A method of incident angle estimation for high resolution spectral recovery in filter-array-based spectrometers

NASA Astrophysics Data System (ADS)

Kim, Cheolsun; Lee, Woong-Bi; Ju, Gun Wu; Cho, Jeonghoon; Kim, Seongmin; Oh, Jinkyung; Lim, Dongsung; Lee, Yong Tak; Lee, Heung-No

2017-02-01

In recent years, there has been an increasing interest in miniature spectrometers for research and development. Especially, filter-array-based spectrometers have advantages of low cost and portability, and can be applied in various fields such as biology, chemistry and food industry. Miniaturization in optical filters causes degradation of spectral resolution due to limitations on spectral responses and the number of filters. Nowadays, many studies have been reported that the filter-array-based spectrometers have achieved resolution improvements by using digital signal processing (DSP) techniques. The performance of the DSP-based spectral recovery highly depends on the prior information of transmission functions (TFs) of the filters. The TFs vary with respect to an incident angle of light onto the filter-array. Conventionally, it is assumed that the incident angle of light on the filters is fixed and the TFs are known to the DSP. However, the incident angle is inconstant according to various environments and applications, and thus TFs also vary, which leads to performance degradation of spectral recovery. In this paper, we propose a method of incident angle estimation (IAE) for high resolution spectral recovery in the filter-array-based spectrometers. By exploiting sparse signal reconstruction of the L1- norm minimization, IAE estimates an incident angle among all possible incident angles which minimizes the error of the reconstructed signal. Based on IAE, DSP effectively provides a high resolution spectral recovery in the filter-array-based spectrometers.

Acquisition and visualization techniques for narrow spectral color imaging.

PubMed

Neumann, László; García, Rafael; Basa, János; Hegedüs, Ramón

2013-06-01

This paper introduces a new approach in narrow-band imaging (NBI). Existing NBI techniques generate images by selecting discrete bands over the full visible spectrum or an even wider spectral range. In contrast, here we perform the sampling with filters covering a tight spectral window. This image acquisition method, named narrow spectral imaging, can be particularly useful when optical information is only available within a narrow spectral window, such as in the case of deep-water transmittance, which constitutes the principal motivation of this work. In this study we demonstrate the potential of the proposed photographic technique on nonunderwater scenes recorded under controlled conditions. To this end three multilayer narrow bandpass filters were employed, which transmit at 440, 456, and 470 nm bluish wavelengths, respectively. Since the differences among the images captured in such a narrow spectral window can be extremely small, both image acquisition and visualization require a novel approach. First, high-bit-depth images were acquired with multilayer narrow-band filters either placed in front of the illumination or mounted on the camera lens. Second, a color-mapping method is proposed, using which the input data can be transformed onto the entire display color gamut with a continuous and perceptually nearly uniform mapping, while ensuring optimally high information content for human perception.

Acousto-optic filtering of lidar signals

NASA Technical Reports Server (NTRS)

Kolarov, G.; Deleva, A.; Mitsev, TS.

1992-01-01

The predominant part of the noise in lidar receivers is created by the background radiation; therefore, one of the most important elements of the receiving optics is a spectrally selecting filter placed in front of the photodetector. Interference filters are usually used to transmit a given wavelength. Specific properties of the interference filters, such as simple design, reliability, small size, and large aperture, combined with high transmission coefficient and narrow spectral band, make them the preferred spectral device in many cases. However, problems arise in applications such as the Differential Absorption Lidar (DIAL) technique, where fast tuning within a wide spectral region is necessary. Tunable acousto-optical filters (TAOF), used recently in astrophysical observations to suppress the background radiation, can be employed with success in lidar sounding. They are attractive due to the possibility for fast spectral scanning with a narrow transmission band. The TAOF's advantages are fully evident in DIAL lidars where one must simultaneously receive signals at two laser frequencies.

Optimal-adaptive filters for modelling spectral shape, site amplification, and source scaling

USGS Publications Warehouse

Safak, Erdal

1989-01-01

This paper introduces some applications of optimal filtering techniques to earthquake engineering by using the so-called ARMAX models. Three applications are presented: (a) spectral modelling of ground accelerations, (b) site amplification (i.e., the relationship between two records obtained at different sites during an earthquake), and (c) source scaling (i.e., the relationship between two records obtained at a site during two different earthquakes). A numerical example for each application is presented by using recorded ground motions. The results show that the optimal filtering techniques provide elegant solutions to above problems, and can be a useful tool in earthquake engineering.

Multispectral interference filter arrays with compensation of angular dependence or extended spectral range.

PubMed

Frey, Laurent; Masarotto, Lilian; Armand, Marilyn; Charles, Marie-Lyne; Lartigue, Olivier

2015-05-04

Thin film Fabry-Perot filter arrays with high selectivity can be realized with a single patterning step, generating a spatial modulation of the effective refractive index in the optical cavity. In this paper, we investigate the ability of this technology to address two applications in the field of image sensors. First, the spectral tuning may be used to compensate the blue-shift of the filters in oblique incidence, provided the filter array is located in an image plane of an optical system with higher field of view than aperture angle. The technique is analyzed for various types of filters and experimental evidence is shown with copper-dielectric infrared filters. Then, we propose a design of a multispectral filter array with an extended spectral range spanning the visible and near-infrared range, using a single set of materials and realizable on a single substrate.

Quantitative comparison between full-spectrum and filter-based imaging in hyperspectral fluorescence microscopy

PubMed Central

GAO, L.; HAGEN, N.; TKACZYK, T.S.

2012-01-01

Summary We implement a filterless illumination scheme on a hyperspectral fluorescence microscope to achieve full-range spectral imaging. The microscope employs polarisation filtering, spatial filtering and spectral unmixing filtering to replace the role of traditional filters. Quantitative comparisons between full-spectrum and filter-based microscopy are provided in the context of signal dynamic range and accuracy of measured fluorophores’ emission spectra. To show potential applications, a five-colour cell immunofluorescence imaging experiment is theoretically simulated. Simulation results indicate that the use of proposed full-spectrum imaging technique may result in three times improvement in signal dynamic range compared to that can be achieved in the filter-based imaging. PMID:22356127

Fundamentals of digital filtering with applications in geophysical prospecting for oil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mesko, A.

This book is a comprehensive work bringing together the important mathematical foundations and computing techniques for numerical filtering methods. The first two parts of the book introduce the techniques, fundamental theory and applications, while the third part treats specific applications in geophysical prospecting. Discussion is limited to linear filters, but takes in related fields such as correlational and spectral analysis.

Adaptive filtering of GOCE-derived gravity gradients of the disturbing potential in the context of the space-wise approach

NASA Astrophysics Data System (ADS)

Piretzidis, Dimitrios; Sideris, Michael G.

2017-09-01

Filtering and signal processing techniques have been widely used in the processing of satellite gravity observations to reduce measurement noise and correlation errors. The parameters and types of filters used depend on the statistical and spectral properties of the signal under investigation. Filtering is usually applied in a non-real-time environment. The present work focuses on the implementation of an adaptive filtering technique to process satellite gravity gradiometry data for gravity field modeling. Adaptive filtering algorithms are commonly used in communication systems, noise and echo cancellation, and biomedical applications. Two independent studies have been performed to introduce adaptive signal processing techniques and test the performance of the least mean-squared (LMS) adaptive algorithm for filtering satellite measurements obtained by the gravity field and steady-state ocean circulation explorer (GOCE) mission. In the first study, a Monte Carlo simulation is performed in order to gain insights about the implementation of the LMS algorithm on data with spectral behavior close to that of real GOCE data. In the second study, the LMS algorithm is implemented on real GOCE data. Experiments are also performed to determine suitable filtering parameters. Only the four accurate components of the full GOCE gravity gradient tensor of the disturbing potential are used. The characteristics of the filtered gravity gradients are examined in the time and spectral domain. The obtained filtered GOCE gravity gradients show an agreement of 63-84 mEötvös (depending on the gravity gradient component), in terms of RMS error, when compared to the gravity gradients derived from the EGM2008 geopotential model. Spectral-domain analysis of the filtered gradients shows that the adaptive filters slightly suppress frequencies in the bandwidth of approximately 10-30 mHz. The limitations of the adaptive LMS algorithm are also discussed. The tested filtering algorithm can be connected to and employed in the first computational steps of the space-wise approach, where a time-wise Wiener filter is applied at the first stage of GOCE gravity gradient filtering. The results of this work can be extended to using other adaptive filtering algorithms, such as the recursive least-squares and recursive least-squares lattice filters.

A wavelet and least square filter based spatial-spectral denoising approach of hyperspectral imagery

NASA Astrophysics Data System (ADS)

Li, Ting; Chen, Xiao-Mei; Chen, Gang; Xue, Bo; Ni, Guo-Qiang

2009-11-01

Noise reduction is a crucial step in hyperspectral imagery pre-processing. Based on sensor characteristics, the noise of hyperspectral imagery represents in both spatial and spectral domain. However, most prevailing denosing techniques process the imagery in only one specific domain, which have not utilized multi-domain nature of hyperspectral imagery. In this paper, a new spatial-spectral noise reduction algorithm is proposed, which is based on wavelet analysis and least squares filtering techniques. First, in the spatial domain, a new stationary wavelet shrinking algorithm with improved threshold function is utilized to adjust the noise level band-by-band. This new algorithm uses BayesShrink for threshold estimation, and amends the traditional soft-threshold function by adding shape tuning parameters. Comparing with soft or hard threshold function, the improved one, which is first-order derivable and has a smooth transitional region between noise and signal, could save more details of image edge and weaken Pseudo-Gibbs. Then, in the spectral domain, cubic Savitzky-Golay filter based on least squares method is used to remove spectral noise and artificial noise that may have been introduced in during the spatial denoising. Appropriately selecting the filter window width according to prior knowledge, this algorithm has effective performance in smoothing the spectral curve. The performance of the new algorithm is experimented on a set of Hyperion imageries acquired in 2007. The result shows that the new spatial-spectral denoising algorithm provides more significant signal-to-noise-ratio improvement than traditional spatial or spectral method, while saves the local spectral absorption features better.

Quantitative filter technique measurements of spectral light absorption by aquatic particles using a portable integrating cavity absorption meter (QFT-ICAM).

PubMed

Röttgers, Rüdiger; Doxaran, David; Dupouy, Cecile

2016-01-25

The accurate determination of light absorption coefficients of particles in water, especially in very oligotrophic oceanic areas, is still a challenging task. Concentrating aquatic particles on a glass fiber filter and using the Quantitative Filter Technique (QFT) is a common practice. Its routine application is limited by the necessary use of high performance spectrophotometers, distinct problems induced by the strong scattering of the filters and artifacts induced by freezing and storing samples. Measurements of the sample inside a large integrating sphere reduce scattering effects and direct field measurements avoid artifacts due to sample preservation. A small, portable, Integrating Cavity Absorption Meter setup (QFT-ICAM) is presented, that allows rapid measurements of a sample filter. The measurement technique takes into account artifacts due to chlorophyll-a fluorescence. The QFT-ICAM is shown to be highly comparable to similar measurements in laboratory spectrophotometers, in terms of accuracy, precision, and path length amplification effects. No spectral artifacts were observed when compared to measurement of samples in suspension, whereas freezing and storing of sample filters induced small losses of water-soluble pigments (probably phycoerythrins). Remaining problems in determining the particulate absorption coefficient with the QFT-ICAM are strong sample-to-sample variations of the path length amplification, as well as fluorescence by pigments that is emitted in a different spectral region than that of chlorophyll-a.

Frequency-selective quantitation of short-echo time 1H magnetic resonance spectra

NASA Astrophysics Data System (ADS)

Poullet, Jean-Baptiste; Sima, Diana M.; Van Huffel, Sabine; Van Hecke, Paul

2007-06-01

Accurate and efficient filtering techniques are required to suppress large nuisance components present in short-echo time magnetic resonance (MR) spectra. This paper discusses two powerful filtering techniques used in long-echo time MR spectral quantitation, the maximum-phase FIR filter (MP-FIR) and the Hankel-Lanczos Singular Value Decomposition with Partial ReOrthogonalization (HLSVD-PRO), and shows that they can be applied to their more complex short-echo time spectral counterparts. Both filters are validated and compared through extensive simulations. Their properties are discussed. In particular, the capability of MP-FIR for dealing with macromolecular components is emphasized. Although this property does not make a large difference for long-echo time MR spectra, it can be important when quantifying short-echo time spectra.

Detecting Proxima b’s Atmosphere with JWST Targeting CO2 at 15 μm Using a High-pass Spectral Filtering Technique

NASA Astrophysics Data System (ADS)

Snellen, I. A. G.; Désert, J.-M.; Waters, L. B. F. M.; Robinson, T.; Meadows, V.; van Dishoeck, E. F.; Brandl, B. R.; Henning, T.; Bouwman, J.; Lahuis, F.; Min, M.; Lovis, C.; Dominik, C.; Van Eylen, V.; Sing, D.; Anglada-Escudé, G.; Birkby, J. L.; Brogi, M.

2017-08-01

Exoplanet Proxima b will be an important laboratory for the search for extraterrestrial life for the decades ahead. Here, we discuss the prospects of detecting carbon dioxide at 15 μm using a spectral filtering technique with the Medium Resolution Spectrograph (MRS) mode of the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). At superior conjunction, the planet is expected to show a contrast of up to 100 ppm with respect to the star. At a spectral resolving power of R = 1790-2640, about 100 spectral CO2 features are visible within the 13.2-15.8 μm (3B) band, which can be combined to boost the planet atmospheric signal by a factor of 3-4, depending on the atmospheric temperature structure and CO2 abundance. If atmospheric conditions are favorable (assuming an Earth-like atmosphere), with this new application to the cross-correlation technique, carbon dioxide can be detected within a few days of JWST observations. However, this can only be achieved if both the instrumental spectral response and the stellar spectrum can be determined to a relative precision of ≤1 × 10-4 between adjacent spectral channels. Absolute flux calibration is not required, and the method is insensitive to the strong broadband variability of the host star. Precise calibration of the spectral features of the host star may only be attainable by obtaining deep observations of the system during inferior conjunction that serve as a reference. The high-pass filter spectroscopic technique with the MIRI MRS can be tested on warm Jupiters, Neptunes, and super-Earths with significantly higher planet/star contrast ratios than the Proxima system.

Wavelength Scanning with a Tilting Interference Filter for Glow-Discharge Elemental Imaging.

PubMed

Storey, Andrew P; Ray, Steven J; Hoffmann, Volker; Voronov, Maxim; Engelhard, Carsten; Buscher, Wolfgang; Hieftje, Gary M

2017-06-01

Glow discharges have long been used for depth profiling and bulk analysis of solid samples. In addition, over the past decade, several methods of obtaining lateral surface elemental distributions have been introduced, each with its own strengths and weaknesses. Challenges for each of these techniques are acceptable optical throughput and added instrumental complexity. Here, these problems are addressed with a tilting-filter instrument. A pulsed glow discharge is coupled to an optical system comprising an adjustable-angle tilting filter, collimating and imaging lenses, and a gated, intensified charge-coupled device (CCD) camera, which together provide surface elemental mapping of solid samples. The tilting-filter spectrometer is instrumentally simpler, produces less image distortion, and achieves higher optical throughput than a monochromator-based instrument, but has a much more limited tunable spectral range and poorer spectral resolution. As a result, the tilting-filter spectrometer is limited to single-element or two-element determinations, and only when the target spectral lines fall within an appropriate spectral range and can be spectrally discerned. Spectral interferences that result from heterogeneous impurities can be flagged and overcome by observing the spatially resolved signal response across the available tunable spectral range. The instrument has been characterized and evaluated for the spatially resolved analysis of glow-discharge emission from selected but representative samples.

Spectral analysis and filtering techniques in digital spatial data processing

USGS Publications Warehouse

Pan, Jeng-Jong

1989-01-01

A filter toolbox has been developed at the EROS Data Center, US Geological Survey, for retrieving or removing specified frequency information from two-dimensional digital spatial data. This filter toolbox provides capabilities to compute the power spectrum of a given data and to design various filters in the frequency domain. Three types of filters are available in the toolbox: point filter, line filter, and area filter. Both the point and line filters employ Gaussian-type notch filters, and the area filter includes the capabilities to perform high-pass, band-pass, low-pass, and wedge filtering techniques. These filters are applied for analyzing satellite multispectral scanner data, airborne visible and infrared imaging spectrometer (AVIRIS) data, gravity data, and the digital elevation models (DEM) data. -from Author

Digital filtering of plume emission spectra

NASA Technical Reports Server (NTRS)

Madzsar, George C.

1990-01-01

Fourier transformation and digital filtering techniques were used to separate the superpositioned spectral phenomena observed in the exhaust plumes of liquid propellant rocket engines. Space shuttle main engine (SSME) spectral data were used to show that extraction of spectral lines in the spatial frequency domain does not introduce error, and extraction of the background continuum introduces only minimal error. Error introduced during band extraction could not be quantified due to poor spectrometer resolution. Based on the atomic and molecular species found in the SSME plume, it was determined that spectrometer resolution must be 0.03 nm for SSME plume spectral monitoring.

Applications of charge-coupled device transversal filters to communication

NASA Technical Reports Server (NTRS)

Buss, D. D.; Bailey, W. H.; Brodersen, R. W.; Hewes, C. R.; Tasch, A. F., Jr.

1975-01-01

The paper discusses the computational power of state-of-the-art charged-coupled device (CCD) transversal filters in communications applications. Some of the performance limitations of CCD transversal filters are discussed, with attention given to time delay and bandwidth, imperfect charge transfer efficiency, weighting coefficient error, noise, and linearity. The application of CCD transversal filters to matched filtering, spectral filtering, and Fourier analysis is examined. Techniques for making programmable transversal filters are briefly outlined.

Near-infrared spectral image analysis of pork marbling based on Gabor filter and wide line detector techniques.

PubMed

Huang, Hui; Liu, Li; Ngadi, Michael O; Gariépy, Claude; Prasher, Shiv O

2014-01-01

Marbling is an important quality attribute of pork. Detection of pork marbling usually involves subjective scoring, which raises the efficiency costs to the processor. In this study, the ability to predict pork marbling using near-infrared (NIR) hyperspectral imaging (900-1700 nm) and the proper image processing techniques were studied. Near-infrared images were collected from pork after marbling evaluation according to current standard chart from the National Pork Producers Council. Image analysis techniques-Gabor filter, wide line detector, and spectral averaging-were applied to extract texture, line, and spectral features, respectively, from NIR images of pork. Samples were grouped into calibration and validation sets. Wavelength selection was performed on calibration set by stepwise regression procedure. Prediction models of pork marbling scores were built using multiple linear regressions based on derivatives of mean spectra and line features at key wavelengths. The results showed that the derivatives of both texture and spectral features produced good results, with correlation coefficients of validation of 0.90 and 0.86, respectively, using wavelengths of 961, 1186, and 1220 nm. The results revealed the great potential of the Gabor filter for analyzing NIR images of pork for the effective and efficient objective evaluation of pork marbling.

Retrieval of the atmospheric compounds using a spectral optical thickness information

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ioltukhovski, A.A.

A spectral inversion technique for retrieval of the atmospheric gases and aerosols contents is proposed. This technique based upon the preliminary measurement or retrieval of the spectral optical thickness. The existence of a priori information about the spectral cross sections for some of the atmospheric components allows to retrieve the relative contents of these components in the atmosphere. Method of smooth filtration makes possible to estimate contents of atmospheric aerosols with known cross sections and to filter out other aerosols; this is done independently from their relative contribution to the optical thickness.

New spectral imaging techniques for blood oximetry in the retina

NASA Astrophysics Data System (ADS)

Alabboud, Ied; Muyo, Gonzalo; Gorman, Alistair; Mordant, David; McNaught, Andrew; Petres, Clement; Petillot, Yvan R.; Harvey, Andrew R.

2007-07-01

Hyperspectral imaging of the retina presents a unique opportunity for direct and quantitative mapping of retinal biochemistry - particularly of the vasculature where blood oximetry is enabled by the strong variation of absorption spectra with oxygenation. This is particularly pertinent both to research and to clinical investigation and diagnosis of retinal diseases such as diabetes, glaucoma and age-related macular degeneration. The optimal exploitation of hyperspectral imaging however, presents a set of challenging problems, including; the poorly characterised and controlled optical environment of structures within the retina to be imaged; the erratic motion of the eye ball; and the compounding effects of the optical sensitivity of the retina and the low numerical aperture of the eye. We have developed two spectral imaging techniques to address these issues. We describe first a system in which a liquid crystal tuneable filter is integrated into the illumination system of a conventional fundus camera to enable time-sequential, random access recording of narrow-band spectral images. Image processing techniques are described to eradicate the artefacts that may be introduced by time-sequential imaging. In addition we describe a unique snapshot spectral imaging technique dubbed IRIS that employs polarising interferometry and Wollaston prism beam splitters to simultaneously replicate and spectrally filter images of the retina into multiple spectral bands onto a single detector array. Results of early clinical trials acquired with these two techniques together with a physical model which enables oximetry map are reported.

Detecting Proxima b’s Atmosphere with JWST Targeting CO{sub 2} at 15 μ m Using a High-pass Spectral Filtering Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snellen, I. A. G.; Van Dishoeck, E. F.; Brandl, B. R.

Exoplanet Proxima b will be an important laboratory for the search for extraterrestrial life for the decades ahead. Here, we discuss the prospects of detecting carbon dioxide at 15 μ m using a spectral filtering technique with the Medium Resolution Spectrograph (MRS) mode of the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope ( JWST ). At superior conjunction, the planet is expected to show a contrast of up to 100 ppm with respect to the star. At a spectral resolving power of R  = 1790–2640, about 100 spectral CO{sub 2} features are visible within the 13.2–15.8 μ m (3B)more » band, which can be combined to boost the planet atmospheric signal by a factor of 3–4, depending on the atmospheric temperature structure and CO{sub 2} abundance. If atmospheric conditions are favorable (assuming an Earth-like atmosphere), with this new application to the cross-correlation technique, carbon dioxide can be detected within a few days of JWST observations. However, this can only be achieved if both the instrumental spectral response and the stellar spectrum can be determined to a relative precision of ≤1 × 10{sup −4} between adjacent spectral channels. Absolute flux calibration is not required, and the method is insensitive to the strong broadband variability of the host star. Precise calibration of the spectral features of the host star may only be attainable by obtaining deep observations of the system during inferior conjunction that serve as a reference. The high-pass filter spectroscopic technique with the MIRI MRS can be tested on warm Jupiters, Neptunes, and super-Earths with significantly higher planet/star contrast ratios than the Proxima system.« less

"Relative CIR": an image enhancement and visualization technique

USGS Publications Warehouse

Fleming, Michael D.

1993-01-01

Many techniques exist to spectrally and spatially enhance digital multispectral scanner data. One technique enhances an image while keeping the colors as they would appear in a color-infrared (CIR) image. This "relative CIR" technique generates an image that is both spectrally and spatially enhanced, while displaying a maximum range of colors. The technique enables an interpreter to visualize either spectral or land cover classes by their relative CIR characteristics. A relative CIR image is generated by developed spectral statistics for each class in the classifications and then, using a nonparametric approach for spectral enhancement, the means of the classes for each band are ranked. A 3 by 3 pixel smoothing filter is applied to the classification for spatial enhancement and the classes are mapped to the representative rank for each band. Practical applications of the technique include displaying an image classification product as a CIR image that was not derived directly from a spectral image, visualizing how a land cover classification would look as a CIR image, and displaying a spectral classification or intermediate product that will be used to label spectral classes.

Wavelet Filter Banks for Super-Resolution SAR Imaging

NASA Technical Reports Server (NTRS)

Sheybani, Ehsan O.; Deshpande, Manohar; Memarsadeghi, Nargess

2011-01-01

This paper discusses Innovative wavelet-based filter banks designed to enhance the analysis of super resolution Synthetic Aperture Radar (SAR) images using parametric spectral methods and signal classification algorithms, SAR finds applications In many of NASA's earth science fields such as deformation, ecosystem structure, and dynamics of Ice, snow and cold land processes, and surface water and ocean topography. Traditionally, standard methods such as Fast-Fourier Transform (FFT) and Inverse Fast-Fourier Transform (IFFT) have been used to extract Images from SAR radar data, Due to non-parametric features of these methods and their resolution limitations and observation time dependence, use of spectral estimation and signal pre- and post-processing techniques based on wavelets to process SAR radar data has been proposed. Multi-resolution wavelet transforms and advanced spectral estimation techniques have proven to offer efficient solutions to this problem.

Landsat multispectral sharpening using a sensor system model and panchromatic image

USGS Publications Warehouse

Lemeshewsky, G.P.; ,

2003-01-01

The thematic mapper (TM) sensor aboard Landsats 4, 5 and enhanced TM plus (ETM+) on Landsat 7 collect imagery at 30-m sample distance in six spectral bands. New with ETM+ is a 15-m panchromatic (P) band. With image sharpening techniques, this higher resolution P data, or as an alternative, the 10-m (or 5-m) P data of the SPOT satellite, can increase the spatial resolution of the multispectral (MS) data. Sharpening requires that the lower resolution MS image be coregistered and resampled to the P data before high spatial frequency information is transferred to the MS data. For visual interpretation and machine classification tasks, it is important that the sharpened data preserve the spectral characteristics of the original low resolution data. A technique was developed for sharpening (in this case, 3:1 spatial resolution enhancement) visible spectral band data, based on a model of the sensor system point spread function (PSF) in order to maintain spectral fidelity. It combines high-pass (HP) filter sharpening methods with iterative image restoration to reduce degradations caused by sensor-system-induced blurring and resembling. Also there is a spectral fidelity requirement: sharpened MS when filtered by the modeled degradations should reproduce the low resolution source MS. Quantitative evaluation of sharpening performance was made by using simulated low resolution data generated from digital color-IR aerial photography. In comparison to the HP-filter-based sharpening method, results for the technique in this paper with simulated data show improved spectral fidelity. Preliminary results with TM 30-m visible band data sharpened with simulated 10-m panchromatic data are promising but require further study.

Analysis Using Bi-Spectral Related Technique

DTIC Science & Technology

1993-11-17

filtering is employed as the data is processed (equation 1). Earlier results have shown that in contrast to the Wigner - Ville Distribution ( WVD ) no spectral...Technique by-o -~ Ralph Hippenstiel November 17, 1993 94 2 22 1 0 Approved for public reslease; distribution unlimited. Prepared for: Naval Command Control...Government. 12a. DISTRIBUTION /AVAILABILITY STATEMENT 12b. DISTRIBUTION ’.ODE Approved for public relkase; distribution unlimited. 13. ABSTRACT (Maximum

Technological development of spectral filters for Sentinel-2

NASA Astrophysics Data System (ADS)

Schröter, Karin; Schallenberg, Uwe; Mohaupt, Matthias

2017-11-01

In the frame of the initiative for Global Monitoring for Environment and Security (GMES), jointly undertaken by the European Commission and the European Space Agency a technological development of two filter assemblies was performed for the Multi- Spectral Instrument (MSI) for Sentinel-2. The multispectral pushbroom imaging of the Earth will be performed in 10 VNIR bands (from 443 nm to 945nm) and 3 SWIR bands (from 1375 nm to 2190 nm). Possible filter coating techniques and masking concepts were considered in the frame of trade-off studies. The selected deposition concept is based on self-blocked all-dielectric multilayer band pass filter. Band pass and blocking characteristic is deposited on the space side of a single filter substrate whereas the detector side of the substrate has an antireflective coating. The space- and detector side masking design is realized by blades integrated in the mechanical parts including the mechanical interface to the filter assembly support on the MSI focal plane. The feasibility and required performance of the VNIR Filter Assembly and SWIR Filter Assembly were successfully demonstrated by breadboarding. Extensive performance tests of spectral and optical parameters and environmental tests (radiation, vibration, shock, thermal vacuum cycling, humidity) were performed on filter stripe- and filter assembly level. The presentation will contain a detailed description of the filter assembly design and the results of the performance and environmental tests.

Solution to the spectral filter problem of residual terrain modelling (RTM)

NASA Astrophysics Data System (ADS)

Rexer, Moritz; Hirt, Christian; Bucha, Blažej; Holmes, Simon

2018-06-01

In physical geodesy, the residual terrain modelling (RTM) technique is frequently used for high-frequency gravity forward modelling. In the RTM technique, a detailed elevation model is high-pass-filtered in the topography domain, which is not equivalent to filtering in the gravity domain. This in-equivalence, denoted as spectral filter problem of the RTM technique, gives rise to two imperfections (errors). The first imperfection is unwanted low-frequency (LF) gravity signals, and the second imperfection is missing high-frequency (HF) signals in the forward-modelled RTM gravity signal. This paper presents new solutions to the RTM spectral filter problem. Our solutions are based on explicit modelling of the two imperfections via corrections. The HF correction is computed using spectral domain gravity forward modelling that delivers the HF gravity signal generated by the long-wavelength RTM reference topography. The LF correction is obtained from pre-computed global RTM gravity grids that are low-pass-filtered using surface or solid spherical harmonics. A numerical case study reveals maximum absolute signal strengths of ˜ 44 mGal (0.5 mGal RMS) for the HF correction and ˜ 33 mGal (0.6 mGal RMS) for the LF correction w.r.t. a degree-2160 reference topography within the data coverage of the SRTM topography model (56°S ≤ φ ≤ 60°N). Application of the LF and HF corrections to pre-computed global gravity models (here the GGMplus gravity maps) demonstrates the efficiency of the new corrections over topographically rugged terrain. Over Switzerland, consideration of the HF and LF corrections reduced the RMS of the residuals between GGMplus and ground-truth gravity from 4.41 to 3.27 mGal, which translates into ˜ 26% improvement. Over a second test area (Canada), our corrections reduced the RMS of the residuals between GGMplus and ground-truth gravity from 5.65 to 5.30 mGal (˜ 6% improvement). Particularly over Switzerland, geophysical signals (associated, e.g. with valley fillings) were found to stand out more clearly in the RTM-reduced gravity measurements when the HF and LF correction are taken into account. In summary, the new RTM filter corrections can be easily computed and applied to improve the spectral filter characteristics of the popular RTM approach. Benefits are expected, e.g. in the context of the development of future ultra-high-resolution global gravity models, smoothing of observed gravity data in mountainous terrain and geophysical interpretations of RTM-reduced gravity measurements.

Spectral shaping of an all-fiber torsional acousto-optic tunable filter.

PubMed

Ko, Jeakwon; Lee, Kwang Jo; Kim, Byoung Yoon

2014-12-20

Spectral shaping of an all-fiber torsional acousto-optic (AO) tunable filter is studied. The technique is based on the axial modulation of AO coupling strength along a highly birefringent optical fiber, which is achieved by tailoring the outer diameter of the fiber along its propagation axis. Two kinds of filter spectral shaping schemes-Gaussian apodization and matched filtering with triple resonance peaks-are proposed and numerically investigated under realistic experimental conditions: at the 50-cm-long AO interaction length of the fiber and at half of the original fiber diameter as the minimum thickness of the tailored fiber section. The results show that the highest peak of sidelobe spectra in filter transmission is suppressed from 11.64% to 0.54% via Gaussian modulation of the AO coupling coefficient (κ). Matched filtering with triple resonance peaks operating with a single radio frequency signal is also achieved by cosine modulation of κ, of which the modulation period determines the spectral distance between two satellite peaks located in both wings of the main resonance peak. The splitting of two satellite peaks in the filter spectra reaches 48.2 nm while the modulation period varies from 7.7 to 50 cm. The overall peak power of two satellite resonances is calculated to be 22% of the main resonance power. The results confirm the validity and practicality of our approach, and we predict robust and stable operation of the designed all-fiber torsional AO filters.

Spectroscopic imaging using acousto-optic tunable filters

NASA Astrophysics Data System (ADS)

Bouhifd, Mounir; Whelan, Maurice

2007-07-01

We report on novel hyper-spectral imaging filter-modules based on acousto-optic tuneable filters (AOTF). The AOTF functions as a full-field tuneable bandpass filter which offers fast continuous or random access tuning with high filtering efficiency. Due to the diffractive nature of the device, the unfiltered zero-order and the filtered first-order images are geometrically separated. The modules developed exploit this feature to simultaneously route both the transmitted white-light image and the filtered fluorescence image to two separate cameras. Incorporation of prisms in the optical paths and careful design of the relay optics in the filter module have overcome a number of aberrations inherent to imaging through AOTFs, leading to excellent spatial resolution. A number of practical uses of this technique, both for in vivo auto-fluorescence endoscopy and in vitro fluorescence microscopy were demonstrated. We describe the operational principle and design of recently improved prototype instruments for fluorescence-based diagnostics and demonstrate their performance by presenting challenging hyper-spectral fluorescence imaging applications.

A simple integrated ratiometric wavelength monitor based on multimode interference structure

NASA Astrophysics Data System (ADS)

Hatta, Agus Muhamad; Farrell, Gerald; Wang, Qian

2008-09-01

Wavelength measurement or monitoring can be implemented using a ratiometric power measurement technique. A ratiometric wavelength monitor normally consists of a Y-branch splitter with two arms: an edge filter arm with a well defined spectral response and a reference arm or alternatively, two edge filters arms with opposite slope spectral responses. In this paper, a simple configuration for an integrated ratiometric wavelength monitor based on a single multimode interference structure is proposed. By optimizing the length of the MMI and the two output port positions, opposite spectral responses for the two output ports can be achieved. The designed structure demonstrates a spectral response suitable for wavelength measurement with potentially a 10 pm resolution over a 100 nm wavelength range.

Computational multispectral video imaging [Invited].

PubMed

Wang, Peng; Menon, Rajesh

2018-01-01

Multispectral imagers reveal information unperceivable to humans and conventional cameras. Here, we demonstrate a compact single-shot multispectral video-imaging camera by placing a micro-structured diffractive filter in close proximity to the image sensor. The diffractive filter converts spectral information to a spatial code on the sensor pixels. Following a calibration step, this code can be inverted via regularization-based linear algebra to compute the multispectral image. We experimentally demonstrated spectral resolution of 9.6 nm within the visible band (430-718 nm). We further show that the spatial resolution is enhanced by over 30% compared with the case without the diffractive filter. We also demonstrate Vis-IR imaging with the same sensor. Because no absorptive color filters are utilized, sensitivity is preserved as well. Finally, the diffractive filters can be easily manufactured using optical lithography and replication techniques.

Electromagnetic Counter-Counter Measure (ECCM) Techniques of the Digital Microwave Radio.

DTIC Science & Technology

1982-05-01

Frequency hopping requires special synthesizers and filter banks. Large bandwidth expansion in a microwave radio relay application can best be achieved with...34 processing gain " performance as a function of jammer modulation type " pulse jammer performance • emission bandwidth and spectral shaping 0... spectral efficiency, implementation complexity, and suitability for ECCK techniques will be considered. A sumary of the requirements and characteristics of

Nanophotonic Image Sensors.

PubMed

Chen, Qin; Hu, Xin; Wen, Long; Yu, Yan; Cumming, David R S

2016-09-01

The increasing miniaturization and resolution of image sensors bring challenges to conventional optical elements such as spectral filters and polarizers, the properties of which are determined mainly by the materials used, including dye polymers. Recent developments in spectral filtering and optical manipulating techniques based on nanophotonics have opened up the possibility of an alternative method to control light spectrally and spatially. By integrating these technologies into image sensors, it will become possible to achieve high compactness, improved process compatibility, robust stability and tunable functionality. In this Review, recent representative achievements on nanophotonic image sensors are presented and analyzed including image sensors with nanophotonic color filters and polarizers, metamaterial-based THz image sensors, filter-free nanowire image sensors and nanostructured-based multispectral image sensors. This novel combination of cutting edge photonics research and well-developed commercial products may not only lead to an important application of nanophotonics but also offer great potential for next generation image sensors beyond Moore's Law expectations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultra compact spectrometer using linear variable filters

NASA Astrophysics Data System (ADS)

Dami, M.; De Vidi, R.; Aroldi, G.; Belli, F.; Chicarella, L.; Piegari, A.; Sytchkova, A.; Bulir, J.; Lemarquis, F.; Lequime, M.; Abel Tibérini, L.; Harnisch, B.

2017-11-01

The Linearly Variable Filters (LVF) are complex optical devices that, integrated in a CCD, can realize a "single chip spectrometer". In the framework of an ESA Study, a team of industries and institutes led by SELEX-Galileo explored the design principles and manufacturing techniques, realizing and characterizing LVF samples based both on All-Dielectric (AD) and Metal-Dielectric (MD) Coating Structures in the VNIR and SWIR spectral ranges. In particular the achieved performances on spectral gradient, transmission bandwidth and Spectral Attenuation (SA) are presented and critically discussed. Potential improvements will be highlighted. In addition the results of a feasibility study of a SWIR Linear Variable Filter are presented with the comparison of design prediction and measured performances. Finally criticalities related to the filter-CCD packaging are discussed. The main achievements reached during these activities have been: - to evaluate by design, manufacturing and test of LVF samples the achievable performances compared with target requirements; - to evaluate the reliability of the projects by analyzing their repeatability; - to define suitable measurement methodologies

Signal Processing Equipment and Techniques for Use in Measuring Ocean Acoustic Multipath Structures

DTIC Science & Technology

1983-12-01

Demodulator 3.4 Digital Demodulator 3.4.1 Number of Bits in the Input A/D Converter Quantization Effects The Demodulator Output Filter Effects of... power caused by ignoring cross spectral term a) First order Butterworth filter b) Second order Butterworth filter 48 3.4 Ordering of e...spectrum 59 3.7 Multiplying D/A Converter input and output spectra a) Input b) Output 60 3.8 Demodulator output spectrum prior to filtering 63

Applying spectral unmixing and support vector machine to airborne hyperspectral imagery for detecting giant reed

USDA-ARS?s Scientific Manuscript database

This study evaluated linear spectral unmixing (LSU), mixture tuned matched filtering (MTMF) and support vector machine (SVM) techniques for detecting and mapping giant reed (Arundo donax L.), an invasive weed that presents a severe threat to agroecosystems and riparian areas throughout the southern ...

Thin-film tunable filters for hyperspectral fluorescence microscopy

PubMed Central

Favreau, Peter; Hernandez, Clarissa; Lindsey, Ashley Stringfellow; Alvarez, Diego F.; Rich, Thomas; Prabhat, Prashant

2013-01-01

Abstract. Hyperspectral imaging is a powerful tool that acquires data from many spectral bands, forming a contiguous spectrum. Hyperspectral imaging was originally developed for remote sensing applications; however, hyperspectral techniques have since been applied to biological fluorescence imaging applications, such as fluorescence microscopy and small animal fluorescence imaging. The spectral filtering method largely determines the sensitivity and specificity of any hyperspectral imaging system. There are several types of spectral filtering hardware available for microscopy systems, most commonly acousto-optic tunable filters (AOTFs) and liquid crystal tunable filters (LCTFs). These filtering technologies have advantages and disadvantages. Here, we present a novel tunable filter for hyperspectral imaging—the thin-film tunable filter (TFTF). The TFTF presents several advantages over AOTFs and LCTFs, most notably, a high percentage transmission and a high out-of-band optical density (OD). We present a comparison of a TFTF-based hyperspectral microscopy system and a commercially available AOTF-based system. We have characterized the light transmission, wavelength calibration, and OD of both systems, and have then evaluated the capability of each system for discriminating between green fluorescent protein and highly autofluorescent lung tissue. Our results suggest that TFTFs are an alternative approach for hyperspectral filtering that offers improved transmission and out-of-band blocking. These characteristics make TFTFs well suited for other biomedical imaging devices, such as ophthalmoscopes or endoscopes. PMID:24077519

Optimization design of spectral discriminator for high-spectral-resolution lidar based on error analysis.

PubMed

Di, Huige; Zhang, Zhanfei; Hua, Hangbo; Zhang, Jiaqi; Hua, Dengxin; Wang, Yufeng; He, Tingyao

2017-03-06

Accurate aerosol optical properties could be obtained via the high spectral resolution lidar (HSRL) technique, which employs a narrow spectral filter to suppress the Rayleigh or Mie scattering in lidar return signals. The ability of the filter to suppress Rayleigh or Mie scattering is critical for HSRL. Meanwhile, it is impossible to increase the rejection of the filter without limitation. How to optimize the spectral discriminator and select the appropriate suppression rate of the signal is important to us. The HSRL technology was thoroughly studied based on error propagation. Error analyses and sensitivity studies were carried out on the transmittance characteristics of the spectral discriminator. Moreover, ratwo different spectroscopic methods for HSRL were described and compared: one is to suppress the Mie scattering; the other is to suppress the Rayleigh scattering. The corresponding HSRLs were simulated and analyzed. The results show that excessive suppression of Rayleigh scattering or Mie scattering in a high-spectral channel is not necessary if the transmittance of the spectral filter for molecular and aerosol scattering signals can be well characterized. When the ratio of transmittance of the spectral filter for aerosol scattering and molecular scattering is less than 0.1 or greater than 10, the detection error does not change much with its value. This conclusion implies that we have more choices for the high-spectral discriminator in HSRL. Moreover, the detection errors of HSRL regarding the two spectroscopic methods vary greatly with the atmospheric backscattering ratio. To reduce the detection error, it is necessary to choose a reasonable spectroscopic method. The detection method of suppressing the Rayleigh signal and extracting the Mie signal can achieve less error in a clear atmosphere, while the method of suppressing the Mie signal and extracting the Rayleigh signal can achieve less error in a polluted atmosphere.

Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics.

PubMed

Harput, Sevan; McLaughlan, James; Cowell, David M J; Freear, Steven

2014-11-01

Superharmonic imaging improves the spatial resolution by using the higher order harmonics generated in tissue. The superharmonic component is formed by combining the third, fourth, and fifth harmonics, which have low energy content and therefore poor SNR. This study uses coded excitation to increase the excitation energy. The SNR improvement is achieved on the receiver side by performing pulse compression with harmonic matched filters. The use of coded signals also introduces new filtering capabilities that are not possible with pulsed excitation. This is especially important when using wideband signals. For narrowband signals, the spectral boundaries of the harmonics are clearly separated and thus easy to filter; however, the available imaging bandwidth is underused. Wideband excitation is preferable for harmonic imaging applications to preserve axial resolution, but it generates spectrally overlapping harmonics that are not possible to filter in time and frequency domains. After pulse compression, this overlap increases the range side lobes, which appear as imaging artifacts and reduce the Bmode image quality. In this study, the isolation of higher order harmonics was achieved in another domain by using the fan chirp transform (FChT). To show the effect of excitation bandwidth in superharmonic imaging, measurements were performed by using linear frequency modulated chirp excitation with varying bandwidths of 10% to 50%. Superharmonic imaging was performed on a wire phantom using a wideband chirp excitation. Results were presented with and without applying the FChT filtering technique by comparing the spatial resolution and side lobe levels. Wideband excitation signals achieved a better resolution as expected, however range side lobes as high as -23 dB were observed for the superharmonic component of chirp excitation with 50% fractional bandwidth. The proposed filtering technique achieved >50 dB range side lobe suppression and improved the image quality without affecting the axial resolution.

