Mean time for target acquisition in collaborative search with multiple imaging sensors

Observations of 1-s average concentration fluctuations during two trials of a U.S. Army diffusion experiment are presented and compared with model predictions based on an exponential probability density function (pdf). The source is near the surface and concentration monitors are on lines about 30 to 100 m downwind of the source. The observed ratio of the standard deviation to the mean of the concentration fluctuations is about 1.3 on the mean plume axis and 4 to 5 on the mean plume edges. Plume intermittency (fraction of non-zero readings) is about 50%; on the mean plume axis and 10%; on the mean plume edges. A meandering plume model is combined with an exponential pdf assumption to produce predictions of the intermittency and the standard deviation of the concentration fluctuations that are within 20%; of the observations.

Two-dimensional large-eddy simulations of bluff-body stabilized flames of methane and propane, exhibiting significant finite-rate chemistry effects, are presented. A partial equilibrium/two-scalar exponential probability density function (PDF) combustion submodel is applied at the subgrid level. Subgrid scale motions are modelled with a first-order closure employing an anisotropic subgrid eddy-viscosity and two equations for the subgrid turbulent kinetic and scalar energies. Statistical independence of the joint PDF scalars is avoided and the necessary moments are obtained from an extended scale-similarity assumption. Extinction is accounted for by comparing the local turbulent Damköhler number against a ‘critical’ local limit related to the Gibson scalar scale and the reaction zone thickness in mixture fraction space. The post-extinction regime is modelled via a Lagrangian transport equation for a reactedness progress variable which follows a linear deterministic relaxation to its mean value (interaction by exchange with the mean model; IEM).Comparisons between simulations and measurements suggested the ability of the adopted methodology to represent the experimental variations in the momentum and scalar fields at conditions close to the lean or the rich blow-out limit. Favourable agreement was achieved in the calculation of the recirculation lengths and the peak temperature and turbulence levels in the near-wake region. Significant experimental trends, such as the suppression of the large-scale organized motions in the developing wake at low and medium fuel injection rates, and the re-emergence of the quasi-periodic shedding activity close to the lean limit, were also reproduced. Quantitative discrepancies increased in the prediction of major species, but the measured trends due to the effects of partial extinction were adequately recovered.

The paper proposes a new variational Bayesian algorithm for l 1 -penalized multivariate regression with attribute-distributed data. The algorithm is based on the variational Bayesian version of the SAGE algorithm that realizes a training of individual agents in a distributed fashion and sparse Bayesian learning (SBL) with hierarchical sparsity prior modeling of the agent weights. The SBL introduces constraints on the weights of individual agents, thus reducing the effects of overfitting and removing/suppressing poorly performing agents in the ensemble estimator. The l 1 constraint is introduced using a product of a Gaussian and an exponential probability density function with the resulting marginalized prior being a Laplace pdf. Such a hierarchical formulation of the prior allows for a computation of the stationary points of the variational update expressions for prior parameters, as well as deriving conditions that ensure convergence to these stationary points. Using synthetic data it is demonstrated that the proposed algorithm performs very well in terms of the achieved MSE, and outperforms other algorithms in the ability to sparsify non-informative agents, while at the same time allowing distributed implementation and flexible agent update protocols.

The performance of various discrete adaptive delta modulation (ADM) systems in the presence of random signal input is analyzed. The ADM systems considered are (a) Winkler system, (b) Abate (1967) system, (c) Bosworth and Candy (1968) system, and (d) Tazaki system (1977). It is assumed that the input random signal has a slope which varies randomly having Gaussian, Rayleigh and exponential probability density function (PDF) and has rectangular and triangular power spectral density (PSD). For an input random signal with specific PSD and PDF of its slope, the SNR has been calculated and plotted against the signal power. A performance evaluation has been made and summarized for the four systems above. >

This study aims to assess the marine hydrodynamics and the potential power of sea currents by simulating the probability distribution functions of the sea current velocity values. For this aim, hourly sea current velocity and direction data measured from the Çanakkale (Turkey) measurement station in the North Aegean Sea were used. These data were measured during two separate periods: January 1 – March 24, 2017, and March 25 – December 31, 2019. First, the vertical structure of the sea currents up to 50 m depth was determined. Then, frequency distributions of hourly sea current velocities were modeled by using the Weibull, Rayleigh, and Exponential probability density functions. According to the results obtained at 5, 10, 20, 30, 40, and 50 m depths below the sea surface level, the annual sea current velocity was 28.8 ± 0.395, 26.1 ± 0.388, 19.4 ± 0.339, 16.1 ± 0.324, 17.5 ± 0.344, and 24.7 ± 0.622 cm/s, respectively, in this sea. Furthermore, the annual sea current power potential was calculated as 30.0, 25.4, 15.0, 12.2, 15.0, and 88.2 W/m2 for 5, 10, 20, 30, 40, and 50 m depths, respectively. The results demonstrated that the Weibull distribution model was the best fit for the sea current velocity in this sea.

