Light Acquisition Research Articles

No-Reference Light Field Image Quality Assessment Based on Spatial-Angular Measurement

Light field image quality assessment (LFI-QA) is a significant and challenging research problem. It helps to better guide light field acquisition, processing and applications. However, only a few objective models have been proposed and none of them completely consider intrinsic factors affecting the LFI quality. In this paper, we propose a No-Reference Light Field image Quality Assessment (NR-LFQA) scheme, where the main idea is to quantify the LFI quality degradation through evaluating the spatial quality and angular consistency. We first measure the spatial quality deterioration by capturing the naturalness distribution of the light field cyclopean image array, which is formed when human observes the LFI. Then, as a transformed representation of LFI, the Epipolar Plane Image (EPI) contains the slopes of lines and involves the angular information. Therefore, EPI is utilized to extract the global and local features from LFI to measure angular consistency degradation. Specifically, the distribution of gradient direction map of EPI is proposed to measure the global angular consistency distortion in the LFI. We further propose the weighted local binary pattern to capture the characteristics of local angular consistency degradation. Extensive experimental results on four publicly available LFI quality datasets demonstrate that the proposed method outperforms state-of-the-art 2D, 3D, multi-view, and LFI quality assessment algorithms.

Relación entre estrategias de historia de vida y atributos funcionales en especies arbóreas del Bosque Atlántico semideciduo de Misiones

Functional characterization of plant responses to ecological factors is a basic goal in ecology. General trends were found indicating associations between functional traits and life history strategies such as acquisitive vs. conservative species. Different regeneration requirements among tropical trees were related to morphological and reproductive traits. Here, we studied if ecological groups of trees in the Atlantic Forest in Misiones are related to differences in height, wood density and seed mass. We also examined the relationships between those traits and leaf traits related to the acquisitive-conservative strategies. Plant height, wood density and seed mass were obtained from the literature for 62 common tree species in the studied area as well as their ecological classification. In addition, leaf area, specific leaf area and leaf thickness, were obtained from the literature for a subset of 39 tree species. Pioneer trees showed lower height and lighter wood than those classified as climax but these values widely overlapped among intermediate groups suggesting the existence of a functional gradient and that discrete classes are difficult to apply. Higher seed mass was observed among trees with medium wood density. No relationship between these traits and foliar traits was observed. Thus, the difference between species with acquisitive or conservative leaves constitutes a different functional axis from the one associated to wood density and height. Based on our results and previous findings we propose a conceptual model for the functional characterization of tree species in the Atlantic Forest in Misiones using wood density, as an indicator shade tolerance, and height, as an indicator of light acquisition strategy and related to dispersal syndrome of seeds.https://doi.org/10.25260/EA.19.29.3.0.827

Multiple facets of diversity effects on plant productivity: Species richness, functional diversity, species identity and intraspecific competition

Abstract Deciphering the mechanisms that drive variation in biomass production across plant communities of contrasting species composition and diversity is a main challenge of biodiversity–ecosystem functioning research. Niche complementarity and selection effect have been widely investigated to address biodiversity–productivity relationships. However, the overlooking of the specific role played by key species has limited so far our capacity to comprehensively assess the relative importance of other potential drivers of biodiversity effects. Here, we conducted a grassland diversity–productivity experiment to test how four potential facets of biodiversity effects, namely species richness, functional diversity, species identity and the relaxation of intraspecific competition, account for variations in above and root biomass production. We grew six plant species in monoculture, as well as in every combination of two, three and six species. Plant density was kept constant across the richness gradient but we additionally grew each species in half‐density monoculture to estimate the strength of intraspecific competition for each studied species. We characterized eight functional traits, including root traits, related to nutrient and light acquisition and computed both the functional dissimilarity and the community‐weighted mean (CWM) of each trait. We further partitioned above‐ground biodiversity effect into complementarity and selection effects. We observed strong positive biodiversity effects on both above‐ground and root biomass as well as strong positive complementarity effect. These arose largely from the presence of a particular species (Plantago lanceolata) and from CWM trait values more than from a higher functional dissimilarity in plant mixtures. P. lanceolata displayed the highest intraspecific competition, which was strongly relaxed in species mixtures. By contrast, the presence of Sanguisorba minor negatively affected the productivity of plant mixtures, this species suffering more from interspecific than intraspecific competition. This study provides strong evidences that the search for key species is critical to understand the role of species diversity on ecosystem functioning and demonstrates the major role that the balance between intraspecific and interspecific competition plays in biodiversity–ecosystem functioning relationships. Developing more integrative approaches in community and ecosystem ecology can offer opportunities to better understand the role that species diversity plays on ecosystem functioning. A free Plain Language Summary can be found within the Supporting Information of this article.