Denoising Algorithm for CFA Image Sensors Considering Inter-Channel Correlation.

PubMed

Lee, Min Seok; Park, Sang Wook; Kang, Moon Gi

2017-05-28

In this paper, a spatio-spectral-temporal filter considering an inter-channel correlation is proposed for the denoising of a color filter array (CFA) sequence acquired by CCD/CMOS image sensors. Owing to the alternating under-sampled grid of the CFA pattern, the inter-channel correlation must be considered in the direct denoising process. The proposed filter is applied in the spatial, spectral, and temporal domain, considering the spatio-tempo-spectral correlation. First, nonlocal means (NLM) spatial filtering with patch-based difference (PBD) refinement is performed by considering both the intra-channel correlation and inter-channel correlation to overcome the spatial resolution degradation occurring with the alternating under-sampled pattern. Second, a motion-compensated temporal filter that employs inter-channel correlated motion estimation and compensation is proposed to remove the noise in the temporal domain. Then, a motion adaptive detection value controls the ratio of the spatial filter and the temporal filter. The denoised CFA sequence can thus be obtained without motion artifacts. Experimental results for both simulated and real CFA sequences are presented with visual and numerical comparisons to several state-of-the-art denoising methods combined with a demosaicing method. Experimental results confirmed that the proposed frameworks outperformed the other techniques in terms of the objective criteria and subjective visual perception in CFA sequences.

Improved Cloud and Snow Screening in MAIAC Aerosol Retrievals Using Spectral and Spatial Analysis

NASA Technical Reports Server (NTRS)

Lyapustin, A.; Wang, Y.; Laszlo, I.; Kokrkin, S.

2012-01-01

An improved cloud/snow screening technique in the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm is described. It is implemented as part of MAIAC aerosol retrievals based on analysis of spectral residuals and spatial variability. Comparisons with AERONET aerosol observations and a large-scale MODIS data analysis show strong suppression of aerosol optical thickness outliers due to unresolved clouds and snow. At the same time, the developed filter does not reduce the aerosol retrieval capability at high 1 km resolution in strongly inhomogeneous environments, such as near centers of the active fires. Despite significant improvement, the optical depth outliers in high spatial resolution data are and will remain the problem to be addressed by the application-dependent specialized filtering techniques.

Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry.

PubMed

Williams, Calum; Rughoobur, Girish; Flewitt, Andrew J; Wilkinson, Timothy D

2016-11-10

A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal-insulator-metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 to 850 nm based on Ag (25 nm) and MgF₂ (75-250 nm). Maximum spectral transmittance is measured at ∼70% with a Q-factor of ∼20.

Multiscale image fusion using the undecimated wavelet transform with spectral factorization and nonorthogonal filter banks.

PubMed

Ellmauthaler, Andreas; Pagliari, Carla L; da Silva, Eduardo A B

2013-03-01

Multiscale transforms are among the most popular techniques in the field of pixel-level image fusion. However, the fusion performance of these methods often deteriorates for images derived from different sensor modalities. In this paper, we demonstrate that for such images, results can be improved using a novel undecimated wavelet transform (UWT)-based fusion scheme, which splits the image decomposition process into two successive filtering operations using spectral factorization of the analysis filters. The actual fusion takes place after convolution with the first filter pair. Its significantly smaller support size leads to the minimization of the unwanted spreading of coefficient values around overlapping image singularities. This usually complicates the feature selection process and may lead to the introduction of reconstruction errors in the fused image. Moreover, we will show that the nonsubsampled nature of the UWT allows the design of nonorthogonal filter banks, which are more robust to artifacts introduced during fusion, additionally improving the obtained results. The combination of these techniques leads to a fusion framework, which provides clear advantages over traditional multiscale fusion approaches, independent of the underlying fusion rule, and reduces unwanted side effects such as ringing artifacts in the fused reconstruction.

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

Here, we discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. Furthermore, we show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. Finally, the combination of narrow absorption peaks in the sample with ultrafast broadbandmore » excitation pulses is especially prone to this effect.« less

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

DOE PAGES

Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

2017-03-06

Here, we discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. Furthermore, we show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. Finally, the combination of narrow absorption peaks in the sample with ultrafast broadbandmore » excitation pulses is especially prone to this effect.« less

Elimination of interference component in Wigner-Ville distribution for the signal with 1/f spectral characteristic.

PubMed

Chan, H L; Lin, J L; Huang, H H; Wu, C P

1997-09-01

A new technique for interference-term suppression in Wigner-Ville distribution (WVD) is proposed for the signal with 1/f spectrum shape. The spectral characteristic of the signal is altered by f alpha filtering before time-frequency analysis and compensated after analysis. With the utilization of the proposed technique in smoothed pseudo Wigner-Ville distribution, an excellent suppression of interference component can be achieved.

Nanophotonic Image Sensors

PubMed Central

Hu, Xin; Wen, Long; Yu, Yan; Cumming, David R. S.

2016-01-01

The increasing miniaturization and resolution of image sensors bring challenges to conventional optical elements such as spectral filters and polarizers, the properties of which are determined mainly by the materials used, including dye polymers. Recent developments in spectral filtering and optical manipulating techniques based on nanophotonics have opened up the possibility of an alternative method to control light spectrally and spatially. By integrating these technologies into image sensors, it will become possible to achieve high compactness, improved process compatibility, robust stability and tunable functionality. In this Review, recent representative achievements on nanophotonic image sensors are presented and analyzed including image sensors with nanophotonic color filters and polarizers, metamaterial‐based THz image sensors, filter‐free nanowire image sensors and nanostructured‐based multispectral image sensors. This novel combination of cutting edge photonics research and well‐developed commercial products may not only lead to an important application of nanophotonics but also offer great potential for next generation image sensors beyond Moore's Law expectations. PMID:27239941

Spectrally tailored supercontinuum generation from single-mode-fiber amplifiers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Qiang; Guo, Zhengru; Zhang, Qingshan

Spectral filtering of an all-normal-dispersion Yb-doped fiber laser was demonstrated effective for broadband supercontinuum generation in the picosecond time region. The picosecond pump pulses were tailored in spectrum with 1 nm band-pass filter installed between two single-mode fiber amplifiers. By tuning the spectral filter around 1028 nm, four-wave mixing was initiated in a photonic crystal fiber spliced with single-mode fiber, as manifested by the simultaneous generation of Stokes wave at 1076 nm and anti-Stokes wave at 984 nm. Four-wave mixing took place in cascade with the influence of stimulated Raman scattering and eventually extended the output spectrum more than 900 nm of 10 dB bandwidth.more » This technique allows smooth octave supercontinuum generation by using simple single-mode fiber amplifiers rather than complicated multistage large-mode-area fiber amplifiers.« less

Wideband bandpass filters employing broadside-coupled microstrip lines for MIC and MMIC applications

NASA Technical Reports Server (NTRS)

Tran, M.; Nguyen, C.

1994-01-01

Wideband bandpass filters employing half-wavelength broadside-coupled microstrip lines suitable for microwave and mm-wave integrated monolithic integrated circuits (MIC and MMIC) are presented. Several filters have been developed at X-band (8 to 12 GHz) with 1 dB insertion loss. Fair agreement between the measured and calculated results has been observed. The analysis of the broadside-coupled microstrip lines used in the filters, based on the quasi-static spectral domain technique, is also described.

Correction of pathlength amplification in the filter-pad technique for measurements of particulate absorption coefficient in the visible spectral region.

PubMed

Stramski, Dariusz; Reynolds, Rick A; Kaczmarek, Sławomir; Uitz, Julia; Zheng, Guangming

2015-08-01

Spectrophotometric measurement of particulate matter retained on filters is the most common and practical method for routine determination of the spectral light absorption coefficient of aquatic particles, a_p(λ), at high spectral resolution over a broad spectral range. The use of differing geometrical measurement configurations and large variations in the reported correction for pathlength amplification induced by the particle/filter matrix have hindered adoption of an established measurement protocol. We describe results of dedicated laboratory experiments with a diversity of particulate sample types to examine variation in the pathlength amplification factor for three filter measurement geometries; the filter in the transmittance configuration (T), the filter in the transmittance-reflectance configuration (T-R), and the filter placed inside an integrating sphere (IS). Relationships between optical density measured on suspensions (OD_s) and filters (OD_f) within the visible portion of the spectrum were evaluated for the formulation of pathlength amplification correction, with power functions providing the best functional representation of the relationship for all three geometries. Whereas the largest uncertainties occur in the T method, the IS method provided the least sample-to-sample variability and the smallest uncertainties in the relationship between OD_s and OD_f. For six different samples measured with 1 nm resolution within the light wavelength range from 400 to 700 nm, a median error of 7.1% is observed for predicted values of OD_s using the IS method. The relationships established for the three filter-pad methods are applicable to historical and ongoing measurements; for future work, the use of the IS method is recommended whenever feasible.

Spectral Characterizations of the Clouds and the Earth's Radiant Energy System (CERES) Thermistor Bolometers using Fourier Transform Spectrometer (FTS) Techniques

NASA Technical Reports Server (NTRS)

Thornhill, K. Lee; Bitting, Herbert; Lee, Robert B., III; Paden, Jack; Pandey, Dhirendra K.; Priestley, Kory J.; Thomas, Susan; Wilson, Robert S.

1998-01-01

Fourier Transform Spectrometer (FTS) techniques are being used to characterize the relative spectral response, or sensitivity, of scanning thermistor bolometers in the infrared (IR) region (2 - >= 100-micrometers). The bolometers are being used in the Clouds and the Earth's Radiant Energy System (CERES) program. The CERES measurements are designed to provide precise, long term monitoring of the Earth's atmospheric radiation energy budget. The CERES instrument houses three bolometric radiometers, a total wavelength (0.3- >= 150-micrometers) sensor, a shortwave (0.3-5-micrometers) sensor, and an atmospheric window (8-12-micrometers) sensor. Accurate spectral characterization is necessary for determining filtered radiances for longwave radiometric calibrations. The CERES bolometers spectral response's are measured in the TRW FTS Vacuum Chamber Facility (FTS - VCF), which uses a FTS as the source and a cavity pyroelectric trap detector as the reference. The CERES bolometers and the cavity detector are contained in a vacuum chamber, while the FTS source is housed in a GN2 purged chamber. Due to the thermal time constant of the CERES bolometers, the FTS must be operated in a step mode. Data are acquired in 6 IR spectral bands covering the entire longwave IR region. In this paper, the TRW spectral calibration facility design and data measurement techniques are described. Two approaches are presented which convert the total channel FTS data into the final CERES spectral characterizations, producing the same calibration coefficients (within 0.1 percent). The resulting spectral response curves are shown, along with error sources in the two procedures. Finally, the impact of each spectral response curve on CERES data validation will be examined through analysis of filtered radiance values from various typical scene types.

An unsupervised technique for optimal feature selection in attribute profiles for spectral-spatial classification of hyperspectral images

NASA Astrophysics Data System (ADS)

Bhardwaj, Kaushal; Patra, Swarnajyoti

2018-04-01

Inclusion of spatial information along with spectral features play a significant role in classification of remote sensing images. Attribute profiles have already proved their ability to represent spatial information. In order to incorporate proper spatial information, multiple attributes are required and for each attribute large profiles need to be constructed by varying the filter parameter values within a wide range. Thus, the constructed profiles that represent spectral-spatial information of an hyperspectral image have huge dimension which leads to Hughes phenomenon and increases computational burden. To mitigate these problems, this work presents an unsupervised feature selection technique that selects a subset of filtered image from the constructed high dimensional multi-attribute profile which are sufficiently informative to discriminate well among classes. In this regard the proposed technique exploits genetic algorithms (GAs). The fitness function of GAs are defined in an unsupervised way with the help of mutual information. The effectiveness of the proposed technique is assessed using one-against-all support vector machine classifier. The experiments conducted on three hyperspectral data sets show the robustness of the proposed method in terms of computation time and classification accuracy.

Development and application of the maximum entropy method and other spectral estimation techniques

NASA Astrophysics Data System (ADS)

King, W. R.

1980-09-01

This summary report is a collection of four separate progress reports prepared under three contracts, which are all sponsored by the Office of Naval Research in Arlington, Virginia. This report contains the results of investigations into the application of the maximum entropy method (MEM), a high resolution, frequency and wavenumber estimation technique. The report also contains a description of two, new, stable, high resolution spectral estimation techniques that is provided in the final report section. Many examples of wavenumber spectral patterns for all investigated techniques are included throughout the report. The maximum entropy method is also known as the maximum entropy spectral analysis (MESA) technique, and both names are used in the report. Many MEM wavenumber spectral patterns are demonstrated using both simulated and measured radar signal and noise data. Methods for obtaining stable MEM wavenumber spectra are discussed, broadband signal detection using the MEM prediction error transform (PET) is discussed, and Doppler radar narrowband signal detection is demonstrated using the MEM technique. It is also shown that MEM cannot be applied to randomly sampled data. The two new, stable, high resolution, spectral estimation techniques discussed in the final report section, are named the Wiener-King and the Fourier spectral estimation techniques. The two new techniques have a similar derivation based upon the Wiener prediction filter, but the two techniques are otherwise quite different. Further development of the techniques and measurement of the technique spectral characteristics is recommended for subsequent investigation.

Snapshot Imaging Spectrometry in the Visible and Long Wave Infrared

NASA Astrophysics Data System (ADS)

Maione, Bryan David

Imaging spectrometry is an optical technique in which the spectral content of an object is measured at each location in space. The main advantage of this modality is that it enables characterization beyond what is possible with a conventional camera, since spectral information is generally related to the chemical composition of the object. Due to this, imaging spectrometers are often capable of detecting targets that are either morphologically inconsistent, or even under resolved. A specific class of imaging spectrometer, known as a snapshot system, seeks to measure all spatial and spectral information simultaneously, thereby rectifying artifacts associated with scanning designs, and enabling the measurement of temporally dynamic scenes. Snapshot designs are the focus of this dissertation. Three designs for snapshot imaging spectrometers are developed, each providing novel contributions to the field of imaging spectrometry. In chapter 2, the first spatially heterodyned snapshot imaging spectrometer is modeled and experimentally validated. Spatial heterodyning is a technique commonly implemented in non-imaging Fourier transform spectrometry. For Fourier transform imaging spectrometers, spatial heterodyning improves the spectral resolution trade space. Additionally, in this chapter a unique neural network based spectral calibration is developed and determined to be an improvement beyond Fourier and linear operator based techniques. Leveraging spatial heterodyning as developed in chapter 2, in chapter 3, a high spectral resolution snapshot Fourier transform imaging spectrometer, based on a Savart plate interferometer, is developed and experimentally validated. The sensor presented in this chapter is the highest spectral resolution sensor in its class. High spectral resolution enables the sensor to discriminate narrowly spaced spectral lines. The capabilities of neural networks in imaging spectrometry are further explored in this chapter. Neural networks are used to perform single target detection on raw instrument data, thereby eliminating the need for an explicit spectral calibration step. As an extension of the results in chapter 2, neural networks are once again demonstrated to be an improvement when compared to linear operator based detection. In chapter 4 a non-interferometric design is developed for the long wave infrared (wavelengths spanning 8-12 microns). The imaging spectrometer developed in this chapter is a multi-aperture filtered microbolometer. Since the detector is uncooled, the presented design is ultra-compact and low power. Additionally, cost effective polymer absorption filters are used in lieu of interference filters. Since, each measurement of the system is spectrally multiplexed, an SNR advantage is realized. A theoretical model for the filtered design is developed, and the performance of the sensor for detecting liquid contaminants is investigated. Similar to past chapters, neural networks are used and achieve false detection rates of less than 1%. Lastly, this dissertation is concluded with a discussion on future work and potential impact of these devices.

Edge technique lidar for high accuracy, high spatial resolution wind measurement in the Planetary Boundary Layer

NASA Technical Reports Server (NTRS)

Korb, C. L.; Gentry, Bruce M.

1995-01-01

The goal of the Army Research Office (ARO) Geosciences Program is to measure the three dimensional wind field in the planetary boundary layer (PBL) over a measurement volume with a 50 meter spatial resolution and with measurement accuracies of the order of 20 cm/sec. The objective of this work is to develop and evaluate a high vertical resolution lidar experiment using the edge technique for high accuracy measurement of the atmospheric wind field to meet the ARO requirements. This experiment allows the powerful capabilities of the edge technique to be quantitatively evaluated. In the edge technique, a laser is located on the steep slope of a high resolution spectral filter. This produces large changes in measured signal for small Doppler shifts. A differential frequency technique renders the Doppler shift measurement insensitive to both laser and filter frequency jitter and drift. The measurement is also relatively insensitive to the laser spectral width for widths less than the width of the edge filter. Thus, the goal is to develop a system which will yield a substantial improvement in the state of the art of wind profile measurement in terms of both vertical resolution and accuracy and which will provide a unique capability for atmospheric wind studies.

Discrimination of binocular color mixtures in dichromacy: evaluation of the Maxwell-Cornsweet conjecture

NASA Astrophysics Data System (ADS)

Knoblauch, Kenneth; McMahon, Matthew J.

1995-10-01

We tested the Maxwell-Cornsweet conjecture that differential spectral filtering of the two eyes can increase the dimensionality of a dichromat's color vision. Sex-linked dichromats wore filters that differentially passed long- and middle-wavelength regions of the spectrum to each eye. Monocularly, temporal modulation thresholds (1.5 Hz) for color mixtures from the Rayleigh region of the spectrum were accounted for by a single, univariant mechanism. Binocularly, univariance was rejected because, as in monocular viewing by trichromats, in no color direction could silent substitution of the color mixtures be obtained. Despite the filter-aided increase in dimension, estimated wavelength discrimination was quite poor in this spectral region, suggesting a limit to the effectiveness of this technique. binocular summation.

Development of a high spectral resolution lidar based on confocal Fabry-Perot spectral filters.

PubMed

Hoffman, David S; Repasky, Kevin S; Reagan, John A; Carlsten, John L

2012-09-01

The high spectral resolution lidar (HSRL) instrument described in this paper utilizes the fundamental and second-harmonic output from an injection seeded Nd:YAG laser as the laser transmitter. The light scattered in the atmosphere is collected using a commercial Schmidt-Cassegrain telescope with the optical receiver train first splitting the fundamental and second-harmonic return signal with the fundament light monitored using an avalanche photodiode. The second-harmonic return signal is mode matched into a tunable confocal Fabry-Perot (CFP) interferometer with a free spectral range of 7.5 GHz and a finesse of 50.7 (312) at 532 nm (1064 nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected from the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to a co-located solar radiometer, demonstrating the successful operation of the instrument. The CFP-based filtering technique successfully employed by this HSRL instrument is easily portable to other arbitrary wavelengths, thus allowing for the future development of multiwavelength HSRL instruments.

Maximum-likelihood spectral estimation and adaptive filtering techniques with application to airborne Doppler weather radar. Thesis Technical Report No. 20

NASA Technical Reports Server (NTRS)

Lai, Jonathan Y.

1994-01-01

This dissertation focuses on the signal processing problems associated with the detection of hazardous windshears using airborne Doppler radar when weak weather returns are in the presence of strong clutter returns. In light of the frequent inadequacy of spectral-processing oriented clutter suppression methods, we model a clutter signal as multiple sinusoids plus Gaussian noise, and propose adaptive filtering approaches that better capture the temporal characteristics of the signal process. This idea leads to two research topics in signal processing: (1) signal modeling and parameter estimation, and (2) adaptive filtering in this particular signal environment. A high-resolution, low SNR threshold maximum likelihood (ML) frequency estimation and signal modeling algorithm is devised and proves capable of delineating both the spectral and temporal nature of the clutter return. Furthermore, the Least Mean Square (LMS) -based adaptive filter's performance for the proposed signal model is investigated, and promising simulation results have testified to its potential for clutter rejection leading to more accurate estimation of windspeed thus obtaining a better assessment of the windshear hazard.

The Double Edge Technique for Doppler lidar wind measurement

NASA Technical Reports Server (NTRS)

Korb, C. Laurence; Gentry, Bruce M.; Li, S. Xingfu; Flesia, Cristina; Chen, Huailin; Mathur, S.

1998-01-01

The edge technique utilizes the edge of a high spectral resolution filter for high accuracy wind measurement using direct detection lidar. The signal is split between an edge filter channel and a broadband energy monitor channel. The energy monitor channel is used for signal normalization. The edge measurement is made as a differential frequency measurement between the outgoing laser signal and the atmospheric backscattered return for each pulse. As a result, the measurement is insensitive to laser and edge filter frequency jitter and drift at a level less than a few parts in 10(exp 10). We will discuss the methodology of the technique in detail, present a broad range of simulation results, and provide preprints of a journal article currently in press.

Apodized RFI filtering of synthetic aperture radar images

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doerry, Armin Walter

2014-02-01

Fine resolution Synthetic Aperture Radar (SAR) systems necessarily require wide bandwidths that often overlap spectrum utilized by other wireless services. These other emitters pose a source of Radio Frequency Interference (RFI) to the SAR echo signals that degrades SAR image quality. Filtering, or excising, the offending spectral contaminants will mitigate the interference, but at a cost of often degrading the SAR image in other ways, notably by raising offensive sidelobe levels. This report proposes borrowing an idea from nonlinear sidelobe apodization techniques to suppress interference without the attendant increase in sidelobe levels. The simple post-processing technique is termed Apodized RFImore » Filtering (ARF).« less

Power spectral ensity of markov texture fields

NASA Technical Reports Server (NTRS)

Shanmugan, K. S.; Holtzman, J. C.

1984-01-01

Texture is an important image characteristic. A variety of spatial domain techniques were proposed for extracting and utilizing textural features for segmenting and classifying images. for the most part, these spatial domain techniques are ad hos in nature. A markov random field model for image texture is discussed. A frequency domain description of image texture is derived in terms of the power spectral density. This model is used for designing optimum frequency domain filters for enhancing, restoring and segmenting images based on their textural properties.

Defeating camouflage and finding explosives through spectral matched filtering of hyperspectral imagery

NASA Astrophysics Data System (ADS)

Dombrowski, Mark S.; Willson, Paul D.; LaBaw, Clayton C.

1997-01-01

In order to achieve their goal of surreptitious operation within a country, terrorist organizations attempt to hide themselves from public view. In many instances such masking takes the form of simply appearing like the surrounding populace. In others, such as training facilities, standard military camouflaging techniques are used to conceal the group's equipment and activities. To effectively monitor and suppress activities of terrorist organizations, defeating the groups' attempt to hide is essential. Although finding individuals hiding within a society is extremely problematic, discovering camouflaged equipment, facilities, and personnel is readily accomplished by proper exploitation of hyperspectral imagery. Camouflage techniques attempt to make an object appear similar to its background, thereby making it difficult to find. Although making an object have similar color to its background is fairly easy, making it have the same spectral appearance is nearly impossible, unless the object is covered in the same material as the background. Even attempting to hide an object by covering it in background material will not work against a spectral imager since the act of moving the background material, e.g., foliage cuttings, changes the material's spectral characteristics. Hence, by collecting and properly exploiting spectral imagery, camouflaged objects can be readily differentiated from their background. This paper presents development of this technique, and of the MIDIS (multi-band identification and discrimination imaging spectroradiometer) instrument capable of real-time discrimination of camouflaged objects throughout a scene. Spectral matched-filtering of hyperspectral imagery also has the potential to find vehicles or structures which may be laden with explosives. Many explosives contain volatile materials, the release of which can be imaged by viewing appropriate spectral regions. Volatiles from the fuel oil in readily-produced ANFO are an example. If such volatiles were seen emanating from a vehicle or structure where they would not normally be expected, closer inspection would be warranted. Additionally, packing a vehicle with explosives often leaves trace residues on the outside of the vehicle. Spectral imaging and matched filtering can be used to identify these residues. Incorporation of spectral imaging surveillance equipment at probable terrorist targets could avert disasters such as the tragic bombing of the Murrah Federal Building in Oklahoma City. Application of MIDIS technology to explosive identification is also detailed.

Sidelobe suppression in all-fiber acousto-optic tunable filter using torsional acoustic wave.

PubMed

Lee, Kwang Jo; Hwang, In-Kag; Park, Hyun Chul; Kim, Byoung Yoon

2010-06-07

We propose two techniques to suppress intrinsic sidelobe spectra in all-fiber acousto-optic tunable filter using torsional acoustic wave. The techniques are based on either double-pass filter configuration or axial tailoring of mode coupling strength along an acousto-optic interaction region in a highly birefringent optical fiber. The sidelobe peak in the filter spectrum is experimentally suppressed from -8.3 dB to -16.4 dB by employing double-pass configuration. Axial modulation of acousto-optic coupling strength is proposed using axial variation of the fiber diameter, and the simulation results show that the maximum side peak of -9.3 dB can be reduced to -22.2dB. We also discuss the possibility of further spectral shaping of the filter based on the axial tailoring of acousto-optic coupling strength.

Principle component analysis and linear discriminant analysis of multi-spectral autofluorescence imaging data for differentiating basal cell carcinoma and healthy skin

NASA Astrophysics Data System (ADS)

Chernomyrdin, Nikita V.; Zaytsev, Kirill I.; Lesnichaya, Anastasiya D.; Kudrin, Konstantin G.; Cherkasova, Olga P.; Kurlov, Vladimir N.; Shikunova, Irina A.; Perchik, Alexei V.; Yurchenko, Stanislav O.; Reshetov, Igor V.

2016-09-01

In present paper, an ability to differentiate basal cell carcinoma (BCC) and healthy skin by combining multi-spectral autofluorescence imaging, principle component analysis (PCA), and linear discriminant analysis (LDA) has been demonstrated. For this purpose, the experimental setup, which includes excitation and detection branches, has been assembled. The excitation branch utilizes a mercury arc lamp equipped with a 365-nm narrow-linewidth excitation filter, a beam homogenizer, and a mechanical chopper. The detection branch employs a set of bandpass filters with the central wavelength of spectral transparency of λ = 400, 450, 500, and 550 nm, and a digital camera. The setup has been used to study three samples of freshly excised BCC. PCA and LDA have been implemented to analyze the data of multi-spectral fluorescence imaging. Observed results of this pilot study highlight the advantages of proposed imaging technique for skin cancer diagnosis.

Tunable resonator-based devices for producing variable delays and narrow spectral linewidths

NASA Technical Reports Server (NTRS)

Savchenkov, Anatoliy (Inventor); Maleki, Lutfollah (Inventor); Matsko, Andrey B. (Inventor); Ilchenko, Vladimir (Inventor)

2006-01-01

Devices with two or more coupled resonators to produce narrow spectral responses due to interference of signals that transmit through the resonators and techniques for operating such devices to achieve certain operating characteristics are described. The devices may be optical devices where optical resonators such as whispering gallery mode resonators may be used. In one implementation, at least one of the coupled optical resonators is a tunable resonator and is tuned to change its resonance frequency to tune the spectral response of the device. The described devices and techniques may be applied in optical filters, optical delays, optical waveform generators, and other applications.

Rapid characterization of chlorogenic acids in Duhaldea nervosa based on ultra-high-performance liquid chromatography-linear trap quadropole-Orbitrap-mass spectrometry and mass spectral trees similarity filter technique.

PubMed

Liu, Lianghong; Zhang, Jiayu; Zheng, Binjie; Guan, Ying; Wang, Liting; Chen, Lei; Cai, Wei

2018-04-01

Duhaldea nervosa (Wallich ex Candolle) A. Anderberg has been traditionally used as a food spice and also in folk medicine for treating traumatic injury and relieving rheumatism, especially accelerating the healing of a fracture. However, so far as we are aware, the chemical constituents have not been fully investigated. In this study, a practical method of mass spectral trees similarity filter, a data-mining technique, was developed and evaluated for the rapid detection and identification complicated constituents based on ultra-high-performance liquid chromatography-linear trap quadropole-Orbitrap-mass spectrometry. Finally, a total of 47 chlorogenic acids, including 19 monoacyl-quinic acids, 22 diacyl-quinic acids, and six triacyl-quinic acids, were unambiguously or tentatively identified based on their accurate mass measurement, chromatographic retention, MS n spectra, and bibliography data. To our best knowledge, it is the first time to report the chlorogenic acids of D. nervosa, which would be beneficial for the further material basis and quality research. Meanwhile, this mass spectral trees similarity filter method could be envisioned to exhibit a wide application for the identification of complicated components from botanical extracts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unenhanced third-generation dual-source chest CT using a tin filter for spectral shaping at 100kVp.

PubMed

Haubenreisser, Holger; Meyer, Mathias; Sudarski, Sonja; Allmendinger, Thomas; Schoenberg, Stefan O; Henzler, Thomas

2015-08-01

To prospectively investigate image quality and radiation dose of 100kVp spectral shaping chest CT using a dedicated tin filter on a 3rd generation dual-source CT (DSCT) in comparison to standard 100kVp chest CT. Sixty patients referred for a non-contrast chest on a 3rd generation DSCT were prospectively included and examined at 100kVp with a dedicated tin filter. These patients were retrospectively matched with patients that were examined on a 2nd generation DSCT at 100kVp without tin filter. Objective and subjective image quality was assessed in various anatomic regions and radiation dose was compared. Radiation dose was decreased by 90% using the tin filter (3.0 vs 0.32mSv). Soft tissue attenuation and image noise was not statistically different for both examination techniques (p>0.05), however image noise was found to be significantly higher in the trachea when using the additional tin filter (p=0.002). SNR was found to be statistically similar in pulmonary tissue, significantly lower when measured in air and significantly higher in the aorta for the scans on the 3rd generation DSCT. Subjective image quality with regard to overall quality and image noise and sharpness was not statistically significantly different (p>0.05). 100kVp spectral shaping chest CT by means of a tube-based tin-filter on a 3rd generation DSCT allows 90% dose reduction when compared to 100kVp chest CT on a 2nd generation DSCT without spectral shaping. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

THz near-field spectral encoding imaging using a rainbow metasurface.

PubMed

Lee, Kanghee; Choi, Hyun Joo; Son, Jaehyeon; Park, Hyun-Sung; Ahn, Jaewook; Min, Bumki

2015-09-24

We demonstrate a fast image acquisition technique in the terahertz range via spectral encoding using a metasurface. The metasurface is composed of spatially varying units of mesh filters that exhibit bandpass features. Each mesh filter is arranged such that the centre frequencies of the mesh filters are proportional to their position within the metasurface, similar to a rainbow. For imaging, the object is placed in front of the rainbow metasurface, and the image is reconstructed by measuring the transmitted broadband THz pulses through both the metasurface and the object. The 1D image information regarding the object is linearly mapped into the spectrum of the transmitted wave of the rainbow metasurface. Thus, 2D images can be successfully reconstructed using simple 1D data acquisition processes.

An excitation wavelength-scanning spectral imaging system for preclinical imaging

NASA Astrophysics Data System (ADS)

Leavesley, Silas; Jiang, Yanan; Patsekin, Valery; Rajwa, Bartek; Robinson, J. Paul

2008-02-01

Small-animal fluorescence imaging is a rapidly growing field, driven by applications in cancer detection and pharmaceutical therapies. However, the practical use of this imaging technology is limited by image-quality issues related to autofluorescence background from animal tissues, as well as attenuation of the fluorescence signal due to scatter and absorption. To combat these problems, spectral imaging and analysis techniques are being employed to separate the fluorescence signal from background autofluorescence. To date, these technologies have focused on detecting the fluorescence emission spectrum at a fixed excitation wavelength. We present an alternative to this technique, an imaging spectrometer that detects the fluorescence excitation spectrum at a fixed emission wavelength. The advantages of this approach include increased available information for discrimination of fluorescent dyes, decreased optical radiation dose to the animal, and ability to scan a continuous wavelength range instead of discrete wavelength sampling. This excitation-scanning imager utilizes an acousto-optic tunable filter (AOTF), with supporting optics, to scan the excitation spectrum. Advanced image acquisition and analysis software has also been developed for classification and unmixing of the spectral image sets. Filtering has been implemented in a single-pass configuration with a bandwidth (full width at half maximum) of 16nm at 550nm central diffracted wavelength. We have characterized AOTF filtering over a wide range of incident light angles, much wider than has been previously reported in the literature, and we show how changes in incident light angle can be used to attenuate AOTF side lobes and alter bandwidth. A new parameter, in-band to out-of-band ratio, was defined to assess the quality of the filtered excitation light. Additional parameters were measured to allow objective characterization of the AOTF and the imager as a whole. This is necessary for comparing the excitation-scanning imager to other spectral and fluorescence imaging technologies. The effectiveness of the hyperspectral imager was tested by imaging and analysis of mice with injected fluorescent dyes. Finally, a discussion of the optimization of spectral fluorescence imagers is given, relating the effects of filter quality on fluorescence images collected and the analysis outcome.

Parameterization of the Voice Source by Combining Spectral Decay and Amplitude Features of the Glottal Flow.

ERIC Educational Resources Information Center

Alku, Paavo; Vilkman, Erkki; Laukkanen, Anne-Maria

1998-01-01

A new method is presented for the parameterization of glottal volume velocity waveforms that have been estimated by inverse filtering acoustic speech pressure signals. The new technique combines two features of voice production: the AC value and the spectral decay of the glottal flow. Testing found the new parameter correlates strongly with the…

Experimental demonstration of passive coherent combining of fiber lasers by phase contrast filtering.

PubMed

Jeux, François; Desfarges-Berthelemot, Agnès; Kermène, Vincent; Barthelemy, Alain

2012-12-17

We report experiments on a new laser architecture involving phase contrast filtering to coherently combine an array of fiber lasers. We demonstrate that the new technique yields a more stable phase-locking than standard methods using only amplitude filtering. A spectral analysis of the output beams shows that the new scheme generates more resonant frequencies common to the coupled lasers. This property can enhance the combining efficiency when the number of lasers to be coupled is large.

Measuring the effects of spectral smearing and enhancement on speech recognition in noise for adults and children

PubMed Central

Nittrouer, Susan; Tarr, Eric; Wucinich, Taylor; Moberly, Aaron C.; Lowenstein, Joanna H.

2015-01-01

Broadened auditory filters associated with sensorineural hearing loss have clearly been shown to diminish speech recognition in noise for adults, but far less is known about potential effects for children. This study examined speech recognition in noise for adults and children using simulated auditory filters of different widths. Specifically, 5 groups (20 listeners each) of adults or children (5 and 7 yrs), were asked to recognize sentences in speech-shaped noise. Seven-year-olds listened at 0 dB signal-to-noise ratio (SNR) only; 5-yr-olds listened at +3 or 0 dB SNR; and adults listened at 0 or −3 dB SNR. Sentence materials were processed both to smear the speech spectrum (i.e., simulate broadened filters), and to enhance the spectrum (i.e., simulate narrowed filters). Results showed: (1) Spectral smearing diminished recognition for listeners of all ages; (2) spectral enhancement did not improve recognition, and in fact diminished it somewhat; and (3) interactions were observed between smearing and SNR, but only for adults. That interaction made age effects difficult to gauge. Nonetheless, it was concluded that efforts to diagnose the extent of broadening of auditory filters and to develop techniques to correct this condition could benefit patients with hearing loss, especially children. PMID:25920851

Three-stage Fabry-Perot liquid crystal tunable filter with extended spectral range.

PubMed

Zheng, Zhenrong; Yang, Guowei; Li, Haifeng; Liu, Xu

2011-01-31

A method to extend spectral range of tunable optical filter is proposed in this paper. Two same tunable Fabry-Perot filters and an additional tunable filter with different free spectral range are cascaded to extend spectral range and reduce sidelobes. Over 400 nm of free spectral range and 4 nm of full width at half maximum of the filter were achieved. Design procedure and simulation are described in detail. An experimental 3-stage tunable Fabry-Perot filter with visible and infrared spectra is demonstrated. The experimental results and the theoretical analysis are presented in detail to verify this method. The results revealed that a compact and extended tunable spectral range of Fabry-Perot filter can be easily attainable by this method.

Bandwidth-variable tunable optical filter unit for illumination and spectral imaging systems using thin-film optical band-pass filters.

PubMed

Hennig, Georg; Brittenham, Gary M; Sroka, Ronald; Kniebühler, Gesa; Vogeser, Michael; Stepp, Herbert

2013-04-01

An optical filter unit is demonstrated, which uses two successively arranged tunable thin-film optical band-pass filters and allows for simultaneous adjustment of the central wavelength in the spectral range 522-555 nm and of the spectral bandwidth in the range 3-16 nm with a wavelength switching time of 8 ms∕nm. Different spectral filter combinations can cover the complete visible spectral range. The transmitted intensity was found to decrease only linearly with the spectral bandwidth for bandwidths >6 nm, allowing a high maximum transmission efficiency of >75%. The image of a fiber bundle was spectrally filtered and analyzed in terms of position-dependency of the transmitted bandwidth and central wavelength.

Modeling of a field-widened Michelson interferometric filter for application in a high spectral resolution lidar

NASA Astrophysics Data System (ADS)

Liu, Dong; Hostetler, Chris; Cook, Anthony; Miller, Ian; Hair, Johnathan

2011-11-01

High spectral resolution lidars (HSRLs) are increasingly being deployed on aircraft and called for on future space-based missions. The HSRL technique relies on spectral discrimination of the atmospheric backscatter signals to enable independent, unambiguous retrieval of aerosol extinction and backscatter. A compact, monolithic field-widened Michelson interferometer is being developed as the spectral discrimination filter for an HSRL system at NASA Langley Research Center. The interferometer consists of a cubic beam splitter, a solid glass arm, and an air arm. The spacer that connects the air arm mirror to the main part of the interferometer is designed to optimize thermal compensation such that the maximum interference can be tuned with great precision to the transmitted laser wavelength. In this paper, a comprehensive radiometric model for the field-widened Michelson interferometeric spectral filter is presented. The model incorporates the angular distribution and finite cross sectional area of the light source, reflectance of all surfaces, loss of absorption, and lack of parallelism between the air-arm and solid arm, etc. The model can be used to assess the performance of the interferometer and thus it is a useful tool to evaluate performance budgets and to set optical specifications for new designs of the same basic interferometer type.

Use of a priori spectral information in the measurement of x-ray flux with filtered diode arrays

DOE PAGES

Marrs, R. E.; Widmann, K.; Brown, G. V.; ...

2015-10-29

Filtered x-ray diode (XRD) arrays are often used to measure x-ray spectra vs. time from spectrally continuous x-ray sources such as hohlraums. A priori models of the incident x-ray spectrum enable a more accurate unfolding of the x-ray flux as compared to the standard technique of modifying a thermal Planckian with spectral peaks or dips at the response energy of each filtered XRD channel. A model x-ray spectrum consisting of a thermal Planckian, a Gaussian at higher energy, and (in some cases) a high energy background provides an excellent fit to XRD-array measurements of x-ray emission from laser heated hohlraums.more » If high-resolution measurements of part of the x-ray emission spectrum are available, that information can be included in the a priori model. In cases where the x-ray emission spectrum is not Planckian, candidate x-ray spectra can be allowed or excluded by fitting them to measured XRD voltages. Here, examples are presented from the filtered XRD arrays, named Dante, at the National Ignition Facility and the Laboratory for Laser Energetics.« less

Laboratory and airborne techniques for measuring fluoresence of natural surfaces

NASA Technical Reports Server (NTRS)

Stoertz, G. E.; Hemphill, W. R.

1972-01-01

Techniques are described for obtaining fluorescence spectra from samples of natural surfaces that can be used to predict spectral regions in which these surfaces would emit solar-stimulated or laser-stimulated fluorescence detectable by remote sensor. Scattered or reflected stray light caused large errors in spectrofluorometer analysis or natural sample surfaces. Most spurious light components can be eliminated by recording successive fluorescence spectra for each sample, using identical instrument settings, first with an appropriate glass or gelatin filter on the excitation side of the sample, and subsequently with the same filter on the emission side of the sample. This technique appears more accurate than any alternative technique for testing the fluorescence of natural surfaces.

Optical filter selection for high confidence discrimination of strongly overlapping infrared chemical spectra.

PubMed

Major, Kevin J; Poutous, Menelaos K; Ewing, Kenneth J; Dunnill, Kevin F; Sanghera, Jasbinder S; Aggarwal, Ishwar D

2015-09-01

Optical filter-based chemical sensing techniques provide a new avenue to develop low-cost infrared sensors. These methods utilize multiple infrared optical filters to selectively measure different response functions for various chemicals, dependent on each chemical's infrared absorption. Rather than identifying distinct spectral features, which can then be used to determine the identity of a target chemical, optical filter-based approaches rely on measuring differences in the ensemble response between a given filter set and specific chemicals of interest. Therefore, the results of such methods are highly dependent on the original optical filter choice, which will dictate the selectivity, sensitivity, and stability of any filter-based sensing method. Recently, a method has been developed that utilizes unique detection vector operations defined by optical multifilter responses, to discriminate between volatile chemical vapors. This method, comparative-discrimination spectral detection (CDSD), is a technique which employs broadband optical filters to selectively discriminate between chemicals with highly overlapping infrared absorption spectra. CDSD has been shown to correctly distinguish between similar chemicals in the carbon-hydrogen stretch region of the infrared absorption spectra from 2800-3100 cm(-1). A key challenge to this approach is how to determine which optical filter sets should be utilized to achieve the greatest discrimination between target chemicals. Previous studies used empirical approaches to select the optical filter set; however this is insufficient to determine the optimum selectivity between strongly overlapping chemical spectra. Here we present a numerical approach to systematically study the effects of filter positioning and bandwidth on a number of three-chemical systems. We describe how both the filter properties, as well as the chemicals in each set, affect the CDSD results and subsequent discrimination. These results demonstrate the importance of choosing the proper filter set and chemicals for comparative discrimination, in order to identify the target chemical of interest in the presence of closely matched chemical interferents. These findings are an integral step in the development of experimental prototype sensors, which will utilize CDSD.

Amplitude and phase measurements based on low-coherence interferometry with acousto-optic spectral image filtration

NASA Astrophysics Data System (ADS)

Machikhin, Alexander; Burmak, Ludmila; Pozhar, Vitold

2018-04-01

The manuscript addresses the advantages and possible applications of acousto-optic image spectral filtration in lowcoherence interferometry. In particular, an effective operation of acousto-optical tunable filters in combination with Michelson-type interferometers is shown. The results of original experiments are presented. It is demonstrated that amplitude and phase spatial distributions of light waves reflected from or transmitted through the object can be fast determined in contactless manner for any spectral intervals with use of the presented techniques.