Software maintenance phase involves modifying and making changes to software due to requirements changes and/or defects reported by users. At this phase, when defects are uncovered, users will inform the problem to software maintenance team. The team has to provide the users the estimated fixing time and then fix the errors. Fault reparation/fixing time of different kinds of errors may be varied due to fault types and program complexity. In this research, an approach to estimate fault reparation time is proposed. The exponential probability density function is mainly used to construct the estimation model. An evaluation of the approach is present by applying the approach to open source software projects. A comparison of fault reparation time estimation between considering fault types and without fault types is reported.

The paper deals with assessing blur amount in images. Blur is a common artefact that attenuates the high frequency components of an image. The main idea turns on analysing the frequency response at transitions through resolutions. To achieve that, the histogram of the multiresolution DCT coefficients is modelled by using an exponential probability density function (pdf). The steepness of the pdf is used as a cue to characterize the blur effect. Faithful scores are obtained while testing the proposed approach on five image collections. The proposed measure is validated on the JPEG2000 lossy compression algorithm and the Lucy-Richardson iterative deblurring approach.

A method for modeling the effects of finite-rate chemistry such as partial extinctions and reignitions is developed and used to compute turbulent CO/H2/N2 or CH4-air-piloted jet diffusion flames close to extinction. The method is combined with a two-dimensional Large Eddy Simulation procedure employing a partial equilibrium/two-scalar exponential Probability Density Function (PDF) combustion submodel applied at the subgrid scale (SGS) level. Subgrid motions are modeled with a first-order closure utilizing an anisotropic subgrid eddy-viscosity and two equations for the subgrid scale turbulent kinetic and scalar energies. Statistical independence of the joint PDF scalars is here avoided and the required moments are obtained from an extended scale-similarity assumption. Extinction is determined by comparing the local Damkohler number against a ‘critical’ local limit related to the Gibson scalar scale and the reaction zone thickness. The post-extinction regime is treated with a reactedness progress variable computed from a Lagrangian transport equation and a two-scalar reacledness-mixture fraction presumed PDF. Comparisons with well documented turbulent flame data suggested the ability of the presented methodology to describe many experimental trends and variations of the momentum and reactive scalar mixing fields at flame conditions close to extinction.

Monochromator is the necessary equipment for spectral imager to calibrate the spectrum continuously. In order to calibrate the hyperspectral imaging spectrometer continuously, a small-type and high-spectral-resolution grating monochromator is designed. The grating monochromator with horizontal Czerny-Turner structure is designed with high-spectral-resolution as a starting point, and the design idea is discussed in detail from choosing the grating, calculating the focal length, the sizes of entrance slit and exit slit, among others. Using this method, the necessary structure parameters are determined, and the impact of the necessary structure parameters for spectral resolution and volume is given. According to the optical characteristics of the grating monochromator, the mechanical structures of the instrument are designed for small and handy from the components of the entrance slit, the collimator lens and imaging objective lens, the scanning structures, the fuselage and so on. The relationship of the sine mechanism parameters for output wavelength and wavelength scanning accuracy is given. The design and adjustment of the instrument are completed. The visible spectrums of mercury lamp are used as calibration lines, and the calibration curve is acquired by using least square method. This paper gives a method that combining the limit error of the step number and the calibration curve to evaluate the wavelength repeatability and wavelength precision. The datum of experiment shows that the spectral resolution of the instrument is better than 0.1 nm in the wavelength band from 400 to 800 nm. Simultaneously the wave-length repeatability reach to ± 0.96 6 nm and the precision reach to ± 0.096 9 nm.

The structure of the imaging system of the contact image sensor(CIS) line array camera is different from that of the ordinary camera. The sensors in the camera are generally bound and encapsulated by multiple independent imaging sensors. The problem of camera non-uniformity exists not only in the independent sensor, but also between each group of sensors. Therefore, in order to solve the problem of non-uniformity in the imaging of the line array camera of contact image sensor, especially the problem of non-uniformity mutation near the stitching gap of each imaging unit of the line array camera, an optimized stretch imaging correction method based on the traditional two-point correction method was proposed in this paper. In this method, multiple images with different exposure times are taken as sample sets and the least square method is used to find the best correction black and white template. Experiments show that the relative error offset of the optimized algorithm is smaller than that of the traditional two-point correction method under different exposure time, and the overall image uniformity is improved by about 40% compared with the traditional two-point correction method in the whole response range. Response near stitching gap transition is more uniform, stitching gap near relative to the traditional two-point method NU most about 50% drop in value, and analyzed the optimization calculation of two-point method is easy to convert the FPGA logic implementation. In the high real-time and wide swath image processing architecture of the large area contact linear array camera, the correction effect can be improved only by modifying the black and white templates of the traditional two-point correction method.

