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In this paper, a comprehensive theoretical framework for understanding surface-enhanced Raman scattering (SERS) measurements in both solution and thin-film setups, focusing on electromagnetic enhancement principles, was presented. Two prevalent types of SERS substrates found in the literature were investigated: plasmonic colloidal particles, including spherical and spheroid nanoparticles, nanoparticle diameters, and thin-film-based SERS substrates, like ultra-thin substrates, bundled nanorods, plasmonic thin films, and porous thin films. The investigation explored the impact of analyte adsorption, orientation, and the polarization of the excitation laser on effective SERS enhancement factors. Notably, it considered the impact of analyte size on the SERS spectrum by examining scenarios where the analyte was significantly smaller or larger than the hot spot dimensions. The analysis also incorporated optical attenuations arising from the optical properties of the analyte and the SERS substrates. The findings provide possible explanations for many observations made in SERS measurements, such as variations in relative peak intensities during SERS assessments, reductions in SERS intensity at high analyte concentrations, and the occurrence of significant baseline fluctuations. This study offers valuable guidance for optimizing SERS substrate design, enhancing SERS measurements, and improving the quantification of SERS detection. [ABSTRACT FROM AUTHOR]

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We developed an analytical model to evaluate the effect of signal pileup on the recorded energy spectrum in X-ray photon-counting detectors affected by dead time and equipped with retrigger capability. The retrigger function allows the system to work in a specific non-paralyzable counting mode by counting the time-over-threshold of piled-up signals in multiples of a predefined and selectable retrigger time. The model, designed for rectangle-like-shaped signals, allows for arbitrary input energy spectra and can significantly help understand and optimize the behavior of counting detectors with spectral capabilities and retrigger mechanisms in applications involving polychromatic beams, e.g., spectral X-ray imaging and computed tomography (CT), in a time-efficient way. Dedicated numerical simulations were used to validate the model under several conditions of incoming flux and threshold energy, with excellent results.

Pansharpening is the fusion of panchromatic (PAN) and multispectral (MS) images to obtain a high spectral and spatial resolution image. Various metrics are introduced to assess the performance of different algorithms of pansharpening. This paper proposes a new metric for spectral quality evaluation of fused images. In the proposed method, spectrum vector of each pixel of fused image is compared to corresponding spectrum of reference image. Area of difference between two spectra is measured, and by applying this process to all pixel vectors of the fused image and taking an average over obtained values, spectral distortion of whole image is obtained. To investigate the efficiency of the proposed index, deliberate spectral distortion is applied to fused image and the proposed metric's ability to detect distortion is examined. Experimental results on real remote sensing images demonstrate the superior performance of the proposed metric compared to other existing metrics.

In this paper, a comprehensive theoretical framework for understanding surface-enhanced Raman scattering (SERS) measurements in both solution and thin-film setups, focusing on electromagnetic enhancement principles, was presented. Two prevalent types of SERS substrates found in the literature were investigated: plasmonic colloidal particles, including spherical and spheroid nanoparticles, nanoparticle diameters, and thin-film-based SERS substrates, like ultra-thin substrates, bundled nanorods, plasmonic thin films, and porous thin films. The investigation explored the impact of analyte adsorption, orientation, and the polarization of the excitation laser on effective SERS enhancement factors. Notably, it considered the impact of analyte size on the SERS spectrum by examining scenarios where the analyte was significantly smaller or larger than the hot spot dimensions. The analysis also incorporated optical attenuations arising from the optical properties of the analyte and the SERS substrates. The findings provide possible explanations for many observations made in SERS measurements, such as variations in relative peak intensities during SERS assessments, reductions in SERS intensity at high analyte concentrations, and the occurrence of significant baseline fluctuations. This study offers valuable guidance for optimizing SERS substrate design, enhancing SERS measurements, and improving the quantification of SERS detection.