Demonstration of a single-wavelength spectral-imaging-based Thai jasmine rice identification

NASA Astrophysics Data System (ADS)

Suwansukho, Kajpanya; Sumriddetchkajorn, Sarun; Buranasiri, Prathan

2011-07-01

A single-wavelength spectral-imaging-based Thai jasmine rice breed identification is demonstrated. Our nondestructive identification approach relies on a combination of fluorescent imaging and simple image processing techniques. Especially, we apply simple image thresholding, blob filtering, and image subtracting processes to either a 545 or a 575nm image in order to identify our desired Thai jasmine rice breed from others. Other key advantages include no waste product and fast identification time. In our demonstration, UVC light is used as our exciting light, a liquid crystal tunable optical filter is used as our wavelength seclector, and a digital camera with 640activepixels×480activepixels is used to capture the desired spectral image. Eight Thai rice breeds having similar size and shape are tested. Our experimental proof of concept shows that by suitably applying image thresholding, blob filtering, and image subtracting processes to the selected fluorescent image, the Thai jasmine rice breed can be identified with measured false acceptance rates of <22.9% and <25.7% for spectral images at 545 and 575nm wavelengths, respectively. A measured fast identification time is 25ms, showing high potential for real-time applications.

Distributed seeding for narrow-line width hard x-ray free-electron lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Dinh Cong; Anisimov, Petr Mikhaylovich; Buechler, Cynthia Eileen

2015-09-09

We describe a new FEL line-narrowing technique called distributed seeding (DS), using Si(111) Bragg crystal monochromators to enhance the spectral brightness of the MaRIE hard X-ray freeelectron laser. DS differs from self-seeding in three important aspects. First, DS relies on spectral filtering of the radiation at multiple locations along the undulator, with a monochromator located every few power gain lengths. Second, DS performs filtering early in the exponential gain region before SASE spikes start to appear in the radiation longitudinal profile. Third, DS provides the option to select a wavelength longer than the peak of the SASE gain curve, whichmore » leads to improved spectral contrast of the seeded FEL over the SASE background. Timedependent Genesis simulations show the power-vs-z growth curves for DS exhibit behaviors of a seeded FEL amplifier, such as exponential growth region immediately after the filters. Of the seeding approaches considered, the two-stage DS spectra produce the highest contrast of seeded FEL over the SASE background and that the three-stage DS provides the narrowest linewidth with a relative spectral FWHM of 8 X 10 -5 .« less

Detection of urban expansion in an urban-rural landscape with multitemporal QuickBird images

PubMed Central

Lu, Dengsheng; Hetrick, Scott; Moran, Emilio; Li, Guiying

2011-01-01

Accurately detecting urban expansion with remote sensing techniques is a challenge due to the complexity of urban landscapes. This paper explored methods for detecting urban expansion with multitemporal QuickBird images in Lucas do Rio Verde, Mato Grosso, Brazil. Different techniques, including image differencing, principal component analysis (PCA), and comparison of classified impervious surface images with the matched filtering method, were used to examine urbanization detection. An impervious surface image classified with the hybrid method was used to modify the urbanization detection results. As a comparison, the original multispectral image and segmentation-based mean-spectral images were used during the detection of urbanization. This research indicates that the comparison of classified impervious surface images with matched filtering method provides the best change detection performance, followed by the image differencing method based on segmentation-based mean spectral images. The PCA is not a good method for urban change detection in this study. Shadows and high spectral variation within the impervious surfaces represent major challenges to the detection of urban expansion when high spatial resolution images are used. PMID:21799706

Design, fabrication and testing of hierarchical micro-optical structures and systems

NASA Astrophysics Data System (ADS)

Cannistra, Aaron Thomas

Micro-optical systems are becoming essential components in imaging, sensing, communications, computing, and other applications. Optically based designs are replacing electronic, chemical and mechanical systems for a variety of reasons, including low power consumption, reduced maintenance, and faster operation. However, as the number and variety of applications increases, micro-optical system designs are becoming smaller, more integrated, and more complicated. Micro and nano-optical systems found in nature, such as the imaging systems found in many insects and crustaceans, can have highly integrated optical structures that vary in size by orders of magnitude. These systems incorporate components such as compound lenses, anti-reflective lens surface structuring, spectral filters, and polarization selective elements. For animals, these hybrid optical systems capable of many optical functions in a compact package have been repeatedly selected during the evolutionary process. Understanding the advantages of these designs gives motivation for synthetic optical systems with comparable functionality. However, alternative fabrication methods that deviate from conventional processes are needed to create such systems. Further complicating the issue, the resulting device geometry may not be readily compatible with existing measurement techniques. This dissertation explores several nontraditional fabrication techniques for optical components with hierarchical geometries and measurement techniques to evaluate performance of such components. A micro-transfer molding process is found to produce high-fidelity micro-optical structures and is used to fabricate a spectral filter on a curved surface. By using a custom measurement setup we demonstrate that the spectral filter retains functionality despite the nontraditional geometry. A compound lens is fabricated using similar fabrication techniques and the imaging performance is analyzed. A spray coating technique for photoresist application to curved surfaces combined with interference lithography is also investigated. Using this technique, we generate polarizers on curved surfaces and measure their performance. This work furthers an understanding of how combining multiple optical components affects the performance of each component, the final integrated devices, and leads towards realization of biomimetically inspired imaging systems.

Investigation of spectral analysis techniques for randomly sampled velocimetry data

NASA Technical Reports Server (NTRS)

Sree, Dave

1993-01-01

It is well known that velocimetry (LV) generates individual realization velocity data that are randomly or unevenly sampled in time. Spectral analysis of such data to obtain the turbulence spectra, and hence turbulence scales information, requires special techniques. The 'slotting' technique of Mayo et al, also described by Roberts and Ajmani, and the 'Direct Transform' method of Gaster and Roberts are well known in the LV community. The slotting technique is faster than the direct transform method in computation. There are practical limitations, however, as to how a high frequency and accurate estimate can be made for a given mean sampling rate. These high frequency estimates are important in obtaining the microscale information of turbulence structure. It was found from previous studies that reliable spectral estimates can be made up to about the mean sampling frequency (mean data rate) or less. If the data were evenly samples, the frequency range would be half the sampling frequency (i.e. up to Nyquist frequency); otherwise, aliasing problem would occur. The mean data rate and the sample size (total number of points) basically limit the frequency range. Also, there are large variabilities or errors associated with the high frequency estimates from randomly sampled signals. Roberts and Ajmani proposed certain pre-filtering techniques to reduce these variabilities, but at the cost of low frequency estimates. The prefiltering acts as a high-pass filter. Further, Shapiro and Silverman showed theoretically that, for Poisson sampled signals, it is possible to obtain alias-free spectral estimates far beyond the mean sampling frequency. But the question is, how far? During his tenure under 1993 NASA-ASEE Summer Faculty Fellowship Program, the author investigated from his studies on the spectral analysis techniques for randomly sampled signals that the spectral estimates can be enhanced or improved up to about 4-5 times the mean sampling frequency by using a suitable prefiltering technique. But, this increased bandwidth comes at the cost of the lower frequency estimates. The studies further showed that large data sets of the order of 100,000 points, or more, high data rates, and Poisson sampling are very crucial for obtaining reliable spectral estimates from randomly sampled data, such as LV data. Some of the results of the current study are presented.

Novel strategy for the determination of illegal adulterants in health foods and herbal medicines using high-performance liquid chromatography with high-resolution mass spectrometry.

PubMed

Wang, Zhe; Wu, Caisheng; Wang, Gangli; Zhang, Qingsheng; Zhang, Jinlan

2015-03-01

The detection, confirmation, and quantification of multiple illegal adulterants in health foods and herbal medicines by using a single analytical method are a challenge. This paper reports on a new strategy to meet this challenge by employing high-performance liquid chromatography coupled with high-resolution mass spectrometry and a mass spectral tree similarity filter technique. This analytical method can rapidly collect high-resolution, high-accuracy, optionally multistage mass data for compounds in samples. After a preliminary screening by retention time and high-resolution mass spectral data, known illegal adulterants can be detected. The mass spectral tree similarity filter technique has been applied to rapidly confirm these adulterants and simultaneously discover unknown ones. By using full-scan mass spectra as stem and data-dependent subsequent stage mass spectra to form branches, mass spectrometry data from detected compounds are converted into mass spectral trees. The known or unknown illegal adulterants in the samples are confirmed or discovered based on the similarity between their mass spectral trees and those of the references in a library, and they are finally quantified against standard curves. This new strategy has been tested by using 50 samples, and the illegal adulterants were rapidly and effectively detected, confirmed and quantified. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of waist diameter and twist on tapered asymmetrical dual-core fiber MZI filter.

PubMed

Liu, Yan; Li, Yang; Yan, Xiaojun; Li, Weidong

2015-10-01

A compact in-fiber Mach-Zehnder interferometer (MZI) filter fabricated from custom-designed asymmetrical dual-core fiber is numerically analyzed in detail and experimentally verified. The asymmetrical dual-core fiber has core diameters and a core pitch of 6.9, 6, and 19.9 μm, respectively. The fiber tapering technique is introduced to fuse the originally uncoupled cores into strong coupling tapered regions. The length and diameter of the waist region have a close impact on the splitting ratio, which further affects the spectral properties of the MZI filter. The field evolution with varied waist parameters is characterized by the finite element method and beam propagation method. Repeatable comb filters with ∼15  dB extinction ratio are successfully achieved under the guidance of simulated optimum conditions. The twist-induced circular birefringence gives rise to a retardance that causes the spectral shifts of the MZI filter. The theoretical and experimental results confirm that the relative wavelength shift is proportional to the retardance, which follows a sinc function in the limit of a large twist rate.

The 1997 North American Interagency Intercomparison of Ultraviolet Spectroradiometers Including Narrowband Filter Radiometers

PubMed Central

Lantz, Kathleen; Disterhoft, Patrick; Early, Edward; Thompson, Ambler; DeLuisi, John; Berndt, Jerry; Harrison, Lee; Kiedron, Peter; Ehramjian, James; Bernhard, Germar; Cabasug, Lauriana; Robertson, James; Mou, Wanfeng; Taylor, Thomas; Slusser, James; Bigelow, David; Durham, Bill; Janson, George; Hayes, Douglass; Beaubien, Mark; Beaubien, Arthur

2002-01-01

The fourth North American Intercomparison of Ultraviolet Monitoring Spectroradiometers was held September 15 to 25, 1997 at Table Mountain outside of Boulder, Colorado, USA. Concern over stratospheric ozone depletion has prompted several government agencies in North America to establish networks of spectroradiometers for monitoring solar ultraviolet irradiance at the surface of the Earth. The main purpose of the Intercomparison was to assess the ability of spectroradiometers to accurately measure solar ultraviolet irradiance, and to compare the results between instruments of different monitoring networks. This Intercomparison was coordinated by NIST and NOAA, and included participants from the ASRC, EPA, NIST, NSF, SERC, USDA, and YES. The UV measuring instruments included scanning spectroradiometers, spectrographs, narrow band multi-filter radiometers, and broadband radiometers. Instruments were characterized for wavelength accuracy, bandwidth, stray-light rejection, and spectral irradiance responsivity. The spectral irradiance responsivity was determined two to three times outdoors to assess temporal stability. Synchronized spectral scans of the solar irradiance were performed over several days. Using the spectral irradiance responsivities determined with the NIST traceable standard lamp, and a simple convolution technique with a Gaussian slit-scattering function to account for the different bandwidths of the instruments, the measured solar irradiance from the spectroradiometers excluding the filter radiometers at 16.5 h UTC had a relative standard deviation of ±4 % for wavelengths greater than 305 nm. The relative standard deviation for the solar irradiance at 16.5 h UTC including the filter radiometer was ±4 % for filter functions above 300 nm. PMID:27446717

Modal Filters for Infrared Interferometry

NASA Technical Reports Server (NTRS)

Ksendzov, Alexander; MacDonald, Daniel R.; Soibel, Alexander

2009-01-01

Modal filters in the approximately equal to 10-micrometer spectral range have been implemented as planar dielectric waveguides in infrared interferometric applications such as searching for Earth-like planets. When looking for a small, dim object ("Earth") in close proximity to a large, bright object ("Sun"), the interferometric technique uses beams from two telescopes combined with a 180 phase shift in order to cancel the light from a brighter object. The interferometer baseline can be adjusted so that, at the same time, the light from the dimmer object arrives at the combiner in phase. This light can be detected and its infrared (IR) optical spectra can be studied. The cancellation of light from the "Sun" to approximately equal to 10(exp 6) is required; this is not possible without special devices-modal filters- that equalize the wavefronts arriving from the two telescopes. Currently, modal filters in the approximately equal to 10-micrometer spectral range are implemented as single- mode fibers. Using semiconductor technology, single-mode waveguides for use as modal filters were fabricated. Two designs were implemented: one using an InGaAs waveguide layer matched to an InP substrate, and one using InAlAs matched to an InP substrate. Photon Design software was used to design the waveguides, with the main feature all designs being single-mode operation in the 10.5- to 17-micrometer spectral range. Preliminary results show that the filter's rejection ratio is 26 dB.

Matched spectral filter based on reflection holograms for analyte identification.

PubMed

Cao, Liangcai; Gu, Claire

2009-12-20

A matched spectral filter set that provides automatic preliminary analyte identification is proposed and analyzed. Each matched spectral filter in the set containing the multiple spectral peaks corresponding to the Raman spectrum of a substance is capable of collecting the specified spectrum into the detector simultaneously. The filter set is implemented by multiplexed volume holographic reflection gratings. The fabrication of a matched spectral filter in an Fe:LiNbO(3) crystal is demonstrated to match the Raman spectrum of the sample Rhodamine 6G (R6G). An interference alignment method is proposed and used in the fabrication to ensure that the multiplexed gratings are in the same direction at a high angular accuracy of 0.0025 degrees . Diffused recording beams are used to control the bandwidth of the spectral peaks. The reflection spectrum of the filter is characterized using a modified Raman spectrometer. The result of the filter's reflection spectrum matches that of the sample R6G. A library of such matched spectral filters will facilitate a fast detection with a higher sensitivity and provide a capability for preliminary molecule identification.

The application of digital signal processing techniques to a teleoperator radar system

NASA Technical Reports Server (NTRS)

Pujol, A.

1982-01-01

A digital signal processing system was studied for the determination of the spectral frequency distribution of echo signals from a teleoperator radar system. The system consisted of a sample and hold circuit, an analog to digital converter, a digital filter, and a Fast Fourier Transform. The system is interfaced to a 16 bit microprocessor. The microprocessor is programmed to control the complete digital signal processing. The digital filtering and Fast Fourier Transform functions are implemented by a S2815 digital filter/utility peripheral chip and a S2814A Fast Fourier Transform chip. The S2815 initially simulates a low-pass Butterworth filter with later expansion to complete filter circuit (bandpass and highpass) synthesizing.

Noise filtering via electromagnetically induced transparency

NASA Astrophysics Data System (ADS)

Jeong, Taek; Bae, In-Ho; Moon, Han Seb

2017-01-01

We report on the intensity-noise reduction of pseudo-thermal light via electromagnetically induced transparency (EIT) in the Λ-type system of the 5S1/2-5P1/2 transition in 87Rb. Noise filtering of the pseudo-thermal probe light was achieved via an EIT filter and measured according to the degree of intensity noise of the pseudo-thermal probe light. Reductions in the intensity and spectral noise of the pseudo-thermal probe light with the EIT filter were observed using the direct intensity fluctuation and heterodyne detection technique, respectively. Comparison of the intensity noise of the pseudo-thermal probe light before and after passing through the EIT filter revealed a significant reduction in the intensity noise.

Absorption Filter Based Optical Diagnostics in High Speed Flows

NASA Technical Reports Server (NTRS)

Samimy, Mo; Elliott, Gregory; Arnette, Stephen

1996-01-01

Two major regimes where laser light scattered by molecules or particles in a flow contains significant information about the flow are Mie scattering and Rayleigh scattering. Mie scattering is used to obtain only velocity information, while Rayleigh scattering can be used to measure both the velocity and the thermodynamic properties of the flow. Now, recently introduced (1990, 1991) absorption filter based diagnostic techniques have started a new era in flow visualization, simultaneous velocity and thermodynamic measurements, and planar velocity measurements. Using a filtered planar velocimetry (FPV) technique, we have modified the optically thick iodine filter profile of Miles, et al., and used it in the pressure-broaden regime which accommodates measurements in a wide range of velocity applications. Measuring velocity and thermodynamic properties simultaneously, using absorption filtered based Rayleigh scattering, involves not only the measurement of the Doppler shift, but also the spectral profile of the Rayleigh scattering signal. Using multiple observation angles, simultaneous measurement of one component velocity and thermodynamic properties in a supersonic jet were measured. Presently, the technique is being extended for simultaneous measurements of all three components of velocity and thermodynamic properties.

An Independent Filter for Gene Set Testing Based on Spectral Enrichment.

PubMed

Frost, H Robert; Li, Zhigang; Asselbergs, Folkert W; Moore, Jason H

2015-01-01

Gene set testing has become an indispensable tool for the analysis of high-dimensional genomic data. An important motivation for testing gene sets, rather than individual genomic variables, is to improve statistical power by reducing the number of tested hypotheses. Given the dramatic growth in common gene set collections, however, testing is often performed with nearly as many gene sets as underlying genomic variables. To address the challenge to statistical power posed by large gene set collections, we have developed spectral gene set filtering (SGSF), a novel technique for independent filtering of gene set collections prior to gene set testing. The SGSF method uses as a filter statistic the p-value measuring the statistical significance of the association between each gene set and the sample principal components (PCs), taking into account the significance of the associated eigenvalues. Because this filter statistic is independent of standard gene set test statistics under the null hypothesis but dependent under the alternative, the proportion of enriched gene sets is increased without impacting the type I error rate. As shown using simulated and real gene expression data, the SGSF algorithm accurately filters gene sets unrelated to the experimental outcome resulting in significantly increased gene set testing power.

Kalman filter approach for uncertainty quantification in time-resolved laser-induced incandescence.

PubMed

Hadwin, Paul J; Sipkens, Timothy A; Thomson, Kevin A; Liu, Fengshan; Daun, Kyle J

2018-03-01

Time-resolved laser-induced incandescence (TiRe-LII) data can be used to infer spatially and temporally resolved volume fractions and primary particle size distributions of soot-laden aerosols, but these estimates are corrupted by measurement noise as well as uncertainties in the spectroscopic and heat transfer submodels used to interpret the data. Estimates of the temperature, concentration, and size distribution of soot primary particles within a sample aerosol are typically made by nonlinear regression of modeled spectral incandescence decay, or effective temperature decay, to experimental data. In this work, we employ nonstationary Bayesian estimation techniques to infer aerosol properties from simulated and experimental LII signals, specifically the extended Kalman filter and Schmidt-Kalman filter. These techniques exploit the time-varying nature of both the measurements and the models, and they reveal how uncertainty in the estimates computed from TiRe-LII data evolves over time. Both techniques perform better when compared with standard deterministic estimates; however, we demonstrate that the Schmidt-Kalman filter produces more realistic uncertainty estimates.

Effect of narrow spectral filter position on the characteristics of active similariton mode-locked femtosecond fiber laser.

PubMed

Kotb, Hussein; Abdelalim, Mohamed A; Anis, Hanan

2015-11-16

A significant change in active similariton characteristics, both numerically and experimentally, is observed as a function of the location of the lumped spectral filter. The closer the spectral filter is to the input of the Yb(3+)-doped fiber, the shorter the de-chirped pulse width. The peak power of the de-chirped pulse has its maximum value at a certain location of the spectral filter. Four different positions of the spectral filter inside the laser cavity have been theoretically studied and two of them have been verified experimentally.

Spectral filters for laser communications

NASA Technical Reports Server (NTRS)

Shaik, K.

1991-01-01

Optical communication systems must perform reliabily under strong background light interference. Since the transmitting lasers operate within a narrow spectral band, high signal to noise ratios can be achieved when narrowband spectral optical filters can be used to reject out of band light. Here, a set of general requirements for such filters are developed, and an overview is given of suitable spectral filter technologies for optical communication systems.

Spectral optimized asymmetric segmented phase-only correlation filter.

PubMed

Leonard, I; Alfalou, A; Brosseau, C

2012-05-10

We suggest a new type of optimized composite filter, i.e., the asymmetric segmented phase-only filter (ASPOF), for improving the effectiveness of a VanderLugt correlator (VLC) when used for face identification. Basically, it consists in merging several reference images after application of a specific spectral optimization method. After segmentation of the spectral filter plane to several areas, each area is assigned to a single winner reference according to a new optimized criterion. The point of the paper is to show that this method offers a significant performance improvement on standard composite filters for face identification. We first briefly revisit composite filters [adapted, phase-only, inverse, compromise optimal, segmented, minimum average correlation energy, optimal trade-off maximum average correlation, and amplitude-modulated phase-only (AMPOF)], which are tools of choice for face recognition based on correlation techniques, and compare their performances with those of the ASPOF. We illustrate some of the drawbacks of current filters for several binary and grayscale image identifications. Next, we describe the optimization steps and introduce the ASPOF that can overcome these technical issues to improve the quality and the reliability of the correlation-based decision. We derive performance measures, i.e., PCE values and receiver operating characteristic curves, to confirm consistency of the results. We numerically find that this filter increases the recognition rate and decreases the false alarm rate. The results show that the discrimination of the ASPOF is comparable to that of the AMPOF, but the ASPOF is more robust than the trade-off maximum average correlation height against rotation and various types of noise sources. Our method has several features that make it amenable to experimental implementation using a VLC.

Statistical analysis of spectral data: a methodology for designing an intelligent monitoring system for the diabetic foot

NASA Astrophysics Data System (ADS)

Liu, Chanjuan; van Netten, Jaap J.; Klein, Marvin E.; van Baal, Jeff G.; Bus, Sicco A.; van der Heijden, Ferdi

2013-12-01

Early detection of (pre-)signs of ulceration on a diabetic foot is valuable for clinical practice. Hyperspectral imaging is a promising technique for detection and classification of such (pre-)signs. However, the number of the spectral bands should be limited to avoid overfitting, which is critical for pixel classification with hyperspectral image data. The goal was to design a detector/classifier based on spectral imaging (SI) with a small number of optical bandpass filters. The performance and stability of the design were also investigated. The selection of the bandpass filters boils down to a feature selection problem. A dataset was built, containing reflectance spectra of 227 skin spots from 64 patients, measured with a spectrometer. Each skin spot was annotated manually by clinicians as "healthy" or a specific (pre-)sign of ulceration. Statistical analysis on the data set showed the number of required filters is between 3 and 7, depending on additional constraints on the filter set. The stability analysis revealed that shot noise was the most critical factor affecting the classification performance. It indicated that this impact could be avoided in future SI systems with a camera sensor whose saturation level is higher than 106, or by postimage processing.

Terahertz wave electro-optic measurements with optical spectral filtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilyakov, I. E., E-mail: igor-ilyakov@mail.ru; Shishkin, B. V.; Kitaeva, G. Kh.

We propose electro-optic detection techniques based on variations of the laser pulse spectrum induced during pulse co-propagation with terahertz wave radiation in a nonlinear crystal. Quantitative comparison with two other detection methods is made. Substantial improvement of the sensitivity compared to the standard electro-optic detection technique (at high frequencies) and to the previously shown technique based on laser pulse energy changes is demonstrated in experiment.

Determination of tailored filter sets to create rayfiles including spatial and angular resolved spectral information.

PubMed

Rotscholl, Ingo; Trampert, Klaus; Krüger, Udo; Perner, Martin; Schmidt, Franz; Neumann, Cornelius

2015-11-16

To simulate and optimize optical designs regarding perceived color and homogeneity in commercial ray tracing software, realistic light source models are needed. Spectral rayfiles provide angular and spatial varying spectral information. We propose a spectral reconstruction method with a minimum of time consuming goniophotometric near field measurements with optical filters for the purpose of creating spectral rayfiles. Our discussion focuses on the selection of the ideal optical filter combination for any arbitrary spectrum out of a given filter set by considering measurement uncertainties with Monte Carlo simulations. We minimize the simulation time by a preselection of all filter combinations, which bases on factorial design.

Methodology for diagnosing of skin cancer on images of dermatologic spots by spectral analysis.

PubMed

Guerra-Rosas, Esperanza; Álvarez-Borrego, Josué

2015-10-01

In this paper a new methodology for the diagnosing of skin cancer on images of dermatologic spots using image processing is presented. Currently skin cancer is one of the most frequent diseases in humans. This methodology is based on Fourier spectral analysis by using filters such as the classic, inverse and k-law nonlinear. The sample images were obtained by a medical specialist and a new spectral technique is developed to obtain a quantitative measurement of the complex pattern found in cancerous skin spots. Finally a spectral index is calculated to obtain a range of spectral indices defined for skin cancer. Our results show a confidence level of 95.4%.

Methodology for diagnosing of skin cancer on images of dermatologic spots by spectral analysis

PubMed Central

Guerra-Rosas, Esperanza; Álvarez-Borrego, Josué

2015-01-01

In this paper a new methodology for the diagnosing of skin cancer on images of dermatologic spots using image processing is presented. Currently skin cancer is one of the most frequent diseases in humans. This methodology is based on Fourier spectral analysis by using filters such as the classic, inverse and k-law nonlinear. The sample images were obtained by a medical specialist and a new spectral technique is developed to obtain a quantitative measurement of the complex pattern found in cancerous skin spots. Finally a spectral index is calculated to obtain a range of spectral indices defined for skin cancer. Our results show a confidence level of 95.4%. PMID:26504638

Integrated filter and detector array for spectral imaging

NASA Technical Reports Server (NTRS)

Labaw, Clayton C. (Inventor)

1992-01-01

A spectral imaging system having an integrated filter and photodetector array is disclosed. The filter has narrow transmission bands which vary in frequency along the photodetector array. The frequency variation of the transmission bands is matched to, and aligned with, the frequency variation of a received spectral image. The filter is deposited directly on the photodetector array by a low temperature deposition process. By depositing the filter directly on the photodetector array, permanent alignment is achieved for all temperatures, spectral crosstalk is substantially eliminated, and a high signal to noise ratio is achieved.

Oil droplets of bird eyes: microlenses acting as spectral filters

PubMed Central

Stavenga, Doekele G.; Wilts, Bodo D.

2014-01-01

An important component of the cone photoreceptors of bird eyes is the oil droplets located in front of the visual-pigment-containing outer segments. The droplets vary in colour and are transparent, clear, pale or rather intensely yellow or red owing to various concentrations of carotenoid pigments. Quantitative modelling of the filter characteristics using known carotenoid pigment spectra indicates that the pigments’ absorption spectra are modified by the high concentrations that are present in the yellow and red droplets. The high carotenoid concentrations not only cause strong spectral filtering but also a distinctly increased refractive index at longer wavelengths. The oil droplets therefore act as powerful spherical microlenses, effectively channelling the spectrally filtered light into the photoreceptor's outer segment, possibly thereby compensating for the light loss caused by the spectral filtering. The spectral filtering causes narrow-band photoreceptor spectral sensitivities, which are well suited for spectral discrimination, especially in birds that have feathers coloured by carotenoid pigments. PMID:24395968

The price for reduced light toxicity: Do endoilluminator spectral filters decrease color contrast during Brilliant Blue G-assisted chromovitrectomy?

PubMed

Henrich, Paul B; Valmaggia, Christophe; Lang, Corina; Cattin, Philippe C

2014-03-01

Vitreoretinal surgeons have been slow to adopt the use of spectral filters for endoillumination to reduce retinal light toxicity. This study shows that spectral filters can be used without a loss in color contrast during brilliant blue G chromovitrectomy. To evaluate the influence of intra operative spectral light filters on perceivable contrast during Brilliant Blue G chromovitrectomy, a prospective, observational clinical study was carried out on 59 consecutive Brilliant Blue G chromovitrectomy interventions in 59 patients admitted for macular holes, macular pucker or vitreomacular traction syndromes. Subsequent to peeling of the internal limiting membrane, six different illumination modes were enabled consecutively: mercury vapor, mercury vapor/xenon, and xenon followed by xenon combined with an amber, green or yellow spectral filter. Main outcome measure was the chromaticity spread between stained internal limiting membrane and unstained retina as a measure for the color contrast perceived by the human eye. Mean chromaticity scores were similar for all light sources: mercury vapor 7.97, mercury vapor/xenon 7.96 (p = 0.96), and xenon 7.41 (p = 0.55). Compared to xenon, the additional use of endoillumination spectral filters did not change contrast recognizability: Chromaticity scores were 9.38 for the amber filter (p = 0.13), 6.63 for the green and 7.02 for the yellow filter (p = 0.37 and 0.64, respectively). When comparing the different filters head-to-head, the amber filter was superior to the green filter (p = 0.03), while the yellow was intermediate and not significantly different from either the amber (p = 0.08) or the green filter (p = 0.51). Color contrast perceptibility during Brilliant Blue G assisted chromovitrectomy is similar with mercury vapor, mercury vapor/xenon or xenon light sources. Spectral filters do not decrease color contrast recognizability. Head-to-head comparison shows a significant advantage for the amber over the green filter with respect to contrast generation, the yellow filter is intermediate. As spectral filters are known to greatly reduce retinal light toxicity, we suggest donor eye studies to validate whether the amber filter should be generally recommended for Brilliant Blue G chromovitrectomy.

Dispersion-free pulse duration reduction of passively Q-switched microchip lasers.

PubMed

Lehneis, R; Steinmetz, A; Jauregui, C; Limpert, J; Tünnermann, A

2012-11-01

We present a dispersion-free method for the pulse duration reduction of passively Q-switched microchip laser (MCL) seed sources. This technique comprises two stages: one that carries out the self-phase modulation induced spectral broadening in a waveguide structure and a subsequent spectral filtering stage in order to shorten the pulses in time domain. The setup of a proof-of-principle experiment consists of a fiber-amplified passively Q-switched MCL, a passive single-mode fiber used as nonlinear element in which the spectrum is broadened, and a reflective volume-Bragg-grating acting as bandpass filter. A reduction of the pulse duration from 118 to 32 ps with high temporal quality has been achieved with this setup.

Importance of Light Filters in Modern Vitreoretinal Surgery: An Update of the Literature.

PubMed

Coppola, Michele; Cicinelli, Maria Vittoria; Rabiolo, Alessandro; Querques, Giuseppe; Bandello, Francesco

2017-01-01

Direct endobulbar illumination during vitreoretinal surgery causes light-induced retinal damage known as phototoxicity. Spectral filters have been proposed to eliminate hazardous wavelengths from the emission spectrum before entering the eye. The purpose of our paper is to review advances in vitreoretinal surgery, focusing on intraoperative light filters. A PubMed and Medline database search was carried out using the terms "spectral filters" associated with "vitreoretinal surgery," "phototoxicity," and "vitrectomy." Original articles, reviews, and book chapters up to March 2017 were reviewed; a few select articles published before 2000 are included for historical purposes. Material from recent meeting presentations was also added. The preferred language for the reviewed literature was English. Spectral filters significantly reduce the risk of phototoxicity associated with endoillumination in vitreoretinal surgery, allowing higher exposure times than with optic light fibers alone. Spectral filters may affect intraoperative luminance, but do not alter color contrast. Amber filters showed superiority over green and yellow filters. The choice of light sources coupled to spectral filters is strongly suggested, especially in dye-assisted chromovitrectomy. Histological donor eye studies and large multicenter trials are needed to validate the amount of photoprotection provided by spectral filters before a general recommendation can be made. © 2017 S. Karger AG, Basel.

A study of gravity-wave spectra in the troposphere and stratosphere at 5-min to 5-day periods with the Poker Flat MST radar

NASA Technical Reports Server (NTRS)

Bemra, R. S.; Rastogi, P. K.; Balsley, B. B.

1986-01-01

An analysis of frequency spectra at periods of about 5 days to 5 min from two 20-day sets of velocity measurements in the stratosphere and troposphere region obtained with the Poker Flat mesosphere-stratosphere-troposphere (MST) radar during January and June, 1984 is presented. A technique based on median filtering and averaged order statistics for automatic editing, smoothing and spectral analysis of velocity time series contaminated with spurious data points or outliers is outlined. The validity of this technique and its effects on the inferred spectral index was tested through simulation. Spectra obtained with this technique are discussed. The measured spectral indices show variability with season and height, especially across the tropopause. The discussion briefly outlines the need for obtaining better climatologies of velocity spectra and for the refinements of the existing theories to explain their behavior.

The effect of spectral filters on visual search in stroke patients.

PubMed

Beasley, Ian G; Davies, Leon N

2013-01-01

Visual search impairment can occur following stroke. The utility of optimal spectral filters on visual search in stroke patients has not been considered to date. The present study measured the effect of optimal spectral filters on visual search response time and accuracy, using a task requiring serial processing. A stroke and control cohort undertook the task three times: (i) using an optimally selected spectral filter; (ii) the subjects were randomly assigned to two groups with group 1 using an optimal filter for two weeks, whereas group 2 used a grey filter for two weeks; (iii) the groups were crossed over with group 1 using a grey filter for a further two weeks and group 2 given an optimal filter, before undertaking the task for the final time. Initial use of an optimal spectral filter improved visual search response time but not error scores in the stroke cohort. Prolonged use of neither an optimal nor a grey filter improved response time or reduced error scores. In fact, response times increased with the filter, regardless of its type, for stroke and control subjects; this outcome may be due to contrast reduction or a reflection of task design, given that significant practice effects were noted.

Dual-energy approach to contrast-enhanced mammography using the balanced filter method: spectral optimization and preliminary phantom measurement.

PubMed

Saito, Masatoshi

2007-11-01

Dual-energy contrast agent-enhanced mammography is a technique of demonstrating breast cancers obscured by a cluttered background resulting from the contrast between soft tissues in the breast. The technique has usually been implemented by exploiting two exposures to different x-ray tube voltages. In this article, another dual-energy approach using the balanced filter method without switching the tube voltages is described. For the spectral optimization of dual-energy mammography using the balanced filters, we applied a theoretical framework reported by Lemacks et al. [Med. Phys. 29, 1739-1751 (2002)] to calculate the signal-to-noise ratio (SNR) in an iodinated contrast agent subtraction image. This permits the selection of beam parameters such as tube voltage and balanced filter material, and the optimization of the latter's thickness with respect to some critical quantity-in this case, mean glandular dose. For an imaging system with a 0.1 mm thick CsI:T1 scintillator, we predict that the optimal tube voltage would be 45 kVp for a tungsten anode using zirconium, iodine, and neodymium balanced filters. A mean glandular dose of 1.0 mGy is required to obtain an SNR of 5 in order to detect 1.0 mg/cm2 iodine in the resulting clutter-free image of a 5 cm thick breast composed of 50% adipose and 50% glandular tissue. In addition to spectral optimization, we carried out phantom measurements to demonstrate the present dual-energy approach for obtaining a clutter-free image, which preferentially shows iodine, of a breast phantom comprising three major components-acrylic spheres, olive oil, and an iodinated contrast agent. The detection of iodine details on the cluttered background originating from the contrast between acrylic spheres and olive oil is analogous to the task of distinguishing contrast agents in a mixture of glandular and adipose tissues.

Directional analysis and filtering for dust storm detection in NOAA-AVHRR imagery

NASA Astrophysics Data System (ADS)

Janugani, S.; Jayaram, V.; Cabrera, S. D.; Rosiles, J. G.; Gill, T. E.; Rivera Rivera, N.

2009-05-01

In this paper, we propose spatio-spectral processing techniques for the detection of dust storms and automatically finding its transport direction in 5-band NOAA-AVHRR imagery. Previous methods that use simple band math analysis have produced promising results but have drawbacks in producing consistent results when low signal to noise ratio (SNR) images are used. Moreover, in seeking to automate the dust storm detection, the presence of clouds in the vicinity of the dust storm creates a challenge in being able to distinguish these two types of image texture. This paper not only addresses the detection of the dust storm in the imagery, it also attempts to find the transport direction and the location of the sources of the dust storm. We propose a spatio-spectral processing approach with two components: visualization and automation. Both approaches are based on digital image processing techniques including directional analysis and filtering. The visualization technique is intended to enhance the image in order to locate the dust sources. The automation technique is proposed to detect the transport direction of the dust storm. These techniques can be used in a system to provide timely warnings of dust storms or hazard assessments for transportation, aviation, environmental safety, and public health.

Single-energy pediatric chest computed tomography with spectral filtration at 100 kVp: effects on radiation parameters and image quality.

PubMed

Bodelle, Boris; Fischbach, Constanze; Booz, Christian; Yel, Ibrahim; Frellesen, Claudia; Kaup, Moritz; Beeres, Martin; Vogl, Thomas J; Scholtz, Jan-Erik

2017-06-01

Most of the applied radiation dose at CT is in the lower photon energy range, which is of limited diagnostic importance. To investigate image quality and effects on radiation parameters of 100-kVp spectral filtration single-energy chest CT using a tin-filter at third-generation dual-source CT in comparison to standard 100-kVp chest CT. Thirty-three children referred for a non-contrast chest CT performed on a third-generation dual-source CT scanner were examined at 100 kVp with a dedicated tin filter with a tube current-time product resulting in standard protocol dose. We compared resulting images with images from children examined using standard single-source chest CT at 100 kVp. We assessed objective and subjective image quality and compared radiation dose parameters. Radiation dose was comparable for children 5 years old and younger, and it was moderately decreased for older children when using spectral filtration (P=0.006). Effective tube current increased significantly (P=0.0001) with spectral filtration, up to a factor of 10. Signal-to-noise ratio and image noise were similar for both examination techniques (P≥0.06). Subjective image quality showed no significant differences (P≥0.2). Using 100-kVp spectral filtration chest CT in children by means of a tube-based tin-filter on a third-generation dual-source CT scanner increases effective tube current up to a factor of 10 to provide similar image quality at equivalent dose compared to standard single-source CT without spectral filtration.

Evaluation of Clipping Based Iterative PAPR Reduction Techniques for FBMC Systems

PubMed Central

Kollár, Zsolt

2014-01-01

This paper investigates filter bankmulticarrier (FBMC), a multicarrier modulation technique exhibiting an extremely low adjacent channel leakage ratio (ACLR) compared to conventional orthogonal frequency division multiplexing (OFDM) technique. The low ACLR of the transmitted FBMC signal makes it especially favorable in cognitive radio applications, where strict requirements are posed on out-of-band radiation. Large dynamic range resulting in high peak-to-average power ratio (PAPR) is characteristic of all sorts of multicarrier signals. The advantageous spectral properties of the high-PAPR FBMC signal are significantly degraded if nonlinearities are present in the transceiver chain. Spectral regrowth may appear, causing harmful interference in the neighboring frequency bands. This paper presents novel clipping based PAPR reduction techniques, evaluated and compared by simulations and measurements, with an emphasis on spectral aspects. The paper gives an overall comparison of PAPR reduction techniques, focusing on the reduction of the dynamic range of FBMC signals without increasing out-of-band radiation. An overview is presented on transmitter oriented techniques employing baseband clipping, which can maintain the system performance with a desired bit error rate (BER). PMID:24558338

Daytime adaptive optics for deep space optical communications

NASA Technical Reports Server (NTRS)

Wilson, Keith; Troy, M.; Srinivasan, M.; Platt, B.; Vilnrotter, V.; Wright, M.; Garkanian, V.; Hemmati, H.

2003-01-01

The deep space optical communications subsystem offers a higher bandwidth communications link in smaller size, lower mass, and lower power consumption subsystem than does RF. To demonstrate the benefit of this technology to deep space communications NASA plans to launch an optical telecommunications package on the 2009 Mars Telecommunications orbiter spacecraft. Current performance goals are 30-Mbps from opposition, and 1-Mbps near conjunction (-3 degrees Sun-Earth-Probe angle). Yet, near conjunction the background noise from the day sky will degrade the performance of the optical link. Spectral and spatial filtering and higher modulation formats can mitigate the effects of background sky. Narrowband spectral filters can result in loss of link margin, and higher modulation formats require higher transmitted peak powers. In contrast, spatial filtering at the receiver has the potential of being lossless while providing the required sky background rejection. Adaptive optics techniques can correct wave front aberrations caused by atmospheric turbulence and enable near-diffraction-limited performance of the receiving telescope. Such performance facilitates spatial filtering, and allows the receiver field-of-view and hence the noise from the sky background to be reduced.

Optical determination of material abundances by using neural networks for the derivation of spectral filters

NASA Astrophysics Data System (ADS)

Krippner, Wolfgang; Wagner, Felix; Bauer, Sebastian; Puente León, Fernando

2017-06-01

Using appropriately designed spectral filters allows to optically determine material abundances. While an infinite number of possibilities exist for determining spectral filters, we take advantage of using neural networks to derive spectral filters leading to precise estimations. To overcome some drawbacks that regularly influence the determination of material abundances using hyperspectral data, we incorporate the spectral variability of the raw materials into the training of the considered neural networks. As a main result, we successfully classify quantized material abundances optically. Thus, the main part of the high computational load, which belongs to the use of neural networks, is avoided. In addition, the derived material abundances become invariant against spatially varying illumination intensity as a remarkable benefit in comparison with spectral filters based on the Moore-Penrose pseudoinverse, for instance.

Practical Implementation of Multiple Model Adaptive Estimation Using Neyman-Pearson Based Hypothesis Testing and Spectral Estimation Tools

DTIC Science & Technology

1996-09-01

Generalized Likelihood Ratio (GLR) and voting techniques. The third class consisted of multiple hypothesis filter detectors, specifically the MMAE. The...vector version, versus a tensor if we use the matrix version of the power spectral density estimate. Using this notation, we will derive an...as MATLAB , have an intrinsic sample covariance computation available, which makes this method quite easy to implement. In practice, the mean for the

Models and methods to characterize site amplification from a pair of records

USGS Publications Warehouse

Safak, E.

1997-01-01

The paper presents a tutorial review of the models and methods that are used to characterize site amplification from the pairs of rock- and soil-site records, and introduces some new techniques with better theoretical foundations. The models and methods discussed include spectral and cross-spectral ratios, spectral ratios for downhole records, response spectral ratios, constant amplification factors, parametric models, physical models, and time-varying filters. An extensive analytical and numerical error analysis of spectral and cross-spectral ratios shows that probabilistically cross-spectral ratios give more reliable estimates of site amplification. Spectral ratios should not be used to determine site amplification from downhole-surface recording pairs because of the feedback in the downhole sensor. Response spectral ratios are appropriate for low frequencies, but overestimate the amplification at high frequencies. The best method to be used depends on how much precision is required in the estimates.

An adaptive demodulation approach for bearing fault detection based on adaptive wavelet filtering and spectral subtraction

NASA Astrophysics Data System (ADS)

Zhang, Yan; Tang, Baoping; Liu, Ziran; Chen, Rengxiang

2016-02-01

Fault diagnosis of rolling element bearings is important for improving mechanical system reliability and performance. Vibration signals contain a wealth of complex information useful for state monitoring and fault diagnosis. However, any fault-related impulses in the original signal are often severely tainted by various noises and the interfering vibrations caused by other machine elements. Narrow-band amplitude demodulation has been an effective technique to detect bearing faults by identifying bearing fault characteristic frequencies. To achieve this, the key step is to remove the corrupting noise and interference, and to enhance the weak signatures of the bearing fault. In this paper, a new method based on adaptive wavelet filtering and spectral subtraction is proposed for fault diagnosis in bearings. First, to eliminate the frequency associated with interfering vibrations, the vibration signal is bandpass filtered with a Morlet wavelet filter whose parameters (i.e. center frequency and bandwidth) are selected in separate steps. An alternative and efficient method of determining the center frequency is proposed that utilizes the statistical information contained in the production functions (PFs). The bandwidth parameter is optimized using a local ‘greedy’ scheme along with Shannon wavelet entropy criterion. Then, to further reduce the residual in-band noise in the filtered signal, a spectral subtraction procedure is elaborated after wavelet filtering. Instead of resorting to a reference signal as in the majority of papers in the literature, the new method estimates the power spectral density of the in-band noise from the associated PF. The effectiveness of the proposed method is validated using simulated data, test rig data, and vibration data recorded from the transmission system of a helicopter. The experimental results and comparisons with other methods indicate that the proposed method is an effective approach to detecting the fault-related impulses hidden in vibration signals and performs well for bearing fault diagnosis.