The singlet plenoptic camera, which consists of a single lens, microlens array (MLA) and image sensor, possesses the superiority that the imaging system is compact and lightweight, which is beneficial to miniaturization. However, such plenoptic cameras suffer from severe optical aberrations and their imaging quality is inferior for post-capture processing. Therefore, this paper proposes an optical-aberrations-corrected light field re-projection method to obtain high-quality singlet plenoptic imaging. First, optical aberrations are modeled by Seidel polynomials and included into point spread function (PSF) modeling. The modeled PSF is subsequently used to reconstruct imaging object information. Finally, the reconstructed imaging object information is re-projected back to the plenoptic imaging plane to obtain high-quality plenoptic images without optical aberrations. PSF modeling is validated by a self-built singlet plenoptic camera and the utility of the proposed optical-aberrations-corrected light field re-projection method is verified by numerical simulations and real imaging experiments.

The perceptual image hash has been widely used for integrity check of digital image content. Existing image hashes fail to identify the origin of image acquisition and non-repudiable authentication is contingent on the privacy of secret key. This paper presents a new and more secure image hashing scheme by exploiting the CMOS image sensor physical unclonable function (PUF) as a root of trust to imprint a birthmark into the image hash. The hash vector is generated directly by the CMOS image sensor based on the content-based features extracted from its captured image and the timestamp of the image without the need for a shared secret key for its authentication. Other than the ability to detect malicious tampering of image content from normal benign image processing operations, the use of CMOS image sensor PUF as a random one-way function to map the extracted feature and the timestamp to a hash vector provides a non-repudiable proof of the original image acquisition device and time of offence when the digital image content is to be presented as an evidence of a crime. As the hash vector can only be generated by the image sensor when it is powered on, it is inherently secure against invasive, data remanence and replay attacks, which are common threats to key-based perceptual image hashes. Our preliminary experimental results on 49 content-preserving and 5 wilfully tampered copies of an original image captured by a 64 × 64 image sensor PUF fabricated in 180 nm 3.3 V CMOS technology have demonstrated that the tampered images and their regions of alteration can be successfully detected from the hash vectors.

The possibility of improving white-light full-field optical coherence tomography (OCT) resolution by image sensor colour balance tuning is shown numerically. We calculated the full-width at half-maximum (FWHM) of a coherence pulse registered by a silicon colour image sensor under various colour balance settings. The calculations were made for both a halogen lamp and white LED sources. The results show that the interference pulse width can be reduced by the proper choice of colour balance coefficients. The reduction is up to 18%, as compared with a colour image sensor with regular settings, and up to 20%, as compared with a monochrome sensor.

Physical characterization of explosive volcanic eruptions based on tephra deposits: Propagation of uncertainties and sensitivity analysis

In many hyperspectral applications it is beneficial to produce 2D spatial images with a single exposure at a few selected wavelength bands instead of 1D spatial and all spectral band images like in push-broom instruments. VTT has developed a new concept based on the Piezo actuated Fabry-Perot Interferometer to enable recording of 2D spatial images at the selected wavelength bands simultaneously. The sensor size is compatible with light weight UAV platforms. In our spectrometer the multiple orders of the Fabry-Perot Interferometer are used at the same time matched to the sensitivities of a multispectral RGB-type image sensor channels. We have built prototypes of the new spectrograph fitting inside of a 40 mm x 40 mm x 20 mm envelope and with a mass less than 50 g. The operational wavelength range of built prototypes can be tuned in the range 400 - 1100 nm and the spectral resolution is in the range 5 - 10 nm @ FWHM. Presently the spatial resolution is 480 x 750 pixels but it can be increased simply by changing the image sensor. The hyperspectral imager records simultaneously a 2D image of the scenery at three narrow wavelength bands determined by the selected three orders of the Fabry-Perot Interferometer which depend on the air gap between the mirrors of the Fabry-Perot Cavity. The new sensor can be applied on UAV, aircraft, and other platforms requiring small volume, mass and power consumption. The new low cost hyperspectral imager can be used also in many industrial and medical applications.