Pansharpening is the fusion of panchromatic (PAN) and multispectral (MS) images to obtain a high spectral and spatial resolution image. Various metrics are introduced to assess the performance of different algorithms of pansharpening. This paper proposes a new metric for spectral quality evaluation of fused images. In the proposed method, spectrum vector of each pixel of fused image is compared to corresponding spectrum of reference image. Area of difference between two spectra is measured, and by applying this process to all pixel vectors of the fused image and taking an average over obtained values, spectral distortion of whole image is obtained. To investigate the efficiency of the proposed index, deliberate spectral distortion is applied to fused image and the proposed metric's ability to detect distortion is examined. Experimental results on real remote sensing images demonstrate the superior performance of the proposed metric compared to other existing metrics. [ABSTRACT FROM AUTHOR]

Spectroscopic data often suffers from spectral distortions due to the influence of the bandwidth function of the spectrograph. In this paper, a spectroscopic bandwidth correction method based on multi-bandwidth functions is proposed. Different from the original bandwidth correction method which only employs one bandwidth function, the proposed method simultaneously uses multi-bandwidth functions collected at different wavelengths to estimate the real spectrum, which effectively eliminates the correction error caused by the differences in bandwidth functions of the whole band. The proposed method and the Richardson-Lucy (R-L) method were used to correct a simulated measured light-emitting diode (LED) spectrum and a simulated measured compact fluorescent lamp (CFL) spectrum. The correction errors, type A uncertainties, and root mean square errors (RMSEs) for the two methods were compared. The result of the comparison shows the superiority of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Polyphase sequences with low aperiodic autocorrelation levels, assessed in terms of the integrated sidelobe level (ISL), can be applied in many engineering fields, such as radars, sonars, and code-division multiple access communication systems. In practice, a polyphase sequence that is optimal in some sense (for example, minimum ISL) could be significantly distorted, thus reducing the detection performance of the radar system. Hence in this article, we focus on designing ISL minimization-based polyphase sequences with spectral distortion taken into consideration, where we first derive an expression for the ISL under spectral distortion, i.e., distorted ISL (DISL), and then we propose an iterative algorithm based on majorization-minimization framework to solve the DISL minimization problem. The proposed algorithm is proved to be nonincreasing and is guaranteed to converge to a stationary point. A variety of design results utilizing the proposed algorithm in different scenarios are presented and compared with those by other methods or some known sequences. The proposed algorithm is proved to be effective to design polyphase sequences with low DISL. [ABSTRACT FROM AUTHOR]

The high-quality pansharpened image with both high spatial resolution and high spectral fidelity is highly desirable in various applications. However, existing pansharpening methods may lead to spatial distortion and spectral distortion. To measure the degrees of distortion caused by the pansharpening methods, we conduct in-deep studies on the subjective and objective quality assessment of pansharpened images. We built a subjective database consisting of 360 images generated from 20 couples of panchromatic (PAN)/multispectral (MS) images using 18 pansharpening methods. Based on the database, we proposed a no-reference quality assessment method to blindly predict the quality of pansharpened images via opinion-unaware learning. The proposed method first extracted features from the MS images' spectral bands and typical information indexes which comprehensively reflect spatial distortion, spectral distortion, and the effects of pansharpening on applications. Based on the features extracted from the pristine MS image training dataset, a benchmark multivariate Gaussian (MVG) model is learned. The distance between the benchmark MVG and the MVG fitted on the test image is calculated to measure the quality. The experimental results show the superiority of our method on our database.

In contrast to spontaneous Raman scattering, coherent Raman scattering techniques, such as femtosecond stimulated Raman scattering (FSRS), show advantages for many applications. Besides an enhanced signal strength, FSRS is free of a nonresonant background but is affected by cross‐phase modulation (XPM). The resulting artifacts in FSRS become relevant for high pulse intensities (GW/cm2‐regime) and ultrashort pulses (<2 ps), both necessary for super‐resolution experiments. As the pulse duration is a crucial parameter for XPM as well as for FSRS, we present a setup in which we adjust the pulse duration across the relevant range (0.5–3 ps), in order to investigate the XPM influence on the spectra. Furthermore, we vary the peak intensity, the temporal overlap between the interacting pulses, and the nonlinear refractive index coefficient n2 of the sample, showing that a trade‐off between all these quantities enables the measurement of unaffected FSRS spectra [ABSTRACT FROM AUTHOR]

