between two measurements were equal. The pelvic inlet and outlet view angles shows a wide range without a standard so we suggest preoperative CT scan to plan the optimal angles before pelvic ring surgery. The difference in these angles due to pelvic tilt during the surgery may be corrected by measuring the sacral slope difference.

Highly linearly polarized light emission from flexible organic light-emitting devices capitalized on integrated ultrathin metal-dielectric nanograting.

Although there have been tremendous achievements ever since the first work on an organic electroluminescent (EL) device that emitted polarized light, the development of flexible polarized emission organic light-emitting devices (OLEDs) is not without hurdles, and the challenge towards real-world applications still requires tremendous effort. In this paper, we proposed highly linearly polarized light-emission from flexible green OLEDs capitalized on integrated ultrathin metal-dielectric nanograting. The acquired polarized device with meticulously optimized geometric parameters yields an angle-invariant average extinction ratio beyond 20.0 dB within a viewing angle range of ± 60°. The detailed analysis illustrates that surface plasmons and cavity modes are simultaneously contributed to the TM-polarized light selection. We hope that the presented approach will open new opportunities for designing flexible polarized light sources.

An intrinsic algorithm for viewing angle tolerance of object discrimination in human subjects.

Prevailing theories suggest that view-invariant object recognition is accomplished via spatiotemporal correlations of multiple views that bind different views to the same object. However, it is unknown how the exposure to multiple views without association affects view-invariant recognition generating. Behavioural studies have shown that monkeys acquired view-invariant object recognition capability in a range of the viewing angles of 30° to 60° after experiencing discrimination of similar objects at each of several viewing angles without associating different views, but the monkeys could not discriminate novel objects from similar distractors when the viewing angle changed. In the present study the development of the view invariance was tested in the human subjects and compared with the results of the monkeys previously reported. The view-invariant object recognition capability of human subjects was tested using either familiar objects that the subjects experienced in a preparatory object discrimination task at the same viewpoints or novel objects that the subjects had never experienced. In the viewing angle range of 30°, human subjects showed significant object discrimination capability across views, with no need for prior experience of the objects. Prior discrimination experience within the same viewpoints endowed the human subjects with broadening of the viewing angle tuning, because an object discrimination test immediately after the prior discrimination experience at a single view showed wider viewing angle tuning than a test without prior experience. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Simulation of a new architecture of organic white-light-emitting diode by quantum dot and photonic crystal to improve efficiency

A novel inverted hybrid quantum dot/organic light-emitting diode (IH-QDOLED) with a transparent conducting oxide photonic crystal structure is proposed in this study. Such improved electrical and optical characteristics as luminescence efficiency, extraction efficiency, external quantum efficiency, carrier injection, size-tunable color of QDs, and solution-processable fabrication make IH-QDOLEDs a good candidate with which to achieve high-performance and low-cost LED (light-emitting diode) devices. These efficient LEDs consist of three rows of CdSe quantum dots with different sizes blended in TPBi. In order to optimize the IH-QDOLED structure, we have performed a simulation based on the finite difference time domain (FDTD) method. Also, the characteristics of this novel structure have been compared with those of a conventional structure. As it is found, the maximum external quantum efficiency (EQE) is increased from 30 % to 50 %, and the turn-on voltage has risen from 4.5 V to 5.5 V, compared to the conventional structure. Our results show that the angular distribution of the radiant power is uniform over a wider range of view angles, which can be attributed to the interaction of guided modes with an embedded photonic crystal structure.

26.2: Invited Paper: Diffused Light Control by Layer‐Structured PDLC for Future Viewing Angle Controllable Display Applications

We have established a control technique of light distribution pattern by controlling an internal polymer structure of PDLCs. We achieved layer‐structured PDLC by using micro convex structures and irradiating them with unidirectional diffused UV light. The backlight system using layer‐structured PDLC and collimated backlight enables to control the viewing angle range of LCDs with high light utilization efficiency.

Fabrication of a controllable anti-peeping device with a laminated structure of microlouver and polymer dispersed liquid crystals film

ABSTRACTDisplay devices with the narrow viewing angle (NVA) and the wide viewing angle (WVA) characteristics can simultaneously meet the demands for privacy protection and information sharing. Herein, we propose a novel method for fabricating a controllable anti-peeping device with a laminated structure of microlouver and polymer dispersed liquid crystals (PDLCs) film, and this device can be reversibly switched between a wider viewing angle range (VAR) for the WVA mode and a narrower viewing angle range (VAR) for the NVA mode at 0 V and 8 V, respectively. Also, the VARs of the controllable anti-peeping device can be dynamically tuned by varying dimensions of the microlouver structures and applying various voltages across the PDLCs film from 0 V to 8 V. The as-fabricated device provides display devices with controllable viewing angle characteristics, which can be applied in the display field with fascinating and practical functions.

3D model based shading correction for the enhancement of multispectral colour measurement accuracy

Shading effects induced by illumination and local object surface orientation could strongly deteriorate the accuracy of colour imaging. Therefore, a shading correction is needed for high colour fidelity. In this work a 3D model based inverse rendering approach is proposed for a narrowband multispectral 3D colour imaging system with a calibrated extern broadband light source. The colourimetric evaluation with an X-Rite colour checker shows that the proposed method could ensure a mean colour difference value CIEDE2000 ΔE < 3 for the viewing angle range -30° to 30°, while the maximal improvement factor concerning mean ΔE comes to 2.86.