First measurements of a magnetically driven fast-ion loss detector on ASDEX Upgrade

A new scintillator-based fast-ion loss detector (FILD) has been deployed ∼45̂ below the midplane of the ASDEX Upgrade tokamak. Port unavailability at this remote location requires an in-situ magnetically driven manipulator to move the diagnostic head horizontally through the scrape-off layer (SOL). The linear displacement is produced by an externally energized coil, whose magnetic dipole tries to align with the toroidal component of the tokamak magnetic field. The insertion is given by force balance between a retaining spring and the energized solenoid, whose current is regulated in real-time, opening the possibility of self-adaptive real-time control of the probe head location based on its temperature. The diagnostic head contains a scintillator screen, Faraday cup, thermocouple and collimator systems. The scintillator image is transferred to a vacuum window using a 3.5 meters quartz image guide. The light acquisition system is composed by a charge coupled device (CCD) camera, for high velocity-space resolution, and by an 8×4 channels avalanche photo diode (APD) camera, for high temporal resolution (up to 2 MHz). First measurements of magnetohydrodynamic (MHD) induced fast-ion losses and radially resolved fast-ion losses are presented.

ZDAQ, a light data acquisition framework based on ZeroMQ

ZDAQ is a light data acquisition system, based on ZeroMQ and mongoose-cpp networking frameworks. Providing binary data collection, events building, web accessible finite state machine and process control, it is well suited to manage distributed data source of laboratory or beam test. It provides a simple event building (one unique process, no parallel building) with flexible data writing formats. It is intensively used for the tests of the Semi Digital HCAL (RPC+Fe) prototype designed for ILD and also for the tests of the new electronic for improved RPC (CMS HL-LHC upgrade)

Plant economic strategies of grassland species control soil carbon dynamics through rhizodeposition

Abstract The plant economics spectrum is increasingly recognized as a major determinant of plant species effects on terrestrial ecosystem functioning related to carbon cycling. However, the role of plant economic strategies in the effects of living root activity on soil organic carbon (SOC) dynamics through rhizodeposition remains unexplored, despite SOC being the largest terrestrial carbon pool. Using a continuous 13C‐labelling method allowing partitioning of plant and soil sources to carbon fluxes and pools, we studied here the linkages between plant economic strategies and SOC cycling processes in a ‘common garden’ greenhouse experiment. It includes a panel of 12 grassland species selected along a gradient of economic traits and belonging to three functionnal groups (C3 grasses, forbs and legumes). All species induced an acceleration of native SOC mineralization but this rhizosphere priming effect (RPE) substantially differed across species and varied eleven‐fold by the end of the experiment (from +26% to +295% relative to unplanted soil). Interspecific variation in RPE was primarily linked to plant photosynthetic activity associated to species economic strategies of light and CO2 resource acquisition and processing. Fast‐growing acquisitive species, such as legumes, featured large RPE, in relation with their high canopy photosynthesis coupled to high leaf photosynthetic capacity and large net primary productivity allocated above‐ground. This large RPE was further associated with high root metabolic activity, rhizodeposition and soil microbial activity. In contrast, fine‐root growth and economic traits related to soil resource foraging ability were poor predictors of RPE. The formation of new root‐derived SOC varied nine‐fold across species and was similarly positively related to the net primary productivity allocated above‐ground. Fast‐growing acquisitive species with a high photosynthetic activity induced a disproportionately large RPE relative to SOC formation. Synthesis. Overall, our study demonstrates that rhizodeposition is a major mechanism through which plant economic strategies of grassland species control soil carbon dynamics. Acquisitive versus conservative species were associated with high versus low rates of photosynthesis and rhizodeposition, in turn leading to fast versus slow SOC turnover. This emphasizes the importance of considering rhizosphere processes for understanding plant species effects on soil biogeochemistry.