Tailoring noise frequency spectrum to improve NIR determinations.

PubMed

Xie, Shaofei; Xiang, Bingren; Yu, Liyan; Deng, Haishan

2009-12-15

Near infrared spectroscopy (NIR) contains excessive background noise and weak analytical signals caused by near infrared overtones and combinations. That makes it difficult to achieve quantitative determinations of low concentration samples by NIR. A simple chemometric approach has been established to modify the noise frequency spectrum to improve NIR determinations. The proposed method is to multiply one Savitzky-Golay filtered NIR spectrum with another reference spectrum added with thermal noises before the other Savitzky-Golay filter. Since Savitzky-Golay filter is a kind of low-pass filter and cannot eliminate low frequency components of NIR spectrum, using one step or two consecutive Savitzky-Golay filter procedures cannot improve the determination of NIR greatly. Meanwhile, significant improvement is achieved via the Savitzky-Golay filtered NIR spectrum processed with the multiplication alteration before the other Savitzky-Golay filter. The frequency range of the modified noise spectrum shifts toward higher frequency regime via multiplication operation. So the second Savitzky-Golay filter is able to provide better filtering efficiency to obtain satisfied result. The improvement of NIR determination with tailoring noise frequency spectrum technique was demonstrated by both simulated dataset and two measured NIR spectral datasets. It is expected that noise frequency spectrum technique will be adopted mostly in applications where quantitative determination of low concentration sample is crucial.

Arbitrary-shaped Brillouin microwave photonic filter by manipulating a directly modulated pump.

PubMed

Wei, Wei; Yi, Lilin; Jaouën, Yves; Hu, Weisheng

2017-10-15

We present a cost-effective gigahertz-wide arbitrary-shaped microwave photonic filter based on stimulated Brillouin scattering in fiber using a directly modulated laser (DML). After analyzing the relationship between the spectral power density and the modulation current of the DML, we manage to precisely adjust the optical spectrum of the DML, thereby controlling the Brillouin filter response arbitrarily for the first time, to the best of our knowledge. The filter performance is evaluated by amplifying a 500 Mb/s non-return-to-zero on-off keying signal using a 1 GHz rectangular filter. The comparison between the proposed DML approach and the previous approach adopting a complex IQ modulator shows similar filter flexibility, shape fidelity, and noise performance, proving that the DML-based Brillouin filter technique is a cost-effective and valid solution for microwave photonic applications.

Enhanced spectral efficiency using bandwidth switchable SAW filtering for mobile satellite communications systems

NASA Technical Reports Server (NTRS)

Peach, Robert; Malarky, Alastair

1990-01-01

Currently proposed mobile satellite communications systems require a high degree of flexibility in assignment of spectral capacity to different geographic locations. Conventionally this results in poor spectral efficiency which may be overcome by the use of bandwidth switchable filtering. Surface acoustic wave (SAW) technology makes it possible to provide banks of filters whose responses may be contiguously combined to form variable bandwidth filters with constant amplitude and phase responses across the entire band. The high selectivity possible with SAW filters, combined with the variable bandwidth capability, makes it possible to achieve spectral efficiencies over the allocated bandwidths of greater than 90 percent, while retaining full system flexibility. Bandwidth switchable SAW filtering (BSSF) achieves these gains with a negligible increase in hardware complexity.

On one-sided filters for spectral Fourier approximations of discontinuous functions

NASA Technical Reports Server (NTRS)

Wei, Cai; Gottlieb, David; Shu, Chi-Wang

1991-01-01

The existence of one-sided filters, for spectral Fourier approximations of discontinuous functions, which can recover spectral accuracy up to discontinuity from one side, was proved. A least square procedure was also used to construct such a filter and test it on several discontinuous functions numerically.

Characterisation of optical filters for broadband UVA radiometer

NASA Astrophysics Data System (ADS)

Alves, Luciana C.; Coelho, Carla T.; Corrêa, Jaqueline S. P. M.; Menegotto, Thiago; Ferreira da Silva, Thiago; Aparecida de Souza, Muriel; Melo da Silva, Elisama; Simões de Lima, Maurício; Dornelles de Alvarenga, Ana Paula

2016-07-01

Optical filters were characterized in order to know its suitability for use in broadband UVA radiometer head for spectral irradiance measurements. The spectral transmittance, the angular dependence and the spatial uniformity of the spectral transmittance of the UVA optical filters were investigated. The temperature dependence of the transmittance was also studied.

Optical filter for highlighting spectral features part I: design and development of the filter for discrimination of human skin with and without an application of cosmetic foundation.

PubMed

Nishino, Ken; Nakamura, Mutsuko; Matsumoto, Masayuki; Tanno, Osamu; Nakauchi, Shigeki

2011-03-28

Light reflected from an object's surface contains much information about its physical and chemical properties. Changes in the physical properties of an object are barely detectable in spectra. Conventional trichromatic systems, on the other hand, cannot detect most spectral features because spectral information is compressively represented as trichromatic signals forming a three-dimensional subspace. We propose a method for designing a filter that optically modulates a camera's spectral sensitivity to find an alternative subspace highlighting an object's spectral features more effectively than the original trichromatic space. We designed and developed a filter that detects cosmetic foundations on human face. Results confirmed that the filter can visualize and nondestructively inspect the foundation distribution.

Spectral Re-Growth Reduction for CCSDS 8-D 8-PSK TCM

NASA Technical Reports Server (NTRS)

Borah, Deva K.

2002-01-01

This report presents a study on the CCSDS recommended 8-dimensional 8 PSK Trellis Coded Modulation (TCM) scheme. The important steps of the CCSDS scheme include: conversion of serial data into parallel form, differential encoding, convolutional encoding, constellation mapping, and filtering the 8-PSK symbols using the square root raised cosine (SRRC) pulses. The last step, namely the filtering of the 8 PSK symbols using SRRC pulses, significantly affects the bandwidth of the signal. If a nonlinear power amplifier is used, the SRRC filtered signal creates spectral regrowth. The purpose of this report is to investigate a technique, called the smooth phase interpolated keying (SPIK), that can provide an alternative to SRRC filtering so that good spectral as well as power efficiencies can be obtained with the CCSDS encoder. The results of this study show that the CCSDS encoder does not affect the spectral shape of the SRRC filtered signal or the SPIK signal. When a nonlinear traveling wave tube amplifier (TWTA) is used, the spectral performance of the SRRC signal degrades significantly while the spectral performance of SPIK remains unaffected. The degrading effect of a nonlinear solid state power amplifier (SSPA) on SRRC is found to be less than that due to a nonlinear TWTA. However, in both cases, the spectral performance of the SRRC modulated signal is worse than that of the SPIK signal. The bit error rate (BER) performance of the SRRC signal in a linear amplifier environment is about 2.5 dB better than that of the SPIK signal when both the receivers use algorithms of similar complexity. In a nonlinear TWTA environment, the SRRC signal requires accurate phase tracking since the TWTA introduces additional phase distortion. This problem does not arise with SPIK signal due to its constant envelope property. When a nonlinear amplifier is used, the SRRC method loses nearly 1 dB in the bit error rate performance. The SPIK signal does not lose any performance. Thus the performance gap between SRRC and SPIK reduces. The BER performance of SPIK can be improved even further by using a more optimal receiver. A similar optimal receiver for SRRC is quite complex since the amplifier distorts the pulse shape. However, this requires further investigation and is not covered in this report.

Spectral estimation of received phase in the presence of amplitude scintillation

NASA Technical Reports Server (NTRS)

Vilnrotter, V. A.; Brown, D. H.; Hurd, W. J.

1988-01-01

A technique is demonstrated for obtaining the spectral parameters of the received carrier phase in the presence of carrier amplitude scintillation, by means of a digital phased locked loop. Since the random amplitude fluctuations generate time-varying loop characteristics, straightforward processing of the phase detector output does not provide accurate results. The method developed here performs a time-varying inverse filtering operation on the corrupted observables, thus recovering the original phase process and enabling accurate estimation of its underlying parameters.

SVD analysis of Aura TES spectral residuals

NASA Technical Reports Server (NTRS)

Beer, Reinhard; Kulawik, Susan S.; Rodgers, Clive D.; Bowman, Kevin W.

2005-01-01

Singular Value Decomposition (SVD) analysis is both a powerful diagnostic tool and an effective method of noise filtering. We present the results of an SVD analysis of an ensemble of spectral residuals acquired in September 2004 from a 16-orbit Aura Tropospheric Emission Spectrometer (TES) Global Survey and compare them to alternative methods such as zonal averages. In particular, the technique highlights issues such as the orbital variation of instrument response and incompletely modeled effects of surface emissivity and atmospheric composition.

A Steady-State Kalman Predictor-Based Filtering Strategy for Non-Overlapping Sub-Band Spectral Estimation

PubMed Central

Li, Zenghui; Xu, Bin; Yang, Jian; Song, Jianshe

2015-01-01

This paper focuses on suppressing spectral overlap for sub-band spectral estimation, with which we can greatly decrease the computational complexity of existing spectral estimation algorithms, such as nonlinear least squares spectral analysis and non-quadratic regularized sparse representation. Firstly, our study shows that the nominal ability of the high-order analysis filter to suppress spectral overlap is greatly weakened when filtering a finite-length sequence, because many meaningless zeros are used as samples in convolution operations. Next, an extrapolation-based filtering strategy is proposed to produce a series of estimates as the substitutions of the zeros and to recover the suppression ability. Meanwhile, a steady-state Kalman predictor is applied to perform a linearly-optimal extrapolation. Finally, several typical methods for spectral analysis are applied to demonstrate the effectiveness of the proposed strategy. PMID:25609038

Integrated Spectral Low Noise Image Sensor with Nanowire Polarization Filters for Low Contrast Imaging

DTIC Science & Technology

2015-11-05

AFRL-AFOSR-VA-TR-2015-0359 Integrated Spectral Low Noise Image Sensor with Nanowire Polarization Filters for Low Contrast Imaging Viktor Gruev...To) 02/15/2011 - 08/15/2015 4. TITLE AND SUBTITLE Integrated Spectral Low Noise Image Sensor with Nanowire Polarization Filters for Low Contrast...investigate alternative spectral imaging architectures based on my previous experience in this research area. I will develop nanowire polarization

Ultraviolet filters in stomatopod crustaceans: diversity, ecology and evolution.

PubMed

Bok, Michael J; Porter, Megan L; Cronin, Thomas W

2015-07-01

Stomatopod crustaceans employ unique ultraviolet (UV) optical filters in order to tune the spectral sensitivities of their UV-sensitive photoreceptors. In the stomatopod species Neogonodactylus oerstedii, we previously found four filter types, produced by five distinct mycosporine-like amino acid pigments in the crystalline cones of their specialized midband ommatidial facets. This UV-spectral tuning array produces receptors with at least six distinct spectral sensitivities, despite expressing only two visual pigments. Here, we present a broad survey of these UV filters across the stomatopod order, examining their spectral absorption properties in 21 species from seven families in four superfamilies. We found that UV filters are present in three of the four superfamilies, and evolutionary character reconstruction implies that at least one class of UV filter was present in the ancestor of all modern stomatopods. Additionally, postlarval stomatopods were observed to produce the UV filters simultaneously alongside development of the adult eye. The absorbance properties of the filters are consistent within a species; however, between species we found a great deal of diversity, both in the number of filters and in their spectral absorbance characteristics. This diversity correlates with the habitat depth ranges of these species, suggesting that species living in shallow, UV-rich environments may tune their UV spectral sensitivities more aggressively. We also found additional, previously unrecognized UV filter types in the crystalline cones of the peripheral eye regions of some species, indicating the possibility for even greater stomatopod visual complexity than previously thought. © 2015. Published by The Company of Biologists Ltd.

Angular Multigrid Preconditioner for Krylov-Based Solution Techniques Applied to the Sn Equations with Highly Forward-Peaked Scattering

NASA Astrophysics Data System (ADS)

Turcksin, Bruno; Ragusa, Jean C.; Morel, Jim E.

2012-01-01

It is well known that the diffusion synthetic acceleration (DSA) methods for the Sn equations become ineffective in the Fokker-Planck forward-peaked scattering limit. In response to this deficiency, Morel and Manteuffel (1991) developed an angular multigrid method for the 1-D Sn equations. This method is very effective, costing roughly twice as much as DSA per source iteration, and yielding a maximum spectral radius of approximately 0.6 in the Fokker-Planck limit. Pautz, Adams, and Morel (PAM) (1999) later generalized the angular multigrid to 2-D, but it was found that the method was unstable with sufficiently forward-peaked mappings between the angular grids. The method was stabilized via a filtering technique based on diffusion operators, but this filtering also degraded the effectiveness of the overall scheme. The spectral radius was not bounded away from unity in the Fokker-Planck limit, although the method remained more effective than DSA. The purpose of this article is to recast the multidimensional PAM angular multigrid method without the filtering as an Sn preconditioner and use it in conjunction with the Generalized Minimal RESidual (GMRES) Krylov method. The approach ensures stability and our computational results demonstrate that it is also significantly more efficient than an analogous DSA-preconditioned Krylov method.

Real-time vehicle noise cancellation techniques for gunshot acoustics

NASA Astrophysics Data System (ADS)

Ramos, Antonio L. L.; Holm, Sverre; Gudvangen, Sigmund; Otterlei, Ragnvald

2012-06-01

Acoustical sniper positioning systems rely on the detection and direction-of-arrival (DOA) estimation of the shockwave and the muzzle blast in order to provide an estimate of a potential snipers location. Field tests have shown that detecting and estimating the DOA of the muzzle blast is a rather difficult task in the presence of background noise sources, e.g., vehicle noise, especially in long range detection and absorbing terrains. In our previous work presented in the 2011 edition of this conference we highlight the importance of improving the SNR of the gunshot signals prior to the detection and recognition stages, aiming at lowering the false alarm and miss-detection rates and, thereby, increasing the reliability of the system. This paper reports on real-time noise cancellation techniques, like Spectral Subtraction and Adaptive Filtering, applied to gunshot signals. Our model assumes the background noise as being short-time stationary and uncorrelated to the impulsive gunshot signals. In practice, relatively long periods without signal occur and can be used to estimate the noise spectrum and its first and second order statistics as required in the spectral subtraction and adaptive filtering techniques, respectively. The results presented in this work are supported with extensive simulations based on real data.

Accelerometer Data Analysis and Presentation Techniques

NASA Technical Reports Server (NTRS)

Rogers, Melissa J. B.; Hrovat, Kenneth; McPherson, Kevin; Moskowitz, Milton E.; Reckart, Timothy

1997-01-01

The NASA Lewis Research Center's Principal Investigator Microgravity Services project analyzes Orbital Acceleration Research Experiment and Space Acceleration Measurement System data for principal investigators of microgravity experiments. Principal investigators need a thorough understanding of data analysis techniques so that they can request appropriate analyses to best interpret accelerometer data. Accelerometer data sampling and filtering is introduced along with the related topics of resolution and aliasing. Specific information about the Orbital Acceleration Research Experiment and Space Acceleration Measurement System data sampling and filtering is given. Time domain data analysis techniques are discussed and example environment interpretations are made using plots of acceleration versus time, interval average acceleration versus time, interval root-mean-square acceleration versus time, trimmean acceleration versus time, quasi-steady three dimensional histograms, and prediction of quasi-steady levels at different locations. An introduction to Fourier transform theory and windowing is provided along with specific analysis techniques and data interpretations. The frequency domain analyses discussed are power spectral density versus frequency, cumulative root-mean-square acceleration versus frequency, root-mean-square acceleration versus frequency, one-third octave band root-mean-square acceleration versus frequency, and power spectral density versus frequency versus time (spectrogram). Instructions for accessing NASA Lewis Research Center accelerometer data and related information using the internet are provided.

TH-CD-202-04: Evaluation of Virtual Non-Contrast Images From a Novel Split-Filter Dual-Energy CT Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, J; Szczykutowicz, T; Bayouth, J

Purpose: To compare the ability of two dual-energy CT techniques, a novel split-filter single-source technique of superior temporal resolution against an established sequential-scan technique, to remove iodine contrast from images with minimal impact on CT number accuracy. Methods: A phantom containing 8 tissue substitute materials and vials of varying iodine concentrations (1.7–20.1 mg I /mL) was imaged using a Siemens Edge CT scanner. Dual-energy virtual non-contrast (VNC) images were generated using the novel split-filter technique, in which a 120kVp spectrum is filtered by tin and gold to create high- and low-energy spectra with < 1 second temporal separation between themore » acquisition of low- and high-energy data. Additionally, VNC images were generated with the sequential-scan technique (80 and 140kVp) for comparison. CT number accuracy was evaluated for all materials at 15, 25, and 35mGy CTDIvol. Results: The spectral separation was greater for the sequential-scan technique than the split-filter technique with dual-energy ratios of 2.18 and 1.26, respectively. Both techniques successfully removed iodine contrast, resulting in mean CT numbers within 60HU of 0HU (split-filter) and 40HU of 0HU (sequential-scan) for all iodine concentrations. Additionally, for iodine vials of varying diameter (2–20 mm) with the same concentration (9.9 mg I /mL), the system accurately detected iodine for all sizes investigated. Both dual-energy techniques resulted in reduced CT numbers for bone materials (by >400HU for the densest bone). Increasing the imaging dose did not improve the CT number accuracy for bone in VNC images. Conclusion: VNC images from the split-filter technique successfully removed iodine contrast. These results demonstrate a potential for improving dose calculation accuracy and reducing patient imaging dose, while achieving superior temporal resolution in comparison sequential scans. For both techniques, inaccuracies in CT numbers for bone materials necessitate consideration for radiation therapy treatment planning.« less

A target detection multi-layer matched filter for color and hyperspectral cameras

NASA Astrophysics Data System (ADS)

Miyanishi, Tomoya; Preece, Bradley L.; Reynolds, Joseph P.

2018-05-01

In this article, a method for applying matched filters to a 3-dimentional hyperspectral data cube is discussed. In many applications, color visible cameras or hyperspectral cameras are used for target detection where the color or spectral optical properties of the imaged materials are partially known in advance. Therefore, the use of matched filtering with spectral data along with shape data is an effective method for detecting certain targets. Since many methods for 2D image filtering have been researched, we propose a multi-layer filter where ordinary spatially matched filters are used before the spectral filters. We discuss a way to layer the spectral filters for a 3D hyperspectral data cube, accompanied by a detectability metric for calculating the SNR of the filter. This method is appropriate for visible color cameras and hyperspectral cameras. We also demonstrate an analysis using the Night Vision Integrated Performance Model (NV-IPM) and a Monte Carlo simulation in order to confirm the effectiveness of the filtering in providing a higher output SNR and a lower false alarm rate.

Thermography-based blood flow imaging in human skin of the hands and feet: a spectral filtering approach.

PubMed

Sagaidachnyi, A A; Fomin, A V; Usanov, D A; Skripal, A V

2017-02-01

The determination of the relationship between skin blood flow and skin temperature dynamics is the main problem in thermography-based blood flow imaging. Oscillations in skin blood flow are the source of thermal waves propagating from micro-vessels toward the skin's surface, as assumed in this study. This hypothesis allows us to use equations for the attenuation and dispersion of thermal waves for converting the temperature signal into the blood flow signal, and vice versa. We developed a spectral filtering approach (SFA), which is a new technique for thermography-based blood flow imaging. In contrast to other processing techniques, the SFA implies calculations in the spectral domain rather than in the time domain. Therefore, it eliminates the need to solve differential equations. The developed technique was verified within 0.005-0.1 Hz, including the endothelial, neurogenic and myogenic frequency bands of blood flow oscillations. The algorithm for an inverse conversion of the blood flow signal into the skin temperature signal is addressed. The examples of blood flow imaging of hands during cuff occlusion and feet during heating of the back are illustrated. The processing of infrared (IR) thermograms using the SFA allowed us to restore the blood flow signals and achieve correlations of about 0.8 with a waveform of a photoplethysmographic signal. The prospective applications of the thermography-based blood flow imaging technique include non-contact monitoring of the blood supply during engraftment of skin flaps and burns healing, as well the use of contact temperature sensors to monitor low-frequency oscillations of peripheral blood flow.

Effect of chromatic filters on visual performance in individuals with mild traumatic brain injury (mTBI): A pilot study.

PubMed

Fimreite, Vanessa; Willeford, Kevin T; Ciuffreda, Kenneth J

2016-01-01

Spectral filters have been used clinically in patients with mild traumatic brain injury (mTBI). However, they have not been formally assessed using objective techniques in this population. Thus, the aim of the present pilot study was to determine the effect of spectral filters on reading performance and visuo-cortical responsivity in adults with mTBI. 12 adults with mTBI/concussion were tested. All reported photosensitivity and reading problems. They were compared to 12 visually-normal, asymptomatic adults. There were several test conditions: three luminance-matched control filters (gray neutral density, blue, and red), the patient-selected 'precision tint lens' that provided the most comfort and clarity of text using the Intuitive Colorimeter System, and baseline without any filters. The Visagraph was used to assess reading eye movements and reading speed objectively with each filter. In addition, both the amplitude and latency of the visual-evoked potential (VEP) were assessed with the same filters. There were few significant group differences in either the reading-related parameters or VEP latency for any of the test filter conditions. Subjective improvements were noted in most with mTBI (11/12). The majority of patients with mTBI chose a tinted filter that resulted in increased visual comfort. While significant findings based on the objective testing were found for some conditions, the subjective results suggest that precision tints should be considered as an adjunctive treatment in patients with mTBI and photosensitivity. Copyright © 2016 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

Rapid Chemometric Filtering of Spectral Data

NASA Technical Reports Server (NTRS)

Beaman, Gregory; Pelletier, Michael; Seshadri, Suresh

2004-01-01

A method of rapid, programmable filtering of spectral transmittance, reflectance, or fluorescence data to measure the concentrations of chemical species has been proposed. By programmable is meant that a variety of spectral analyses can readily be performed and modified in software, firmware, and/or electronic hardware, without need to change optical filters or other optical hardware of the associated spectrometers. The method is intended to enable real-time identification of single or multiple target chemical species in applications that involve high-throughput screening of multiple samples. Examples of such applications include (but are not limited to) combinatorial chemistry, flow cytometry, bead assays, testing drugs, remote sensing, and identification of targets. The basic concept of the proposed method is to perform real-time crosscorrelations of a measured spectrum with one or more analytical function(s) of wavelength that could be, for example, the known spectra of target species. Assuming that measured spectral intensities are proportional to concentrations of target species plus background spectral intensities, then after subtraction of background levels, it should be possible to determine target species concentrations from cross-correlation values. Of course, the problem of determining the concentrations is more complex when spectra of different species overlap, but the problem can be solved by use of multiple analytical functions in combination with computational techniques that have been developed previously for analyses of this type. The method is applicable to the design and operation of a spectrometer in which spectrally dispersed light is measured by means of an active-pixel sensor (APS) array. The row or column dimension of such an array is generally chosen to be aligned along the spectral-dispersion dimension, so that each pixel intercepts light in a narrow spectral band centered on a wavelength that is a known function of the pixel position. The proposed method admits of two hardware implementations for computing cross-correlations in real time.

Spectrum sensing and resource allocation for multicarrier cognitive radio systems under interference and power constraints

NASA Astrophysics Data System (ADS)

Dikmese, Sener; Srinivasan, Sudharsan; Shaat, Musbah; Bader, Faouzi; Renfors, Markku

2014-12-01

Multicarrier waveforms have been commonly recognized as strong candidates for cognitive radio. In this paper, we study the dynamics of spectrum sensing and spectrum allocation functions in cognitive radio context using very practical signal models for the primary users (PUs), including the effects of power amplifier nonlinearities. We start by sensing the spectrum with energy detection-based wideband multichannel spectrum sensing algorithm and continue by investigating optimal resource allocation methods. Along the way, we examine the effects of spectral regrowth due to the inevitable power amplifier nonlinearities of the PU transmitters. The signal model includes frequency selective block-fading channel models for both secondary and primary transmissions. Filter bank-based wideband spectrum sensing techniques are applied for detecting spectral holes and filter bank-based multicarrier (FBMC) modulation is selected for transmission as an alternative multicarrier waveform to avoid the disadvantage of limited spectral containment of orthogonal frequency-division multiplexing (OFDM)-based multicarrier systems. The optimization technique used for the resource allocation approach considered in this study utilizes the information obtained through spectrum sensing and knowledge of spectrum leakage effects of the underlying waveforms, including a practical power amplifier model for the PU transmitter. This study utilizes a computationally efficient algorithm to maximize the SU link capacity with power and interference constraints. It is seen that the SU transmission capacity depends critically on the spectral containment of the PU waveform, and these effects are quantified in a case study using an 802.11-g WLAN scenario.

Hyperspectral small animal fluorescence imaging: spectral selection imaging

NASA Astrophysics Data System (ADS)

Leavesley, Silas; Jiang, Yanan; Patsekin, Valery; Hall, Heidi; Vizard, Douglas; Robinson, J. Paul

2008-02-01

Molecular imaging is a rapidly growing area of research, fueled by needs in pharmaceutical drug-development for methods for high-throughput screening, pre-clinical and clinical screening for visualizing tumor growth and drug targeting, and a growing number of applications in the molecular biology fields. Small animal fluorescence imaging employs fluorescent probes to target molecular events in vivo, with a large number of molecular targeting probes readily available. The ease at which new targeting compounds can be developed, the short acquisition times, and the low cost (compared to microCT, MRI, or PET) makes fluorescence imaging attractive. However, small animal fluorescence imaging suffers from high optical scattering, absorption, and autofluorescence. Much of these problems can be overcome through multispectral imaging techniques, which collect images at different fluorescence emission wavelengths, followed by analysis, classification, and spectral deconvolution methods to isolate signals from fluorescence emission. We present an alternative to the current method, using hyperspectral excitation scanning (spectral selection imaging), a technique that allows excitation at any wavelength in the visible and near-infrared wavelength range. In many cases, excitation imaging may be more effective at identifying specific fluorescence signals because of the higher complexity of the fluorophore excitation spectrum. Because the excitation is filtered and not the emission, the resolution limit and image shift imposed by acousto-optic tunable filters have no effect on imager performance. We will discuss design of the imager, optimizing the imager for use in small animal fluorescence imaging, and application of spectral analysis and classification methods for identifying specific fluorescence signals.

Fractional-order Fourier analysis for ultrashort pulse characterization.

PubMed

Brunel, Marc; Coetmellec, Sébastien; Lelek, Mickael; Louradour, Frédéric

2007-06-01

We report what we believe to be the first experimental demonstration of ultrashort pulse characterization using fractional-order Fourier analysis. The analysis is applied to the interpretation of spectral interferometry resolved in time (SPIRIT) traces [which are spectral phase interferometry for direct electric field reconstruction (SPIDER)-like interferograms]. First, the fractional-order Fourier transformation is shown to naturally allow the determination of the cubic spectral phase coefficient of pulses to be analyzed. A simultaneous determination of both cubic and quadratic spectral phase coefficients of the pulses using the fractional-order Fourier series expansion is further demonstrated. This latter technique consists of localizing relative maxima in a 2D cartography representing decomposition coefficients. It is further used to reconstruct or filter SPIRIT traces.

Filter design for cancellation of baseline-fluctuation in needle EMG recordings.

PubMed

Rodríguez-Carreño, I; Malanda-Trigueros, A; Gila-Useros, L; Navallas-Irujo, J; Rodríguez-Falces, J

2006-01-01

Appropriate cancellation of the baseline fluctuation (BLF) is an important issue when recording EMG signals as it may degrade signal quality and distort qualitative and quantitative analysis. We present a novel filter-design approach for automatic cancellation of the BLF based on several signal processing techniques used sequentially. The methodology is to estimate the spectral content of the BLF, and then to use this estimation to design a high-pass FIR filter that cancel the BLF present in the signal. Two merit figures are devised for measuring the degree of BLF present in an EMG record. These figures are used to compare our method with the conventional approach, which naively considers the baseline course to be of constant (without any fluctuation) potential shift. Applications of the technique on real and simulated EMG signals show the superior performance of our approach in terms of both visual inspection and the merit figures.

Experimental Demonstration of Adaptive Infrared Multispectral Imaging using Plasmonic Filter Array.

PubMed

Jang, Woo-Yong; Ku, Zahyun; Jeon, Jiyeon; Kim, Jun Oh; Lee, Sang Jun; Park, James; Noyola, Michael J; Urbas, Augustine

2016-10-10

In our previous theoretical study, we performed target detection using a plasmonic sensor array incorporating the data-processing technique termed "algorithmic spectrometry". We achieved the reconstruction of a target spectrum by extracting intensity at multiple wavelengths with high resolution from the image data obtained from the plasmonic array. The ultimate goal is to develop a full-scale focal plane array with a plasmonic opto-coupler in order to move towards the next generation of versatile infrared cameras. To this end, and as an intermediate step, this paper reports the experimental demonstration of adaptive multispectral imagery using fabricated plasmonic spectral filter arrays and proposed target detection scenarios. Each plasmonic filter was designed using periodic circular holes perforated through a gold layer, and an enhanced target detection strategy was proposed to refine the original spectrometry concept for spatial and spectral computation of the data measured from the plasmonic array. Both the spectrum of blackbody radiation and a metal ring object at multiple wavelengths were successfully reconstructed using the weighted superposition of plasmonic output images as specified in the proposed detection strategy. In addition, plasmonic filter arrays were theoretically tested on a target at extremely high temperature as a challenging scenario for the detection scheme.

Tunable thin-film optical filters for hyperspectral microscopy

NASA Astrophysics Data System (ADS)

Favreau, Peter F.; Rich, Thomas C.; Prabhat, Prashant; Leavesley, Silas J.

2013-02-01

Hyperspectral imaging was originally developed for use in remote sensing applications. More recently, it has been applied to biological imaging systems, such as fluorescence microscopes. The ability to distinguish molecules based on spectral differences has been especially advantageous for identifying fluorophores in highly autofluorescent tissues. A key component of hyperspectral imaging systems is wavelength filtering. Each filtering technology used for hyperspectral imaging has corresponding advantages and disadvantages. Recently, a new optical filtering technology has been developed that uses multi-layered thin-film optical filters that can be rotated, with respect to incident light, to control the center wavelength of the pass-band. Compared to the majority of tunable filter technologies, these filters have superior optical performance including greater than 90% transmission, steep spectral edges and high out-of-band blocking. Hence, tunable thin-film optical filters present optical characteristics that may make them well-suited for many biological spectral imaging applications. An array of tunable thin-film filters was implemented on an inverted fluorescence microscope (TE 2000, Nikon Instruments) to cover the full visible wavelength range. Images of a previously published model, GFP-expressing endothelial cells in the lung, were acquired using a charge-coupled device camera (Rolera EM-C2, Q-Imaging). This model sample presents fluorescently-labeled cells in a highly autofluorescent environment. Linear unmixing of hyperspectral images indicates that thin-film tunable filters provide equivalent spectral discrimination to our previous acousto-optic tunable filter-based approach, with increased signal-to-noise characteristics. Hence, tunable multi-layered thin film optical filters may provide greatly improved spectral filtering characteristics and therefore enable wider acceptance of hyperspectral widefield microscopy.

White-Light Optical Information Processing and Holography.

DTIC Science & Technology

1982-05-03

artifact noise . I. wever, the deblurring spatial filter that we used were a narrow spectral band centered at 5154A green light. To compensate for the scaling...Processing, White-Light 11olographyv, Image Profcessing, Optical Signal Process inI, Image Subtraction, Image Deblurring . 70. A S’ R ACT (Continua on crow ad...optical processing technique, we had shown that the incoherent source techniques provides better image quality, and very low coherent artifact noise

Silicon Nitride Grating Coupler with Flexible Bandwidth Incorporating a Serially Concatenated Multimode Interference Filter

NASA Astrophysics Data System (ADS)

Kim, Woo-Ju; Lee, Hak-Soon; Lee, Sang-Shin

2012-04-01

A compact silicon nitride grating coupler with flexible bandwidth was demonstrated taking advantage of a basic grating integrated with a serially connected multistage multimode interference (MMI) filter. The spectral response could be tailored by varying the order of the MMI filter, without affecting the basic grating structure. The dependence of the spectral response of the proposed device on the order of the MMI stage was thoroughly investigated. As regards the fabricated grating coupler with a four-stage MMI filter, the observed spectral bandwidth was efficiently altered from 53 to 21 nm in the ˜1550 nm spectral band.

All-fiber optical filter with an ultranarrow and rectangular spectral response.

PubMed

Zou, Xihua; Li, Ming; Pan, Wei; Yan, Lianshan; Azaña, José; Yao, Jianping

2013-08-15

Optical filters with an ultranarrow and rectangular spectral response are highly desired for high-resolution optical/electrical signal processing. An all-fiber optical filter based on a fiber Bragg grating with a large number of phase shifts is designed and fabricated. The measured spectral response shows a 3 dB bandwidth of 650 MHz and a rectangular shape factor of 0.513 at the 25 dB bandwidth. This is the narrowest rectangular bandpass response ever reported for an all-fiber filter, to the best of our knowledge. The filter has also the intrinsic advantages of an all-fiber implementation.

Speckle imaging techniques of the turbulence degraded images

NASA Astrophysics Data System (ADS)

Liu, Jin; Huang, Zongfu; Mao, Hongjun; Liang, Yonghui

2018-03-01

We propose a speckle imaging algorithm in which we use the improved form of spectral ratio to obtain the Fried parameter, we also use a filter to reduce the high frequency noise effects. Our algorithm makes an improvement in the quality of the reconstructed images. The performance is illustrated by computer simulations.

Spectral Absorption By Particulate Impurities in Snow Determined By Photometric Analysis Of Filters

NASA Astrophysics Data System (ADS)

Grenfell, T. C.; Doherty, S. J.; Clarke, A. D.

2009-12-01

Our work is motivated by the 1983-84 survey by Clarke and Noone (Atmos. Environ., 1985) of soot in Arctic snow. Our objective is to resurvey the original area they covered and to extend the observations around the entire Arctic Basin under the auspices of the IPY program. We use the filtering and integrating sandwich techniques developed by Clarke and Noone to process the snow samples. Among the advantages of this method are that (a) it provides a direct measure of light absorption and the result is closely related to the actual absorption of sunlight in the snow or ice, (b) processing and filtering of the snow samples can be carried out in remote locations and (c) it is not necessary to transport large quantities of snow back to our home laboratory. Here we describe the construction, calibration, and some applications of an integrating sphere spectrophotometer system designed to take advantage of recent advances in instrumentation to improve the accuracy of measurements of absorption by particulate impurities collected on nuclepore filters used in our survey. Filter loading in terms of effective black carbon (BC) amount is determined together with the ratio of non-BC to BC concentrations using a set of reference filters with known loadings of Monarch 71 BC prepared by A. D. Clarke. The new spectrophotometer system has (a) system stability of approximately 0.5%; (b) precision relative to ADC standards of 3-4% for filter loadings greater than about 0.5 microgm Carbon/cm2. (c) We can distinguish BC from non-BC from relative spectral shapes of the energy absorption curves with an accuracy that depends on our knowledge of the spectral absorption curves of the non-BC components; and (d) by-eye estimates are consistent with spectrophotometric results. The major outstanding uncertainty is the appropriate value to use for the mass absorption efficiency for BC.

Spectral characterization and calibration of AOTF spectrometers and hyper-spectral imaging system

NASA Astrophysics Data System (ADS)

Katrašnik, Jaka; Pernuš, Franjo; Likar, Boštjan

2010-02-01

The goal of this article is to present a novel method for spectral characterization and calibration of spectrometers and hyper-spectral imaging systems based on non-collinear acousto-optical tunable filters. The method characterizes the spectral tuning curve (frequency-wavelength characteristic) of the AOTF (Acousto-Optic Tunable Filter) filter by matching the acquired and modeled spectra of the HgAr calibration lamp, which emits line spectrum that can be well modeled via AOTF transfer function. In this way, not only tuning curve characterization and corresponding spectral calibration but also spectral resolution assessment is performed. The obtained results indicated that the proposed method is efficient, accurate and feasible for routine calibration of AOTF spectrometers and hyper-spectral imaging systems and thereby a highly competitive alternative to the existing calibration methods.

Ratiometric wavelength monitor based on X-type spectral response using two edge filters

NASA Astrophysics Data System (ADS)

Hatta, Agus Muhamad; Rajan, Ginu; Farrell, Gerald; Semenova, Yuliya

2009-05-01

The performance of an all-fiber ratiometric wavelength measurement system is compared for the case of two edge filters and the case of one edge filter. The two fiber edge filters are used with overlapping and opposite slope spectral responses, a so called "X-type spectral response", each based on singlemode-multimode-singlemode (SMS) fiber structures. Noise and polarization dependent loss (PDL) are the two parameters that determine the resolution and an accuracy of the system. It is demonstrated that the use of two SMS edge filters for a ratiometric wavelength measurement system can increase the resolution and the accuracy when compared with a system using only one edge filter.

Bowtie filters for dedicated breast CT: Theory and computational implementation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kontson, Kimberly, E-mail: Kimberly.Kontson@fda.hhs.gov; Jennings, Robert J.

Purpose: To design bowtie filters with improved properties for dedicated breast CT to improve image quality and reduce dose to the patient. Methods: The authors present three different bowtie filters designed for a cylindrical 14-cm diameter phantom with a uniform composition of 40/60 breast tissue, which vary in their design objectives and performance improvements. Bowtie design #1 is based on single material spectral matching and produces nearly uniform spectral shape for radiation incident upon the detector. Bowtie design #2 uses the idea of basis material decomposition to produce the same spectral shape and intensity at the detector, using two differentmore » materials. Bowtie design #3 eliminates the beam hardening effect in the reconstructed image by adjusting the bowtie filter thickness so that the effective attenuation coefficient for every ray is the same. All three designs are obtained using analytical computational methods and linear attenuation coefficients. Thus, the designs do not take into account the effects of scatter. The authors considered this to be a reasonable approach to the filter design problem since the use of Monte Carlo methods would have been computationally intensive. The filter profiles for a cone-angle of 0° were used for the entire length of each filter because the differences between those profiles and the correct cone-beam profiles for the cone angles in our system are very small, and the constant profiles allowed construction of the filters with the facilities available to us. For evaluation of the filters, we used Monte Carlo simulation techniques and the full cone-beam geometry. Images were generated with and without each bowtie filter to analyze the effect on dose distribution, noise uniformity, and contrast-to-noise ratio (CNR) homogeneity. Line profiles through the reconstructed images generated from the simulated projection images were also used as validation for the filter designs. Results: Examples of the three designs are presented. Initial verification of performance of the designs was done using analytical computations of HVL, intensity, and effective attenuation coefficient behind the phantom as a function of fan-angle with a cone-angle of 0°. The performance of the designs depends only weakly on incident spectrum and tissue composition. For all designs, the dynamic range requirement on the detector was reduced compared to the no-bowtie-filter case. Further verification of the filter designs was achieved through analysis of reconstructed images from simulations. Simulation data also showed that the use of our bowtie filters can reduce peripheral dose to the breast by 61% and provide uniform noise and CNR distributions. The bowtie filter design concepts validated in this work were then used to create a computational realization of a 3D anthropomorphic bowtie filter capable of achieving a constant effective attenuation coefficient behind the entire field-of-view of an anthropomorphic breast phantom. Conclusions: Three different bowtie filter designs that vary in performance improvements were described and evaluated using computational and simulation techniques. Results indicate that the designs are robust against variations in breast diameter, breast composition, and tube voltage, and that the use of these filters can reduce patient dose and improve image quality compared to the no-bowtie-filter case.« less

Storage and retrieval of mass spectral information

NASA Technical Reports Server (NTRS)

Hohn, M. E.; Humberston, M. J.; Eglinton, G.

1977-01-01

Computer handling of mass spectra serves two main purposes: the interpretation of the occasional, problematic mass spectrum, and the identification of the large number of spectra generated in the gas-chromatographic-mass spectrometric (GC-MS) analysis of complex natural and synthetic mixtures. Methods available fall into the three categories of library search, artificial intelligence, and learning machine. Optional procedures for coding, abbreviating and filtering a library of spectra minimize time and storage requirements. Newer techniques make increasing use of probability and information theory in accessing files of mass spectral information.

Optimized Multi-Spectral Filter Array Based Imaging of Natural Scenes.

PubMed

Li, Yuqi; Majumder, Aditi; Zhang, Hao; Gopi, M

2018-04-12

Multi-spectral imaging using a camera with more than three channels is an efficient method to acquire and reconstruct spectral data and is used extensively in tasks like object recognition, relighted rendering, and color constancy. Recently developed methods are used to only guide content-dependent filter selection where the set of spectral reflectances to be recovered are known a priori. We present the first content-independent spectral imaging pipeline that allows optimal selection of multiple channels. We also present algorithms for optimal placement of the channels in the color filter array yielding an efficient demosaicing order resulting in accurate spectral recovery of natural reflectance functions. These reflectance functions have the property that their power spectrum statistically exhibits a power-law behavior. Using this property, we propose power-law based error descriptors that are minimized to optimize the imaging pipeline. We extensively verify our models and optimizations using large sets of commercially available wide-band filters to demonstrate the greater accuracy and efficiency of our multi-spectral imaging pipeline over existing methods.

Optimized Multi-Spectral Filter Array Based Imaging of Natural Scenes

PubMed Central

Li, Yuqi; Majumder, Aditi; Zhang, Hao; Gopi, M.

2018-01-01

Multi-spectral imaging using a camera with more than three channels is an efficient method to acquire and reconstruct spectral data and is used extensively in tasks like object recognition, relighted rendering, and color constancy. Recently developed methods are used to only guide content-dependent filter selection where the set of spectral reflectances to be recovered are known a priori. We present the first content-independent spectral imaging pipeline that allows optimal selection of multiple channels. We also present algorithms for optimal placement of the channels in the color filter array yielding an efficient demosaicing order resulting in accurate spectral recovery of natural reflectance functions. These reflectance functions have the property that their power spectrum statistically exhibits a power-law behavior. Using this property, we propose power-law based error descriptors that are minimized to optimize the imaging pipeline. We extensively verify our models and optimizations using large sets of commercially available wide-band filters to demonstrate the greater accuracy and efficiency of our multi-spectral imaging pipeline over existing methods. PMID:29649114

Doppler lidar wind measurement with the edge technique

NASA Technical Reports Server (NTRS)

Korb, C. Laurence; Gentry, Bruce M.