Assessment of Satellite-Derived Surface Reflectances by NASA’s CAR Airborne Radiometer over Railroad Valley Playa

CAR (Cloud Absorption Radiometer) is a multi-angular and multi-spectral airborne radiometer instrument, whose radiometric and geometric characteristics are well calibrated and adjusted before and after each flight campaign. CAR was built by NASA (National Aeronautics and Space Administration) in 1984. On 16 May 2008, a CAR flight campaign took place over the well-known calibration and validation site of Railroad Valley in Nevada, USA (38.504°N, 115.692°W). The campaign coincided with the overpasses of several key EO (Earth Observation) satellites such as Landsat-7, Envisat and Terra. Thus, there are nearly simultaneous measurements from these satellites and the CAR airborne sensor over the same calibration site. The CAR spectral bands are close to those of most EO satellites. CAR has the ability to cover the whole range of azimuth view angles and a variety of zenith angles depending on altitude and, as a consequence, the biases seen between satellite and CAR measurements due to both unmatched spectral bands and unmatched angles can be significantly reduced. A comparison is presented here between CAR’s land surface reflectance (BRF or Bidirectional Reflectance Factor) with those derived from Terra/MODIS (MOD09 and MAIAC), Terra/MISR, Envisat/MERIS and Landsat-7. In this study, we utilized CAR data from low altitude flights (approx. 180 m above the surface) in order to minimize the effects of the atmosphere on these measurements and then obtain a valuable ground-truth data set of surface reflectance. Furthermore, this study shows that differences between measurements caused by surface heterogeneity can be tolerated, thanks to the high homogeneity of the study site on the one hand, and on the other hand, to the spatial sampling and the large number of CAR samples. These results demonstrate that satellite BRF measurements over this site are in good agreement with CAR with variable biases across different spectral bands. This is most likely due to residual aerosol effects in the EO derived reflectances.

Simulation and SMAP Observation of Sun-Glint Over the Land Surface at the L-Band

We investigate the magnitude of Sun-glint through modeling the Soil Moisture Active Passive (SMAP) brightness temperature (BT). Model results show that the specular reflection of Sun-glint in the L-band can spread over a wide range of view angles due to the roughness and undulation of the land surface and therefore affect SMAP radiometer observations. Due to SMAP’s low incidence angle (40°), Sun-glint in the specular direction is never observed, and only the noncoherent component of Sun-glint has influence on SMAP observations. Sun-glint is particularly an issue over wet soil surfaces at low solar zenith angles (SZAs), and caution has to be taken for the terrain effect even for high SZAs, because the local solar incident angle can be significantly changed by the terrain slope and then the specular reflection of Sun-glint can be viewed by SMAP. Model results also show that BT in V-pol is less contaminated by Sun-glint than that in H-pol. During an intense solar radio burst, it was found that the land surface BT in H-pol increased by 50 K in the forward scattering direction from the SMAP observation. This is roughly equivalent to 1 K increment by every 100 solar flux units on a dry soil and/or dense vegetation. When the solar activity is quiet in 2015, the Sun-glint from both wet land and ocean surfaces can reach up to 10 K in the SMAP L1B BT product. This paper suggests that BT observations around the solar specular direction should be masked for soil moisture retrieval at the L-band.

Minimizing Reflectance Anisotropy Effects in Airborne Spectroscopy Data Using Ross–Li Model Inversion With Continuous Field Land Cover Stratification

The spectral and radiometric quality of airborne imaging spectrometer data is affected by the anisotropic reflectance behavior of the imaged surface. Illumination and observation angle-dependent patterns of surface reflected radiation propagate into products, hinder quantitative assessment of biophysical/biochemical parameters, and decrease the comparability of data from multiple flight lines. The Ross–Li model, originally developed for multiangular observations, can be inverted to estimate and correct for surface anisotropy effects. This requires land cover be stratified into distinct types of scattering behavior. When the observations subsumed in these classes cover a range of view angles, a pseudo multiangular view on the surface can be employed to invert the Ross–Li model. A discrete land cover classification, however, bears the risk of inappropriate scattering correction resulting in spatial artifacts in the corrected data, predominantly in transition regions of two land cover types (e.g., soil and sparse vegetation with varying fractions). We invert the Ross–Li model on continuous land cover fraction layers. We decompose land cover in dominating structural types using linear spectral unmixing. Ross–Li kernel weights and formulations are estimated for each type independently; the correction is then applied pixel-wise according to the fractional distribution. The corrected Airborne Prism EXperiment imaging spectrometer data show significant reduction of anisotropic reflectance effects of up to 90% (average 60% to 75%, $p=0.05$ ), measured in the overlapping regions of adjacent flight lines. No spatial artifacts or spectral irregularities are observed after correction.

The impact of size variations in the ground instantaneous field of view of pixels on MODIS BRDF modelling

Bidirectional reflectance distribution functions (BRDF) seek to represent surface reflectance anisotropy resulting from surface physical structure and changes in a satellite sensor’s view and solar illumination angles. NASA’s MODerate resolution imaging spectroradiometer (MODIS) is a wide field of view sensor that generates observations over a large range of view angles. Based on MODIS observations, a BRDF product and several sub-products have been developed by MODIS science teams, i.e. the MCD43 product suite. Variations in pixels’ ground instantaneous field of view (GIFOV), i.e. the size of a pixel’s footprint on the ground, is a well known effect associated with wide field of view sensors such as MODIS, but is not specifically considered in the MODIS BRDF algorithm nor has research been undertaken into its effects on MODIS BRDF modelling. This paper introduces two metrics to examine the relationship between reflectance variations associated with changes in MODIS pixels’ GIFOV and the MODIS BRDF (MCD43) product. These metrics are applied to four different study areas and epochs across the Australian continent. The two metrics are shown to be well correlated (mean correlation coefficient of 0.81 for the four study areas); suggesting that variations in pixels’ GIFOV are a consistent, non-random source of variance in MODIS BRDF modelling. The results contained in this paper suggest that all downstream products which include MODIS BRDF processing in their derivation and results directly based on MODIS BRDF processing may need to be reassessed.