Spectral Mismatches Research Articles

Renewable energy for a green future: Electricity produced from efficient luminescent solar concentrators

This article proposes an overarching review of the technologies engaged in world wide energy demand which uses from non-renewable to renewable energies. The electricity generated from renewable systems is largely reducing CO2 emissions, one of the greenhouse gasses realesed from non-renewable energy sources that contribute to the global warming. The photovoltaic (PV) system is the technology with stronger potential to produce affordable electricity using solar energy. Therefore, we are focusing on the PVs regarding i) how they are assembled, ii) the energy losses from spectral mismatches, and iii) the improvements of their efficiencies by several ways, which include the connection of PVs with new techologies, e.g. the luminescent solar concentrator (LSC). Recent studies have reported advantages of applying LSCs connected to PVs’ cells, as well as some strategies for minimizing or eliminating self-absorption losses. Moreover, some efficiency meters evaluate LSCs’ operation. Guided by mainly recent researches, this article approaches flexibility, low cost, easy fabrication, and great efficiency of LSCs, the main goal for the PVs’ productions upon power electricity demand.

Too Many Shades of Grey: Photometrically and Spectrally Mismatched Targets and Backgrounds in Printed Acuity Tests for Infants and Young Children.

PurposeAcuity tests for infants and young children use preferential looking methods that require a perceptual match of brightness and color between grey background and target spatial average. As a first step in exploring this matching, this article measures photometric and colorimetric matches in these acuity tests.MethodsThe luminance, uniformity, contrast, and color spectra of Teller Acuity Cards, Keeler Acuity Cards for Infants, and Lea Paddles under ambient, warm, and cold lighting, and of grey-emulating patterns on four digital displays, were measured. Five normal adults’ acuities were tested at 10 m observationally.ResultsLuminance and spectral mismatches between target and background were found for the printed tests (Weber contrasts of 0.3% [Teller Acuity Cards], −1.7% [Keeler Acuity Cards for Infants], and −26% [Lea Paddles]). Lighting condition had little effect on contrast, and all printed tests and digital displays met established adult test luminance and uniformity standards. Digital display grey backgrounds had very similar luminance and color whether generated by a checkerboard, vertical grating, or horizontal grating. Improbably good psychophysical acuities (better than −0.300 logMAR: (logarithm of the minimum angle of resolution)) were recorded from adults using the printed tests at 10 m, but not using the digital test Peekaboo Vision.ConclusionsPerceptible contrast between target and background could lead to an incorrectly measured, excessively good acuity. It is not clear whether the luminance and spectral contrasts described here have clinically meaningful consequences for the target patient group, but they may be avoidable using digital tests.Translational RelevanceCurrent clinical infant acuity tests present photometric mismatches that may return inaccurate testing results.

Can UAVs fill the gap between in situ surveys and satellites for habitat mapping?

Habitat mapping is an essential descriptor to monitor and manage natural or semi-natural ecosystems. Habitats integrate both the environmental conditions and the related biodiversity. However, it remains challenging to map certain habitats such as inland wetlands due to spectral, spatial and temporal variability in the vegetation cover. Currently, no satellite constellations optimize the spectral, spatial and temporal resolutions required to map wetlands according to the habitats discriminated from in situ surveys. Our approach aims to combine satellite and unmanned aerial vehicle (UAV) data to exceed their respective limitations. Both data sources were combined through a spectral unmixing algorithm with the hypothesis that endmembers from UAV data are pure enough to enhance plant community abundances estimated from satellite data. The experiment was conducted on the regional preserve of the Sougéal marsh, a wet grassland of 174 ha located upstream of the Mont-Saint-Michel Bay. Two satellite data sources - Sentinel-2 and Pleiades - and three acquisition periods - November 2017, April 2018 and May 2018 - were considered. A reference map of plant community distribution was produced from UAV multitemporal data and floristic surveys to validate the unmixing of satellite data. This study shows innovative results and perspectives: while UAV can improve habitat discrimination, results vary among acquisition periods and habitats. Results illustrate well the great potential of combined UAV and satellite data but also demonstrate the influence of endmembers on the unmixing process and technical limitations (e.g. spectral mismatches between sensors), which can be overcome using domain adaptation.