1992-01-01

The edge technique is a new and powerful method for measuring small frequency shifts. Range resolved lidar measurements of winds can be made with high accuracy and high vertical resolution using the edge technique to measure the Doppler shift of an atmospheric backscattered signal from a pulsed laser. The edge technique can be used at near-infrared or visible wavelengths using well developed solid state lasers and detectors with various edge filters. In the edge technique, the laser frequency is located on the steep slope of the spectral response function of a high resolution optical filter. Due to the steep slope of the edge, very small frequency shifts cause large changes in measured signal. The frequency of the outgoing laser pulse is determined by measuring its location on the edge of the filter. This is accomplished by sending a small portion of the beam to the edge detection setup where the incoming light is split into two channels - an edge filter and an energy monitor channel. The energy monitor signal is used to normalize the edge filter signal for magnitude. The laser return backscattered from the atmosphere is collected by a telescope and directed through the edge detection setup to determine its frequency (location on the edge) in a similar manner for each range element. The Doppler shift, and thus the wind, is determined from a differential measurement of the frequency of the outgoing laser pulse and the frequency of the laser return backscattered from the atmosphere. We have conducted simulations of the performance of an edge lidar system using an injection seeded pulsed Nd:YAG laser at 1.06 microns. The central fringe of a Fabry-Perot etalon is used as a high resolution edge filter to measure the shift of the aerosol return.

Specialized Color Targets for Spectral Reflectance Reconstruction of Magnified Images

NASA Astrophysics Data System (ADS)

Kruschwitz, Jennifer D. T.

Digital images are used almost exclusively instead of film to capture visual information across many scientific fields. The colorimetric color representation within these digital images can be relayed from the digital counts produced by the camera with the use of a known color target. In image capture of magnified images, there is currently no reliable color target that can be used at multiple magnifications and give the user a solid understanding of the color ground truth within those images. The first part of this dissertation included the design, fabrication, and testing of a color target produced with optical interference coated microlenses for use in an off-axis illumination, compound microscope. An ideal target was designed to increase the color gamut for colorimetric imaging and provide the necessary "Block Dye" spectral reflectance profiles across the visible spectrum to reduce the number of color patches necessary for multiple filter imaging systems that rely on statistical models for spectral reflectance reconstruction. There are other scientific disciplines that can benefit from a specialized color target to determine the color ground truth in their magnified images and perform spectral estimation. Not every discipline has the luxury of having a multi-filter imaging system. The second part of this dissertation developed two unique ways of using an interference coated color mirror target: one that relies on multiple light-source angles, and one that leverages a dynamic color change with time. The source multi-angle technique would be used for the microelectronic discipline where the reconstructed spectral reflectance would be used to determine a dielectric film thickness on a silicon substrate, and the time varying technique would be used for a biomedical example to determine the thickness of human tear film.

Multi-spectral imaging of oxygen saturation

NASA Astrophysics Data System (ADS)

Savelieva, Tatiana A.; Stratonnikov, Aleksander A.; Loschenov, Victor B.

2008-06-01

The system of multi-spectral imaging of oxygen saturation is an instrument that can record both spectral and spatial information about a sample. In this project, the spectral imaging technique is used for monitoring of oxygen saturation of hemoglobin in human tissues. This system can be used for monitoring spatial distribution of oxygen saturation in photodynamic therapy, surgery or sports medicine. Diffuse reflectance spectroscopy in the visible range is an effective and extensively used technique for the non-invasive study and characterization of various biological tissues. In this article, a short review of modeling techniques being currently in use for diffuse reflection from semi-infinite turbid media is presented. A simple and practical model for use with a real-time imaging system is proposed. This model is based on linear approximation of the dependence of the diffuse reflectance coefficient on relation between absorbance and reduced scattering coefficient. This dependence was obtained with the Monte Carlo simulation of photon propagation in turbid media. Spectra of the oxygenated and deoxygenated forms of hemoglobin differ mostly in the red area (520 - 600 nm) and have several characteristic points there. Thus four band-pass filters were used for multi-spectral imaging. After having measured the reflectance, the data obtained are used for fitting the concentration of oxygenated and free hemoglobin, and hemoglobin oxygen saturation.

Devices based on surface plasmon interference filters

NASA Technical Reports Server (NTRS)

Wang, Yu (Inventor)

2001-01-01

Devices based on surface plasmon filters having at least one metal-dielectric interface to support surface plasmon waves. A multi-layer-coupled surface plasmon notch filter is provided to have more than two symmetric metal-dielectric interfaces coupled with one another to produce a transmission spectral window with desired spectral profile and bandwidth. Such notch filters can form various color filtering devices for color flat panel displays.

Efficient generation and characterization of spectrally factorable biphotons.

PubMed

Chen, Changchen; Bo, Cao; Niu, Murphy Yuezhen; Xu, Feihu; Zhang, Zheshen; Shapiro, Jeffrey H; Wong, Franco N C

2017-04-03

Spectrally unentangled biphotons with high single-spatiotemporal-mode purity are highly desirable for many quantum information processing tasks. We generate biphotons with an inferred heralded-state spectral purity of 99%, the highest to date without any spectral filtering, by pulsed spontaneous parametric downconversion in a custom-fabricated periodically-poled KTiOPO₄ crystal under extended Gaussian phase-matching conditions. To efficiently characterize the joint spectral intensity of the generated biphotons at high spectral resolution, we employ a commercially available dispersion compensation module (DCM) with a dispersion equivalent to 100 km of standard optical fiber and with an insertion loss of only 2.8 dB. Compared with the typical method of using two temperature-stabilized equal-length fibers that incurs an insertion loss of 20 dB per fiber, the DCM approach achieves high spectral resolution in a much shorter measurement time. Because the dispersion amount and center wavelengths of DCMs can be easily customized, spectral characterization in a wide range of quantum photonic applications should benefit significantly from this technique.

Optical filters for the Multispectral Instrument (MSI) on Sentinel-2

NASA Astrophysics Data System (ADS)

Merschdorf, M.; Camus, F.; Kirschner, V.

2017-11-01

Multi-spectral optical filters are essential parts of spaceborne optical imagers such as the Multispectral Instrument (MSI) for the Sentinel-2 satellite in the framework of ESA's GMES programme for earth observation. In this development, Jena-Optronik is responsible for the design, manufacturing and test of the spectral filter assemblies. They are the key elements that define the spectral quality of the instrument. Besides the challenging spectral requirements straylight aspects are of crucial importance due to the close neighbourhood of the filter elements to the detector. Results will be presented of the extensive analyses and measurements that have been performed on component and assembly level to ensure the optical performance.

Compact Micromachined Bandpass Filters for Infrared Planetary Spectroscopy

NASA Technical Reports Server (NTRS)

Brown, Ari D.; Aslam, Shahid; Chervenak, James A.; Huang, Wei-Chung; Merrell, Willie; Quijada, Manuel

2011-01-01

The thermal instrument strawman payload of the Jupiter Europa Orbiter on the Europa Jupiter Science Mission will map out thermal anomalies, the structure, and atmospheric conditions of Europa and Jupiter within the 7-100 micron spectral range. One key requirement for the payload is that the mass cannot exceed 3.7 kg. Consequently, a new generation of light-weight miniaturized spectrometers needs to be developed. On the path toward developing these spectrometers is development of ancillary miniaturized spectroscopic components. In this paper, we present a strategy for making radiation hard and low mass FIR band pass metal mesh filters. Our strategy involves using MEMS-based fabrication techniques, which will permit the quasi-optical filter structures to be made with micron-scale precision. This will enable us to achieve tight control over both the pass band of the filter and the micromachined silicon support structure architecture, which will facilitate integration of the filters for a variety of applications.

Cyclic additional optical true time delay for microwave beam steering with spectral filtering.

PubMed

Cao, Z; Lu, R; Wang, Q; Tessema, N; Jiao, Y; van den Boom, H P A; Tangdiongga, E; Koonen, A M J

2014-06-15

Optical true time delay (OTTD) is an attractive way to realize microwave beam steering (MBS) due to its inherent features of broadband, low-loss, and compactness. In this Letter, we propose a novel OTTD approach named cyclic additional optical true time delay (CAO-TTD). It applies additional integer delays of the microwave carrier frequency to achieve spectral filtering but without disturbing the spatial filtering (beam steering). Based on such concept, a broadband MBS scheme for high-capacity wireless communication is proposed, which allows the tuning of both spectral filtering and spatial filtering. The experimental results match well with the theoretical analysis.

Identification of the chemical components of Saussurea involucrata by high-resolution mass spectrometry and the mass spectral trees similarity filter technique.

PubMed

Jia, Zhixin; Wu, Caisheng; Jin, Hongtao; Zhang, Jinlan

2014-11-15

Saussurea involucrata is a rare traditional Chinese medicine (TCM) that displays anti-fatigue, anti-inflammatory and anti-tumor effects. In this paper, the different chemical components of Saussurea involucrata were characterized and identified over a wide dynamic range by high-performance liquid chromatography coupled with high-resolution hybrid mass spectrometry (HPLC/HRMS/MS(n)) and the mass spectral trees similarity filter (MTSF) technique. The aerial parts of Saussurea involucrata were extracted with 75% ethanol. The partial extract was separated on a chromatography column to concentrate the low-concentration compounds. Mass data were acquired using full-scan mass analysis (resolving power 50,000) with data-dependent incorporation of dynamic exclusion analysis. The identified compounds were used as templates to construct a database of mass spectral trees. Data for the unknown compounds were matched with those templates and matching candidate structures were obtained. The detected compounds were characterized based on matching to candidate structures by the MTSF technique and were further identified by their accurate mass weight, multiple-stage analysis and fragmentation patterns and through comparison with literature data. A total of 38 compounds were identified including 19 flavones, 11 phenylpropanoids and 8 sphingolipids. Among them, 7 flavonoids, 8 phenylpropanoids and 8 sphingolipids were identified for the first time in Saussurea involucrata. HPLC/HRMS/MS(n) combined with MTSF was successfully used to discover and identify the chemical compounds in Saussurea involucrata. The results indicated that this combined technique was extremely useful for the rapid detection and identification of the chemical components in TCMs. Copyright © 2014 John Wiley & Sons, Ltd.

Hyperspectral imaging for the detection of retinal disease

NASA Astrophysics Data System (ADS)

Harvey, Andrew R.; Lawlor, Joanne; McNaught, Andrew I.; Williams, John W.; Fletcher-Holmes, David W.

2002-11-01

Hyperspectral imaging (HSI) shows great promise for the detection and classification of several diseases, particularly in the fields of "optical biopsy" as applied to oncology, and functional retinal imaging in ophthalmology. In this paper, we discuss the application of HSI to the detection of retinal diseases and technological solutions that address some of the fundamental difficulties of spectral imaging within the eye. HSI of the retina offers a route to non-invasively deduce biochemical and metabolic processes within the retina. For example it shows promise for the mapping of retinal blood perfusion using spectral signatures of oxygenated and deoxygenated hemoglobin. Compared with other techniques using just a few spectral measurements, it offers improved classification in the presence of spectral cross-contamination by pigments and other components within the retina. There are potential applications for this imaging technique in the investigation and treatment of the eye complications of diabetes, and other diseases involving disturbances to the retinal, or optic-nerve-head circulation. It is well known that high-performance HSI requires high signal-to-noise ratios (SNR) whereas the application of any imaging technique within the eye must cope with the twin limitations of the small numerical aperture provided by the entrance pupil to the eye and the limit on the radiant power at the retina. We advocate the use of spectrally-multiplexed spectral imaging techniques (the traditional filter wheel is a traditional example). These approaches enable a flexible approach to spectral imaging, with wider spectral range, higher SNRs and lower light intensity at the retina than could be achieved using a Fourier-transform (FT) approach. We report the use of spectral imaging to provide calibrated spectral albedo images of healthy and diseased retinas and the use of this data for screening purposes. These images clearly demonstrate the ability to distinguish between oxygenated and deoxygenated hemoglobin using spectral imaging and this shows promise for the early detection of various retinopathies.

Hybrid fusion of linear, non-linear and spectral models for the dynamic modeling of sEMG and skeletal muscle force: an application to upper extremity amputation.

PubMed

Potluri, Chandrasekhar; Anugolu, Madhavi; Schoen, Marco P; Subbaram Naidu, D; Urfer, Alex; Chiu, Steve

2013-11-01

Estimating skeletal muscle (finger) forces using surface Electromyography (sEMG) signals poses many challenges. In general, the sEMG measurements are based on single sensor data. In this paper, two novel hybrid fusion techniques for estimating the skeletal muscle force from the sEMG array sensors are proposed. The sEMG signals are pre-processed using five different filters: Butterworth, Chebychev Type II, Exponential, Half-Gaussian and Wavelet transforms. Dynamic models are extracted from the acquired data using Nonlinear Wiener Hammerstein (NLWH) models and Spectral Analysis Frequency Dependent Resolution (SPAFDR) models based system identification techniques. A detailed comparison is provided for the proposed filters and models using 18 healthy subjects. Wavelet transforms give higher mean correlation of 72.6 ± 1.7 (mean ± SD) and 70.4 ± 1.5 (mean ± SD) for NLWH and SPAFDR models, respectively, when compared to the other filters used in this work. Experimental verification of the fusion based hybrid models with wavelet transform shows a 96% mean correlation and 3.9% mean relative error with a standard deviation of ± 1.3 and ± 0.9 respectively between the overall hybrid fusion algorithm estimated and the actual force for 18 test subjects' k-fold cross validation data. © 2013 Elsevier Ltd. All rights reserved.

Spectroscopic investigation of inner filter effect by magnolol solutions

NASA Astrophysics Data System (ADS)

Li, Hongmei; YuzhuHu

2007-12-01

Spectroscopy is useful tool for aggregation studies on fluorephores. One of the major problems with this technique is that the inner filter effect becomes unavoidable since the samples are used at high concentration. In this work, our investigation on magnolol spectroscopic properties shows that the inner filter effect (IFE) of fluorescence plays a critical role in the spectra of magnolol. The strong dependence of the fluorescence parameters on the concentration accounts for the apparent experimental evidence of magnolol aggregation at high concentrations. There are some questions despite the aggregation model based on fluorescent aggregates seems to describe the behavior of the system. The mathematical correction on the emission intensities shows the linear fluorescence-concentration relationship. Furthermore, we propose a mathematic model of excitation spectrum based on the primary IFE (absorption of light of excitation wavelength), which provide a correct explanation of the unusual spectral shift and spectral narrowing in the excitation spectra of magnolol at high concentrations. The shapes of spectra are completely independent on magnolol aggregation and are due only to experimental artifacts, i.e. IFE.

Adaptive angular-velocity Vold-Kalman filter order tracking - Theoretical basis, numerical implementation and parameter investigation

NASA Astrophysics Data System (ADS)

Pan, M.-Ch.; Chu, W.-Ch.; Le, Duc-Do

2016-12-01

The paper presents an alternative Vold-Kalman filter order tracking (VKF_OT) method, i.e. adaptive angular-velocity VKF_OT technique, to extract and characterize order components in an adaptive manner for the condition monitoring and fault diagnosis of rotary machinery. The order/spectral waveforms to be tracked can be recursively solved by using Kalman filter based on the one-step state prediction. The paper comprises theoretical derivation of computation scheme, numerical implementation, and parameter investigation. Comparisons of the adaptive VKF_OT scheme with two other ones are performed through processing synthetic signals of designated order components. Processing parameters such as the weighting factor and the correlation matrix of process noise, and data conditions like the sampling frequency, which influence tracking behavior, are explored. The merits such as adaptive processing nature and computation efficiency brought by the proposed scheme are addressed although the computation was performed in off-line conditions. The proposed scheme can simultaneously extract multiple spectral components, and effectively decouple close and crossing orders associated with multi-axial reference rotating speeds.

Biophysical and spectral modeling for crop identification and assessment

NASA Technical Reports Server (NTRS)

Goel, N. S. (Principal Investigator)

1984-01-01

The development of a technique for estimating all canopy parameters occurring in a canopy reflectance model from the measured canopy reflectance data is summarized. The Suits and the SAIL model for a uniform and homogeneous crop canopy were used to determine if the leaf area index and the leaf angle distribution could be estimated. Optimal solar/view angles for measuring CR were also investigated. The use of CR in many wavelengths or spectral bands and of linear and nonlinear transforms of CRs for various solar/view angles and various spectral bands is discussed as well as the inversion of rediance data inside the canopy, angle transforms for filtering out terrain slope effects, and modification of one dimensional models.

Automated thermal mapping techniques using chromatic image analysis

NASA Technical Reports Server (NTRS)

Buck, Gregory M.

1989-01-01

Thermal imaging techniques are introduced using a chromatic image analysis system and temperature sensitive coatings. These techniques are used for thermal mapping and surface heat transfer measurements on aerothermodynamic test models in hypersonic wind tunnels. Measurements are made on complex vehicle configurations in a timely manner and at minimal expense. The image analysis system uses separate wavelength filtered images to analyze surface spectral intensity data. The system was initially developed for quantitative surface temperature mapping using two-color thermographic phosphors but was found useful in interpreting phase change paint and liquid crystal data as well.

Real-time colouring and filtering with graphics shaders

NASA Astrophysics Data System (ADS)

Vohl, D.; Fluke, C. J.; Barnes, D. G.; Hassan, A. H.

2017-11-01

Despite the popularity of the Graphics Processing Unit (GPU) for general purpose computing, one should not forget about the practicality of the GPU for fast scientific visualization. As astronomers have increasing access to three-dimensional (3D) data from instruments and facilities like integral field units and radio interferometers, visualization techniques such as volume rendering offer means to quickly explore spectral cubes as a whole. As most 3D visualization techniques have been developed in fields of research like medical imaging and fluid dynamics, many transfer functions are not optimal for astronomical data. We demonstrate how transfer functions and graphics shaders can be exploited to provide new astronomy-specific explorative colouring methods. We present 12 shaders, including four novel transfer functions specifically designed to produce intuitive and informative 3D visualizations of spectral cube data. We compare their utility to classic colour mapping. The remaining shaders highlight how common computation like filtering, smoothing and line ratio algorithms can be integrated as part of the graphics pipeline. We discuss how this can be achieved by utilizing the parallelism of modern GPUs along with a shading language, letting astronomers apply these new techniques at interactive frame rates. All shaders investigated in this work are included in the open source software shwirl (Vohl 2017).

Digital Signal Processing Techniques for the GIFTS SM EDU

NASA Technical Reports Server (NTRS)

Tian, Jialin; Reisse, Robert A.; Gazarik, Michael J.

2007-01-01

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Sensor Module (SM) Engineering Demonstration Unit (EDU) is a high resolution spectral imager designed to measure infrared (IR) radiance using a Fourier transform spectrometer (FTS). The GIFTS instrument employs three Focal Plane Arrays (FPAs), which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands. The raw interferogram measurements are radiometrically and spectrally calibrated to produce radiance spectra, which are further processed to obtain atmospheric profiles via retrieval algorithms. This paper describes several digital signal processing (DSP) techniques involved in the development of the calibration model. In the first stage, the measured raw interferograms must undergo a series of processing steps that include filtering, decimation, and detector nonlinearity correction. The digital filtering is achieved by employing a linear-phase even-length FIR complex filter that is designed based on the optimum equiripple criteria. Next, the detector nonlinearity effect is compensated for using a set of pre-determined detector response characteristics. In the next stage, a phase correction algorithm is applied to the decimated interferograms. This is accomplished by first estimating the phase function from the spectral phase response of the windowed interferogram, and then correcting the entire interferogram based on the estimated phase function. In the calibration stage, we first compute the spectral responsivity based on the previous results and the ideal Planck blackbody spectra at the given temperatures, from which, the calibrated ambient blackbody (ABB), hot blackbody (HBB), and scene spectra can be obtained. In the post-calibration stage, we estimate the Noise Equivalent Spectral Radiance (NESR) from the calibrated ABB and HBB spectra. The NESR is generally considered as a measure of the instrument noise performance, and can be estimated as the standard deviation of calibrated radiance spectra from multiple scans. To obtain an estimate of the FPA performance, we developed an efficient method of generating pixel performance assessments. In addition, a random pixel selection scheme is developed based on the pixel performance evaluation. This would allow us to perform the calibration procedures on a random pixel population that is a good statistical representation of the entire FPA. The design and implementation of each individual component will be discussed in details.

MURI: Adaptive Waveform Design for Full Spectral Dominance

DTIC Science & Technology

2011-03-11

a three- dimensional urban tracking model, based on the nonlinear measurement model (that uses the urban multipath geometry with different types of ... the time evolution of the scattering function with a high dimensional dynamic system; a multiple particle filter technique is used to sequentially...integration of space -time coding with a fixed set of beams. It complements the

Improving the detection of cocoa bean fermentation-related changes using image fusion

NASA Astrophysics Data System (ADS)

Ochoa, Daniel; Criollo, Ronald; Liao, Wenzhi; Cevallos-Cevallos, Juan; Castro, Rodrigo; Bayona, Oswaldo

2017-05-01

Complex chemical processes occur in during cocoa bean fermentation. To select well-fermented beans, experts take a sample of beans, cut them in half and visually check its color. Often farmers mix high and low quality beans therefore, chocolate properties are difficult to control. In this paper, we explore how close-range hyper- spectral (HS) data can be used to characterize the fermentation process of two types of cocoa beans (CCN51 and National). Our aim is to find spectral differences to allow bean classification. The main issue is to extract reliable spectral data as openings resulting from the loss of water during fermentation, can cover up to 40% of the bean surface. We exploit HS pan-sharpening techniques to increase the spatial resolution of HS images and filter out uneven surface regions. In particular, the guided filter PCA approach which has proved suitable to use high-resolution RGB data as guide image. Our preliminary results show that this pre-processing step improves the separability of classes corresponding to each fermentation stage compared to using the average spectrum of the bean surface.

Spectral resampling based on user-defined inter-band correlation filter: C3 and C4 grass species classification

NASA Astrophysics Data System (ADS)

Adjorlolo, Clement; Mutanga, Onisimo; Cho, Moses A.; Ismail, Riyad

2013-04-01

In this paper, a user-defined inter-band correlation filter function was used to resample hyperspectral data and thereby mitigate the problem of multicollinearity in classification analysis. The proposed resampling technique convolves the spectral dependence information between a chosen band-centre and its shorter and longer wavelength neighbours. Weighting threshold of inter-band correlation (WTC, Pearson's r) was calculated, whereby r = 1 at the band-centre. Various WTC (r = 0.99, r = 0.95 and r = 0.90) were assessed, and bands with coefficients beyond a chosen threshold were assigned r = 0. The resultant data were used in the random forest analysis to classify in situ C3 and C4 grass canopy reflectance. The respective WTC datasets yielded improved classification accuracies (kappa = 0.82, 0.79 and 0.76) with less correlated wavebands when compared to resampled Hyperion bands (kappa = 0.76). Overall, the results obtained from this study suggested that resampling of hyperspectral data should account for the spectral dependence information to improve overall classification accuracy as well as reducing the problem of multicollinearity.

Design and fabrication of cascaded dichromate gelatin holographic filters for spectrum-splitting PV systems

NASA Astrophysics Data System (ADS)

Wu, Yuechen; Chrysler, Benjamin; Kostuk, Raymond K.

2018-01-01

The technique of designing, optimizing, and fabricating broadband volume transmission holograms using dichromate gelatin (DCG) is summarized for solar spectrum-splitting applications. The spectrum-splitting photovoltaic (PV) system uses a series of single-bandgap PV cells that have different spectral conversion efficiency properties to more fully utilize the solar spectrum. In such a system, one or more high-performance optical filters are usually required to split the solar spectrum and efficiently send them to the corresponding PV cells. An ideal spectral filter should have a rectangular shape with sharp transition wavelengths. A methodology of designing and modeling a transmission DCG hologram using coupled wave analysis for different PV bandgap combinations is described. To achieve a broad diffraction bandwidth and sharp cutoff wavelength, a cascaded structure of multiple thick holograms is described. A search algorithm is then developed to optimize both single- and two-layer cascaded holographic spectrum-splitting elements for the best bandgap combinations of two- and three-junction spectrum-splitting photovoltaic (SSPV) systems illuminated under the AM1.5 solar spectrum. The power conversion efficiencies of the optimized systems are found to be 42.56% and 48.41%, respectively, using the detailed balance method, and show an improvement compared with a tandem multijunction system. A fabrication method for cascaded DCG holographic filters is also described and used to prototype the optimized filter for the three-junction SSPV system.

Multispectral and geomorphic studies of processed Voyager 2 images of Europa

NASA Technical Reports Server (NTRS)

Meier, T. A.

1984-01-01

High resolution images of Europa taken by the Voyager 2 spacecraft were used to study a portion of Europa's dark lineations and the major white line feature Agenor Linea. Initial image processing of images 1195J2-001 (violet filter), 1198J2-001 (blue filter), 1201J2-001 (orange filter), and 1204J2-001 (ultraviolet filter) was performed at the U.S.G.S. Branch of Astrogeology in Flagstaff, Arizona. Processing was completed through the stages of image registration and color ratio image construction. Pixel printouts were used in a new technique of linear feature profiling to compensate for image misregistration through the mapping of features on the printouts. In all, 193 dark lineation segments were mapped and profiled. The more accurate multispectral data derived by this method was plotted using a new application of the ternary diagram, with orange, blue, and violet relative spectral reflectances serving as end members. Statistical techniques were then applied to the ternary diagram plots. The image products generated at LPI were used mainly to cross-check and verify the results of the ternary diagram analysis.

Computer simulations and models for the performance characteristics of spectrally equivalent X-ray beams in medical diagnostic radiology

PubMed Central

Okunade, Akintunde A.

2007-01-01

In order to achieve uniformity in radiological imaging, it is recommended that the concept of equivalence in shape (quality) and size (quantity) of clinical Xray beams should be used for carrying out the comparative evaluation of image and patient dose. When used under the same irradiation geometry, X-ray beams that are strictly or relatively equivalent in terms of shape and size will produce identical or relatively identical image quality and patient dose. Simple mathematical models and software program EQSPECT.FOR were developed for the comparative evaluation of the performance characteristics in terms of contrast (C), contrast to noise ratio (CNR) and figure-of-merit (FOM = CNR2/DOSE) for spectrally equivalent beams transmitted through filter materials referred to as conventional and k-edged. At the same value of operating potential (kVp), results show that spectrally equivalent beam transmitted through conventional filter with higher atomic number (Z-value) in comparison with that transmitted through conventional filter with lower Z-value resulted in the same value of C and FOM. However, in comparison with the spectrally equivalent beam transmitted through filter of lower Z-value, the beam through filter of higher Z-value produced higher value of CNR and DOSE at equal tube loading (mAs) and kVp. Under the condition of equivalence of spectrum, at scaled (or reduced) tube loading and same kVp, filter materials of higher Z-value can produce the same values of C, CNR, DOSE and FOM as filter materials of lower Z-value. Unlike the case of comparison of spectrally equivalent beam transmitted through one conventional filter and that through another conventional filter, it is not possible to derive simple mathematical formulations for the relative performance of spectrally equivalent beam transmitted through a given conventional filter material and that through kedge filter material. PMID:21224928

Continuously tunable optical notch filter and band-pass filter systems that cover the visible to near-infrared spectral ranges.

PubMed

Jeong, Mi-Yun; Mang, Jin Yeob

2018-03-10

Spatially continuous tunable optical notch and band-pass filter systems that cover the visible (VIS) and near-infrared (NIR) spectral ranges from ∼460  nm to ∼1,000  nm are realized by combining left- and right-handed circular cholesteric liquid crystal (CLC) wedge cells with continuous pitch gradient. The notch filter system is polarization independent in all of the spectral ranges. The band-pass filter system, when the left- and right-handed CLCs are arranged in a row, is polarization independent, while when they are arranged at right angles, they are polarization dependent; furthermore, the full-width at half-maximum of the band-pass filter can be changed reversibly from the original bandwidth of 36 nm to 16 nm. Depending on the CLC materials, this strategy could be applied to the UV, VIS, and IR spectral ranges. Due to the high performance in the broad spectral range, cost-effective facile fabrication process, simple mechanical control, and small size, it is expected that our optical tunable filter strategies could become one of the key parts of laser-based Raman spectroscopy, fluorescence, life science devices, optical communication systems, astronomical telescopes, and so forth.

Method for optimizing output in ultrashort-pulse multipass laser amplifiers with selective use of a spectral filter

DOEpatents

Backus, Sterling J [Erie, CO; Kapteyn, Henry C [Boulder, CO

2007-07-10

A method for optimizing multipass laser amplifier output utilizes a spectral filter in early passes but not in later passes. The pulses shift position slightly for each pass through the amplifier, and the filter is placed such that early passes intersect the filter while later passes bypass it. The filter position may be adjust offline in order to adjust the number of passes in each category. The filter may be optimized for use in a cryogenic amplifier.

Characterization of a compact 6-band multifunctional camera based on patterned spectral filters in the focal plane

NASA Astrophysics Data System (ADS)

Torkildsen, H. E.; Hovland, H.; Opsahl, T.; Haavardsholm, T. V.; Nicolas, S.; Skauli, T.

2014-06-01

In some applications of multi- or hyperspectral imaging, it is important to have a compact sensor. The most compact spectral imaging sensors are based on spectral filtering in the focal plane. For hyperspectral imaging, it has been proposed to use a "linearly variable" bandpass filter in the focal plane, combined with scanning of the field of view. As the image of a given object in the scene moves across the field of view, it is observed through parts of the filter with varying center wavelength, and a complete spectrum can be assembled. However if the radiance received from the object varies with viewing angle, or with time, then the reconstructed spectrum will be distorted. We describe a camera design where this hyperspectral functionality is traded for multispectral imaging with better spectral integrity. Spectral distortion is minimized by using a patterned filter with 6 bands arranged close together, so that a scene object is seen by each spectral band in rapid succession and with minimal change in viewing angle. The set of 6 bands is repeated 4 times so that the spectral data can be checked for internal consistency. Still the total extent of the filter in the scan direction is small. Therefore the remainder of the image sensor can be used for conventional imaging with potential for using motion tracking and 3D reconstruction to support the spectral imaging function. We show detailed characterization of the point spread function of the camera, demonstrating the importance of such characterization as a basis for image reconstruction. A simplified image reconstruction based on feature-based image coregistration is shown to yield reasonable results. Elimination of spectral artifacts due to scene motion is demonstrated.

Dense grid sibling frames with linear phase filters

NASA Astrophysics Data System (ADS)

Abdelnour, Farras

2013-09-01

We introduce new 5-band dyadic sibling frames with dense time-frequency grid. Given a lowpass filter satisfying certain conditions, the remaining filters are obtained using spectral factorization. The analysis and synthesis filterbanks share the same lowpass and bandpass filters but have different and oversampled highpass filters. This leads to wavelets approximating shift-invariance. The filters are FIR, have linear phase, and the resulting wavelets have vanishing moments. The filters are designed using spectral factorization method. The proposed method leads to smooth limit functions with higher approximation order, and computationally stable filterbanks.

Reconstructing Spectral Scenes Using Statistical Estimation to Enhance Space Situational Awareness

DTIC Science & Technology

2006-12-01

simultane- ously spatially and spectrally deblur the images collected from ASIS. The algorithms are based on proven estimation theories and do not...collected with any system using a filtering technology known as Electronic Tunable Filters (ETFs). Previous methods to deblur spectral images collected...spectrally deblurring then the previously investigated methods. This algorithm expands on a method used for increasing the spectral resolution in gamma-ray

SearchLight: a freely available web-based quantitative spectral analysis tool (Conference Presentation)

NASA Astrophysics Data System (ADS)

Prabhat, Prashant; Peet, Michael; Erdogan, Turan

2016-03-01

In order to design a fluorescence experiment, typically the spectra of a fluorophore and of a filter set are overlaid on a single graph and the spectral overlap is evaluated intuitively. However, in a typical fluorescence imaging system the fluorophores and optical filters are not the only wavelength dependent variables - even the excitation light sources have been changing. For example, LED Light Engines may have a significantly different spectral response compared to the traditional metal-halide lamps. Therefore, for a more accurate assessment of fluorophore-to-filter-set compatibility, all sources of spectral variation should be taken into account simultaneously. Additionally, intuitive or qualitative evaluation of many spectra does not necessarily provide a realistic assessment of the system performance. "SearchLight" is a freely available web-based spectral plotting and analysis tool that can be used to address the need for accurate, quantitative spectral evaluation of fluorescence measurement systems. This tool is available at: http://searchlight.semrock.com/. Based on a detailed mathematical framework [1], SearchLight calculates signal, noise, and signal-to-noise ratio for multiple combinations of fluorophores, filter sets, light sources and detectors. SearchLight allows for qualitative and quantitative evaluation of the compatibility of filter sets with fluorophores, analysis of bleed-through, identification of optimized spectral edge locations for a set of filters under specific experimental conditions, and guidance regarding labeling protocols in multiplexing imaging assays. Entire SearchLight sessions can be shared with colleagues and collaborators and saved for future reference. [1] Anderson, N., Prabhat, P. and Erdogan, T., Spectral Modeling in Fluorescence Microscopy, http://www.semrock.com (2010).

Hemispherical-field-of-view, nonimaging narrow-band spectral filter

NASA Technical Reports Server (NTRS)

Miles, R. B.; Webb, S. G.; Griffith, E. L.

1981-01-01

Two compound parabolic concentrators are used to create a 180-deg-field-of-view spectral filter. The collection optics are reflective and are designed to collimate the light through a multilayer interference filter and then to refocus it onto an optical detector. Assuming unit reflectance and no loss through the optical filter, this device operates at the thermodynamic collection limit.

Hemispherical-field-of-view, nonimaging narrow-band spectral filter.

PubMed

Miles, R B; Webb, S G; Griffith, E L

1981-12-01

Two compound parabolic concentrators are used to create a 180 degrees -field-of-view spectral filter. The collection optics are reflective and are designed to collimate the light through a multilayer interference filter and then to refocus it onto an optical detector. Assuming unit reflectance and no loss through the optical filter, this device operates at the thermodynamic collection limit.

The development of a tunable, single-frequency ultraviolet laser source for UV filtered Rayleigh scattering

NASA Technical Reports Server (NTRS)

Finkelstein, N.; Gambogi, J.; Lempert, Walter R.; Miles, Richard B.; Rines, G. A.; Finch, A.; Schwarz, R. A.

1995-01-01

We present the development of a flexible, high power, narrow line width, tunable ultraviolet source for diagnostic application. By frequency tripling the output of a pulsed titanium-sapphire laser, we achieve broadly tunable (227-360 nm) ultraviolet light with high quality spatial and spectral resolution. We also present the characterization of a mercury vapor cell which provides a narrow band, sharp edge absorption filter at 253.7 nm. These two components form the basis for the extension of the Filtered Rayleigh Scattering technique into the ultraviolet. The UV-FRS system is comprised of four pieces: a single frequency, cw tunable Ti:Sapphire seeding source; a high-powered pulsed Ti:Sapphire oscillator; a third harmonic generator system; and an atomic mercury vapor filter. In this paper we discuss the development and characterization of each of these elements.

[Study on the Spectral Characteristics of the Narrow-Band Filter in SHS].

PubMed

Luo, Hai-yan; Shi, Hai-liang; Li, Zhi-wei; Li, Shuang; Xiong, Wei; Hong, Jin

2015-04-01

The spectral response of spatial heterodyne spectroscopy (SHS) is determined by the spectrum property of narrow-band filter. As discussed in previous studies, the symmetric heterodyned interferogram of high frequency waves modulated by SHS and lack of sample lead to spectral confusion, which is associated with the true and ghost spectra. Because of the deviation from theoretical index of narrow-band filter in the process of coating, the boarded spectral response and middle wave shift are presented, and conditions in the theoretical Littrow wavelength made the effective wavelength range of SHS reduced. According to the measured curve of filter, a new wavenumber of zero spatial frequency can be reset by tunable laser, and it is easy for SHS to improve the spectral aliasing distortion. The results show that it is utilized to the maximum extent of the effective bandwidth by adjusting the grating angle of rotation to change the Littrow wavelength of the basic frequency, and the spectral region increased to 14.9 nm from original 12.9 nm.

Simulator spectral characterization using balloon calibrated solar cells with narrow band pass filters

NASA Technical Reports Server (NTRS)

Goodelle, G. S.; Brooks, G. R.; Seaman, C. H.

1981-01-01

The development and implementation of an instrument for spectral measurement of solar simulators for testing solar cell characteristics is reported. The device was constructed for detecting changes in solar simulator behavior and for comparing simulator spectral irradiance to solar AM0 output. It consists of a standard solar cell equipped with a band pass filter narrow enough so that, when flown on a balloon to sufficient altitude along with sufficient numbers of cells, each equipped with filters of different bandpass ratings, the entire spectral response of the standard cell can be determined. Measured short circuit currents from the balloon flights thus produce cell devices which, when exposed to solar simulator light, have a current which does or does not respond as observed under actual AM0 conditions. Improvements of the filtered cells in terms of finer bandpass filter tuning and measurement of temperature coefficients are indicated.

Handling of uncertainty due to interference fringe in FT-NIR transmittance spectroscopy - Performance comparison of interference elimination techniques using glucose-water system

NASA Astrophysics Data System (ADS)

Beganović, Anel; Beć, Krzysztof B.; Henn, Raphael; Huck, Christian W.

2018-05-01

The applicability of two elimination techniques for interferences occurring in measurements with cells of short pathlength using Fourier transform near-infrared (FT-NIR) spectroscopy was evaluated. Due to the growing interest in the field of vibrational spectroscopy in aqueous biological fluids (e.g. glucose in blood), aqueous solutions of D-(+)-glucose were prepared and split into a calibration set and an independent validation set. All samples were measured with two FT-NIR spectrometers at various spectral resolutions. Moving average smoothing (MAS) and fast Fourier transform filter (FFT filter) were applied to the interference affected FT-NIR spectra in order to eliminate the interference pattern. After data pre-treatment, partial least squares regression (PLSR) models using different NIR regions were constructed using untreated (interference affected) spectra and spectra treated with MAS and FFT filter. The prediction of the independent validation set revealed information about the performance of the utilized interference elimination techniques, as well as the different NIR regions. The results showed that the combination band of water at approx. 5200 cm-1 is of great importance since its performance was superior to the one of the so-called first overtone of water at approx. 6800 cm-1. Furthermore, this work demonstrated that MAS and FFT filter are fast and easy-to-use techniques for the elimination of interference fringes in FT-NIR transmittance spectroscopy.

Improving and Assessing Planet Sensitivity of the GPI Exoplanet Survey with a Forward Model Matched Filter

NASA Astrophysics Data System (ADS)

Ruffio, Jean-Baptiste; Macintosh, Bruce; Wang, Jason J.; Pueyo, Laurent; Nielsen, Eric L.; De Rosa, Robert J.; Czekala, Ian; Marley, Mark S.; Arriaga, Pauline; Bailey, Vanessa P.; Barman, Travis; Bulger, Joanna; Chilcote, Jeffrey; Cotten, Tara; Doyon, Rene; Duchêne, Gaspard; Fitzgerald, Michael P.; Follette, Katherine B.; Gerard, Benjamin L.; Goodsell, Stephen J.; Graham, James R.; Greenbaum, Alexandra Z.; Hibon, Pascale; Hung, Li-Wei; Ingraham, Patrick; Kalas, Paul; Konopacky, Quinn; Larkin, James E.; Maire, Jérôme; Marchis, Franck; Marois, Christian; Metchev, Stanimir; Millar-Blanchaer, Maxwell A.; Morzinski, Katie M.; Oppenheimer, Rebecca; Palmer, David; Patience, Jennifer; Perrin, Marshall; Poyneer, Lisa; Rajan, Abhijith; Rameau, Julien; Rantakyrö, Fredrik T.; Savransky, Dmitry; Schneider, Adam C.; Sivaramakrishnan, Anand; Song, Inseok; Soummer, Remi; Thomas, Sandrine; Wallace, J. Kent; Ward-Duong, Kimberly; Wiktorowicz, Sloane; Wolff, Schuyler

2017-06-01

We present a new matched-filter algorithm for direct detection of point sources in the immediate vicinity of bright stars. The stellar point-spread function (PSF) is first subtracted using a Karhunen-Loéve image processing (KLIP) algorithm with angular and spectral differential imaging (ADI and SDI). The KLIP-induced distortion of the astrophysical signal is included in the matched-filter template by computing a forward model of the PSF at every position in the image. To optimize the performance of the algorithm, we conduct extensive planet injection and recovery tests and tune the exoplanet spectra template and KLIP reduction aggressiveness to maximize the signal-to-noise ratio (S/N) of the recovered planets. We show that only two spectral templates are necessary to recover any young Jovian exoplanets with minimal S/N loss. We also developed a complete pipeline for the automated detection of point-source candidates, the calculation of receiver operating characteristics (ROC), contrast curves based on false positives, and completeness contours. We process in a uniform manner more than 330 data sets from the Gemini Planet Imager Exoplanet Survey and assess GPI typical sensitivity as a function of the star and the hypothetical companion spectral type. This work allows for the first time a comparison of different detection algorithms at a survey scale accounting for both planet completeness and false-positive rate. We show that the new forward model matched filter allows the detection of 50% fainter objects than a conventional cross-correlation technique with a Gaussian PSF template for the same false-positive rate.

Improvement on Gabor order tracking and objective comparison with Vold Kalman filtering order tracking

NASA Astrophysics Data System (ADS)

Pan, Min-Chun; Liao, Shiu-Wei; Chiu, Chun-Chin

2007-02-01

The waveform-reconstruction schemes of order tracking (OT) such as the Gabor and the Vold-Kalman filtering (VKF) techniques can extract specific order and/or spectral components in addition to characterizing the processed signal in rpm-frequency domain. The study first improves the Gabor OT (GOT) technique to handle the order-crossing problem, and then objectively compares the features of the improved GOT scheme and the angular-displacement VKF OT technique. It is numerically observed the improved method performs less accurately than the VKF_OT scheme at the crossing occurrences, but without end effect in the reconstructed waveform. As OT is not exact science, it may well be that the decrease in computation time can justify the reduced accuracy. The characterisation and discrimination of riding noise with crossing orders emitted by an electrical scooter are conducted as an example of the application.