Multipole Resonance in Arrays of Diamond Dielectric: A Metamaterial Perfect Absorber in the Visible Regime.

Excellent characteristics and promising application prospects promote the rapid development of metamaterials. We have numerically proposed and demonstrated a novel subwavelength broadband metamaterial perfect absorber (BMPA) based on diamond dielectric arrays. The proposed absorber is composed of an ultra-thin two-layer structure covering the dielectric periodic array on a metal substrate. The materials of dielectric silicon (Si) and gold (Au) substrate are discussed in detail. In addition, different dielectric and refractory materials are also applied to achieve broadband absorption, which will make the proposed absorber greatly broaden the application field. A perfect absorption window (i.e., absorption rate exceeding 90%) can be obtained from near-ultraviolet to the visible range. The average absorption rate of 93.3% is achieved in the visible range. The results of multipole decomposition show that broadband absorption is mainly caused by electromagnetic dipole resonance and lattice resonance in a periodic array of Si. The proposed absorber can be extended freely by adjusting the structural parameters. The polarization-independent and incident angle insensitivity are proved. The proposed absorber may well be used in light energy acquisition, as well as for the scalability of optoelectronic and sensing devices.

Flexibly Connectable Light Field System For Free View Exploration

Conventional captured-image-based virtual reality (VR) systems have three degrees of freedom (DoFs), where only rotational user motion is tracked for view rendering. This is a major cause of the reduced sense of reality. To increase user immersion levels akin to the real world, 3-DoF+ VR systems that support not only rotational but also translational view changes have been proposed. The light-field (LF) approach is suitable for this type of 3-DoF+ VR because it renders a view from a free view position by simply combining lights. Many previous systems have limited scalability because they assume a single LF for the acquisition and representation of light. One recent work connects multiple LFs at a physical intersection to increase the scalability. However, these fixed connection points limit the renderable view range and the layout of multiple LFs. Furthermore, in conventional single- or multiple-LF systems, the representable ranges of the view positions are highly dependent on the input field-of-view (FOV) of the camera used. In order to realize a wide view exploration range, the above-mentioned limitations must be overcome. This paper proposes a flexible connection scheme for multiple-LF systems taking advantage of the constant radiance of rays in LF theory. The proposed flexibly connectable LF system is able to widen the range of the renderable view position under reasonable conditions of the camera FOV. A light-field unit (LFU) which uses the proposed flexible connection is implemented. The LFU has a square-shaped structure and is thus easily stackable. This offers the advantage of dramatically expanding the scope of view explorations. The proposed LFU achieves 3-DoF+ VR with good quality as well as high scalability. Its cost-performance outcome is also better compared to those in previous works.

Noise-reduced optical ultrasound sensor via signal duplication for photoacoustic microscopy

Fiber-laser-based ultrasound sensors have attracted great interest because of their applications in compact and endoscopic imaging modalities. The noises of such an ultrasound sensor may originate from its light source, optical amplifier, photodetector, and data acquisition card. Here we present an optical signal duplication technique that can increase the signal-to-noise ratio by 1.6–2.4 times. Furthermore, this technique does not require multiple signal excitations in a single voxel and, thus, allows for a high imaging speed in most applications. We demonstrate the optical signal duplication technique in all-optical laser-scanning photoacoustic microscopy. In vivo microvascular imaging shows that the noise-reduced sensor can enhance the contrast-to-noise ratio by 3.5 dB.

Effects of light conditions on growth and defense compound contents of Datura inoxia and D. stramonium.