Autoregressive Model Based Polarimetric Adaptive Detection Scheme Part II: Performance Assessment Under Spectral Model Mismatch

This article addresses the problem of target detection in coherent radar systems equipped with multiple polarimetric channels. In “Part I” of this two-part study, a multichannel autoregressive model based polarimetric detection scheme has been developed and its performance has been studied against clutter with characteristics exactly matching the adopted parametric model. In the second part of this study, the performance assessment is extended, by means of theoretical and simulated analyses, to include the case of disturbance components with diverse spectral characteristics. Consequently, an appropriate modification is introduced to the detection scheme to make it robust to typical spectral mismatches occurring in practical situations. Finally, the effectiveness of the resulting detection scheme is proved against simulated and experimental data.

Sparse Hyperspectral Unmixing Using Spectral Library Adaptive Adjustment

Sparse regression methods based on the spectral libraries have shown promise for hyperspectral unmixing, which assumes that the observed image can be represented linearly by a small subset of a known spectral library. However, the spectral mismatches are often assumed to occur between the actual endmembers and the corresponding signatures in the spectral library, which greatly limits the application of the sparse unmixing method. In this article, we address the abovementioned problem by adaptively adjusting the spectral library to match the current hyperspectral image during the unmixing procedure and propose a spectral library adaptive collaborative sparse unmixing model. In our model, we introduce both the spectral scaling factors and the spectral residual variables, which can adjust the spectral library in terms of spectral intensity and local spectral variations, respectively. Moreover, the first-order sparse property of the spectral difference is utilized to improve the accuracy of the spectral library adjustment. We solve our model by the alternating direction method of multipliers. Simulations and real-data experiments show that the proposed method is effective for reducing the impact of spectral library mismatches compared with state-of-the-art algorithms.

Spectral tuning of luminance cameras: A theoretical model and validation measurements

Presently, luminance distribution measurement devices, using High Dynamic Range technology, are increasingly used as they provide a lot of relevant data related to the lit environment at once. However, the accuracy of these devices can be a concern. It is expected that the accuracy would be improved by incorporating the effect of the camera spectral responsivity and the spectral power distribution of the illuminant under which the measurements are conducted. This study introduces two optimization criteria incorporating these aspects to improve the spectral match and the performance of luminance distribution measurement devices. Both criteria are tested in a theoretical model and in practical measurements using two cameras and three illuminants: LED, halogen and fluorescent. Both methodologies support the hypothesis that the conventional method to determine the luminance introduces spectral mismatches that can be limited by optimizing relative to the spectral responsivity of the camera. Additionally, substantial evidence was found, by both the theoretical model and the validation measurements, that the spectral power distribution of the illuminant also has an effect on the performance.

A New Unit Selection Optimisation Algorithm for Corpus-Based TTS Systems Using the RBF-Based Data Compression Technique

A major drawback of corpus-based speech synthesis systems is the use of large acoustic inventories, and currently one of the main challenges is the optimal representation of concatenation costs associated with units in the acoustic inventory. These concatenation costs are used to evaluate spectral mismatches between the acoustic units to be concatenated. The combinatorics of costs grows exponentially with the size of the acoustic inventories and can result in hundreds of millions or even billions of concatenation costs to be processed. Therefore, in this paper, we represent a novel unit selection optimization algorithm, which minimizes the size of concatenation costs through the vector quantization-based compression technique and tuple structures. Furthermore, the proposed optimization algorithm is designed to be used as an objective measure to optimize the performance of the unit selection cost function regarding the quality of the speech output, and to evaluate the effect of the vector quantization-based compression technique on its performance. The results obtained show that even when data compression is above 50%, the effect on the quality of the synthesized speech is negligible.

Proposal and evaluation of subordinate standard solar irradiance spectra for applications in solar energy systems