Modeling of a tilted pressure-tuned field-widened Michelson interferometer for application in high spectral resolution lidar

NASA Astrophysics Data System (ADS)

Liu, Dong; Hostetler, Chris; Miller, Ian; Cook, Anthony; Hair, Jonathan

2011-10-01

High spectral resolution lidars (HSRLs) designed for aerosol and cloud remote sensing are increasingly being deployed on aircraft and called for on future space-based missions. The HSRL technique relies on spectral discrimination of the atmospheric backscatter signals to enable independent, unambiguous retrieval of aerosol extinction and backscatter. A compact, monolithic field-widened Michelson interferometer is being developed as the spectral discrimination filter for an HSRL system at NASA Langley Research Center. The Michelson interferometer consists of a cubic beam splitter, a solid glass arm, and an air arm. The spacer that connects the air arm mirror to the main part of the interferometer is designed to optimize thermal compensation such that the frequency of maximum interference can be tuned with great precision to the transmitted laser wavelength. In this paper, a comprehensive radiometric model for the field-widened Michelson interferometeric spectral filter is presented. The model incorporates the angular distribution and finite cross sectional area of the light source, reflectance of all surfaces, loss of absorption, and lack of parallelism between the airarm and solid arm, etc. The model can be used to assess the performance of the interferometer and thus it is a useful tool to evaluate performance budgets and to set optical specifications for new designs of the same basic interferometer type.

Experimental Demonstration of Adaptive Infrared Multispectral Imaging using Plasmonic Filter Array

PubMed Central

Jang, Woo-Yong; Ku, Zahyun; Jeon, Jiyeon; Kim, Jun Oh; Lee, Sang Jun; Park, James; Noyola, Michael J.; Urbas, Augustine

2016-01-01

In our previous theoretical study, we performed target detection using a plasmonic sensor array incorporating the data-processing technique termed “algorithmic spectrometry”. We achieved the reconstruction of a target spectrum by extracting intensity at multiple wavelengths with high resolution from the image data obtained from the plasmonic array. The ultimate goal is to develop a full-scale focal plane array with a plasmonic opto-coupler in order to move towards the next generation of versatile infrared cameras. To this end, and as an intermediate step, this paper reports the experimental demonstration of adaptive multispectral imagery using fabricated plasmonic spectral filter arrays and proposed target detection scenarios. Each plasmonic filter was designed using periodic circular holes perforated through a gold layer, and an enhanced target detection strategy was proposed to refine the original spectrometry concept for spatial and spectral computation of the data measured from the plasmonic array. Both the spectrum of blackbody radiation and a metal ring object at multiple wavelengths were successfully reconstructed using the weighted superposition of plasmonic output images as specified in the proposed detection strategy. In addition, plasmonic filter arrays were theoretically tested on a target at extremely high temperature as a challenging scenario for the detection scheme. PMID:27721506

Hyperspectral Infrared Imaging of Flames Using a Spectrally Scanning Fabry-Perot Filter

NASA Technical Reports Server (NTRS)

Rawlins, W. T.; Lawrence, W. G.; Marinelli, W. J.; Allen, M. G.; Piltch, N. (Technical Monitor)

2001-01-01

The temperatures and compositions of gases in and around flames can be diagnosed using infrared emission spectroscopy to observe molecular band shapes and intensities. We have combined this approach with a low-order scanning Fabry-Perot filter and an infrared camera to obtain spectrally scanned infrared emission images of a laboratory flame and exhaust plume from 3.7 to 5.0 micrometers, at a spectral resolution of 0.043 micrometers, and a spatial resolution of 1 mm. The scanning filter or AIRIS (Adaptive Infrared Imaging Spectroradiometer) is a Fabry-Perot etalon operating in low order (mirror spacing = wavelength) such that the central spot, containing a monochromatic image of the scene, is viewed by the detector array. The detection system is a 128 x 128 liquid-nitrogen-cooled InSb focal plane array. The field of view is controlled by a 50 mm focal length multielement lens and an V4.8 aperture, resulting in an image 6.4 x 6.4 cm in extent at the flame and a depth of field of approximately 4 cm. Hyperspectral images above a laboratory CH4/air flame show primarily the strong emission from CO2 at 4.3 micrometers, and weaker emissions from CO and H2O. We discuss techniques to analyze the spectra, and plans to use this instrument in microgravity flame spread experiments.

Study of the spectral bandwidth of a double-pass acousto-optic system [Invited].

PubMed

Champagne, Justine; Kastelik, Jean-Claude; Dupont, Samuel; Gazalet, Joseph

2018-04-01

Acousto-optic tunable filters are known as efficient instruments for spectral and spatial filtering of light. In this paper, we analyze the bandwidth dependence of a double-pass filter. The interaction geometry chosen allows the simultaneous diffraction of the ordinary and the extraordinary optical modes by a single ultrasonic frequency. We present the main parameters of a custom device (design, optical range, driving frequency) and experimental results concerning the angular deviation of the beams including the effect of optical birefringence. The spectral resolution and the side lobes' significance are discussed. Spectral bandwidth of such a system is analyzed.

AGARD Flight Test Techniques Series. Volume 14. Introduction to Flight Test Engineering (Introduction a la Technique d’essais en vol)

DTIC Science & Technology

1995-09-01

path and aircraft attitude and other flight or aircraft parameters • Calculations in the frequency domain ( Fast Fourier Transform) • Data analysis...Signal filtering Image processing of video and radar data Parameter identification Statistical analysis Power spectral density Fast Fourier Transform...airspeeds both fast and slow, altitude, load factor both above and below 1g, centers of gravity (fore and aft), and with system/subsystem failures. Whether

DOE Office of Scientific and Technical Information (OSTI.GOV)

Son, Young-Sun; Yoon, Wang-Jung

The purpose of this study is to map pyprophyllite distribution at surface of the Nohwa deposit, Korea by using Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) data. For this, combined Spectral Angle Mapper (SAM), and Matched Filtering (MF) technique based on mathematical algorithm was applied. The regional distribution of high-grade and low-grade pyrophyllite in the Nohwa deposit area could be differentiated by this method. The results of this study show that ASTER data analysis using combination of SAM and MF techniques will assist in exploration of pyrophyllite at the exposed surface.

On the power spectral density of quadrature modulated signals. [satellite communication

NASA Technical Reports Server (NTRS)

Yan, T. Y.

1981-01-01

The conventional (no-offset) quadriphase modulation technique suffers from the fact that hardlimiting will restore the frequency sidelobes removed by proper filtering. Thus, offset keyed quadriphase modulation techniques are often proposed for satellite communication with bandpass hardlimiting. A unified theory is developed which is capable of describing the power spectral density before and after the hardlimiting process. Using the in-phase and the quadrature phase channel with arbitrary pulse shaping, analytical results are established for generalized quadriphase modulation. In particular MSK, OPSK or the recently introduced overlapped raised cosine keying all fall into this general category. It is shown that for a linear communication channel, the power spectral density of the modulated signal remains unchanged regardless of the offset delay. Furthermore, if the in phase and the quadrature phase channel have identical pulse shapes without offset, the spectrum after bandpass hardlimiting will be identical to that of the conventional QPSK modulation. Numerical examples are given for various modulation techniques. A case of different pulse shapes in the in phase and the quadrature phase channel is also considered.

A flat spectral Faraday filter for sodium lidar.

PubMed

Yang, Yong; Cheng, Xuewu; Li, Faquan; Hu, Xiong; Lin, Xin; Gong, Shunsheng

2011-04-01

We report a flat spectral Faraday anomalous dispersion optical filter (FS-FADOF) for sodium lidar. The physical and technical considerations for obtaining a FS-FADOF with a 3.5 GHz flat spectral transmission function are presented. It was found that the effective transmission of this filter was much higher (>94%) and more uniform than that of the ultranarrowband FADOF, and therefore were less sensitive to laser-frequency drift. Thus, the FS-FADOF can improve lidar efficiency and precision.

High Spectral Resolution Lidar: System Calibration

NASA Astrophysics Data System (ADS)

Vivek Vivekanandan, J.; Morley, Bruce; Spuler, Scott; Eloranta, Edwin

2015-04-01

One of the unique features of the high spectral resolution lidar (HSRL) is simultaneous measurements of backscatter and extinction of atmosphere. It separates molecular scattering from aerosol and cloud particle backscatter based on their Doppler spectrum width. Scattering from aerosol and cloud particle are referred as Mie scattering. Molecular or Rayleigh scattering is used as a reference for estimating aerosol extinction and backscatter cross-section. Absolute accuracy of the backscattered signals and their separation into Rayleigh and Mie scattering depends on spectral purity of the transmitted signals, accurate measurement of transmit power, and precise performance of filters. Internal calibration is used to characterize optical subsystems Descriptions of high spectral resolution lidar system and its measurement technique can be found in Eloronta (2005) and Hair et al.(2001). Four photon counting detectors are used to measure the backscatter from the combined Rayleigh and molecular scattering (high and low gain), molecular scattering and cross-polarized signal. All of the detectors are sensitive to crosstalk or leakage through the optical filters used to separate the received signals and special data files are used to remove these effects as much as possible. Received signals are normalized with respect to the combined channel response to Mie and Rayleigh scattering. The laser transmit frequency is continually monitored and tuned to the 1109 Iodine absorption line. Aerosol backscatter cross-section is measured by referencing the aerosol return signal to the molecular return signal. Extinction measurements are calculated based on the differences between the expected (theoretical) and actual change in the molecular return. In this paper an overview of calibration of the HSRL is presented. References: Eloranta, E. W., High Spectral Resolution Lidar in Lidar: Range-Resolved Optical Remote Sensing of the Atmosphere, Klaus Weitkamp editor, Springer Series in Optical Sciences, Springer-Verlag, New York, 2005. Hair, JW; Caldwell, LM; Krueger, D. A.Krueger, and C.Y. She 2001: High-spectral-resolution lidar with iodine-vapor filters: measurement of atmospheric-state and aerosol profiles. Appl. Optics, 40, 5280-5294.

Ultranarrow bandwidth spectral filtering for long-range free-space quantum key distribution at daytime.

PubMed

Höckel, David; Koch, Lars; Martin, Eugen; Benson, Oliver

2009-10-15

We describe a Fabry-Perot-based spectral filter for free-space quantum key distribution (QKD). A multipass etalon filter was built, and its performance was studied. The whole filter setup was carefully optimized to add less than 2 dB attenuation to a signal beam but block stray light by 21 dB. Simulations show that such a filter might be sufficient to allow QKD satellite downlinks during daytime with the current technology.

Recovery of Spectrally Overlapping QPSK Signals Using a Nonlinear Optoelectronic Filter

DTIC Science & Technology

2017-03-19

Spectrally Overlapping QPSK Signals Using a Nonlinear Optoelectronic Filter William Loh, Siva Yegnanarayanan, Kenneth E. Kolodziej, and Paul...recovery of a weak QPSK signal buried 35-dB beneath an interfering QPSK signal having an overlapping spectrum. This nonlinear optoelectronic filter ...from increased detection sensitivity. Here, we demonstrate an optoelectronic filter that enables the detection of a desired signal hidden beneath a

On the Origin of the Flare Emission in IRIS ’ SJI 2832 Filter:Balmer Continuum or Spectral Lines?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleint, Lucia; Krucker, Säm; Heinzel, Petr

Continuum (“white-light,” WL) emission dominates the energetics of flares. Filter-based observations, such as the IRIS SJI 2832 filter, show WL-like brightenings during flares, but it is unclear whether the emission arises from real continuum emission or enhanced spectral lines, possibly turning into emission. The difficulty in filter-based observations, contrary to spectral observations, is to determine which processes contribute to the observed brightening during flares. Here we determine the contribution of the Balmer continuum and the spectral line emission to IRIS ’ SJI 2832 emission by analyzing the appropriate passband in simultaneous IRIS NUV spectra. We find that spectral line emissionmore » can contribute up to 100% to the observed slitjaw images (SJI) emission, that the relative contributions usually temporally vary, and that the highest SJI enhancements that are observed are most likely because of the Balmer continuum. We conclude that care should be taken when calling SJI 2832 a continuum filter during flares, because the influence of the lines on the emission can be significant.« less

Modems for emerging digital cellular-mobile radio system

NASA Technical Reports Server (NTRS)

Feher, Kamilo

1991-01-01

Digital modem techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed. In particular, theoretical performance, experimental results, principles of operation, and various architectures of pi/4-QPSK (pi/4-shifted coherent or differential QPSK) modems for second-generation US digital cellular radio system applications are presented. The spectral/power efficiency and performance of the pi/4-QPSK modems (American and Japanese digital cellular emerging standards) are studied and briefly compared to GMSK (Gaussian minimum-shift keying) modems (proposed for European DECT and GSM cellular standards). Improved filtering strategies and digital pilot-aided (digital channel sounding) techniques are also considered for pi/4-QPSK and other digital modems. These techniques could significantly improve the performance of digital cellular and other digital land mobile and satellite mobile radio systems. More spectrally efficient modem trends for future cellular/mobile (land mobile) and satellite communication systems applications are also highlighted.

Rapid spontaneous Raman light sheet microscopy using cw-lasers and tunable filters

PubMed Central

Rocha-Mendoza, Israel; Licea-Rodriguez, Jacob; Marro, Mónica; Olarte, Omar E.; Plata-Sanchez, Marcos; Loza-Alvarez, Pablo

2015-01-01

We perform rapid spontaneous Raman 2D imaging in light-sheet microscopy using continuous wave lasers and interferometric tunable filters. By angularly tuning the filter, the cut-on/off edge transitions are scanned along the excited Stokes wavelengths. This allows obtaining cumulative intensity profiles of the scanned vibrational bands, which are recorded on image stacks; resembling a spectral version of the knife-edge technique to measure intensity profiles. A further differentiation of the stack retrieves the Raman spectra at each pixel of the image which inherits the 3D resolution of the host light sheet system. We demonstrate this technique using solvent solutions and composites of polystyrene beads and lipid droplets immersed in agar and by imaging the C–H (2800-3100cm−1) region in a C. elegans worm. The image acquisition time results in 4 orders of magnitude faster than confocal point scanning Raman systems, allowing the possibility of performing fast spontaneous Raman·3D-imaging on biological samples. PMID:26417514

Comparison of existing digital image analysis systems for the analysis of Thematic Mapper data

NASA Technical Reports Server (NTRS)

Likens, W. C.; Wrigley, R. C.

1984-01-01

Most existing image analysis systems were designed with the Landsat Multi-Spectral Scanner in mind, leaving open the question of whether or not these systems could adequately process Thematic Mapper data. In this report, both hardware and software systems have been evaluated for compatibility with TM data. Lack of spectral analysis capability was not found to be a problem, though techniques for spatial filtering and texture varied. Computer processing speed and data storage of currently existing mini-computer based systems may be less than adequate. Upgrading to more powerful hardware may be required for many TM applications.

Large tunable optical delays via self-phase modulation and dispersion

NASA Astrophysics Data System (ADS)

Okawachi, Yoshitomo; Sharping, Jay E.; Xu, Chris; Gaeta, Alexander L.

2006-12-01

We demonstrate all-optically tunable delays in optical fiber via a dispersive stage and two stages of nonlinear spectral broadening and filtering. With this scheme, we achieve continuously tunable delays of 3.5- ps pulses and advancements over a total range of more than 1200 pulsewidths. Our technique is applicable to a wide range of pulse durations and delays.

Pulse shaping in mode-locked fiber lasers by in-cavity spectral filter.

PubMed

Boscolo, Sonia; Finot, Christophe; Karakuzu, Huseyin; Petropoulos, Periklis

2014-02-01

We numerically show the possibility of pulse shaping in a passively mode-locked fiber laser by inclusion of a spectral filter into the laser cavity. Depending on the amplitude transfer function of the filter, we are able to achieve various regimes of advanced temporal waveform generation, including ones featuring bright and dark parabolic-, flat-top-, triangular- and saw-tooth-profiled pulses. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for controlling the dynamics of mode-locked fiber lasers.

A System for Compressive Spectral and Polarization Imaging at Short Wave Infrared (SWIR) Wavelengths

DTIC Science & Technology

2017-10-18

2016). H. Rueda, H. Arguello and G. R. Arce, “DMD-based implementation of patterned optical filter arrays for compressive spectral imaging”, Journal...3)  a  set  of   optical   filters  which   allow   to   discriminate   spectrally   the   coded   and   sheared...system   that   includes   objective   lens,   spatial   light   modulator,   dispersive   element,   optical   filters

Radiometric Measurements by the MIDAS III System at Key West. Volume I. Cloud Backgrounds.

DTIC Science & Technology

1979-09-01

13 13.3 System Relative Spectral Response - Filter No. 2 5(4.4-4.77 pim ) ............................................. 14 3.4 System Relative Spectral...Response - Filter No. 5 (3.8-4.2 pim ) .............................................. 15 3.5 System Relative Spectral Response - Filter No. 6 (3.4-4.3...5 dat a was recorded dirtxet l ott t he recordinig osc ml logrtt1 Witereis tilt- 8-13 data was recorded on t tiet I ape, recorders i xst itd laxter p

Carrier Estimation Using Classic Spectral Estimation Techniques for the Proposed Demand Assignment Multiple Access Service

NASA Technical Reports Server (NTRS)

Scaife, Bradley James

1999-01-01

In any satellite communication, the Doppler shift associated with the satellite's position and velocity must be calculated in order to determine the carrier frequency. If the satellite state vector is unknown then some estimate must be formed of the Doppler-shifted carrier frequency. One elementary technique is to examine the signal spectrum and base the estimate on the dominant spectral component. If, however, the carrier is spread (as in most satellite communications) this technique may fail unless the chip rate-to-data rate ratio (processing gain) associated with the carrier is small. In this case, there may be enough spectral energy to allow peak detection against a noise background. In this thesis, we present a method to estimate the frequency (without knowledge of the Doppler shift) of a spread-spectrum carrier assuming a small processing gain and binary-phase shift keying (BPSK) modulation. Our method relies on an averaged discrete Fourier transform along with peak detection on spectral match filtered data. We provide theory and simulation results indicating the accuracy of this method. In addition, we will describe an all-digital hardware design based around a Motorola DSP56303 and high-speed A/D which implements this technique in real-time. The hardware design is to be used in NMSU's implementation of NASA's demand assignment, multiple access (DAMA) service.

A narrow linewidth tunable single longitudinal mode Ga-EDF fiber laser

NASA Astrophysics Data System (ADS)

Mohamed Halip, N. H.; Abu Bakar, M. H.; Latif, A. A.; Muhd-Yasin, S. Z.; Zulkifli, M. I.; Mat-Sharif, K. A.; Omar, N. Y. M.; Mansoor, A.; Abdul-Rashid, H. A.; Mahdi, M. A.

2018-05-01

A tunable ring cavity single longitudinal mode (SLM) fiber laser incorporating Gallium-Erbium co-doped fiber (Ga-EDF) gain medium and several mode filtration techniques is demonstrated. With Ga-EDF, high emission power was accorded in short fiber length, allowing shorter overall cavity length and wider free spectral range. Tunable bandpass filter, sub-ring structure, and cascaded dissimilar fiber taper were utilized to filter multi-longitudinal modes. Each of the filter mechanism was tested individually within the laser cavity to assess its performance. Once the performance of each filter was obtained, all of them were deployed into the laser system. Ultimately, the 1561.47 nm SLM laser achieved a narrow linewidth laser, optical signal-to-noise ratio, and power fluctuation of 1.19 kHz, 61.52 dB and 0.16 dB, respectively. This work validates the feasibility of Ga-EDF to attain a stable SLM output in simple laser configuration.

Measurements of global UV irradiance at Terranova Bay, Antactica, by a home made narrow band filter radiometer

NASA Astrophysics Data System (ADS)

Salvatore, Scaglione; di Sarcina, Ilaria; Flori, Daniele; Menchini, Francesca

2010-05-01

Filter radiometers measure the solar radiation in several channels (typically 4 to 7) with a bandwith from 2 to 10 nm. They require less maintenance than the spectroradiometer and they are able to work in hostile environment as for instance the polar regions. The spectral resolution depends on the width at half maximum (FWHM) of the filters and is generally lower than the spectroradiometer resolution (0.5 nm). Other than the robustness of this instruments, the main advantage of the filter radiometers is the high frequency with which all wavelengths can be measured, making this class of instrument well suited for investigating short term irradiance variation. In this work is presented the results of UV irradiance measurements performed by a very narrow band (FWHM less than 1 nm) filter radiometer at Antarctica Italia Base, Mario Zucchelli Station, Terranova Bay, lat. 74° 41.6084' south and lon. 164° 05.9224' est. All-dielectric Fabry-Perot filters were manufactured in the laboratories of the Optical Coating Group, ENEA, by the ion beam assistance physical vapor deposition technique. Nine filters select nine different wavelengths in the UV spectral range from 296.5 nm to 377 nm with about 1 minute of measurement period, i.e. each wavelength is measured about 1250 times per day. At the moment the radiometer are permanently located near MZS and the data are daily downloaded in ENEA, Rome, by a dedicated satellite channel. During the Antarctica winter the radiometer will be in standby mode, in this season MZS is closed, and it will be start to measure again in the Antarctica spring.

Ross filter development for absolute measurement of Al line radiation on MST

NASA Astrophysics Data System (ADS)

Lauersdorf, N.; Reusch, L. M.; den Hartog, D. J.; Goetz, J. A.; Franz, P.; Vanmeter, P.

2017-10-01

The MST has a two-color soft x-ray tomography (SXT) diagnostic that, using the double-filter technique, measures electron temperature (Te) from the slope of the soft x-ray (SXR) continuum. Because MST has an aluminum plasma-facing surface, bright Al line radiation occurs in the SXR spectrum. In past application of the double-filter technique, these lines have been filtered out using thick Be filters ( 400 μm and 800 μm), restricting the measurement temperature range to >=1 keV due to the signal strength having a positive correlation with Te. Another way to deal with the line radiation is to explicitly include it into the SXR spectrum analysis from which Te is derived. A Ross filter set has been designed to measure this line radiation, and will enable the absolute intensities of the aluminum lines to be quantified and incorporated into the analysis. The Ross filter will be used to measure Al+11 and Al+12 lines, occurring between 1.59 and 2.04 keV. By using multiple detectors with filters made of varying element concentrations, we create spectral bins in which the dominant transmission is the line radiation. Absolute measurement of Al line intensities will enable use of thinner filters in the SXT diagnostic and accurate measurement of Te < 1 keV. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences program under Award Numbers DE-FC02-05ER54814 and DE-SC0015474.

A Fast Smoothing Algorithm for Post-Processing of Surface Reflectance Spectra Retrieved from Airborne Imaging Spectrometer Data

PubMed Central

Gao, Bo-Cai; Liu, Ming

2013-01-01

Surface reflectance spectra retrieved from remotely sensed hyperspectral imaging data using radiative transfer models often contain residual atmospheric absorption and scattering effects. The reflectance spectra may also contain minor artifacts due to errors in radiometric and spectral calibrations. We have developed a fast smoothing technique for post-processing of retrieved surface reflectance spectra. In the present spectral smoothing technique, model-derived reflectance spectra are first fit using moving filters derived with a cubic spline smoothing algorithm. A common gain curve, which contains minor artifacts in the model-derived reflectance spectra, is then derived. This gain curve is finally applied to all of the reflectance spectra in a scene to obtain the spectrally smoothed surface reflectance spectra. Results from analysis of hyperspectral imaging data collected with the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data are given. Comparisons between the smoothed spectra and those derived with the empirical line method are also presented. PMID:24129022

Nonlinear multilayers as optical limiters

NASA Astrophysics Data System (ADS)

Turner-Valle, Jennifer Anne

1998-10-01

In this work we present a non-iterative technique for computing the steady-state optical properties of nonlinear multilayers and we examine nonlinear multilayer designs for optical limiters. Optical limiters are filters with intensity-dependent transmission designed to curtail the transmission of incident light above a threshold irradiance value in order to protect optical sensors from damage due to intense light. Thin film multilayers composed of nonlinear materials exhibiting an intensity-dependent refractive index are used as the basis for optical limiter designs in order to enhance the nonlinear filter response by magnifying the electric field in the nonlinear materials through interference effects. The nonlinear multilayer designs considered in this work are based on linear optical interference filter designs which are selected for their spectral properties and electric field distributions. Quarter wave stacks and cavity filters are examined for their suitability as sensor protectors and their manufacturability. The underlying non-iterative technique used to calculate the optical response of these filters derives from recognizing that the multi-valued calculation of output irradiance as a function of incident irradiance may be turned into a single-valued calculation of incident irradiance as a function of output irradiance. Finally, the benefits and drawbacks of using nonlinear multilayer for optical limiting are examined and future research directions are proposed.

Principal Component Analysis in the Spectral Analysis of the Dynamic Laser Speckle Patterns

NASA Astrophysics Data System (ADS)

Ribeiro, K. M.; Braga, R. A., Jr.; Horgan, G. W.; Ferreira, D. D.; Safadi, T.

2014-02-01

Dynamic laser speckle is a phenomenon that interprets an optical patterns formed by illuminating a surface under changes with coherent light. Therefore, the dynamic change of the speckle patterns caused by biological material is known as biospeckle. Usually, these patterns of optical interference evolving in time are analyzed by graphical or numerical methods, and the analysis in frequency domain has also been an option, however involving large computational requirements which demands new approaches to filter the images in time. Principal component analysis (PCA) works with the statistical decorrelation of data and it can be used as a data filtering. In this context, the present work evaluated the PCA technique to filter in time the data from the biospeckle images aiming the reduction of time computer consuming and improving the robustness of the filtering. It was used 64 images of biospeckle in time observed in a maize seed. The images were arranged in a data matrix and statistically uncorrelated by PCA technique, and the reconstructed signals were analyzed using the routine graphical and numerical methods to analyze the biospeckle. Results showed the potential of the PCA tool in filtering the dynamic laser speckle data, with the definition of markers of principal components related to the biological phenomena and with the advantage of fast computational processing.

Mapping Surface Water DOC in the Northern Gulf of Mexico Using CDOM Absorption Coefficients and Remote Sensing Imagery

NASA Astrophysics Data System (ADS)

Kelly, B.; Chelsky, A.; Bulygina, E.; Roberts, B. J.

2017-12-01

Remote sensing techniques have become valuable tools to researchers, providing the capability to measure and visualize important parameters without the need for time or resource intensive sampling trips. Relationships between dissolved organic carbon (DOC), colored dissolved organic matter (CDOM) and spectral data have been used to remotely sense DOC concentrations in riverine systems, however, this approach has not been applied to the northern Gulf of Mexico (GoM) and needs to be tested to determine how accurate these relationships are in riverine-dominated shelf systems. In April, July, and October 2017 we sampled surface water from 80+ sites over an area of 100,000 km2 along the Louisiana-Texas shelf in the northern GoM. DOC concentrations were measured on filtered water samples using a Shimadzu TOC-VCSH analyzer using standard techniques. Additionally, DOC concentrations were estimated from CDOM absorption coefficients of filtered water samples on a UV-Vis spectrophotometer using a modification of the methods of Fichot and Benner (2011). These values were regressed against Landsat visible band spectral data for those same locations to establish a relationship between the spectral data, CDOM absorption coefficients. This allowed us to spatially map CDOM absorption coefficients in the Gulf of Mexico using the Landsat spectral data in GIS. We then used a multiple linear regressions model to derive DOC concentrations from the CDOM absorption coefficients and applied those to our map. This study provides an evaluation of the viability of scaling up CDOM absorption coefficient and remote-sensing derived estimates of DOC concentrations to the scale of the LA-TX shelf ecosystem.

Thermal control design of the Lightning Mapper Sensor narrow-band spectral filter

NASA Technical Reports Server (NTRS)

Flannery, Martin R.; Potter, John; Raab, Jeff R.; Manlief, Scott K.

1992-01-01

The performance of the Lightning Mapper Sensor is dependent on the temperature shifts of its narrowband spectral filter. To perform over a 10 degree FOV with an 0.8 nm bandwidth, the filter must be 15 cm in diameter and mounted externally to the telescope optics. The filter thermal control required a filter design optimized for minimum bandpass shift with temperature, a thermal analysis of substrate materials for maximum temperature uniformity, and a thermal radiation analysis to determine the parameter sensitivity of the radiation shield for the filter, the filter thermal recovery time after occultation, and heater power to maintain filter performance in the earth-staring geosynchronous environment.

Metric for evaluation of filter efficiency in spectral cameras.

PubMed

Nahavandi, Alireza Mahmoudi; Tehran, Mohammad Amani

2016-11-10

Although metric functions that show the performance of a colorimetric imaging device have been investigated, a metric for performance analysis of a set of filters in wideband filter-based spectral cameras has rarely been studied. Based on a generalization of Vora's Measure of Goodness (MOG) and the spanning theorem, a single function metric that estimates the effectiveness of a filter set is introduced. The improved metric, named MMOG, varies between one, for a perfect, and zero, for the worst possible set of filters. Results showed that MMOG exhibits a trend that is more similar to the mean square of spectral reflectance reconstruction errors than does Vora's MOG index, and it is robust to noise in the imaging system. MMOG as a single metric could be exploited for further analysis of manufacturing errors.

Design of a Monocular Multi-Spectral Skin Detection, Melanin Estimation, and False-Alarm Suppression System

DTIC Science & Technology

2010-03-01

3-21 3.22. Measured transmission of the Semrock FF01-1060/13-25 NIR bandpass filter at normal incidence. . . . . . . . . . . . . . . . 3-22...3.23. Measured transmission of the Semrock NIR01-1570/3-25 NIR bandpass filter at normal incidence. . . . . . . . . . . . . . . . 3-23 3.24. Measured...shows the configuration without additional filtering while the blue adds the Semrock bandpass filter. . . . 3-30 3.34. (Left) Spectral transmittance

A blue optical filter for narrow-band imaging in endoscopic capsules

NASA Astrophysics Data System (ADS)

Silva, M. F.; Ghaderi, M.; Goncalves, L. M.; de Graaf, G.; Wolffenbuttel, R. F.; Correia, J. H.

2014-05-01

This paper presents the design, simulation, fabrication, and characterization of a thin-film Fabry-Perot resonator composed of titanium dioxide (TiO2) and silicon dioxide (SiO2) thin-films. The optical filter is developed to be integrated with a light emitting diode (LED) for enabling narrow-band imaging (NBI) in endoscopy. The NBI is a high resolution imaging technique that uses spectrally centered blue light (415 nm) and green light (540 nm) to illuminate the target tissue. The light at 415 nm enhances the imaging of superficial veins due to their hemoglobin absorption, while the light at 540 nm penetrates deeper into the mucosa, thus enhances the sub-epithelial vessels imaging. Typically the endoscopes and endoscopic capsules use white light for acquiring images of the gastrointestinal (GI) tract. However, implementing the NBI technique in endoscopic capsules enhances their capabilities for the clinical applications. A commercially available blue LED with a maximum peak intensity at 404 nm and Full Width Half Maximum (FWHM) of 20 nm is integrated with a narrow band blue filter as the NBI light source. The thin film simulations show a maximum spectral transmittance of 36 %, that is centered at 415 nm with FWHM of 13 nm for combined the blue LED and a Fabry Perot resonator system. A custom made deposition scheme was developed for the fabrication of the blue optical filter by RF sputtering. RF powered reactive sputtering at 200 W with the gas flows of argon and oxygen that are controlled for a 5:1 ratio gives the optimum optical conditions for TiO2 thin films. For SiO2 thin films, a non-reactive RF sputtering at 150 W with argon gas flow at 15 sccm results in the best optical performance. The TiO2 and SiO2 thin films were fully characterized by an ellipsometer in the wavelength range between 250 nm to 1600 nm. Finally, the optical performance of the blue optical filter is measured and presented.

Rapid perfusion quantification using Welch-Satterthwaite approximation and analytical spectral filtering

NASA Astrophysics Data System (ADS)

Krishnan, Karthik; Reddy, Kasireddy V.; Ajani, Bhavya; Yalavarthy, Phaneendra K.

2017-02-01

CT and MR perfusion weighted imaging (PWI) enable quantification of perfusion parameters in stroke studies. These parameters are calculated from the residual impulse response function (IRF) based on a physiological model for tissue perfusion. The standard approach for estimating the IRF is deconvolution using oscillatory-limited singular value decomposition (oSVD) or Frequency Domain Deconvolution (FDD). FDD is widely recognized as the fastest approach currently available for deconvolution of CT Perfusion/MR PWI. In this work, three faster methods are proposed. The first is a direct (model based) crude approximation to the final perfusion quantities (Blood flow, Blood volume, Mean Transit Time and Delay) using the Welch-Satterthwaite approximation for gamma fitted concentration time curves (CTC). The second method is a fast accurate deconvolution method, we call Analytical Fourier Filtering (AFF). The third is another fast accurate deconvolution technique using Showalter's method, we call Analytical Showalter's Spectral Filtering (ASSF). Through systematic evaluation on phantom and clinical data, the proposed methods are shown to be computationally more than twice as fast as FDD. The two deconvolution based methods, AFF and ASSF, are also shown to be quantitatively accurate compared to FDD and oSVD.

Observation of IPL spectra using detector system incorporating broadband optical filters

NASA Astrophysics Data System (ADS)

Clarkson, D. McG.

2007-07-01

Systems using intense pulsed light are being increasingly used in therapy applications where issues related to safety of devices and also of performance are becoming more urgent to address. Mechanisms to address this include a suitable standards framework and also the development and application of appropriate measurement techniques. An approach of using conventional bandpass optical filters and silicon photodetectors has been implemented using an analogue USB data capture interfaces linked to a laptop PC. An initial system with 8 concurrent channels has been upgraded to a separate system sampling up to 16 analogue channels. Sampling takes place at the maximum hardware conversion rate of the USB device. Observations have been made of a range of intense pulsed light systems, including a Lumenis One unit with a range of discrete filters. The system has been of value in determining the basic parameters of output pulse profile and spectral composition. This has in turn been related to aspects of standards development for both device manufacture and allocation of appropriate safety eyewear. Initial assessments of a subset of intense pulsed light systems indicate significant complexities in terms, for example, of variation in spectral content as a function of device output setting.

Robust Speech Enhancement Using Two-Stage Filtered Minima Controlled Recursive Averaging

NASA Astrophysics Data System (ADS)

Ghourchian, Negar; Selouani, Sid-Ahmed; O'Shaughnessy, Douglas

In this paper we propose an algorithm for estimating noise in highly non-stationary noisy environments, which is a challenging problem in speech enhancement. This method is based on minima-controlled recursive averaging (MCRA) whereby an accurate, robust and efficient noise power spectrum estimation is demonstrated. We propose a two-stage technique to prevent the appearance of musical noise after enhancement. This algorithm filters the noisy speech to achieve a robust signal with minimum distortion in the first stage. Subsequently, it estimates the residual noise using MCRA and removes it with spectral subtraction. The proposed Filtered MCRA (FMCRA) performance is evaluated using objective tests on the Aurora database under various noisy environments. These measures indicate the higher output SNR and lower output residual noise and distortion.

Guided-mode resonant filters and reflectors: Principles, design, and fabrication

NASA Astrophysics Data System (ADS)

Niraula, Manoj

In this dissertation, we overview the operational principles of these resonant periodic structures, discuss the methods of their design and fabrication, and propose and demonstrate novel functionalities for spatial and spectral filtering, and unpolarized wideband reflection. Fashioned with materially sparse gratings, these optical devices are easy to fabricate and integration friendly compared to their traditional multi-layer counterparts making their research and development critical for practical applications. We study, theoretically, modal properties and parametric dependence of resonant periodic bandpass filters operating in the mid- and near-infrared spectral domains. We investigate three different device architectures consisting of single, double, and triple layers based on all-transparent dielectric and semiconductor thin films. We present three modal coupling configurations forming complex mixtures of two or three distinct leaky modes coupling at different evanescent diffraction orders. Our modal analysis demonstrates key attributes of subwavelength periodic thin-film structures in multiple-modal blending to achieve desired transmission spectra. We provide the first experimental demonstration of high-efficiency and narrow-linewidth resonant bandpass filter applying a single patterned silicon layer on a quartz substrate. Its performance corresponds to bandpass filters requiring 15 traditional Si/SiO2 thin-film layers. The feasibility of sparse narrowband, high-efficiency bandpass filters with extremely wide, flat, and low sidebands is thereby demonstrated. The proposed technology is integration-friendly and opens doors for further development in various disciplines and spectral regions where thin-film solutions are traditionally applied. We demonstrate concurrent spatial and spectral filtering as a new outstanding attribute of resonant periodic devices. This functionality is enabled by a unique, near-complete, reflection state that is discrete in both angular and spectral domains and realized with carefully crafted nanogratings operating in the non-subwavelength regime. We study the pathway and inter-modal interference effects inducing this intriguing reflection state. In a proof-of-concept experiment, we obtain angular and spectral bandwidths of 4 mrad and 1 nm, respectively. This filter concept can be used for focus-free spectral and spatial filtering in compact holographic and interferometric optical instruments. We report unpolarized broadband reflectors enabled by a serial arrangement of a pair of polarized subwavelength gratings. Optimized with inverse numerical methods, our elemental gratings consist of a partially etched crystalline-silicon film on a quartz substrate. The resulting reflectors exhibit extremely wide spectral reflection bands in one polarization. By arranging two such reflectors sequentially with orthogonal periodicities, there results an unpolarized spectral band possessing bandwidth exceeding those of the individual polarized bands. In the experiments reported herein, we achieve zero-order reflectance exceeding 97% under unpolarized light incidence over a 500-nm-wide wavelength band in the near-infrared domain. Moreover, the resonant unpolarized broadband accommodates an ultra-high-reflection band spanning 85 nm and exceeding 99.9% in efficiency. The elemental polarization-sensitive reflectors based on one-dimensional resonant gratings have simple design, robust performance, and are straightforward to fabricate. Hence, this technology is a promising alternative to traditional multilayer thin-film reflectors especially at longer wavelengths of light where multilayer deposition may be infeasible or impractical. We demonstrate an interesting attribute of resonant bandpass filters which is high angular stability for fully conical light incidence. Fashioning an experimental bandpass filter with a subwavelength silicon grating on a quartz substrate, we show that fully conical incidence provides an angular full-width at half-maximum linewidth of 9.5° compared to a linewidth of 0.1° for classical incidence. Slow angular variation of the central wavelength with full conical incidence arises via a corresponding slow angular variation of the resonant second diffraction orders driving the pertinent leaky modes. Moreover, full conical incidence maintains a profile with a single passband as opposed to the formation of two passbands characteristic of resonant subwavelength gratings under classical incidence. Our experimental results demonstrate excellent stability in angle, spectral profile, linewidth, and efficiency. Finally, we propose a novel method of design and fabrication of photonic lattices that incorporates the best of both worlds: a polarized resonant grating can be designed and converted to its unpolarized lattice equivalent using the same design parameters to obtain a similar performance. We show this in context of a single-layer polarized bandpass filter operating at 1550 nm with 100% transmission efficiency. An unpolarized square-hole lattice with identical parameters operates as a bandpass filter at 1560 nm with 70% transmission efficiency. Moreover, conventional laser interference lithography technique for mask patterning is limited to circular-hole photoresist lattice. We propose a method to lay down a metal hard-mask by lifting-off patterned photoresist in two steps for a square-hole lattice. Our comprehensive study provides new principles for easy design and fabrication of square-hole photonic lattices for unpolarized guided-mode resonance applications. (Abstract shortened by ProQuest.).

Dynamics of short-pulse generation via spectral filtering from intensely excited gain-switched 1.55-μm distributed-feedback laser diodes.

PubMed

Chen, Shaoqiang; Yoshita, Masahiro; Sato, Aya; Ito, Takashi; Akiyama, Hidefumi; Yokoyama, Hiroyuki

2013-05-06

Picosecond-pulse-generation dynamics and pulse-width limiting factors via spectral filtering from intensely pulse-excited gain-switched 1.55-μm distributed-feedback laser diodes were studied. The spectral and temporal characteristics of the spectrally filtered pulses indicated that the short-wavelength component stems from the initial part of the gain-switched main pulse and has a nearly linear down-chirp of 5.2 ps/nm, whereas long-wavelength components include chirped pulse-lasing components and steady-state-lasing components. Rate-equation calculations with a model of linear change in refractive index with carrier density explained the major features of the experimental results. The analysis of the expected pulse widths with optimum spectral widths was also consistent with the experimental data.

Improving and Assessing Planet Sensitivity of the GPI Exoplanet Survey with a Forward Model Matched Filter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruffio, Jean-Baptiste; Macintosh, Bruce; Nielsen, Eric L.

We present a new matched-filter algorithm for direct detection of point sources in the immediate vicinity of bright stars. The stellar point-spread function (PSF) is first subtracted using a Karhunen-Loéve image processing (KLIP) algorithm with angular and spectral differential imaging (ADI and SDI). The KLIP-induced distortion of the astrophysical signal is included in the matched-filter template by computing a forward model of the PSF at every position in the image. To optimize the performance of the algorithm, we conduct extensive planet injection and recovery tests and tune the exoplanet spectra template and KLIP reduction aggressiveness to maximize the signal-to-noise ratiomore » (S/N) of the recovered planets. We show that only two spectral templates are necessary to recover any young Jovian exoplanets with minimal S/N loss. We also developed a complete pipeline for the automated detection of point-source candidates, the calculation of receiver operating characteristics (ROC), contrast curves based on false positives, and completeness contours. We process in a uniform manner more than 330 data sets from the Gemini Planet Imager Exoplanet Survey and assess GPI typical sensitivity as a function of the star and the hypothetical companion spectral type. This work allows for the first time a comparison of different detection algorithms at a survey scale accounting for both planet completeness and false-positive rate. We show that the new forward model matched filter allows the detection of 50% fainter objects than a conventional cross-correlation technique with a Gaussian PSF template for the same false-positive rate.« less

A rigorous analysis of digital pre-emphasis and DAC resolution for interleaved DAC Nyquist-WDM signal generation in high-speed coherent optical transmission systems

NASA Astrophysics Data System (ADS)

Weng, Yi; Wang, Junyi; He, Xuan; Pan, Zhongqi

2018-02-01

The Nyquist spectral shaping techniques facilitate a promising solution to enhance spectral efficiency (SE) and further reduce the cost-per-bit in high-speed wavelength-division multiplexing (WDM) transmission systems. Hypothetically, any Nyquist WDM signals with arbitrary shapes can be generated by the use of the digital signal processing (DSP) based electrical filters (E-filter). Nonetheless, in actual 100G/ 200G coherent systems, the performance as well as DSP complexity are increasingly restricted by cost and power consumption. Henceforward it is indispensable to optimize DSP to accomplish the preferred performance at the least complexity. In this paper, we systematically investigated the minimum requirements and challenges of Nyquist WDM signal generation, particularly for higher-order modulation formats, including 16 quadrature amplitude modulation (QAM) or 64QAM. A variety of interrelated parameters, such as channel spacing and roll-off factor, have been evaluated to optimize the requirements of the digital-to-analog converter (DAC) resolution and transmitter E-filter bandwidth. The impact of spectral pre-emphasis has been predominantly enhanced via the proposed interleaved DAC architecture by at least 4%, and hence reducing the required optical signal to noise ratio (OSNR) at a bit error rate (BER) of 10-3 by over 0.45 dB at a channel spacing of 1.05 symbol rate and an optimized roll-off factor of 0.1. Furthermore, the requirements of sampling rate for different types of super-Gaussian E-filters are discussed for 64QAM Nyquist WDM transmission systems. Finally, the impact of the non-50% duty cycle error between sub-DACs upon the quality of the generated signals for the interleaved DAC structure has been analyzed.