We examined the effects of light conditions on plant growth and production of defense compounds in the toxic species Datura inoxia and D. stramonium. Specifically, we investigated morphological and physiological traits, including the contents of nitrogen-based tropane alkaloids (atropine and scopolamine) as defense compounds, under three light conditions: 100%, 80%, and 50% of full sunlight. Both species showed similar morphological and physiological responses to exposure to different intensities of light. Although the total plant mass decreased under lower light conditions, the total leaf area per plant increased. The reason being that the leaf mass per plant did not decrease, while the leaf mass per unit area decreased. Leaf nitrogen and chlorophyll concentrations and the chlorophyll/nitrogen ratio increased under lower light conditions, whereas the chlorophyll a/b ratio decreased. These morphological and physiological changes may be seen as ways to increase light acquisition under low light conditions. Leaf atropine and scopolamine concentrations did not differ among the three light conditions for both species. In conclusion, both Datura species underwent morphological and physiological changes under low light conditions, enabling them to use carbon and nitrogen to increase light acquisition while maintaining their chemical defense capability.

Preparation and properties of visible light responsive RGO/In2TiO5 nanobelts for photocatalytic degradation of organic pollutants

Electrospinning and solvothermal methods were used to synthesize RGO/In2TiO5 nanobelts. The prepared samples were characterized with XRD, SEM, UV–vis DRS, N2 adsorption-desorption isotherms, FT-IR and Raman spectroscopy. The results have shown that the samples presented an orthorhombic structure without any secondary phase, and the morphology was not noticeably changed after coupling RGO. The RGO (1 wt%)/In2TiO5 nanobelts showed the highest photocatalytic activity. After 120 min of simulated sunlight irradiation, the degradation rate of RhB was up to 97.5%. Meanwhile, RGO/In2TiO5 nanobelts showed excellent photocatalytic degradation property for fluoroquinolone antibiotic levofloxacin (LEV). The increased electrons and holes separation, enhanced active sites and improved light acquisition were the reasons for the outstanding photocatalytic performances of the photocatalyst. Moreover, terephthalic acid photoluminescence (TA-PL) experiments confirmed that the hydroxyl radicals (OH) were generated during the photocatalysis processes. The enhanced photocatalytic activity allows RGO/In2TiO5 nanobelts to be a promising candidate to treat antibiotic medical wastewater field in the future.

Precise measurement of the light curves for space debris with wide field of view telescope

Optical means are the main techniques for space debris observations. Wide field of view telescopes play important roles and exhibit specially high efficiency in space debris surveys and catalogue maintenance. However, due to the defects of the extreme optical design of the telescope, as well as the errors caused by non-standard photometric systems, challenges arise for the light curve acquisition and precise photometry. As the rise of the demand of rotational characteristics investigations for space debris and active debris removal, measuring the brightness variations of space debris with high accuracy is crucial and important. Under this circumstance, an improved method which measures the light curves of space debris precisely for wide field of view telescopes is proposed. In our pipeline the background stellar is optimally selected, then the local reference frame is built through consecutive frames, and the brightness variation of the object is obtained directly based on the ratio of the intensity itself and the one of reference star. Trial observations are performed and a number of raw CCD images is utilized to test the method. It is demonstrated that the proposed method exhibits a better accuracy and robustness than the standard photometric technique on measuring the light curves of space debris. It provides a new solution for precise measurement of light curves with wide field of view sensors, and deserves wide applications in researches of light curves and rotational characteristics for space debris.

Groundwater discharge gives periphyton a competitive advantage over macrophytes

Lacustrine groundwater discharge (LGD) can significantly contribute to nutrient budgets of lakes. LGD usually occurs in shallow littoral zones, and thus, potentially affects periphyton and macrophytes. These benthic primary producers asymmetrically compete for resources, with periphyton and rooted macrophytes having an advantage in either light or sediment nutrient acquisition, respectively. LGD can advectively transport sediment phosphorus (P) into the water, supporting periphyton growth. We hypothesised that above a threshold level of sediment P concentrations, negative effects of periphyton shading exceed the positive effects of sediment P on macrophytes. We performed laboratory experiments comparing the growth of periphyton and a macrophyte (Stuckenia pectinata) at four different sediment P concentrations with and without simulated LGD. In LGD treatments, P mobilized from sediment promoted periphyton growth, and macrophyte growth rates negatively correlated with periphyton shading when experiments were performed with young plants. Macrophytes died when shading levels exceeded 75% of incident light. Our results confirm that LGD can significantly affect the competition between benthic primary producers at the expense of macrophytes. This process is supposed to be most relevant in oligotrophic water bodies or during periods of P deficiency in the open water, when advective transport of sediment P by LGD can prevent nutrient limitation in periphyton.