Reference solar irradiance spectra are needed to specify key parameters of solar technologies such as photovoltaic cell efficiency, in a comparable way. The IEC 60904-3 and ASTM G173 standards present such spectra for Direct Normal Irradiance (DNI) and Global Tilted Irradiance (GTI) on a 37° tilted sun-facing surface for one set of clear-sky conditions with an air mass of 1.5 and low aerosol content. The IEC/G173 standard spectra are the widely accepted references for these purposes. Hence, the authors support the future replacement of the outdated ISO 9845 spectra with the IEC spectra within the ongoing update of this ISO standard.The use of a single reference spectrum per component of irradiance is important for clarity when comparing and rating solar devices such as PV cells. However, at some locations the average spectra can differ strongly from those defined in the IEC/G173 standards due to widely different atmospheric conditions and collector tilt angles. Therefore, additional subordinate standard spectra for other atmospheric conditions and tilt angles are of interest for a rough comparison of product performance under representative field conditions, in addition to using the main standard spectrum for product certification under standard test conditions. This simplifies the product selection for solar power systems when a fully-detailed performance analysis is not feasible (e.g. small installations). Also, the effort for a detailed yield analyses can be reduced by decreasing the number of initial product options.After appropriate testing, this contribution suggests a number of additional spectra related to eight sets of atmospheric conditions and tilt angles that are currently considered within ASTM and ISO working groups. The additional spectra, called subordinate standard spectra, are motivated by significant spectral mismatches compared to the IEC/G173 spectra (up to 6.5%, for PV at 37° tilt and 10–15% for CPV). These mismatches correspond to potential accuracy improvements for a quick estimation of the average efficiency by applying the appropriate subordinate standard spectrum instead of the IEC/G173 spectra.The applicability of these spectra for PV performance analyses is confirmed at five test sites, for which subordinate spectra could be intuitively selected based on the average atmospheric aerosol optical depth (AOD) and precipitable water vapor at those locations.The development of subordinate standard spectra for DNI and concentrating solar power (CSP) and concentrating PV (CPV) is also considered. However, it is found that many more sets of atmospheric conditions would be required to allow the intuitive selection of DNI spectra for the five test sites, due in particular to the stronger effect of AOD on DNI compared to GTI.The matrix of subordinate GTI spectra described in this paper are recommended to appear as an option in the annex of future standards, in addition to the obligatory use of the main spectrum from the ASTM G173 and IEC 60904 standards.

An improved electronic determination of the Boltzmann constant by Johnson noise thermometry

Recent measurements using acoustic gas thermometry have determined the value of the Boltzmann constant, k, with a relative uncertainty less than 1 × 10−6. These results have been supported by a measurement with a relative uncertainty of 1.9 × 10−6 made with dielectric-constant gas thermometry. Together, the measurements meet the requirements of the International Committee for Weights and Measures and enable them to proceed with the redefinition of the kelvin in 2018. In further support, we provide a new determination of k using a purely electronic approach, Johnson noise thermometry, in which the thermal noise power generated by a sensing resistor immersed in a triple-point-of-water cell is compared to the noise power of a quantum-accurate pseudo-random noise waveform of nominally equal noise power. The experimental setup differs from that of the 2015 determination in several respects: a 100 Ω resistor is used as the thermal noise source, identical thin coaxial cables made of solid beryllium–copper conductors and foam dielectrics are used to connect the thermal and quantum-accurate noise sources to the correlator so as to minimize the temperature and frequency sensitivity of the impedances in the connecting leads, and no trimming capacitors or inductors are inserted into the connecting leads. The combination of reduced uncertainty due to spectral mismatches in the connecting leads and reduced statistical uncertainty due to a longer integration period of 100 d results in an improved determination of k = 1.380 649 7(37) × 10−23 J K−1 with a relative standard uncertainty of 2.7 × 10−6 and a relative offset of 0.89 × 10−6 from the CODATA 2014 recommended value. The most significant terms in the uncertainty budget, the statistical uncertainty and the spectral-mismatch uncertainty, are uncorrelated with the corresponding uncertainties in the 2015 measurements.

The Effect of Interaural Mismatches on Contralateral Unmasking With Single-Sided Vocoders.