As one of the most popular kinds of the component substitution (CS)‐based pansharpening methods, the intensity‐hue‐saturation (IHS) method can produce the pan‐sharpened images with high spatial quality while causing some spectral distortion, mainly owing to it cannot estimate an accurate intensity image in the IHS space. To solve this issue in the IHS method, in this study, the authors propose a new pansharpening method with gradient transferring in the generalised IHS transform space, which aims at estimating a more accurate intensity image. More specifically, the novelty of the proposed method consists of building a novel variational gradient transferring model to transfer the spatial gradient information of the panchromatic image into the new intensity image as well as preserve the local spectral information from the low resolution multispectral image. Finally, they compare the proposed method with some CS methods using the Pleiades, QuickBird, and GeoEye‐1 satellite datasets from both the subjective and objective aspects. Specifically, the experimental results show that the proposed method yields better pansharpening results than the other methods in terms of higher spatial and spectral qualities. [ABSTRACT FROM AUTHOR]

Highlights • The AFBG and UFBG sensors' behavior for structure crack propagation monitoring is investigated. • The reflective spectral behavior of both UFBG and AFBG sensors under crack-generated non-linear strain are illustrated. • The simulated and experimental results proved the UFBG sensors have higher sensitivity compared with AFBG sensors. Abstract Due to their light weight, small size and immunity to electromagnetic interference, Fiber Bragg Gratings (FBG) have shown great potential in structural health monitoring (SHM) area. Ordinarily, FBGs are used as the quasi-distributed sensors to detect structural damage by central wavelengths shifting, which has robust problem in real engineering application. It is found that the FBG reflection spectra can also be distorted with the non-uniform strain field caused by crack. Multiple indices can be extracted from the reflection spectra which can provides more information on the crack propagation. However, till now no researches have been investigated regarding the behaviors of different kinds of FBGs for crack propagation monitoring based on the FBG reflection spectra. In this paper, behaviors of the apodized FBG (AFBG) and the uniform FBG (UFBG) sensors for structural crack propagation monitoring are investigated. The reflective spectral behaviors of both UFBG and AFBG sensors under crack-generated non-uniform strain are illustrated by simulation and experiment. Three spectra indices, namely the central wavelength shift, the ratio of side lobe to main lobe and the information entropy, are proposed to indicate the propagation of the crack. The results show the UFBG sensors have better performance than the AFBG sensors which are more suitable for crack propagation monitoring. [ABSTRACT FROM AUTHOR]

Spectral distortions are complex and unpredictable in fiber Bragg grating (FBG) sensing applications. An inappropriate choice of FBG demodulation algorithm will lead to unacceptable results in practice. Although many demodulation algorithms have been developed for distorted spectra, they may be limited for some types of spectral distortion. Until now, no model of FBG spectral distortion has been proposed to test different demodulation algorithms. Here, we fulfill this aim by introducing a comprehensive model with asymmetrical distortion, multi-peaks distortion, interferometric noise, background noise, and random noise. Using numerical simulations, we evaluate the performance of eight most typical demodulation algorithms with this model. We show that different algorithms should be used within specific ranges of spectral distortions. Altogether, this study provides a guide map as useful reference for selecting an appropriate FBG demodulation algorithm for practical applications. Furthermore, our proposed model paves the way for developing more reliable FBG demodulation algorithms for different spectral distortions. [ABSTRACT FROM AUTHOR]

Change detection based on satellite images acquired from an area at different dates is of widespread interest, according to the increasing number of flood-related disasters. The images help to generate products that support emergency response and flood management at a global scale. In this paper, a novel unsupervised change detection approach based on image fusion is introduced. The approach aims to extract the reliable flood extent from very high-resolution (VHR) bi-temporal images. The method takes an advantage of the spectral distortion that occurs during image fusion process to detect the change areas by flood. To this end, a change candidate image is extracted from the fused image generated with bi-temporal images by considering a local spectral distortion. This can be done by employing a universal image quality index (UIQI), which is a measure for local evaluation of spectral distortion. The decision threshold for the determination of changed pixels is set by applying a probability mixture model to the change candidate image based on expectation maximization (EM) algorithm. We used bi-temporal KOMPSAT-2 satellite images to detect the flooded area in the city of N′djamena in Chad. The performance of the proposed method was visually and quantitatively compared with existing change detection methods. The results showed that the proposed method achieved an overall accuracy (OA = 75.04) close to that of the support vector machine (SVM)-based supervised change detection method. Moreover, the proposed method showed a better performance in differentiating the flooded area and the permanent water body compared to the existing change detection methods.