Enhancement of color saturation and color gamut enabled by a dual-band color filter exhibiting an adjustable spectral response.

PubMed

Shrestha, Vivek Raj; Park, Chul-Soon; Lee, Sang-Shin

2014-02-10

The enhancement of color saturation and color gamut has been demonstrated, by taking advantage of a dual-band color filter based on a subwavelength rectangular metal-dielectric resonant grating, which exhibits an adjustable spectral response with respect to its relative transmittances at the two bands of green and red, thereby producing any color in between green and red, through the adjustment of incoming light polarization. Also, the prominent features of the spectral response of the filter, namely the bandwidth and resonant wavelength, can be readily adjusted by varying the dielectric layer thickness and the grating pitch, respectively. The dependence of chromaticity coordinates of the filter in the CIE (International Commission on Illumination) 1931 chromaticity diagram upon the parameters of the spectral response, including the center wavelength, spectral bandwidth and sideband level, has been rigorously examined, and their influence on the color gamut and the excitation purity, which is a colorimetric measure of saturation, has been analytically explored at the same time, in order to optimize the color performance of the filters. In particular, a device with wider spectral bandwidth was observed to efficiently extend the color gamut and enhance the color saturation, i.e. the excitation purity for a given sideband level. Two dual-band green-red filters, exhibiting different bandwidths of about 17 and 36 nm, were specifically designed and fabricated. As compared with the case with narrower bandwidth, the device with wider bandwidth was observed to provide both higher excitation purity leading to better color saturation and greater separation of the chromaticity coordinates for the filter output for different incident polarizations, which provides extended color gamut. The proposed device structure may permit the color tuning span to encompass all primary color bands, by adjusting the grating pitch.

High Dynamic Range Spectral Imaging Pipeline For Multispectral Filter Array Cameras.

PubMed

Lapray, Pierre-Jean; Thomas, Jean-Baptiste; Gouton, Pierre

2017-06-03

Spectral filter arrays imaging exhibits a strong similarity with color filter arrays. This permits us to embed this technology in practical vision systems with little adaptation of the existing solutions. In this communication, we define an imaging pipeline that permits high dynamic range (HDR)-spectral imaging, which is extended from color filter arrays. We propose an implementation of this pipeline on a prototype sensor and evaluate the quality of our implementation results on real data with objective metrics and visual examples. We demonstrate that we reduce noise, and, in particular we solve the problem of noise generated by the lack of energy balance. Data are provided to the community in an image database for further research.

Characterization of aerosol scattering and spectral absorption by unique methods: a polar/imaging nephelometer and spectral reflectance measurements of aerosol samples collected on filters

NASA Astrophysics Data System (ADS)

Dolgos, Gergely; Martins, J. Vanderlei; Remer, Lorraine A.; Correia, Alexandre L.; Tabacniks, Manfredo; Lima, Adriana R.

2010-02-01

Characterization of aerosol scattering and absorption properties is essential to accurate radiative transfer calculations in the atmosphere. Applications of this work include remote sensing of aerosols, corrections for aerosol distortions in satellite imagery of the surface, global climate models, and atmospheric beam propagation. Here we demonstrate successful instrument development at the Laboratory for Aerosols, Clouds and Optics at UMBC that better characterizes aerosol scattering phase matrix using an imaging polar nephelometer (LACO-I-Neph) and enables measurement of spectral aerosol absorption from 200 nm to 2500 nm. The LACO-I-Neph measures the scattering phase function from 1.5° to 178.5° scattering angle with sufficient sensitivity to match theoretical expectations of Rayleigh scattering of various gases. Previous measurements either lack a sufficiently wide range of measured scattering angles or their sensitivity is too low and therefore the required sample amount is prohibitively high for in situ measurements. The LACO-I-Neph also returns expected characterization of the linear polarization signal of Rayleigh scattering. Previous work demonstrated the ability of measuring spectral absorption of aerosol particles using a reflectance technique characterization of aerosol samples collected on Nuclepore filters. This first generation methodology yielded absorption measurements from 350 nm to 2500 nm. Here we demonstrate the possibility of extending this wavelength range into the deep UV, to 200 nm. This extended UV region holds much promise in identifying and characterizing aerosol types and species. The second generation, deep UV, procedure requires careful choice of filter substrates. Here the choice of substrates is explored and preliminary results are provided.

Cap integration in spectral gravity forward modelling: near- and far-zone gravity effects via Molodensky's truncation coefficients

NASA Astrophysics Data System (ADS)

Bucha, Blažej; Hirt, Christian; Kuhn, Michael

2018-04-01

Spectral gravity forward modelling is a technique that converts a band-limited topography into its implied gravitational field. This conversion implicitly relies on global integration of topographic masses. In this paper, a modification of the spectral technique is presented that provides gravity effects induced only by the masses located inside or outside a spherical cap centred at the evaluation point. This is achieved by altitude-dependent Molodensky's truncation coefficients, for which we provide infinite series expansions and recurrence relations with a fixed number of terms. Both representations are generalized for an arbitrary integer power of the topography and arbitrary radial derivative. Because of the altitude-dependency of the truncation coefficients, a straightforward synthesis of the near- and far-zone gravity effects at dense grids on irregular surfaces (e.g. the Earth's topography) is computationally extremely demanding. However, we show that this task can be efficiently performed using an analytical continuation based on the gradient approach, provided that formulae for radial derivatives of the truncation coefficients are available. To demonstrate the new cap-modified spectral technique, we forward model the Earth's degree-360 topography, obtaining near- and far-zone effects on gravity disturbances expanded up to degree 3600. The computation is carried out on the Earth's surface and the results are validated against an independent spatial-domain Newtonian integration (1 μGal RMS agreement). The new technique is expected to assist in mitigating the spectral filter problem of residual terrain modelling and in the efficient construction of full-scale global gravity maps of highest spatial resolution.

An Eulerian time filtering technique to study large-scale transient flow phenomena

NASA Astrophysics Data System (ADS)

Vanierschot, Maarten; Persoons, Tim; van den Bulck, Eric

2009-10-01

Unsteady fluctuating velocity fields can contain large-scale periodic motions with frequencies well separated from those of turbulence. Examples are the wake behind a cylinder or the processing vortex core in a swirling jet. These turbulent flow fields contain large-scale, low-frequency oscillations, which are obscured by turbulence, making it impossible to identify them. In this paper, we present an Eulerian time filtering (ETF) technique to extract the large-scale motions from unsteady statistical non-stationary velocity fields or flow fields with multiple phenomena that have sufficiently separated spectral content. The ETF method is based on non-causal time filtering of the velocity records in each point of the flow field. It is shown that the ETF technique gives good results, similar to the ones obtained by the phase-averaging method. In this paper, not only the influence of the temporal filter is checked, but also parameters such as the cut-off frequency and sampling frequency of the data are investigated. The technique is validated on a selected set of time-resolved stereoscopic particle image velocimetry measurements such as the initial region of an annular jet and the transition between flow patterns in an annular jet. The major advantage of the ETF method in the extraction of large scales is that it is computationally less expensive and it requires less measurement time compared to other extraction methods. Therefore, the technique is suitable in the startup phase of an experiment or in a measurement campaign where several experiments are needed such as parametric studies.

Fluorescent marker-based and marker-free discrimination between healthy and cancerous human tissues using hyper-spectral imaging

NASA Astrophysics Data System (ADS)

Arnold, Thomas; De Biasio, Martin; Leitner, Raimund

2015-06-01

Two problems are addressed in this paper (i) the fluorescent marker-based and the (ii) marker-free discrimination between healthy and cancerous human tissues. For both applications the performance of hyper-spectral methods are quantified. Fluorescent marker-based tissue classification uses a number of fluorescent markers to dye specific parts of a human cell. The challenge is that the emission spectra of the fluorescent dyes overlap considerably. They are, furthermore disturbed by the inherent auto-fluorescence of human tissue. This results in ambiguities and decreased image contrast causing difficulties for the treatment decision. The higher spectral resolution introduced by tunable-filter-based spectral imaging in combination with spectral unmixing techniques results in an improvement of the image contrast and therefore more reliable information for the physician to choose the treatment decision. Marker-free tissue classification is based solely on the subtle spectral features of human tissue without the use of artificial markers. The challenge in this case is that the spectral differences between healthy and cancerous tissues are subtle and embedded in intra- and inter-patient variations of these features. The contributions of this paper are (i) the evaluation of hyper-spectral imaging in combination with spectral unmixing techniques for fluorescence marker-based tissue classification, (ii) the evaluation of spectral imaging for marker-free intra surgery tissue classification. Within this paper, we consider real hyper-spectral fluorescence and endoscopy data sets to emphasize the practical capability of the proposed methods. It is shown that the combination of spectral imaging with multivariate statistical methods can improve the sensitivity and specificity of the detection and the staging of cancerous tissues compared to standard procedures.

Multiple-channel guided mode resonance Brewster filter with controllable spectral separation.

PubMed

Ma, Jianyong; Cao, Hongchao; Zhou, Changhe

2014-05-01

In this work, a single-layer, multiple-channel guided mode resonance (GMR) Brewster filter with controllable spectral separation is proposed using the plane waveguide method and rigorous coupled-wave analysis. Based on the normalized eigenvalue equation, the controllability of the spectral separation is analyzed when the fill ratio of the grating layer is changed while its effective index is identical to that of the substrate. The location and the separation between resonances can be specifically controlled by modifying the fill ratio of the grating layer. In contrast to the ordinary GMR filter, where the location of the resonances is material dependent, it is demonstrated that the spectral separation for the first and second resonances can be linearly controlled by altering the fill ratio of the grating layer. In addition, the maximal shift of the second resonance is up to 5% of the first resonant wavelength using the single-layer Brewster filter.

A Spectral Reconstruction Algorithm of Miniature Spectrometer Based on Sparse Optimization and Dictionary Learning.

PubMed

Zhang, Shang; Dong, Yuhan; Fu, Hongyan; Huang, Shao-Lun; Zhang, Lin

2018-02-22

The miniaturization of spectrometer can broaden the application area of spectrometry, which has huge academic and industrial value. Among various miniaturization approaches, filter-based miniaturization is a promising implementation by utilizing broadband filters with distinct transmission functions. Mathematically, filter-based spectral reconstruction can be modeled as solving a system of linear equations. In this paper, we propose an algorithm of spectral reconstruction based on sparse optimization and dictionary learning. To verify the feasibility of the reconstruction algorithm, we design and implement a simple prototype of a filter-based miniature spectrometer. The experimental results demonstrate that sparse optimization is well applicable to spectral reconstruction whether the spectra are directly sparse or not. As for the non-directly sparse spectra, their sparsity can be enhanced by dictionary learning. In conclusion, the proposed approach has a bright application prospect in fabricating a practical miniature spectrometer.

A Spectral Reconstruction Algorithm of Miniature Spectrometer Based on Sparse Optimization and Dictionary Learning

PubMed Central

Zhang, Shang; Fu, Hongyan; Huang, Shao-Lun; Zhang, Lin

2018-01-01

The miniaturization of spectrometer can broaden the application area of spectrometry, which has huge academic and industrial value. Among various miniaturization approaches, filter-based miniaturization is a promising implementation by utilizing broadband filters with distinct transmission functions. Mathematically, filter-based spectral reconstruction can be modeled as solving a system of linear equations. In this paper, we propose an algorithm of spectral reconstruction based on sparse optimization and dictionary learning. To verify the feasibility of the reconstruction algorithm, we design and implement a simple prototype of a filter-based miniature spectrometer. The experimental results demonstrate that sparse optimization is well applicable to spectral reconstruction whether the spectra are directly sparse or not. As for the non-directly sparse spectra, their sparsity can be enhanced by dictionary learning. In conclusion, the proposed approach has a bright application prospect in fabricating a practical miniature spectrometer. PMID:29470406

Optical filters for wavelength selection in fluorescence instrumentation.

PubMed

Erdogan, Turan

2011-04-01

Fluorescence imaging and analysis techniques have become ubiquitous in life science research, and they are poised to play an equally vital role in in vitro diagnostics (IVD) in the future. Optical filters are crucial for nearly all fluorescence microscopes and instruments, not only to provide the obvious function of spectral control, but also to ensure the highest possible detection sensitivity and imaging resolution. Filters make it possible for the sample to "see" light within only the absorption band, and the detector to "see" light within only the emission band. Without filters, the detector would not be able to distinguish the desired fluorescence from scattered excitation light and autofluorescence from the sample, substrate, and other optics in the system. Today the vast majority of fluorescence instruments, including the widely popular fluorescence microscope, use thin-film interference filters to control the spectra of the excitation and emission light. Hence, this unit emphasizes thin-film filters. After briefly introducing different types of thin-film filters and how they are made, the unit describes in detail different optical filter configurations in fluorescence instruments, including both single-color and multicolor imaging systems. Several key properties of thin-film filters, which can significantly affect optical system performance, are then described. In the final section, tunable optical filters are also addressed in a relative comparison.

Wavelength-Filter Based Spectral Calibrated Wave number - Linearization in 1.3 mm Spectral Domain Optical Coherence.

PubMed

Wijeisnghe, Ruchire Eranga Henry; Cho, Nam Hyun; Park, Kibeom; Shin, Yongseung; Kim, Jeehyun

2013-12-01

In this study, we demonstrate the enhanced spectral calibration method for 1.3 μm spectral-domain optical coherence tomography (SD-OCT). The calibration method using wavelength-filter simplifies the SD-OCT system, and also the axial resolution and the entire speed of the OCT system can be dramatically improved as well. An externally connected wavelength-filter is utilized to obtain the information of the wavenumber and the pixel position. During the calibration process the wavelength-filter is placed after a broadband source by connecting through an optical circulator. The filtered spectrum with a narrow line width of 0.5 nm is detected by using a line-scan camera. The method does not require a filter or a software recalibration algorithm for imaging as it simply resamples the OCT signal from the detector array without employing rescaling or interpolation methods. One of the main drawbacks of SD-OCT is the broadened point spread functions (PSFs) with increasing imaging depth can be compensated by increasing the wavenumber-linearization order. The sensitivity of our system was measured at 99.8 dB at an imaging depth of 2.1 mm compared with the uncompensated case.

Study of carbonate concretions using imaging spectroscopy in the Frontier Formation, Wyoming

NASA Astrophysics Data System (ADS)

de Linaje, Virginia Alonso; Khan, Shuhab D.; Bhattacharya, Janok

2018-04-01

Imaging spectroscopy is applied to study diagenetic processes of the Wall Creek Member of the Cretaceous Frontier Formation, Wyoming. Visible Near-Infrared and Shortwave-Infrared hyperspectral cameras were used to scan near vertical and well-exposed outcrop walls to analyze lateral and vertical geochemical variations. Reflectance spectra were analyzed and compared with high-resolution laboratory spectral and hyperspectral imaging data. Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) classification algorithms were applied to quantify facies and mineral abundances in the Frontier Formation. MTMF is the most effective and reliable technique when studying spectrally similar materials. Classification results show that calcite cement in concretions associated with the channel facies is homogeneously distributed, whereas the bar facies was shown to be interbedded with layers of non-calcite-cemented sandstone.

Efficient state initialization by a quantum spectral filtering algorithm

NASA Astrophysics Data System (ADS)

Fillion-Gourdeau, François; MacLean, Steve; Laflamme, Raymond

2017-04-01

An algorithm that initializes a quantum register to a state with a specified energy range is given, corresponding to a quantum implementation of the celebrated Feit-Fleck method. This is performed by introducing a nondeterministic quantum implementation of a standard spectral filtering procedure combined with an apodization technique, allowing for accurate state initialization. It is shown that the implementation requires only two ancilla qubits. A lower bound for the total probability of success of this algorithm is derived, showing that this scheme can be realized using a finite, relatively low number of trials. Assuming the time evolution can be performed efficiently and using a trial state polynomially close to the desired states, it is demonstrated that the number of operations required scales polynomially with the number of qubits. Tradeoffs between accuracy and performance are demonstrated in a simple example: the harmonic oscillator. This algorithm would be useful for the initialization phase of the simulation of quantum systems on digital quantum computers.

Infrared and visible image fusion with spectral graph wavelet transform.

PubMed

Yan, Xiang; Qin, Hanlin; Li, Jia; Zhou, Huixin; Zong, Jing-guo

2015-09-01

Infrared and visible image fusion technique is a popular topic in image analysis because it can integrate complementary information and obtain reliable and accurate description of scenes. Multiscale transform theory as a signal representation method is widely used in image fusion. In this paper, a novel infrared and visible image fusion method is proposed based on spectral graph wavelet transform (SGWT) and bilateral filter. The main novelty of this study is that SGWT is used for image fusion. On the one hand, source images are decomposed by SGWT in its transform domain. The proposed approach not only effectively preserves the details of different source images, but also excellently represents the irregular areas of the source images. On the other hand, a novel weighted average method based on bilateral filter is proposed to fuse low- and high-frequency subbands by taking advantage of spatial consistency of natural images. Experimental results demonstrate that the proposed method outperforms seven recently proposed image fusion methods in terms of both visual effect and objective evaluation metrics.

Polarization-correlation investigation of biotissue multifractal structure and diagnostics of its pathological change

NASA Astrophysics Data System (ADS)

Angelsky, Oleg V.; Pishak, Vasyl P.; Ushenko, Alexander G.; Burkovets, Dimitry N.; Pishak, Olga V.

2001-05-01

The paper presents the results of polarization-correlation investigation of multifractal collagen structure of physiologically normal and pathologically changed tissues of women's reproductive sphere and of skin. The technique of polarization selection of coherent biotissues' images followed by determination of their autocorrelation functions and spectral densities is suggested. The correlation- optical criteria of early diagnostics of pathological changes' appearance of myometry (forming of the germ of fibromyoma) and of skin (psoriasis) are determined. The present paper examines the possibilities of diagnostics of pathological changes of biotissues' morphological structure by means of determining the polarizationally filtered autocorrelation functions (ACF) and corresponding spectral densities of their coherent images.

Information-efficient spectral imaging sensor

DOEpatents

Sweatt, William C.; Gentry, Stephen M.; Boye, Clinton A.; Grotbeck, Carter L.; Stallard, Brian R.; Descour, Michael R.

2003-01-01

A programmable optical filter for use in multispectral and hyperspectral imaging. The filter splits the light collected by an optical telescope into two channels for each of the pixels in a row in a scanned image, one channel to handle the positive elements of a spectral basis filter and one for the negative elements of the spectral basis filter. Each channel for each pixel disperses its light into n spectral bins, with the light in each bin being attenuated in accordance with the value of the associated positive or negative element of the spectral basis vector. The spectral basis vector is constructed so that its positive elements emphasize the presence of a target and its negative elements emphasize the presence of the constituents of the background of the imaged scene. The attenuated light in the channels is re-imaged onto separate detectors for each pixel and then the signals from the detectors are combined to give an indication of the presence or not of the target in each pixel of the scanned scene. This system provides for a very efficient optical determination of the presence of the target, as opposed to the very data intensive data manipulations that are required in conventional hyperspectral imaging systems.

The effect of spectral filters on VEP and alpha-wave responses.

PubMed

Willeford, Kevin T; Fimreite, Vanessa; Ciuffreda, Kenneth J

2016-01-01

Spectral filters are used to treat light sensitivity in individuals with traumatic brain injury (TBI); however, the effect of these filters on normal visual function has not been elucidated. Thus, the current study aimed to determine the effect of spectral filters on objectively-measured visual-evoked potential (VEP) and alpha-wave responses in the visually-normal population. The full-field (15°H×17°V), pattern-reversal VEP (20' check size, mean luminance 52cd/m(2)) was administered to 20 visually-normal individuals. They were tested with four Intuitive-Colorimeter-derived, broad-band, spectral filters (i.e., gray/neutral density, blue, yellow, and red), which produced similar luminance values for the test stimulus. The VEP N75 and P100 latencies, and VEP amplitude, were recorded. Power spectrum analysis was used to derive the respective powers at each frequency, and peak frequency, for the selected 9-11Hz components of the alpha band. Both N75 and P100 latencies increased with the addition of each filter when compared to baseline. Additionally, each filter numerically reduced intra-session amplitude variability relative to baseline. There were no significant effects on either the mean VEP amplitude or alpha wave parameters. The Intuitive Colorimeter filters significantly increased both N75 and P100 latencies, an effect which is primarily attributable (∼75%) to luminance, and in some cases, specific spectral effects (e.g., blue and red). VEP amplitude and alpha power were not significantly affected. These findings provide an important reference to which either amplitude or power changes in light-sensitive, younger clinical groups can be compared. Copyright © 2015 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.

The effect of spectral filters on VEP and alpha-wave responses

PubMed Central

Willeford, Kevin T.; Fimreite, Vanessa; Ciuffreda, Kenneth J.

2015-01-01

Purpose Spectral filters are used to treat light sensitivity in individuals with traumatic brain injury (TBI); however, the effect of these filters on normal visual function has not been elucidated. Thus, the current study aimed to determine the effect of spectral filters on objectively-measured visual-evoked potential (VEP) and alpha-wave responses in the visually-normal population. Methods The full-field (15°H × 17°V), pattern-reversal VEP (20′ check size, mean luminance 52 cd/m2) was administered to 20 visually-normal individuals. They were tested with four Intuitive-Colorimeter-derived, broad-band, spectral filters (i.e., gray/neutral density, blue, yellow, and red), which produced similar luminance values for the test stimulus. The VEP N75 and P100 latencies, and VEP amplitude, were recorded. Power spectrum analysis was used to derive the respective powers at each frequency, and peak frequency, for the selected 9–11 Hz components of the alpha band. Results Both N75 and P100 latencies increased with the addition of each filter when compared to baseline. Additionally, each filter numerically reduced intra-session amplitude variability relative to baseline. There were no significant effects on either the mean VEP amplitude or alpha wave parameters. Conclusions The Intuitive Colorimeter filters significantly increased both N75 and P100 latencies, an effect which is primarily attributable (∼75%) to luminance, and in some cases, specific spectral effects (e.g., blue and red). VEP amplitude and alpha power were not significantly affected. These findings provide an important reference to which either amplitude or power changes in light-sensitive, younger clinical groups can be compared. PMID:26293969

Use of alpha spectroscopy for conducting rapid surveys of transuranic activity on air sample filters and smears.

PubMed

Hayes, Robert B; Peña, Adan M; Goff, Thomas E

2005-08-01

This paper demonstrates the utility of a portable alpha Continuous Air Monitor (CAM) as a bench top scalar counter for multiple sample types. These include using the CAM to count fixed air sample filters and radiological smears. In counting radiological smears, the CAM is used very much like a gas flow proportional counter (GFPC), albeit with a lower efficiency. Due to the typically low background in this configuration, the minimum detectable activity for a 5-min count should be in the range of about 10 dpm which is acceptably below the 20 dpm limit for transuranic isotopes. When counting fixed air sample filters, the CAM algorithm along with other measurable characteristics can be used to identify and quantify the presence of transuranic isotopes in the samples. When the radiological control technician wants to take some credit from naturally occurring radioactive material contributions due to radon progeny producing higher energy peaks (as in the case with a fixed air sample filter), then more elaborate techniques are required. The techniques presented here will generate a decision level of about 43 dpm for such applications. The calibration for this application should alternatively be done using the default values of channels 92-126 for region of interest 1. This can be done within 10 to 15 min resulting in a method to rapidly evaluate air filters for transuranic activity. When compared to the 1-h count technique described by , the technique presented in the present work demonstrates a technique whereby more than two thirds of samples can be rapidly shown (within 10 to 15 min) to be within regulatory compliant limits. In both cases, however, spectral quality checks are required to insure sample self attenuation is not a significant bias in the activity estimates. This will allow the same level of confidence when using these techniques for activity quantification as is presently available for air monitoring activity quantification using CAMs.

Demosaicking for full motion video 9-band SWIR sensor

NASA Astrophysics Data System (ADS)

Kanaev, Andrey V.; Rawhouser, Marjorie; Kutteruf, Mary R.; Yetzbacher, Michael K.; DePrenger, Michael J.; Novak, Kyle M.; Miller, Corey A.; Miller, Christopher W.

2014-05-01

Short wave infrared (SWIR) spectral imaging systems are vital for Intelligence, Surveillance, and Reconnaissance (ISR) applications because of their abilities to autonomously detect targets and classify materials. Typically the spectral imagers are incapable of providing Full Motion Video (FMV) because of their reliance on line scanning. We enable FMV capability for a SWIR multi-spectral camera by creating a repeating pattern of 3x3 spectral filters on a staring focal plane array (FPA). In this paper we present the imagery from an FMV SWIR camera with nine discrete bands and discuss image processing algorithms necessary for its operation. The main task of image processing in this case is demosaicking of the spectral bands i.e. reconstructing full spectral images with original FPA resolution from spatially subsampled and incomplete spectral data acquired with the choice of filter array pattern. To the best of author's knowledge, the demosaicking algorithms for nine or more equally sampled bands have not been reported before. Moreover all existing algorithms developed for demosaicking visible color filter arrays with less than nine colors assume either certain relationship between the visible colors, which are not valid for SWIR imaging, or presence of one color band with higher sampling rate compared to the rest of the bands, which does not conform to our spectral filter pattern. We will discuss and present results for two novel approaches to demosaicking: interpolation using multi-band edge information and application of multi-frame super-resolution to a single frame resolution enhancement of multi-spectral spatially multiplexed images.

Guided-mode resonance reflection and transmission filters in the optical and microwave spectral ranges

NASA Astrophysics Data System (ADS)

Tibuleac, Sorin

In this dissertation, new reflection and transmission filters are developed and characterized in the optical and microwave spectral regions. These guided-mode resonance (GMR) filters are implemented by integrating diffraction gratings into classical thin-film multilayers to produce high efficiency filter response and low sidebands extended over a large spectral range. Diffraction from phase-shifted gratings and gratings with different periods is analyzed using rigorous coupled-wave theory yielding a new approach to filter linewidth broadening, line-shaping, and multi-line filters at normal incidence. New single-grating transmission filters presented have narrow linewidth, high peak transmittance, and low sideband reflectance. A comparison with classical thin-film filters shows that GMR devices require significantly fewer layers to obtain narrow linewidth and high peak response. All-dielectric microwave frequency- selective surfaces operating in reflection or transmission are shown to be realizable with only a few layers using common microwave materials. Single-layer and multilayer waveguide gratings operating as reflection and transmission filters, respectively, were built and tested in the 4-20 GHz frequency range. The presence of GMR notches and peaks is clearly established by the experimental results, and their spectral location and lineshape found to be in excellent agreement with the theoretical predictions. A new computer program using genetic algorithms and rigorous coupled-wave analysis was developed for optimization of multilayer structures containing homogeneous and diffractive layers. This program was utilized to find GMR filters possessing features not previously known. Thus, numerous examples of transmission filters with peaks approaching 100%, narrow linewidths (~0.03%), and low sidebands have been found in structures containing only 1-3 layers. A new type of GMR device integrating a waveguide grating with subwavelength period on the endface of an optical fiber is developed for high-resolution biomedical or chemical sensors and spectral filtering applications. Diffraction gratings with submicron periods exhibiting high efficiencies have been recorded for the first time on coated and uncoated endfaces of single-mode and multimode fibers. Guided-mode resonance transmittance notches of ~18% were experimentally obtained with structures consisting of photoresist gratings on thin films of Si3N4 deposited on optical fiber endfaces.

Jammed-array wideband sawtooth filter.

PubMed

Tan, Zhongwei; Wang, Chao; Goda, Keisuke; Malik, Omer; Jalali, Bahram

2011-11-21

We present an all-optical passive low-cost spectral filter that exhibits a high-resolution periodic sawtooth spectral pattern without the need for active optoelectronic components. The principle of the filter is the partial masking of a phased array of virtual light sources with multiply jammed diffraction orders. We utilize the filter's periodic linear map between frequency and intensity to demonstrate fast sensitive interrogation of fiber Bragg grating sensor arrays and ultrahigh-frequency electrical sawtooth waveform generation. © 2011 Optical Society of America

An efficient implementation of a high-order filter for a cubed-sphere spectral element model

NASA Astrophysics Data System (ADS)

Kang, Hyun-Gyu; Cheong, Hyeong-Bin

2017-03-01

A parallel-scalable, isotropic, scale-selective spatial filter was developed for the cubed-sphere spectral element model on the sphere. The filter equation is a high-order elliptic (Helmholtz) equation based on the spherical Laplacian operator, which is transformed into cubed-sphere local coordinates. The Laplacian operator is discretized on the computational domain, i.e., on each cell, by the spectral element method with Gauss-Lobatto Lagrange interpolating polynomials (GLLIPs) as the orthogonal basis functions. On the global domain, the discrete filter equation yielded a linear system represented by a highly sparse matrix. The density of this matrix increases quadratically (linearly) with the order of GLLIP (order of the filter), and the linear system is solved in only O (Ng) operations, where Ng is the total number of grid points. The solution, obtained by a row reduction method, demonstrated the typical accuracy and convergence rate of the cubed-sphere spectral element method. To achieve computational efficiency on parallel computers, the linear system was treated by an inverse matrix method (a sparse matrix-vector multiplication). The density of the inverse matrix was lowered to only a few times of the original sparse matrix without degrading the accuracy of the solution. For better computational efficiency, a local-domain high-order filter was introduced: The filter equation is applied to multiple cells, and then the central cell was only used to reconstruct the filtered field. The parallel efficiency of applying the inverse matrix method to the global- and local-domain filter was evaluated by the scalability on a distributed-memory parallel computer. The scale-selective performance of the filter was demonstrated on Earth topography. The usefulness of the filter as a hyper-viscosity for the vorticity equation was also demonstrated.

New theoretical models and ratio imaging techniques associated with the NASA earth resources spectral information system

NASA Technical Reports Server (NTRS)

Vincent, R. K.

1974-01-01

Four independent investigations are reported; in general these are concerned with improving and utilizing the correlation between the physical properties of natural materials as evidenced in laboratory spectra and spectral data collected by multispectral scanners. In one investigation, two theoretical models were devised that permit the calculation of spectral emittance spectra for rock and mineral surfaces of various particle sizes. The simpler of the two models can be used to qualitatively predict the effect of texture on the spectral emittance of rocks and minerals; it is also potentially useful as an aid in predicting the identification of natural atmospheric aerosol constituents. The second investigation determined, via an infrared ratio imaging technique, the best pair of infrared filters for silicate rock-type discrimination. In a third investigation, laboratory spectra of natural materials were compressed into 11-digit ratio codes for use in feature selection, in searches for false alarm candidates, and eventually for use as training sets in completely automatic data processors. In the fourth investigation, general outlines of a ratio preprocessor and an automatic recognition map processor are developed for on-board data processing in the space shuttle era.

Enhanced 40 and 80 Gb/s wavelength conversion using a rectangular shaped optical filter for both red and blue spectral slicing.

PubMed

Raz, O; Herrera, J; Dorren, H J S

2009-02-02

By using a tunable filter with tunability of both bandwidth and wavelength and a very sharp filter roll-off, considerable improvement of all optical Wavelength Conversion, based on Cross Gain and Phase Modulation effects in a Semiconductor Optical Amplifier and spectral slicing, is shown. At 40 Gb/s slicing of blue spectral components is shown to result in a small penalty of 0.7 dB, with a minimal eye broadening, and at 80 Gb/s the low demonstrated 0.5 dB penalty is a dramatic improvement over previously reported wavelength converters using the same principal. Additionally, we give for the first time quantitative results for the case of red spectral slicing at 40 Gb/s which we found to have only 0.5 dB penalty and a narrower time response, as anticipated by previously published theoretical papers. Numerical simulations for the dependence of the eye opening on the filter characteristics highlight the importance of the combination of a sharp filter roll-off and a broad passband.

Tunable-Bandwidth Filter System

NASA Technical Reports Server (NTRS)

Bailey, John W.

2004-01-01

A tunable-bandwidth filter system (TBFS), now undergoing development, is intended to be part of a remote sensing multispectral imaging system that will operate in the visible and near infrared spectral region (wavelengths from 400 to 900 nm). Attributes of the TBFS include rapid tunability of the pass band over a wide wavelength range and high transmission efficiency. The TBFS is based on a unique integration of two pairs of broadband Raman reflection holographic filters with two rotating spherical lenses. In experiments, a prototype of the TBFS, was shown to be capable of spectral sampling of images in the visible range over a 200 nm spectral range with a spectral resolution of 30 nm. The figure depicts the optical layout of a prototype of the TBFS as part of a laboratory multispectral imaging system for the spectral sampling of color test images in two orthogonal polarizations. Each pair of broadband Raman reflection holographic filters is mounted at an equatorial plane between two halves of a spherical lens. The two filters in each pair are characterized by steep spectral slopes (equivalently, narrow spectral edges), no ripple or side lobes in their pass bands, and a few nanometers of non-overlapping wavelength range between their pass bands. Each spherical lens and thus the filter pair within it is rotated in order to rapidly tune its pass band. The rotations of are effected by electronically controlled, programmable, high-precision rotation stages. The rotations are coordinated by electronic circuits operating under overall supervision of a personal computer in order to obtain the desired variation of the overall pass bands with time. Embedding the filters inside the spherical lenses increases the range of the hologram incidence angles, making it possible to continuously tune the pass and stop bands of the filters over a wider wavelength range. In addition, each spherical lens also serves as part of the imaging optics: The telephoto lens focuses incoming light to a field stop that is also a focal point of each spherical lens. A correcting lens in front of the field stop compensates for the spherical aberration of the spherical lenses. The front surface of each spherical lens collimates the light coming from the field stop. After the collimated light passes through the filter in the spherical lens, the rear surface of the lens focuses the light onto a charge-coupled-device image detector.

Tunable-Bandwidth Filter System

NASA Technical Reports Server (NTRS)

Aye, Tin; Yu, Kevin; Dimov, Fedor; Savant, Gajendra

2006-01-01

A tunable-bandwidth filter system (TBFS), now undergoing development, is intended to be part of a remote-sensing multispectral imaging system that will operate in the visible and near infrared spectral region (wavelengths from 400 to 900 nm). Attributes of the TBFS include rapid tunability of the pass band over a wide wavelength range and high transmission efficiency. The TBFS is based on a unique integration of two pairs of broadband Raman reflection holographic filters with two rotating spherical lenses. In experiments, a prototype of the TBFS was shown to be capable of spectral sampling of images in the visible range over a 200-nm spectral range with a spectral resolution of .30 nm. The figure depicts the optical layout of a prototype of the TBFS as part of a laboratory multispectral imaging system for the spectral sampling of color test images in two orthogonal polarizations. Each pair of broadband Raman reflection holographic filters is mounted at an equatorial plane between two halves of a spherical lens. The two filters in each pair are characterized by steep spectral slopes (equivalently, narrow spectral edges), no ripple or side lobes in their pass bands, and a few nanometers of non-overlapping wavelength range between their pass bands. Each spherical lens and thus the filter pair within it is rotated in order to rapidly tune its pass band. The rotations of the lenses are effected by electronically controlled, programmable, high-precision rotation stages. The rotations are coordinated by electronic circuits operating under overall supervision of a personal computer in order to obtain the desired variation of the overall pass bands with time. Embedding the filters inside the spherical lenses increases the range of the hologram incidence angles, making it possible to continuously tune the pass and stop bands of the filters over a wider wavelength range. In addition, each spherical lens also serves as part of the imaging optics: The telephoto lens focuses incoming light to a field stop that is also a focal point of each spherical lens. A correcting lens in front of the field stop compensates for the spherical aberration of the spherical lenses. The front surface of each spherical lens collimates the light coming from the field stop. After the collimated light passes through the filter in the spherical lens, the rear surface of the lens focuses the light onto a charge-coupled-device image detector.

Comparison of digital signal-signal beat interference compensation techniques in direct-detection subcarrier modulation systems.

PubMed

Li, Zhe; Erkilinc, M Sezer; Galdino, Lidia; Shi, Kai; Thomsen, Benn C; Bayvel, Polina; Killey, Robert I

2016-12-12

Single-polarization direct-detection transceivers may offer advantages compared to digital coherent technology for some metro, back-haul, access and inter-data center applications since they offer low-cost and complexity solutions. However, a direct-detection receiver introduces nonlinearity upon photo detection, since it is a square-law device, which results in signal distortion due to signal-signal beat interference (SSBI). Consequently, it is desirable to develop effective and low-cost SSBI compensation techniques to improve the performance of such transceivers. In this paper, we compare the performance of a number of recently proposed digital signal processing-based SSBI compensation schemes, including the use of single- and two-stage linearization filters, an iterative linearization filter and a SSBI estimation and cancellation technique. Their performance is assessed experimentally using a 7 × 25 Gb/s wavelength division multiplexed (WDM) single-sideband 16-QAM Nyquist-subcarrier modulation system operating at a net information spectral density of 2.3 (b/s)/Hz.

Spectral imagery with an acousto-optic tunable filter

NASA Technical Reports Server (NTRS)

Smith, W. Hayden; Schempp, W. V.; Conner, C. P.; Katzka, P.

1987-01-01

.A spectral imager for astronomy and aeronomy has been fabricated using collinear or non-collinear acoustooptic tunable filters (AOTFs). The AOTF provides high transparency, rapid tunability over a wide wavelength range, a capability of varying the bandwidth by more than an order of magnitude, high etendue, and linearly polarized output. Some typical observational applications of acoustooptic tunable filters used in several configurations at astronomical telescopes are demonstrated.

Calibration of the Multi-Spectral Solar Telescope Array multilayer mirrors and XUV filters

NASA Technical Reports Server (NTRS)

Allen, Maxwell J.; Willis, Thomas D.; Kankelborg, Charles C.; O'Neal, Ray H.; Martinez-Galarce, Dennis S.; Deforest, Craig E.; Jackson, Lisa; Lindblom, Joakim; Walker, Arthur B. C., Jr.; Barbee, Troy W., Jr.

1993-01-01

The Multi-Spectral Solar Telescope Array (MSSTA), a rocket-borne solar observatory, was successfully flown in May, 1991, obtaining solar images in eight XUV and FUV bands with 12 compact multilayer telescopes. Extensive measurements have recently been carried out on the multilayer telescopes and thin film filters at the Stanford Synchrotron Radiation Laboratory. These measurements are the first high spectral resolution calibrations of the MSSTA instruments. Previous measurements and/or calculations of telescope throughputs have been confirmed with greater accuracy. Results are presented on Mo/Si multilayer bandpass changes with time and experimental potassium bromide and tellurium filters.

Technological development of multispectral filter assemblies for micro bolometer

NASA Astrophysics Data System (ADS)

Le Goff, Roland; Tanguy, François; Fuss, Philippe; Etcheto, Pierre

2017-11-01

Since 2007 Sodern has successfully developed visible and near infrared multispectral filter assemblies for Earth remote sensing imagers. Filter assembly is manufactured by assembling several sliced filter elements (so-called strips), each corresponding to one spectral band. These strips are cut from wafers using a two dimensional accuracy precision process. In the frame of a 2011 R&T preparatory initiative undertaken by the French agency CNES, the filter assembly concept was adapted by Sodern to the long wave infrared spectral band taken into account the germanium substrate, the multilayer bandpass filters and the F-number of the optics. Indeed the current trend in space instrumentation toward more compact uncooled infrared radiometer leads to replace the filter wheel with a multispectral filter assembly mounted directly above the micro bolometer window. The filter assembly was customized to fit the bolometer size. For this development activity we consider a ULIS VGA LWIR micro bolometer with 640 by 480 pixels and 25 microns pixel pitch. The feasibility of the concept and the ability to withstand space environment were investigated and demonstrated by bread boarding activities. The presentation will contain a detailed description of the bolometer and filter assembly design, the stray light modeling analysis assessing the crosstalk between adjacent spectral bands and the results of the manufacturing and environmental tests (damp heat and thermal vacuum cycling).

A reflective-type, quasi-optical metasurface filter

NASA Astrophysics Data System (ADS)

Sima, Boyu; Momeni Hasan Abadi, Seyed Mohamad Amin; Behdad, Nader

2017-08-01

We introduce a new technique for designing quasi-optical, reflective-type spatial filters. The proposed filter is a reflective metasurface with a one dimensional, frequency-dependent phase gradient along the aperture. By careful design of each unit cell of the metasurface, the phase shift gradient provided by the adjacent unit cells can be engineered to steer the beam towards a desired, anomalous reflection direction over the passband region of the filter. Outside of that range, the phase shift gradient required to produce the anomalous reflection is not present and hence, the wave is reflected towards the specular reflection direction. This way, the metasurface acts as a reflective filter in a quasi-optical system where the detector is placed along the direction of anomalous reflection. The spectral selectivity of this filter is determined by the frequency dispersion of the metasurface's phase response. Based on this principle, a prototype of the proposed metasurface filter, which operates at 10 GHz and has a bandwidth of 3%, is designed. The device is modeled using a combination of theoretical analysis using the phased-array theory and full-wave electromagnetic simulations. A prototype of this device is also fabricated and characterized using a free-space measurement system. Experimental results agree well with the simulations.

Quantitative Surface Emissivity and Temperature Measurements of a Burning Solid Fuel Accompanied by Soot Formation

NASA Technical Reports Server (NTRS)

Piltch, Nancy D.; Pettegrew, Richard D.; Ferkul, Paul; Sacksteder, K. (Technical Monitor)

2001-01-01

Surface radiometry is an established technique for noncontact temperature measurement of solids. We adapt this technique to the study of solid surface combustion where the solid fuel undergoes physical and chemical changes as pyrolysis proceeds, and additionally may produce soot. The physical and chemical changes alter the fuel surface emissivity, and soot contributes to the infrared signature in the same spectral band as the signal of interest. We have developed a measurement that isolates the fuel's surface emissions in the presence of soot, and determine the surface emissivity as a function of temperature. A commercially available infrared camera images the two-dimensional surface of ashless filter paper burning in concurrent flow. The camera is sensitive in the 2 to 5 gm band, but spectrally filtered to reduce the interference from hot gas phase combustion products. Results show a strong functional dependence of emissivity on temperature, attributed to the combined effects of thermal and oxidative processes. Using the measured emissivity, radiance measurements from several burning samples were corrected for the presence of soot and for changes in emissivity, to yield quantitative surface temperature measurements. Ultimately the results will be used to develop a full-field, non-contact temperature measurement that will be used in spacebased combustion investigations.

Remote sensing of vigor loss in conifers due to dwarf mistletoe

NASA Technical Reports Server (NTRS)

Meyer, M. P.; French, D. W.; Latham, R. P.; Nelson, C. A.; Douglass, R. W.