Light limitation increases multidimensional trait evenness in phytoplankton populations

Individual-level variation arising from responses to environmental gradients influences population and community dynamics. How such responses empirically relate to the mechanisms that govern species coexistence is, however, poorly understood. Previous results from l ake phytoplankton communities suggested that the evenness of organismal traits in multiple dimensions increases with resource limitation, possibly due to resource partitioning at the individual level. Here we experimentally tested the emergence of this pattern by growing two phytoplankton species (Pseudokirchneriella subcapitata and Microcystis aeruginosa) under a gradient of light intensity, in monoculture and jointly. Under low light (resource) conditions, the populations diversified into a wide range of phenotypes, which were evenly distributed in multidimensional trait space (defined by four pigment-related trait dimensions), consistent with the observed field pattern. Our interpretation is that under conditions of light limitation, individual phytoplankton cells alter photosynthetic traits to reduce overlap in light acquisition, acquiring unexploited resources and thereby likely maximising individual success. Our results provide prime experimental evidence that resource limitation increases the evenness of conspecific and heterospecific microbial phenotypes along trait axes, advancing our understanding of trait-based coexistence.

Single Remote Sensing Multispectral Image Dehazing Based on a Learning Framework

Given that a single remote sensing image dehazing is an ill-posed problem, this is still a challenging task. In order to improve the visibility of a single hazy remote sensing multispectral image, we developed a novel and effective algorithm based on a learning framework. A linear regression model with the relevant features of haze was established. And the gradient descent method is applied to the learning model. Then a hazy image accurate transmission map is obtained by learning the coefficients of the linear model. In addition, we proposed a more effective method to estimate the atmospheric light, which can restrain the influence of highlight areas on the atmospheric light acquisition. Compared with the traditional haze removal methods, the experimental results demonstrate that the proposed algorithm can achieve better visual effect and color fidelity. Both subjective evaluation and objective assessments indicate that the proposed method achieves a better performance than the state-of-the-art methods.

Measurement method of carbon dioxide using spatial decomposed parallel computing

According to the carbon dioxide (CO2) characteristics of weak absorption in the ultraviolet and visible (UV-VIS) bands, a measurement method based on spatial decomposed parallel computing of traditional differential optical absorption spectroscopy is proposed to measure CO2 vertical column concentration in ambient atmosphere. Firstly, American Standard Profile is used to define solar absorption spectrum, and the spectrum acquisition of the incident light converged by the telescope is described as observed parameters. On these bases, spectrometer line model is established. Then, atmospheric radiation transmission is simulated using parallel computing, which obviously reduces the computational complexity while balancing the interference that participates in the fitting. Simulation analyses show that the proposed method can reduce the computational complexity, and run time is reduced by 1.18 s compared with IMLM and IMAP-DOAS in the same configuration. The proposed method can also increase accuracy, with its inversion error reduced by 5.3% and residual reduced by 0.8% than differential optical absorption spectroscopy. The spatial decomposed parallel computing method has advantages in processing CO2, and it can be further used in the research of carbon sink.