The working principle of fiber Bragg grating (FBG) sensors is mostly based on the tracking of the Bragg wavelength shift. To accomplish this task, different algorithms have been proposed, from conventional maximum and centroid detection algorithms to more recently-developed correlation-based techniques. Several studies regarding the performance of these algorithms have been conducted, but they did not take into account spectral distortions, which appear in many practical applications. This paper addresses this issue and analyzes the performance of four different wavelength tracking algorithms (maximum detection, centroid detection, cross-correlation and fast phase-correlation) when applied to distorted FBG spectra used for measuring dynamic loads. Both simulations and experiments are used for the analyses. The dynamic behavior of distorted FBG spectra is simulated using the transfer-matrix approach, and the amount of distortion of the spectra is quantified using dedicated distortion indices. The algorithms are compared in terms of achievable precision and accuracy. To corroborate the simulation results, experiments were conducted using three FBG sensors glued on a steel plate and subjected to a combination of transverse force and vibration loads. The analysis of the results showed that the fast phase-correlation algorithm guarantees the best combination of versatility, precision and accuracy.

Purpose: Smaller pixel sizes of x‐ray photon counting detectors (PCDs) benefit count rate capabilities but increase cross‐talk and "double‐counting" between neighboring PCD pixels. When an x‐ray photon produces multiple (n) counts at neighboring (sub‐)pixels and they are added during post‐acquisition N × N binning process, the variance of the final PCD output‐pixel will be larger than its mean. In the meantime, anti‐scatter grids are placed at the pixel boundaries in most of x‐ray CT systems and will decrease cross‐talk between sub‐pixels because the grids mask sub‐pixels underneath them, block the primary x‐rays, and increase the separation distance between active sub‐pixels. The aim of this paper was, first, to study the PCD statistics with various N × N binning schemes and three different masking methods in the presence of cross‐talks, and second, to assess one of the most fundamental performances of x‐ray CT: soft tissue contrast visibility. Methods: We used a PCD cross‐talk model (Photon counting toolkit, PcTK) and produced cross‐talk data between 3 × 3 neighboring sub‐pixels and calculated the mean, variance, and covariance of output‐pixels with each of N × N binning scheme [4 × 4 binning, 2 × 2 binning, and 1 × 1 binning (i.e., no binning)] and three different sub‐pixel masking methods (no mask, 1‐D mask, and 2‐D mask). We then set up simulation to evaluate the soft tissue contrast visibility. X‐rays of 120 kVp were attenuated by 10–40 cm‐thick water, with the right side of PCDs having 0.5 cm thicker water than the left side. A pair of output‐pixels across the left‐right boundary were used to assess the sensitivity index (SI or d′), which typically ranges 0–1 and is a generalized signal‐to‐noise ratio and a statistics used in signal detection theory. Results: Binning a larger number of sub‐pixels resulted in larger mean counts and larger variance‐to‐mean ratio when the lower threshold of the energy window was lower than the half of the incident energy. Mean counts are in the order of no mask (the largest), 1‐D mask, and 2‐D mask but the difference in variance‐to‐mean ratio was small. For a given sub‐pixel size and masking method, binning more sub‐pixels degraded the normalized SI values but the difference between 4 × 4 binning and 1 × 1 binning was typically less than 0.06. 1‐D mask provided better normalized SI values than no mask and 2‐D mask for side‐by‐side case and the improvements were larger with fewer binnings, although the difference was less than 0.10. 2‐D mask was the best for embedded case. The normalized SI values of combined binning, sub‐pixel size, and masking were in the order of 1 × 1 (900 μm)2 binning, 2 × 2 (450 μm)2 binning, and 4 × 4 (225 μm)2 binning for a given masking method but the difference between each of them were typically 0.02–0.05. Conclusion: We have evaluated the effect of double‐counting between PCD sub‐pixels with various binning and masking methods. SI values were better with fewer number of binning and larger sub‐pixels. The difference among various binning and masking methods, however, was typically less than 0.06, which might result in a dose penalty of 13% if the CT system were linear. [ABSTRACT FROM AUTHOR]