Cochlear-implant (CI) users with single-sided deafness (SSD)-that is, one normal-hearing (NH) ear and one CI ear-can obtain some unmasking benefits when a mixture of target and masking voices is presented to the NH ear and a copy of just the masking voices is presented to the CI ear. NH listeners show similar benefits in a simulation of SSD-CI listening, whereby a mixture of target and masking voices is presented to one ear and a vocoded copy of the masking voices is presented to the opposite ear. However, the magnitude of the benefit for SSD-CI listeners is highly variable across individuals and is on average less than for NH listeners presented with vocoded stimuli. One possible explanation for the limited benefit observed for some SSD-CI users is that temporal and spectral discrepancies between the acoustic and electric ears might interfere with contralateral unmasking. The present study presented vocoder simulations to NH participants to examine the effects of interaural temporal and spectral mismatches on contralateral unmasking. Speech-reception performance was measured in a competing-talker paradigm for NH listeners presented with vocoder simulations of SSD-CI listening. In the monaural condition, listeners identified target speech masked by two same-gender interferers, presented to the left ear. In the bilateral condition, the same stimuli were presented to the left ear, but the right ear was presented with a noise-vocoded copy of the interfering voices. This paradigm tested whether listeners could integrate the interfering voices across the ears to better hear the monaural target. Three common distortions inherent in CI processing were introduced to the vocoder processing: spectral shifts, temporal delays, and reduced frequency selectivity. In experiment 1, contralateral unmasking (i.e., the benefit from adding the vocoded maskers to the second ear) was impaired by spectral mismatches of four equivalent rectangular bandwidths or greater. This is equivalent to roughly a 3.6-mm mismatch between the cochlear places stimulated in the electric and acoustic ears, which is on the low end of the average expected mismatch for SSD-CI listeners. In experiment 2, performance was negatively affected by a temporal mismatch of 24 ms or greater, but not for mismatches in the 0 to 12 ms range expected for SSD-CI listeners. Experiment 3 showed an interaction between spectral shift and spectral resolution, with less effect of interaural spectral mismatches when the number of vocoder channels was reduced. Experiment 4 applied interaural spectral and temporal mismatches in combination. Performance was best when both frequency and timing were aligned, but in cases where a mismatch was present in one dimension (either frequency or latency), the addition of mismatch in the second dimension did not further disrupt performance. These results emphasize the need for interaural alignment-in timing and especially in frequency-to maximize contralateral unmasking for NH listeners presented with vocoder simulations of SSD-CI listening. Improved processing strategies that reduce mismatch between the electric and acoustic ears of SSD-CI listeners might improve their ability to obtain binaural benefits in multitalker environments.

Binaural Benefit With and Without a Bilateral Spectral Mismatch in Acoustic Simulations of Cochlear Implant Processing

This study investigated whether a spectral mismatch across ears influences the benefit of redundancy, squelch, and head shadow differently in speech perception using acoustic simulation of bilateral cochlear implant (CI) processing. Ten normal-hearing subjects participated in the study, and acoustic simulations of CIs were used to test these subjects. Sentence recognition, presented unilaterally and bilaterally, was measured at +5 dB and +10 dB signal-to-noise ratios (SNRs) with bilaterally matched and mismatched conditions. Unilateral and bilateral CIs were simulated using 8-channel sine wave vocoders. Binaural spectral mismatch was introduced by changing the relative simulated insertion depths across ears. Subjects were tested while listening with headphones; head-related transfer functions were applied before the vocoder processing to preserve natural interaural level and time differences. For both SNRs, greater and more consistent binaural benefit of squelch and redundancy occurred for the matched condition whereas binaural interference of squelch and redundancy occurred for the mismatched condition. However, significant binaural benefit of head shadow existed irrespective of spectral mismatches and SNRs. The results suggest that bilateral spectral mismatch may have a negative impact on the binaural benefit of squelch and redundancy for bilateral CI users. The results also suggest that clinical mapping should be carefully administrated for bilateral CI users to minimize the difference in spectral patterns between the two CIs.

(A)ATSR Solar Channel On-Orbit Radiometric Calibration

Data from the solar reflectance channels of the Along Track Scanning Radiometer (ATSR) series of instruments are being used in applications for monitoring trends in many climate variables, for example, clouds and aerosols. In order to provide quantitative information, the radiometric calibrations of the sensors must be consistent, stable, and ideally traced to international standards with uncertainties quantified. In this paper, the authors describe the current methodology used to monitor the long-term drifts and determine the relative biases of the ATSR solar channel radiometric calibrations. Top-of-atmosphere bidirectional reflectance factors (BRFs) over quasi-stable desert and ice sites are extracted from level-1 images and compared against a reference BRF model derived from averages of measurements over the site from a reference sensor. This enables comparisons to be performed where there is limited or no temporal overlap between sensors. The results of the drift monitoring and intercomparisons are used to provide lookup tables to be applied by users for existing products and in subsequent reprocessing of ATSR data. The method is extended to perform comparisons against the Medium Resolution Imaging Spectrometer and the Moderate Resolution Imaging Spectrometer. Results of the comparisons are presented and show that the sensors are stable throughout the mission lifetime and biases relative to the Advanced ATSR are presented. Improvements to the methodology are discussed to account for spectral mismatches of the sensors under comparison and to increase the range of view angles that the BRF model presently covers.