Measurement method of carbon dioxide using spatial decomposed parallel computing

According to the carbon dioxide (CO2) characteristics of weak absorption in the ultraviolet and visible (UV-VIS) bands, a measurement method based on spatial decomposed parallel computing of traditional differential optical absorption spectroscopy is proposed to measure CO2 vertical column concentration in ambient atmosphere. Firstly, American Standard Profile is used to define solar absorption spectrum, and the spectrum acquisition of the incident light converged by the telescope is described as observed parameters. On these bases, spectrometer line model is established. Then, atmospheric radiation transmission is simulated using parallel computing, which obviously reduces the computational complexity while balancing the interference that participates in the fitting. Simulation analyses show that the proposed method can reduce the computational complexity, and run time is reduced by 1.18 s compared with IMLM and IMAP-DOAS in the same configuration. The proposed method can also increase accuracy, with its inversion error reduced by 5.3% and residual reduced by 0.8% than differential optical absorption spectroscopy. The spatial decomposed parallel computing method has advantages in processing CO2, and it can be further used in the research of carbon sink.

Registration Algorithm for Point Cloud Based on Normalized Cross-Correlation

We propose a registration algorithm based on neighborhood similarity for 3D point clouds collected by optical measurement and without prior information. The algorithm first applies the improved minimum spanning tree (Prim algorithm) to classify the point cloud in order to obtain the topology information of the data. Specifically, vectors among root nodes and child nodes are processed, and the points on nodes are classified into different levels according to their scanning angle to simplify data and preserve the most representative points. Then, through the perspective conversion between 2D and 3D and according to the corresponding point set obtained by previous classification, the fast normalized cross-correlation (a 2D matching criterion) is applied to determine the relationship between initial characteristic points. Finally, distance constraints remove the errors between point pairs and allow calculating the registration parameters. Experimental results show that the algorithm has high registration accuracy and is suitable for point cloud data obtained by laser and structured light acquisition.

A system for acquiring, processing, and rendering panoramic light field stills for virtual reality

We present a system for acquiring, processing, and rendering panoramic light field still photography for display in Virtual Reality (VR). We acquire spherical light field datasets with two novel light field camera rigs designed for portable and efficient light field acquisition. We introduce a novel real-time light field reconstruction algorithm that uses a per-view geometry and a disk-based blending field. We also demonstrate how to use a light field prefiltering operation to project from a high-quality offline reconstruction model into our real-time model while suppressing artifacts. We introduce a practical approach for compressing light fields by modifying the VP9 video codec to provide high quality compression with real-time, random access decompression. We combine these components into a complete light field system offering convenient acquisition, compact file size, and high-quality rendering while generating stereo views at 90Hz on commodity VR hardware. Using our system, we built a freely available light field experience application called Welcome to Light Fields featuring a library of panoramic light field stills for consumer VR which has been downloaded over 15,000 times.

Variation in species light acquisition traits under fluctuating light regimes: implications for non‐equilibrium coexistence

Resource distribution heterogeneity offers niche opportunities for species with different functional traits to develop and potentially coexist. Available light (photosynthetically active radiation or PAR) for suspended algae (phytoplankton) may fluctuate greatly over time and space. Species‐specific light acquisition traits capture important aspects of the ecophysiology of phytoplankton and characterize species growth at either limiting or saturating daily PAR supply. Efforts have been made to explain phytoplankton coexistence using species‐specific light acquisition traits under constant light conditions, but not under fluctuating light regimes that should facilitate non‐equilibrium coexistence. In the well‐mixed, hypertrophic Lake TaiHu (China), we incubated the phytoplankton community in bottles placed either at fixed depths or moved vertically through the water column to mimic vertical mixing. Incubations at constant depths received only the diurnal changes in light, while the moving bottles received rapidly fluctuating light. Species‐specific light acquisition traits of dominant cyanobacteria (Anabaena flos‐aquae, Microcystis spp.) and diatom (Aulacoseira granulata, Cyclotella pseudostelligera) species were characterized from their growth–light relationships that could explain relative biomasses along the daily PAR gradient under both constant and fluctuating light. Our study demonstrates the importance of interspecific differences in affinities to limiting and saturating light for the coexistence of phytoplankton species in spatially heterogeneous light conditions. Furthermore, we observed strong intraspecific differences in light acquisition traits between incubation under constant and fluctuating light – leading to the reversal of light utilization strategies of species. This increased the niche space for acclimated species, precluding competitive exclusion. These observations could enhance our understanding of the mechanisms behind the Paradox of the Plankton.