Purpose: The interpixel cross‐talk of energy‐sensitive photon counting x‐ray detectors (PCDs) has been studied and an analytical model (version 2.1) has been developed for double‐counting between neighboring pixels due to charge sharing and K‐shell fluorescence x‐ray emission followed by its reabsorption (Taguchi K, et al., Medical Physics 2016;43(12):6386–6404). While the model version 2.1 simulated the spectral degradation well, it had the following problems that has been found to be significant recently: (1) The spectrum is inaccurate with smaller pixel sizes; (2) the charge cloud size must be smaller than the pixel size; (3) the model underestimates the spectrum/counts for 10–40 keV; and (4) the model version 2.1 cannot handlen‐tuple‐counting withn > 2 (i.e., triple‐counting or higher). These problems are inherent to the design of the model version 2.1; therefore, we developed a new model and addressed these problems in this study. Methods: We propose a new PCD cross‐talk model (version 3.2; Pc TK for “photon counting toolkit”) that is based on a completely different design concept from the previous version. It uses a numerical approach and starts with a 2‐D model of charge sharing (as opposed to an analytical approach and a 1‐D model with version 2.1) and addresses all of the four problems. The model takes the following factors into account: (1) shift‐variant electron density of the charge cloud (Gaussian‐distributed), (2) detection efficiency, (3) interactions between photons and PCDs via photoelectric effect, and (4) electronic noise. Correlated noisy PCD data can be generated using either a multivariate normal random number generator or a Poisson random number generator. The effect of the two parameters, the effective charge cloud diameter (d0) and pixel size (dpix), was studied and results were compared with Monte Carlo simulations and the previous model version 2.1. Finally, a script for the workflow for CT image quality assessment has been developed, which started with a few material density images, generated material‐specific sinogram (line integrals) data, noisy PCD data with spectral distortion using the model version 3.2, and reconstructed PCD‐ CT images for four energy windows. Results: The model version 3.2 addressed all of the four problems listed above. The spectra withdpix = 56–113 μm agreed with that of Medipix3 detector withdpix = 55–110 μm without charge summing mode qualitatively. The counts for 10–40 keV were larger than the previous model (version 2.1) and agreed with MC simulations very well (root‐mean‐square difference values with model version 3.2 were decreased to 16%–67% of the values with version 2.1). There were many non‐zero off‐diagonal elements withn‐tuple‐counting withn > 2 in the normalized covariance matrix of 3 × 3 neighboring pixels. Reconstructed images showed biases and artifacts attributed to the spectral distortion due to the charge sharing and fluorescence x rays. Conclusion: We have developed a new PCD model for spatio‐energetic cross‐talk and correlation between PCD pixels. The workflow demonstrated the utility of the model for general or task‐specific image quality assessments for the PCD‐ CT.Note: The program (Pc TK) and the workflow scripts have been made available to academic researchers. Interested readers should visit the website (pctk.jhu.edu) or contact the corresponding author. [ABSTRACT FROM AUTHOR]

Numerous pansharpening methods were proposed in recent decades for fusing low-spatial-resolution multispectral (MS) images with high-spatial-resolution (HSR) panchromatic (PAN) bands to produce fused HSR MS images, which are widely used in various remote sensing tasks. The effect of misregistration between MS and PAN bands on quality of fused products has gained much attention in recent years. An improved method for misaligned MS and PAN imagery is proposed, through two improvements made on a previously published method named RMI (reduce misalignment impact). The performance of the proposed method was assessed by comparing with some outstanding fusion methods, such as adaptive Gram-Schmidt and generalized Laplacian pyramid. Experimental results show that the improved version can reduce spectral distortions of fused dark pixels and sharpen boundaries between different image objects, as well as obtain similar quality indexes with the original RMI method. In addition, the proposed method was evaluated with respect to its sensitivity to misalignments between MS and PAN bands. It is certified that the proposed method is more robust to misalignments between MS and PAN bands than the other methods. [ABSTRACT FROM AUTHOR]