Effects of Extreme Tonotopic Mismatches Between Bilateral Cochlear Implants on Electric Pitch Perception: A Case Study

Recent studies suggest that pitch perceived through cochlear implants (CIs) changes with experience to minimize spectral mismatches between electric and acoustic hearing. This study aimed to test whether perceived spectral mismatches are similarly minimized between two electric inputs. Pitch perception was studied in a subject with a 10-mm CI in one ear and a 24-mm CI in the other ear. Both processors were programmed to allocate information from the same frequency range of 188-7938 Hz, despite the large differences in putative insertion depth and stimulated cochlear locations between the CIs. After 2 and 3 years of experience, pitch-matched electrode pairs between CIs were aligned closer to the processor-provided frequencies than to cochlear position. Pitch perception may have adapted to reduce perceived spectral discrepancies between bilateral CI inputs, despite 2-3 octave differences in tonotopic mapping.

Controlling magnetic dipole transition with magnetic plasmonic structures

A plasmonic structure with double gold patches is proposed for enhancing the spontaneous emission of a magnetic dipole transition through a magnetic hot area. A Purcell factor of nearly 2000 can be obtained at optical frequencies together with a low sensitivity in spatial and spectral mismatches between the light emitter and the resonance mode. The associated resonance can be tuned from the visible to the IR frequencies, enabling efficient control of forbidden transitions using plasmonic structures.

Cochlear Implant Speech Processor Frequency Allocations May Influence Pitch Perception

To investigate the effects of assigning cochlear implant speech processor frequencies normally associated with more apical cochlear locations to the shallow insertion depths of the Iowa/Nucleus Hybrid electrode. Subjects using the Hybrid implant for more than 1 year were tested on speech recognition with Consonant-Nucleus-Consonant words and consonant stimuli. Pitch sensations of individual electrodes were also measured electrically through the implant and acoustically in the contralateral ear. Tertiary care center. Most subjects showed large improvements in speech recognition within 12 months after implantation. Furthermore, after longer periods of 24-plus months, some individuals were able to achieve high levels of consonant discrimination with electric-only processing comparable to long-electrode patients with deeper electrode insertions. Pitch perceptions obtained from individual electrodes in these subjects were closer to the frequency map assigned an electrode than the place-frequency predicted from cochlear location. These results suggest that over time, pitch sensations may be determined more by the implant map than by cochlear location. In other words, the brain may adapt to spectral mismatches by remapping pitch. Furthermore, patients can perform well with shifted frequency allocations for speech recognition. The successful application of shifted frequency allocations also supports the idea of shallower insertions and greater preservation of residual hearing for all cochlear implants, regardless of the patient's frequency range of usable residual hearing.

Gradient-index optical filter synthesis with controllable and predictable refractive index profiles

The Fourier transform thin film synthesis method often results in solutions that call for indices that lie outside the range of values of the available materials. To make the resulting refractive index profiles always realizable in our meta-mode sputtering machine, a modified Fourier transform synthesis method is proposed with which the reflectance spectra can be accurately synthesized with controllable and predictable refractive index profiles. In our procedure, an optimal phase function is explored to yield acceptable refractive index profiles. Then the overall thickness is estimated using the Parseval theorem. Finally, several errors inherent to the Fourier transform method, including the imprecision of the spectral function, the truncation of the film and the apodization of the refractive index profiles, are compensated by successive corrections to the magnitude of the spectral function. An explicit iterative formula based on the derivative of the magnitude function is proposed for the compensation of the spectral mismatches. We show with a number of examples that, with the proposed method, it is possible to synthesize gradient-index optical filters with almost any desired spectral performance using experimentally realizable refractive indices.

太陽系小天体の変遷

Orbital evolutions and spectral changes of small bodies in the solar system are discussed. Recent discovery of Kuiper belt objects changed the image of our solar system. The size of the largest body is close to that of Pluto. Orbital stability and simulation studies clarified a route from Kuiper belt objects to short period comets through Jupiter family comets. Recent dynamical studies including chaos and Yarkovsky effect clarified a route from main belt asteroids to near Earth asteroids and meteorites. Space weathering process not only solved spectral mismatches between asteroids and meteorites but also should provide age information of asteroids. Color variation of Kuiper belt objects may reflect ongoing surface alteration process.

Encoder reverberations in adaptive predictive coding

In the past, the nonlinear effects of quantization in differential speech coders either were modeled as additive white Gaussian noise or were ignored in analysis and quantified experimentally. Describing functions are used to model the nonlinear quantizer effects of coarsely quantized difference signals found primarily in adaptive predictive coding (APC) systems. The analysis predicts marginal instabilities in APC encoders. The marginal instabilities result in ringing distortions in the reconstructed signal which, in the past, may have been attributed to pitch and spectral predictor mismatches. Adaptive order prediction is introduced, analyzed, and offered as a method for increasing the robustness of APC encoders. >