In recent, photon counting detectors (PCDs) have been replacing the energy-integrating detectors in many medical imaging applications due to the formers‘ high resolution, low noise, and high efficiency. Under a high flux X-ray exposure, however, a superimposition of pulses, i.e., pulse pile-up, frequently occurs due to the finite output pulse width, causing distortions in the energy spectrum as a consequence. Therefore, pulse pile-up is considered as a major constraint in using PCDs for high flux X-ray applications. In this study, a new photon counting method is proposed to minimize degradations in PCD performance due to pulse pile-up. The proposed circuit was incorporated into a pixel with a size of 200 × 200 μ m 2 . It was fabricated by using a 1-poly 6-metal 0 . 18 μ m complementary metal–oxide–semiconductor (CMOS) process and had a power consumption of 7 . 8 μ W ∕ pixel . From the result, it was shown that the maximum count rate of the proposed circuit was increased by a factor of 4.7 when compared to that of the conventional circuit at the same pulse width of 700 ns. This implies that the energy spectrum obtained by the proposed circuit is 4.7 times more resistant to distortions than the conventional energy-resolving circuit does under higher X-ray fluxes. [ABSTRACT FROM AUTHOR]

Multicarrier signals using orthogonal frequency division multiplexing (OFDM) bring many advantages to radar such as low probability of intercept, improved target detection performance, optimisation of both radar transmitter and receiver etc. A major drawback of multicarrier OFDM signals is their high peak‐to‐mean envelope power ratio, which reduces the working efficiency of the used power amplifiers. To solve this problem, a digital constant‐envelope modulation scheme is proposed for radar using multicarrier OFDM signals. The scheme can transmit multicarrier OFDM signals through power amplifiers being operated near saturation levels (and thus maximising power efficiency) with little spectral distortion, even in the presence of channel mismatch. Given the speed limitations of field programmable gate arrays (FPGAs), the proposed scheme is implemented in an FPGA at intermediate frequency level using a polyphase processing structure. [ABSTRACT FROM AUTHOR]

Modern optical satellites can acquire bundles of panchSromatic (PAN) and multispectral (MS) images of the scene simultaneously. Because of the complexity of the sensors and amount of data involved, an MS image always has lower spatial resolution than the corresponding PAN image. Pansharpening aims at fusing MS images and PAN images, characterized by the spectral content of the former and the spatial details of the latter. There are two main large families of pansharpening algorithms, i.e., component substitution (CS) and multiresolution analysis (MRA). Generally speaking, the CS algorithms have better performance on spatial detail injection, while the MRA shows better spectral content preservation. In this paper, we propose a novel pansharpening algorithm, which combines the conceptions of CS and MRA. This proposed algorithm can be regarded as a generalized version of the existing band-dependent spatial-detail (BDSD) algorithm. A semisimulated dataset and three real datasets are adopted to compare the performance among the generalized-BDSD algorithm and six existing popular pansharpening algorithms. It shows that the proposed method has much lower spectral distortion and good visual appearance. In other words, the proposed method aggregates the advantages of CS and MRA, which shows effectiveness in practice. [ABSTRACT FROM PUBLISHER]

[Display omitted] • Pure absorption spectra without any spectral distortion. • More than 10 times more sensitive than conventional Field Modulation EPR. • Superheterodyne EPR spectrometer without special equipment for NARS. • The triangular field repetition rate of the order of units of hertz (LF NARS). • Deep non-adiabaticity, large amplitude, and high linearity of the field sweep. In this article, the possibilities of recording EPR spectra by the non-adiabatic rapid sweep (NARS) method on a superheterodyne spectrometer are investigated. This method allows recording the pure EPR absorption spectrum of the object under investigation without the need for lineshape–lineheight compromise, while increasing sensitivity by suppressing low-frequency noise. In the NARS method, a low-amplitude sinusoidal modulation of a magnetic field is not used, and an oscillating triangular-shaped bipolar magnetic field is superimposed on the main permanent magnetic field. The triangular field repetition rate should be higher than that of the undesirable noise, and the amplitude is such that the rate of field change satisfies the Bloch non-adiabaticity criterion. The EPR absorption signal is digitized by a fast ADC and accumulated over a large number (n) of triangular field periods. In this case, for low-frequency noise, the spectrum of which is located below the repetition frequency of the triangular field, an accumulation process occurs with an increase in the signal-to-noise ratio (SNR) in proportion to n . A remarkable property of a superheterodyne spectrometer is that the frequency below which low-frequency noise prevails over white noise is significantly lower for it than for a homodyne spectrometer. This allows the use of a low repetition rate (LF NARS), which makes it much easier to obtain a highly linear triangular field of significant amplitude even in microwave resonators with a massive metal case since the harmful effects of eddy currents are reduced. The conditions of non-adiabaticity become easily feasible. At the same time, the noise suppression effect during accumulation turns out to be so significant that the SNR of the LF NARS spectrum exceeds that of the traditional spectrum with magnetic field modulation, with the same recording time, by more than 10 times. [ABSTRACT FROM AUTHOR]

Purpose: An x-ray photon interacts with photon counting detectors (PCDs) and generates an electron charge cloud or multiple clouds. The clouds (thus, the photon energy) may be split between two adjacent PCD pixels when the interaction occurs near pixel boundaries, producing a count at both of the pixels. This is called double-counting with charge sharing. (A photoelectric effect with K-shell fluorescence x-ray emission would result in double-counting as well). As a result, PCD data are spatially and energetically correlated, although the output of individual PCD pixels is Poisson distributed. Major problems include the lack of a detector noise model for the spatio-energetic cross talk and lack of a computationally efficient simulation tool for generating correlated Poisson data. A Monte Carlo (MC) simulation can accurately simulate these phenomena and produce noisy data; however, it is not computationally efficient. Methods: In this study, the authors developed a new detector model and implemented it in an efficient software simulator that uses a Poisson random number generator to produce correlated noisy integer counts. The detector model takes the following effects into account: (1) detection efficiency; (2) incomplete charge collection and ballistic effect; (3) interaction with PCDs via photoelectric effect (with or without K-shell fluorescence x-ray emission, which may escape from the PCDs or be reabsorbed); and (4) electronic noise. The correlation was modeled by using these two simplifying assumptions: energy conservation and mutual exclusiveness. The mutual exclusiveness is that no more than two pixels measure energy from one photon. The effect of model parameters has been studied and results were compared withMCsimulations. The agreement, with respect to the spectrum, was evaluated using the reduced χ² statistics or a weighted sum of squared errors, χ² red (≥1), where χ² red = 1 indicates a perfect fit. Results: The model produced spectra with flat field irradiation that qualitatively agree with previous studies. The spectra generated with different model and geometry parameters allowed for understanding the effect of the parameters on the spectrum and the correlation of data. The agreement between the model and MC data was very strong. The mean spectra with 90 keV and 140 kVp agreed exceptionally well: χ² red values were 1.049 with 90 keV data and 1.007 with 140 kVp data. The degrees of cross talk (in terms of the relative increase from single pixel irradiation to flat field irradiation) were 22% with 90 keV and 19% with 140 kVp for MC simulations, while they were 21% and 17%, respectively, for the model. The covariance was in strong agreement qualitatively, although it was overestimated. The noisy data generation was very efficient, taking less than a CPU minute as opposed to CPU hours for MC simulators. Conclusions: The authors have developed a novel, computationally efficient PCD model that takes into account double-counting and resulting spatio-energetic correlation between PCD pixels. The MC simulation validated the accuracy. [ABSTRACT FROM AUTHOR]

Numerous pansharpening methods were proposed in recent decades for fusing low-spatial-resolution multispectral (MS) images with high-spatial-resolution (HSR) panchromatic (PAN) bands to produce fused HSR MS images, which are widely used in various remote sensing tasks. The effect of misregistration between MS and PAN bands on quality of fused products has gained much attention in recent years. An improved method for misaligned MS and PAN imagery is proposed, through two improvements made on a previously published method named RMI (reduce misalignment impact). The performance of the proposed method was assessed by comparing with some outstanding fusion methods, such as adaptive Gram-Schmidt and generalized Laplacian pyramid. Experimental results show that the improved version can reduce spectral distortions of fused dark pixels and sharpen boundaries between different image objects, as well as obtain similar quality indexes with the original RMI method. In addition, the proposed method was evaluated with respect to its sensitivity to misalignments between MS and PAN bands. It is certified that the proposed method is more robust to misalignments between MS and PAN bands than the other methods.