1971-01-01

The initial operation of a multiband/multidate tower-tramway test site in northeastern Minnesota for the development of specifications for subsequent multiband aerial photography of more extensive study areas was completed. Multiband/multidate configurations suggested by the tower-tramway studies were and will be flown with local equipment over the Togo test site. This site was photographed by the NASA RB57F aircraft in August and September 1971. It appears that, of all the film/filter combinations attempted to date (including optical recombining of several spectral band images via photo enhancement techniques), Ektachrome infrared film with a Wratten 12 filter is the best for detecting dwarf mistletoe, and other tree diseases as well. Using this film/filter combination, infection centers are easily detectable even on the smallest photo scale (1:100,000) obtained on the Togo site.

CAM-SE: A scalable spectral element dynamical core for the Community Atmosphere Model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dennis, John; Edwards, Jim; Evans, Kate J

2012-01-01

The Community Atmosphere Model (CAM) version 5 includes a spectral element dynamical core option from NCAR's High-Order Method Modeling Environment. It is a continuous Galerkin spectral finite element method designed for fully unstructured quadrilateral meshes. The current configurations in CAM are based on the cubed-sphere grid. The main motivation for including a spectral element dynamical core is to improve the scalability of CAM by allowing quasi-uniform grids for the sphere that do not require polar filters. In addition, the approach provides other state-of-the-art capabilities such as improved conservation properties. Spectral elements are used for the horizontal discretization, while most othermore » aspects of the dynamical core are a hybrid of well tested techniques from CAM's finite volume and global spectral dynamical core options. Here we first give a overview of the spectral element dynamical core as used in CAM. We then give scalability and performance results from CAM running with three different dynamical core options within the Community Earth System Model, using a pre-industrial time-slice configuration. We focus on high resolution simulations of 1/4 degree, 1/8 degree, and T340 spectral truncation.« less

UV filters for lighting of plants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doehring, T.; Koefferlein, M.; Thiel, S.

1994-12-31

Different filter glasses are available which provide absorption properties suitable for gradual changes of the spectral UV-B illumination of artificial lighting. Using a distinct set of lamps and filter glasses an acceptable simulation of the UV-B part of natural global radiation can be achieved. The ageing of these and other filter materials under the extreme UV radiation in the lamphouse of a solar simulator is presently unavoidable. This instability can be dealt with only by a precise spectral monitoring and by replacing the filters accordingly. For this reason attempts would be useful to develop real ozone filters which can replacemore » glass filters. In any case chamber experiments require a careful selection of the filter material used and must be accompanied by a continuous UV-B monitoring.« less

Gender identification from high-pass filtered vowel segments: the use of high-frequency energy.

PubMed

Donai, Jeremy J; Lass, Norman J

2015-10-01

The purpose of this study was to examine the use of high-frequency information for making gender identity judgments from high-pass filtered vowel segments produced by adult speakers. Specifically, the effect of removing lower-frequency spectral detail (i.e., F3 and below) from vowel segments via high-pass filtering was evaluated. Thirty listeners (ages 18-35) with normal hearing participated in the experiment. A within-subjects design was used to measure gender identification for six 250-ms vowel segments (/æ/, /ɪ /, /ɝ/, /ʌ/, /ɔ/, and /u/), produced by ten male and ten female speakers. The results of this experiment demonstrated that despite the removal of low-frequency spectral detail, the listeners were accurate in identifying speaker gender from the vowel segments, and did so with performance significantly above chance. The removal of low-frequency spectral detail reduced gender identification by approximately 16 % relative to unfiltered vowel segments. Classification results using linear discriminant function analyses followed the perceptual data, using spectral and temporal representations derived from the high-pass filtered segments. Cumulatively, these findings indicate that normal-hearing listeners are able to make accurate perceptual judgments regarding speaker gender from vowel segments with low-frequency spectral detail removed via high-pass filtering. Therefore, it is reasonable to suggest the presence of perceptual cues related to gender identity in the high-frequency region of naturally produced vowel signals. Implications of these findings and possible mechanisms for performing the gender identification task from high-pass filtered stimuli are discussed.

EFQPSK Versus CERN: A Comparative Study

NASA Technical Reports Server (NTRS)

Borah, Deva K.; Horan, Stephen

2001-01-01

This report presents a comparative study on Enhanced Feher's Quadrature Phase Shift Keying (EFQPSK) and Constrained Envelope Root Nyquist (CERN) techniques. These two techniques have been developed in recent times to provide high spectral and power efficiencies under nonlinear amplifier environment. The purpose of this study is to gain insights into these techniques and to help system planners and designers with an appropriate set of guidelines for using these techniques. The comparative study presented in this report relies on effective simulation models and procedures. Therefore, a significant part of this report is devoted to understanding the mathematical and simulation models of the techniques and their set-up procedures. In particular, mathematical models of EFQPSK and CERN, effects of the sampling rate in discrete time signal representation, and modeling of nonlinear amplifiers and predistorters have been considered in detail. The results of this study show that both EFQPSK and CERN signals provide spectrally efficient communications compared to filtered conventional linear modulation techniques when a nonlinear power amplifier is used. However, there are important differences. The spectral efficiency of CERN signals, with a small amount of input backoff, is significantly better than that of EFQPSK signals if the nonlinear amplifier is an ideal clipper. However, to achieve such spectral efficiencies with a practical nonlinear amplifier, CERN processing requires a predistorter which effectively translates the amplifier's characteristics close to those of an ideal clipper. Thus, the spectral performance of CERN signals strongly depends on the predistorter. EFQPSK signals, on the other hand, do not need such predistorters since their spectra are almost unaffected by the nonlinear amplifier, Ibis report discusses several receiver structures for EFQPSK signals. It is observed that optimal receiver structures can be realized for both coded and uncoded EFQPSK signals with not too much increase in computational complexity. When a nonlinear amplifier is used, the bit error rate (BER) performance of the CERN signals with a matched filter receiver is found to be more than one decibel (dB) worse compared to the bit error performance of EFQPSK signals. Although channel coding is found to provide BER performance improvement for both EFQPSK and CERN signals, the performance of EFQPSK signals remains better than that of CERN. Optimal receiver structures for CERN signals with nonlinear equalization is left as a possible future work. Based on the numerical results, it is concluded that, in nonlinear channels, CERN processing leads towards better bandwidth efficiency with a compromise in power efficiency. Hence for bandwidth efficient communications needs, CERN is a good solution provided effective adaptive predistorters can be realized. On the other hand, EFQPSK signals provide a good power efficient solution with a compromise in band width efficiency.

A robust pseudo-inverse spectral filter applied to the Earth Radiation Budget Experiment (ERBE) scanning channels

NASA Technical Reports Server (NTRS)

Avis, L. M.; Green, R. N.; Suttles, J. T.; Gupta, S. K.

1984-01-01

Computer simulations of a least squares estimator operating on the ERBE scanning channels are discussed. The estimator is designed to minimize the errors produced by nonideal spectral response to spectrally varying and uncertain radiant input. The three ERBE scanning channels cover a shortwave band a longwave band and a ""total'' band from which the pseudo inverse spectral filter estimates the radiance components in the shortwave band and a longwave band. The radiance estimator draws on instantaneous field of view (IFOV) scene type information supplied by another algorithm of the ERBE software, and on a priori probabilistic models of the responses of the scanning channels to the IFOV scene types for given Sun scene spacecraft geometry. It is found that the pseudoinverse spectral filter is stable, tolerant of errors in scene identification and in channel response modeling, and, in the absence of such errors, yields minimum variance and essentially unbiased radiance estimates.

Aerosol column absorption measurements using co-located UV-MFRSR and AERONET CIMEL instruments

NASA Astrophysics Data System (ADS)

Krotkov, N.; Labow, G.; Herman, J.; Slusser, J.; Tree, R.; Janson, G.; Durham, B.; Eck, T.; Holben, B.

2009-08-01

Column aerosol absorption properties in the visible wavelengths are measured routinely in worldwide locations by NASA AERONET network (http://aeronet.gsfc.nasa.gov), while similar optical properties in UV can be derived from diffuse and global irradiance measurements measured with Multifilter Rotating Shadowband Radiometer (MFRSR) instruments of the USDA UV-MFRSR network (http://uvb.nrel.colostate.edu). To enable direct comparisons between the two techniques, we have modified our UV-MFRSR by replacing standard 300nm filter with 440nm filter used in AERONET network. The modified UV/VIS-MFRSR has been mostly deployed at AERONET calibration site at NASA GSFC in Greenbelt, MD, but also at number of field campaigns. While the UV-MSFRSR instrument is highly susceptible to calibration drifts, these drifts can be accurately assessed using co-located AERONET direct-sun AOT data. In 2006 quartz dome has been installed atop the MFRSR diffuser, which stabilized calibration drifts in 2007-2009. After correcting for remaining calibration changes, the AOT and single scattering albedo (SSA) at the UV wavelengths can be accurately inferred by fitting the measurements of global and diffuse atmospheric transmittances with the forward RT model at each UV-MFRSR spectral channel. Derived AOT and SSA at common wavelength 440nm by two different techniques are generally in good agreement. We also found that SSA becomes smaller in the UV wavelengths and has strong wavelength dependence across blue and near-UV spectral range. The measured enhanced UV absorption might suggest the presence of selectively UV absorbing aerosols. High spectral resolution SSA measurements in UV-VIS wavelengths are called for.

System optimization of a field-widened Michelson interferometric spectral filter for high spectral resolution lidar

NASA Astrophysics Data System (ADS)

Liu, Dong; Miller, Ian; Hostetler, Chris; Cook, Anthony; Hair, Johnathan

2011-06-01

High spectral resolution lidars (HSRLs) have recently shown great value in aerosol measurements form aircraft and are being called for in future space-based aerosol remote sensing applications. A quasi-monolithic field-widened, off-axis Michelson interferometer had been developed as the spectral discrimination filter for an HSRL currently under development at NASA Langley Research Center (LaRC). The Michelson filter consists of a cubic beam splitter, a solid arm and an air arm. The input light is injected at 1.5° off-axis to provide two output channels: standard Michelson output and the reflected complementary signal. Piezo packs connect the air arm mirror to the main part of the filter that allows it to be tuned within a small range. In this paper, analyses of the throughput wavephase, locking error, AR coating, and tilt angle of the interferometer are described. The transmission ratio for monochromatic light at the transmitted wavelength is used as a figure of merit for assessing each of these parameters.

Linear spectral response of a Fano-resonant graded-stub filter based on pillar-photonic-crystal waveguides.

PubMed

Tokushima, Masatoshi

2018-02-01

To achieve high spectral linearity, we developed a Fano-resonant graded-stub filter on the basis of a pillar-photonic-crystal (PhC) waveguide. In a numerical simulation, the availability of a linear region within a peak-to-bottom wavelength span was nearly doubled compared to that of a sinusoidal spectrum, which was experimentally demonstrated with a fabricated silicon-pillar PhC stub filter. The high linearity of this filter is suitable for optical modulators used in multilevel amplitude modulation.

A simple biota removal algorithm for 35 GHz cloud radar measurements

NASA Astrophysics Data System (ADS)

Kalapureddy, Madhu Chandra R.; Sukanya, Patra; Das, Subrata K.; Deshpande, Sachin M.; Pandithurai, Govindan; Pazamany, Andrew L.; Ambuj K., Jha; Chakravarty, Kaustav; Kalekar, Prasad; Krishna Devisetty, Hari; Annam, Sreenivas

2018-03-01

Cloud radar reflectivity profiles can be an important measurement for the investigation of cloud vertical structure (CVS). However, extracting intended meteorological cloud content from the measurement often demands an effective technique or algorithm that can reduce error and observational uncertainties in the recorded data. In this work, a technique is proposed to identify and separate cloud and non-hydrometeor echoes using the radar Doppler spectral moments profile measurements. The point and volume target-based theoretical radar sensitivity curves are used for removing the receiver noise floor and identified radar echoes are scrutinized according to the signal decorrelation period. Here, it is hypothesized that cloud echoes are observed to be temporally more coherent and homogenous and have a longer correlation period than biota. That can be checked statistically using ˜ 4 s sliding mean and standard deviation value of reflectivity profiles. The above step helps in screen out clouds critically by filtering out the biota. The final important step strives for the retrieval of cloud height. The proposed algorithm potentially identifies cloud height solely through the systematic characterization of Z variability using the local atmospheric vertical structure knowledge besides to the theoretical, statistical and echo tracing tools. Thus, characterization of high-resolution cloud radar reflectivity profile measurements has been done with the theoretical echo sensitivity curves and observed echo statistics for the true cloud height tracking (TEST). TEST showed superior performance in screening out clouds and filtering out isolated insects. TEST constrained with polarimetric measurements was found to be more promising under high-density biota whereas TEST combined with linear depolarization ratio and spectral width perform potentially to filter out biota within the highly turbulent shallow cumulus clouds in the convective boundary layer (CBL). This TEST technique is promisingly simple in realization but powerful in performance due to the flexibility in constraining, identifying and filtering out the biota and screening out the true cloud content, especially the CBL clouds. Therefore, the TEST algorithm is superior for screening out the low-level clouds that are strongly linked to the rainmaking mechanism associated with the Indian Summer Monsoon region's CVS.

Spectral analysis comparisons of Fourier-theory-based methods and minimum variance (Capon) methods

NASA Astrophysics Data System (ADS)

Garbanzo-Salas, Marcial; Hocking, Wayne. K.

2015-09-01

In recent years, adaptive (data dependent) methods have been introduced into many areas where Fourier spectral analysis has traditionally been used. Although the data-dependent methods are often advanced as being superior to Fourier methods, they do require some finesse in choosing the order of the relevant filters. In performing comparisons, we have found some concerns about the mappings, particularly when related to cases involving many spectral lines or even continuous spectral signals. Using numerical simulations, several comparisons between Fourier transform procedures and minimum variance method (MVM) have been performed. For multiple frequency signals, the MVM resolves most of the frequency content only for filters that have more degrees of freedom than the number of distinct spectral lines in the signal. In the case of Gaussian spectral approximation, MVM will always underestimate the width, and can misappropriate the location of spectral line in some circumstances. Large filters can be used to improve results with multiple frequency signals, but are computationally inefficient. Significant biases can occur when using MVM to study spectral information or echo power from the atmosphere. Artifacts and artificial narrowing of turbulent layers is one such impact.

Spatial arrangement of color filter array for multispectral image acquisition

NASA Astrophysics Data System (ADS)

Shrestha, Raju; Hardeberg, Jon Y.; Khan, Rahat

2011-03-01

In the past few years there has been a significant volume of research work carried out in the field of multispectral image acquisition. The focus of most of these has been to facilitate a type of multispectral image acquisition systems that usually requires multiple subsequent shots (e.g. systems based on filter wheels, liquid crystal tunable filters, or active lighting). Recently, an alternative approach for one-shot multispectral image acquisition has been proposed; based on an extension of the color filter array (CFA) standard to produce more than three channels. We can thus introduce the concept of multispectral color filter array (MCFA). But this field has not been much explored, particularly little focus has been given in developing systems which focuses on the reconstruction of scene spectral reflectance. In this paper, we have explored how the spatial arrangement of multispectral color filter array affects the acquisition accuracy with the construction of MCFAs of different sizes. We have simulated acquisitions of several spectral scenes using different number of filters/channels, and compared the results with those obtained by the conventional regular MCFA arrangement, evaluating the precision of the reconstructed scene spectral reflectance in terms of spectral RMS error, and colorimetric ▵E*ab color differences. It has been found that the precision and the the quality of the reconstructed images are significantly influenced by the spatial arrangement of the MCFA and the effect will be more and more prominent with the increase in the number of channels. We believe that MCFA-based systems can be a viable alternative for affordable acquisition of multispectral color images, in particular for applications where spatial resolution can be traded off for spectral resolution. We have shown that the spatial arrangement of the array is an important design issue.

Estimation of surface heat and moisture fluxes over a prairie grassland. II - Two-dimensional time filtering and site variability

NASA Technical Reports Server (NTRS)

Crosson, William L.; Smith, Eric A.

1992-01-01

The behavior of in situ measurements of surface fluxes obtained during FIFE 1987 is examined by using correlative and spectral techniques in order to assess the significance of fluctuations on various time scales, from subdiurnal up to synoptic, intraseasonal, and annual scales. The objectives of this analysis are: (1) to determine which temporal scales have a significant impact on areal averaged fluxes and (2) to design a procedure for filtering an extended flux time series that preserves the basic diurnal features and longer time scales while removing high frequency noise that cannot be attributed to site-induced variation. These objectives are accomplished through the use of a two-dimensional cross-time Fourier transform, which serves to separate processes inherently related to diurnal and subdiurnal variability from those which impact flux variations on the longer time scales. A filtering procedure is desirable before the measurements are utilized as input with an experimental biosphere model, to insure that model based intercomparisons at multiple sites are uncontaminated by input variance not related to true site behavior. Analysis of the spectral decomposition indicates that subdiurnal time scales having periods shorter than 6 hours have little site-to-site consistency and therefore little impact on areal integrated fluxes.

Transmittance measurements of ultra violet and visible wavelength interference filters flown aboard LDEF

NASA Technical Reports Server (NTRS)

Mooney, Thomas A.; Smajkiewicz, Ali

1991-01-01

A set of ten interference filters for the UV and VIS spectral region were flown on the surface of the Long Duration Exposure Facility (LDEF) Tray B-8 along with earth radiation budget (ERB) components from the Eppley Laboratory. Transmittance changes and other degradation observed after the return of the filters to Barr are reported. Substrates, coatings, and (where applicable) cement materials are identified. In general, all filters except those containing lead compounds survived well. Metal dielectric filters for the UV developed large numbers of pinholes which caused an increase in transmittance. Band shapes and spectral positioning, however, did not change.

Slowing light down by low magnetic fields: pulse delay by transient spectral hole-burning in ruby.

PubMed

Riesen, Hans; Rebane, Aleksander K; Szabo, Alex; Carceller, Ivana

2012-08-13

We report on the observation of slow light induced by transient spectral hole-burning in a solid, that is based on excited-state population storage. Experiments were conducted in the R1-line (2E←4A2 transition) of a 2.3 mm thick pink ruby (Al2O3:Cr(III) 130 ppm). Importantly, the pulse delay can be controlled by the application of a low external magnetic field B||c≤9 mT and delays of up to 11 ns with minimal pulse distortion are observed for ~55 ns Gaussian pulses. The delay corresponds to a group velocity value of ~c/1400. The experiment is very well modelled by linear spectral filter theory and the results indicate the possibility of using transient hole-burning based slow light experiments as a spectroscopic technique.

Spectral information enhancement using wavelet-based iterative filtering for in vivo gamma spectrometry.

PubMed

Paul, Sabyasachi; Sarkar, P K

2013-04-01

Use of wavelet transformation in stationary signal processing has been demonstrated for denoising the measured spectra and characterisation of radionuclides in the in vivo monitoring analysis, where difficulties arise due to very low activity level to be estimated in biological systems. The large statistical fluctuations often make the identification of characteristic gammas from radionuclides highly uncertain, particularly when interferences from progenies are also present. A new wavelet-based noise filtering methodology has been developed for better detection of gamma peaks in noisy data. This sequential, iterative filtering method uses the wavelet multi-resolution approach for noise rejection and an inverse transform after soft 'thresholding' over the generated coefficients. Analyses of in vivo monitoring data of (235)U and (238)U were carried out using this method without disturbing the peak position and amplitude while achieving a 3-fold improvement in the signal-to-noise ratio, compared with the original measured spectrum. When compared with other data-filtering techniques, the wavelet-based method shows the best results.

Reference-free fatigue crack detection using nonlinear ultrasonic modulation under various temperature and loading conditions

NASA Astrophysics Data System (ADS)

Lim, Hyung Jin; Sohn, Hoon; DeSimio, Martin P.; Brown, Kevin

2014-04-01

This study presents a reference-free fatigue crack detection technique using nonlinear ultrasonic modulation. When low frequency (LF) and high frequency (HF) inputs generated by two surface-mounted lead zirconate titanate (PZT) transducers are applied to a structure, the presence of a fatigue crack can provide a mechanism for nonlinear ultrasonic modulation and create spectral sidebands around the frequency of the HF signal. The crack-induced spectral sidebands are isolated using a combination of linear response subtraction (LRS), synchronous demodulation (SD) and continuous wavelet transform (CWT) filtering. Then, a sequential outlier analysis is performed on the extracted sidebands to identify the crack presence without referring any baseline data obtained from the intact condition of the structure. Finally, the robustness of the proposed technique is demonstrated using actual test data obtained from simple aluminum plate and complex aircraft fitting-lug specimens under varying temperature and loading variations.

Recognition of a porphyry system using ASTER data in Bideghan - Qom province (central of Iran)

NASA Astrophysics Data System (ADS)

Feizi, F.; Mansouri, E.

2014-07-01

The Bideghan area is located south of the Qom province (central of Iran). The most impressive geological features in the studied area are the Eocene sequences which are intruded by volcanic rocks with basic compositions. Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) image processing have been used for hydrothermal alteration mapping and lineaments identification in the investigated area. In this research false color composite, band ratio, Principal Component Analysis (PCA), Least Square Fit (LS-Fit) and Spectral Angel Mapping (SAM) techniques were applied on ASTER data and argillic, phyllic, Iron oxide and propylitic alteration zones were separated. Lineaments were identified by aid of false color composite, high pass filters and hill-shade DEM techniques. The results of this study demonstrate the usefulness of remote sensing method and ASTER multi-spectral data for alteration and lineament mapping. Finally, the results were confirmed by field investigation.

Cavity-enhanced Raman microscopy of individual carbon nanotubes

PubMed Central

Hümmer, Thomas; Noe, Jonathan; Hofmann, Matthias S.; Hänsch, Theodor W.; Högele, Alexander; Hunger, David

2016-01-01

Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. Here, we demonstrate Purcell enhancement of Raman scattering in a tunable high-finesse microcavity, and utilize it for molecular diagnostics by combined Raman and absorption imaging. Studying individual single-wall carbon nanotubes, we identify crucial structural parameters such as nanotube radius, electronic structure and extinction cross-section. We observe a 320-times enhanced Raman scattering spectral density and an effective Purcell factor of 6.2, together with a collection efficiency of 60%. Potential for significantly higher enhancement, quantitative signals, inherent spectral filtering and absence of intrinsic background in cavity-vacuum stimulated Raman scattering render the technique a promising tool for molecular imaging. Furthermore, cavity-enhanced Raman transitions involving localized excitons could potentially be used for gaining quantum control over nanomechanical motion and open a route for molecular cavity optomechanics. PMID:27402165

Impact of atmospheric correction and image filtering on hyperspectral classification of tree species using support vector machine

NASA Astrophysics Data System (ADS)

Shahriari Nia, Morteza; Wang, Daisy Zhe; Bohlman, Stephanie Ann; Gader, Paul; Graves, Sarah J.; Petrovic, Milenko

2015-01-01

Hyperspectral images can be used to identify savannah tree species at the landscape scale, which is a key step in measuring biomass and carbon, and tracking changes in species distributions, including invasive species, in these ecosystems. Before automated species mapping can be performed, image processing and atmospheric correction is often performed, which can potentially affect the performance of classification algorithms. We determine how three processing and correction techniques (atmospheric correction, Gaussian filters, and shade/green vegetation filters) affect the prediction accuracy of classification of tree species at pixel level from airborne visible/infrared imaging spectrometer imagery of longleaf pine savanna in Central Florida, United States. Species classification using fast line-of-sight atmospheric analysis of spectral hypercubes (FLAASH) atmospheric correction outperformed ATCOR in the majority of cases. Green vegetation (normalized difference vegetation index) and shade (near-infrared) filters did not increase classification accuracy when applied to large and continuous patches of specific species. Finally, applying a Gaussian filter reduces interband noise and increases species classification accuracy. Using the optimal preprocessing steps, our classification accuracy of six species classes is about 75%.

Note: Broadly tunable all-fiber ytterbium laser with 0.05 nm spectral width based on multimode interference filter.

PubMed

Mukhopadhyay, Pranab K; Gupta, Pradeep K; Singh, Amarjeet; Sharma, Sunil K; Bindra, Kushvinder S; Oak, Shrikant M

2014-05-01

A multimode interference filter with narrow transmission bandwidth and large self-imaging wavelength interval is constructed and implemented in an ytterbium doped fiber laser in all-fiber format for broad wavelength tunability as well as narrow spectral width of the output beam. The peak transmission wavelength of the multimode interference filter was tuned with the help of a standard in-fiber polarization controller. With this simple mechanism more than 30 nm (1038 nm-1070 nm) tuning range is demonstrated. The spectral width of the output beam from the laser was measured to be 0.05 nm.

Note: Broadly tunable all-fiber ytterbium laser with 0.05 nm spectral width based on multimode interference filter

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Pranab K.; Gupta, Pradeep K.; Singh, Amarjeet; Sharma, Sunil K.; Bindra, Kushvinder S.; Oak, Shrikant M.

2014-05-01

A multimode interference filter with narrow transmission bandwidth and large self-imaging wavelength interval is constructed and implemented in an ytterbium doped fiber laser in all-fiber format for broad wavelength tunability as well as narrow spectral width of the output beam. The peak transmission wavelength of the multimode interference filter was tuned with the help of a standard in-fiber polarization controller. With this simple mechanism more than 30 nm (1038 nm-1070 nm) tuning range is demonstrated. The spectral width of the output beam from the laser was measured to be 0.05 nm.

Note: Broadly tunable all-fiber ytterbium laser with 0.05 nm spectral width based on multimode interference filter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukhopadhyay, Pranab K., E-mail: pkm@rrcat.gov.in; Gupta, Pradeep K.; Singh, Amarjeet

2014-05-15

A multimode interference filter with narrow transmission bandwidth and large self-imaging wavelength interval is constructed and implemented in an ytterbium doped fiber laser in all-fiber format for broad wavelength tunability as well as narrow spectral width of the output beam. The peak transmission wavelength of the multimode interference filter was tuned with the help of a standard in-fiber polarization controller. With this simple mechanism more than 30 nm (1038 nm–1070 nm) tuning range is demonstrated. The spectral width of the output beam from the laser was measured to be 0.05 nm.

Designing manufacturable filters for a 16-band plenoptic camera using differential evolution

NASA Astrophysics Data System (ADS)

Doster, Timothy; Olson, Colin C.; Fleet, Erin; Yetzbacher, Michael; Kanaev, Andrey; Lebow, Paul; Leathers, Robert

2017-05-01

A 16-band plenoptic camera allows for the rapid exchange of filter sets via a 4x4 filter array on the lens's front aperture. This ability to change out filters allows for an operator to quickly adapt to different locales or threat intelligence. Typically, such a system incorporates a default set of 16 equally spaced at-topped filters. Knowing the operating theater or the likely targets of interest it becomes advantageous to tune the filters. We propose using a modified beta distribution to parameterize the different possible filters and differential evolution (DE) to search over the space of possible filter designs. The modified beta distribution allows us to jointly optimize the width, taper and wavelength center of each single- or multi-pass filter in the set over a number of evolutionary steps. Further, by constraining the function parameters we can develop solutions which are not just theoretical but manufacturable. We examine two independent tasks: general spectral sensing and target detection. In the general spectral sensing task we utilize the theory of compressive sensing (CS) and find filters that generate codings which minimize the CS reconstruction error based on a fixed spectral dictionary of endmembers. For the target detection task and a set of known targets, we train the filters to optimize the separation of the background and target signature. We compare our results to the default 16 at-topped non-overlapping filter set which comes with the plenoptic camera and full hyperspectral resolution data which was previously acquired.

Photon counting spectral breast CT: effect of adaptive filtration on CT numbers, noise, and contrast to noise ratio.

PubMed

Silkwood, Justin D; Matthews, Kenneth L; Shikhaliev, Polad M

2013-05-01

Photon counting spectral (PCS) computed tomography (CT) shows promise for breast imaging. An issue with current photon-counting detectors is low count rate capabilities, artifacts resulting from nonuniform count rate across the field of view, and suboptimal spectral information. These issues are addressed in part by using tissue-equivalent adaptive filtration of the x-ray beam. The purpose of the study was to investigate the effect of adaptive filtration on different aspects of PCS breast CT. The theoretical formulation for the filter shape was derived for different filter materials and evaluated by simulation and an experimental prototype of the filter was fabricated from a tissue-like material (acrylic). The PCS CT images of a glandular breast phantom with adipose and iodine contrast elements were simulated at 40, 60, 90, and 120 kVp tube voltages, with and without adaptive filter. The CT numbers, CT noise, and contrast-to-noise ratio (CNR) were compared for spectral CT images acquired with and without adaptive filters. Similar comparison was made for material-decomposed PCS CT images. The adaptive filter improved the uniformity of CT numbers, CT noise, and CNR in both ordinary and material decomposed PCS CT images. At the same tube output the average CT noise with adaptive filter, although uniform, was higher than the average noise without adaptive filter due to x-ray absorption by the filter. Increasing tube output, so that average skin exposure with the adaptive filter was same as without filter, made the noise with adaptive filter comparable to or lower than that without adaptive filter. Similar effects were observed when energy weighting was applied, and when material decompositions were performed using energy selective CT data. An adaptive filter decreases count rate requirements to the photon counting detectors which enables PCS breast CT based on commercially available detector technologies. Adaptive filter also improves image quality in PCS breast CT by decreasing beam hardening artifacts and by eliminating spatial nonuniformities of CT numbers, noise, and CNR.

Integration of adaptive guided filtering, deep feature learning, and edge-detection techniques for hyperspectral image classification

NASA Astrophysics Data System (ADS)

Wan, Xiaoqing; Zhao, Chunhui; Gao, Bing

2017-11-01

The integration of an edge-preserving filtering technique in the classification of a hyperspectral image (HSI) has been proven effective in enhancing classification performance. This paper proposes an ensemble strategy for HSI classification using an edge-preserving filter along with a deep learning model and edge detection. First, an adaptive guided filter is applied to the original HSI to reduce the noise in degraded images and to extract powerful spectral-spatial features. Second, the extracted features are fed as input to a stacked sparse autoencoder to adaptively exploit more invariant and deep feature representations; then, a random forest classifier is applied to fine-tune the entire pretrained network and determine the classification output. Third, a Prewitt compass operator is further performed on the HSI to extract the edges of the first principal component after dimension reduction. Moreover, the regional growth rule is applied to the resulting edge logical image to determine the local region for each unlabeled pixel. Finally, the categories of the corresponding neighborhood samples are determined in the original classification map; then, the major voting mechanism is implemented to generate the final output. Extensive experiments proved that the proposed method achieves competitive performance compared with several traditional approaches.

Robust chemical and chemical-resistant material detection using hyper-spectral imager and a new bend interpolation and local scaling HSI sharpening method

NASA Astrophysics Data System (ADS)

Chen, Hai-Wen; McGurr, Michael; Brickhouse, Mark

2015-05-01

We present new results from our ongoing research activity for chemical threat detection using hyper-spectral imager (HSI) detection techniques by detecting nontraditional threat spectral signatures of agent usage, such as protective equipment, coatings, paints, spills, and stains that are worn by human or on trucks or other objects. We have applied several current state-of-the-art HSI target detection methods such as Matched Filter (MF), Adaptive Coherence Estimator (ACE), Constrained Energy Minimization (CEM), and Spectral Angle Mapper (SAM). We are interested in detecting several chemical related materials: (a) Tyvek clothing is chemical resistance and Tyvek coveralls are one-piece garments for protecting human body from harmful chemicals, and (b) ammonium salts from background could be representative of spills from scrubbers or related to other chemical activities. The HSI dataset that we used for detection covers a chemical test field with more than 50 different kinds of chemicals, protective materials, coatings, and paints. Among them, there are four different kinds of Tyvek material, three types of ammonium salts, and one yellow jugs. The imagery cube data were collected by a HSI sensor with a spectral range of 400-2,500nm. Preliminary testing results are promising, and very high probability of detection (Pd) and low probability of false detection are achieved with the usage of full spectral range (400- 2,500nm). In the second part of this paper, we present our newly developed HSI sharpening technique. A new Band Interpolation and Local Scaling (BILS) method has been developed to improve HSI spatial resolution by 4-16 times with a low-cost high-resolution pen-chromatic camera and a RGB camera. Preliminary results indicate that this new technique is promising.

Pathogenic changes of dispersion and contrast of coherent images of biotissues

NASA Astrophysics Data System (ADS)

Pishak, Olga V.

2002-02-01

The paper presents the results of polarization-correlation investigation of multifractal collagen structure of physiologically normal and pathologically changed tissues of women's reproductive sphere and of skin. The technique of polarization selection of coherent biotissues' images with the following determination of their autocorrelation functions and spectral densities is suggested. The correlation-optical criteria of early diagnostics of pathological changes' appearance of myometry (forming of the germ of fibromyoma) and of skin(psoriasis) are determined. The suggested paper is directed to investigation of the possibilities of pathological changes of biotissues' morphological structure by means of determining the polarizationally filtered autocorrelation functions (ACF) and corresponding spectral densities of their coherent images.

A-TEEMTM, a new molecular fingerprinting technique: simultaneous absorbance-transmission and fluorescence excitation-emission matrix method

NASA Astrophysics Data System (ADS)

Quatela, Alessia; Gilmore, Adam M.; Steege Gall, Karen E.; Sandros, Marinella; Csatorday, Karoly; Siemiarczuk, Alex; (Ben Yang, Boqian; Camenen, Loïc

2018-04-01

We investigate the new simultaneous absorbance-transmission and fluorescence excitation-emission matrix method for rapid and effective characterization of the varying components from a mixture. The absorbance-transmission and fluorescence excitation-emission matrix method uniquely facilitates correction of fluorescence inner-filter effects to yield quantitative fluorescence spectral information that is largely independent of component concentration. This is significant because it allows one to effectively monitor quantitative component changes using multivariate methods and to generate and evaluate spectral libraries. We present the use of this novel instrument in different fields: i.e. tracking changes in complex mixtures including natural water, wine as well as monitoring stability and aggregation of hormones for biotherapeutics.

Daylight operation of a free space, entanglement-based quantum key distribution system

NASA Astrophysics Data System (ADS)

Peloso, Matthew P.; Gerhardt, Ilja; Ho, Caleb; Lamas-Linares, Antía; Kurtsiefer, Christian

2009-04-01

Many quantum key distribution (QKD) implementations using a free space transmission path are restricted to operation at night time in order to distinguish the signal photons used for a secure key establishment from the background light. Here, we present a lean entanglement-based QKD system overcoming that limitation. By implementing spectral, spatial and temporal filtering techniques, we establish a secure key continuously over several days under varying light and weather conditions.

Non-invasive detection of the freezing of gait in Parkinson's disease using spectral and wavelet features.

PubMed

Nazarzadeh, Kimia; Arjunan, Sridhar P; Kumar, Dinesh K; Das, Debi Prasad

2016-08-01

In this study, we have analyzed the accelerometer data recorded during gait analysis of Parkinson disease patients for detecting freezing of gait (FOG) episodes. The proposed method filters the recordings for noise reduction of the leg movement changes and computes the wavelet coefficients to detect FOG events. Publicly available FOG database was used and the technique was evaluated using receiver operating characteristic (ROC) analysis. Results show a higher performance of the wavelet feature in discrimination of the FOG events from the background activity when compared with the existing technique.

Spectral transmittance of intraocular lenses under natural and artificial illumination: criteria analysis for choosing a suitable filter.

PubMed

Artigas, Jose M; Felipe, Adelina; Navea, Amparo; Artigas, Cristina; García-Domene, Maria C

2011-01-01

To compare the spectral transmission of different intraocular lenses (IOLs) with either ultraviolet (UV) or blue-light filters, and to analyze the performance of these filters with artificial light sources as well as sunlight. Experimental study. The spectral transmission curve of 10 IOLs was measured using a PerkinElmer Lambda 800 UV/VIS spectrometer (Waltham, MA). Different filtering simulations were performed using the D65 standard illuminant as daylight and standard incandescent lamp and fluorescent bulb illuminants. Spectral transmittance of the IOLs. All the IOLs studied provide good UVC (200-280 nm) and UVB (280-315 nm) protection, except for one that presented an appreciable window at 270 nm. Nevertheless, both natural and artificial sources have practically no emission under 300 nm. In the UVA (315-380 nm) range the curves of the different IOLs manifested different degrees of absorption. Not all the UV filters incorporated in different IOLs protect equally. The filters that provide greater photoprotection against UV radiation, even blue light, are yellow and orange. Then, yellow and orange IOL filters may be best suited for cases requiring special retinal protection. The filters that favor better photoreception of visible light (380-780 nm) are those that transmit this radiation close to 100%. Artificial illumination practically does not emit in the UV range, but its levels of illumination are very low when compared with solar light. A possible balance between photoprotection and photoreception could be a sharp cutoff filter with the cutoff wavelength near 400 nm and a maximum transmittance around 100%. Copyright © 2011 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

A practical approach to spectral calibration of short wavelength infrared hyper-spectral imaging systems

NASA Astrophysics Data System (ADS)

Bürmen, Miran; Pernuš, Franjo; Likar, Boštjan

2010-02-01

Near-infrared spectroscopy is a promising, rapidly developing, reliable and noninvasive technique, used extensively in the biomedicine and in pharmaceutical industry. With the introduction of acousto-optic tunable filters (AOTF) and highly sensitive InGaAs focal plane sensor arrays, real-time high resolution hyper-spectral imaging has become feasible for a number of new biomedical in vivo applications. However, due to the specificity of the AOTF technology and lack of spectral calibration standardization, maintaining long-term stability and compatibility of the acquired hyper-spectral images across different systems is still a challenging problem. Efficiently solving both is essential as the majority of methods for analysis of hyper-spectral images relay on a priori knowledge extracted from large spectral databases, serving as the basis for reliable qualitative or quantitative analysis of various biological samples. In this study, we propose and evaluate fast and reliable spectral calibration of hyper-spectral imaging systems in the short wavelength infrared spectral region. The proposed spectral calibration method is based on light sources or materials, exhibiting distinct spectral features, which enable robust non-rigid registration of the acquired spectra. The calibration accounts for all of the components of a typical hyper-spectral imaging system such as AOTF, light source, lens and optical fibers. The obtained results indicated that practical, fast and reliable spectral calibration of hyper-spectral imaging systems is possible, thereby assuring long-term stability and inter-system compatibility of the acquired hyper-spectral images.

Spectral splitting for thermal management in photovoltaic cells

NASA Astrophysics Data System (ADS)

Apostoleris, Harry; Chiou, Yu-Cheng; Chiesa, Matteo; Almansouri, Ibraheem

2017-09-01

Spectral splitting is widely employed as a way to divide light between different solar cells or processes to optimize energy conversion. Well-understood but less explored is the use of spectrum splitting or filtering to combat solar cell heating. This has impacts both on cell performance and on the surrounding environment. In this manuscript we explore the design of spectral filtering systems that can improve the thermal and power-conversion performance of commercial PV modules.

Acousto-Optic Tunable Filter Hyperspectral Microscope Imaging Method for Characterizing Spectra from Foodborne Pathogens.

USDA-ARS?s Scientific Manuscript database

Hyperspectral microscope imaging (HMI) method, which provides both spatial and spectral characteristics of samples, can be effective for foodborne pathogen detection. The acousto-optic tunable filter (AOTF)-based HMI method can be used to characterize spectral properties of biofilms formed by Salmon...

Improvement of LOD in Fluorescence Detection with Spectrally Nonuniform Background by Optimization of Emission Filtering.

PubMed

Galievsky, Victor A; Stasheuski, Alexander S; Krylov, Sergey N

2017-10-17

The limit-of-detection (LOD) in analytical instruments with fluorescence detection can be improved by reducing noise of optical background. Efficiently reducing optical background noise in systems with spectrally nonuniform background requires complex optimization of an emission filter-the main element of spectral filtration. Here, we introduce a filter-optimization method, which utilizes an expression for the signal-to-noise ratio (SNR) as a function of (i) all noise components (dark, shot, and flicker), (ii) emission spectrum of the analyte, (iii) emission spectrum of the optical background, and (iv) transmittance spectrum of the emission filter. In essence, the noise components and the emission spectra are determined experimentally and substituted into the expression. This leaves a single variable-the transmittance spectrum of the filter-which is optimized numerically by maximizing SNR. Maximizing SNR provides an accurate way of filter optimization, while a previously used approach based on maximizing a signal-to-background ratio (SBR) is the approximation that can lead to much poorer LOD specifically in detection of fluorescently labeled biomolecules. The proposed filter-optimization method will be an indispensable tool for developing new and improving existing fluorescence-detection systems aiming at ultimately low LOD.

A Narrow-Linewidth Atomic Line Filter for Free Space Quantum Key Distribution under Daytime Atmospheric Conditions

NASA Astrophysics Data System (ADS)

Brown, Justin; Woolf, David; Hensley, Joel

2016-05-01

Quantum key distribution can provide secure optical data links using the established BB84 protocol, though solar backgrounds severely limit the performance through free space. Several approaches to reduce the solar background include time-gating the photon signal, limiting the field of view through geometrical design of the optical system, and spectral rejection using interference filters. Despite optimization of these parameters, the solar background continues to dominate under daytime atmospheric conditions. We demonstrate an improved spectral filter by replacing the interference filter (Δν ~ 50 GHz) with an atomic line filter (Δν ~ 1 GHz) based on optical rotation of linearly polarized light through a warm Rb vapor. By controlling the magnetic field and the optical depth of the vapor, a spectrally narrow region can be transmitted between crossed polarizers. We find that the transmission is more complex than a single peak and evaluate peak transmission as well as a ratio of peak transmission to average transmission of the local spectrum. We compare filters containing a natural abundance of Rb with those containing isotopically pure 87 Rb and 85 Rb. A filter providing > 95 % transmission and Δν ~ 1.1 GHz is achieved.

UV filters for lighting of plants

NASA Astrophysics Data System (ADS)

Doehring, T.; Koefferlein, M.; Thiel, S.; Seidlitz, H. K.; Payer, H. D.

1994-03-01

The wavelength dependent interaction of biological systems with radiation is commonly described by appropriate action spectra. Particularly effective plant responses are obtained for ultraviolet (UV) radiation. Excess shortwave UV-B radiation will induce genetic defects and plant damage. Besides the ecological discussion of the deleterious effects of the excess UV radiation there is increasing interest in horticultural applications of this spectral region. Several metabolic pathways leading to valuable secondary plant products like colors, odors, taste, or resulting in mechanical strength and vitality are triggered by UV radiation. Thus, in ecologically as well as in economically oriented experiments the exact generation and knowledge of the spectral irradiance, particularly near the UV absorption edge, is essential. The ideal filter 'material' to control the UV absorption edge would be ozone itself. However, due to problems in controlling the toxic and chemically aggressive, instable gas, only rather 'small ozone filters' have been realized so far. In artificial plant lighting conventional solid filter materials such as glass sheets and plastic foils (celluloseacetate or cellulosetriacetate) which can be easily handled have been used to absorb the UV-C and the excess shortwave UV-B radiation of the lamp emissions. Different filter glasses are available which provide absorption properties suitable for gradual changes of the spectral UV-B illumination of artificial lighting. Using a distinct set of lamps and filter glasses an acceptable simulation of the UV-B part of natural global radiation can be achieved. The aging of these and other filter materials under the extreme UV radiation in the lamphouse of a solar simulator is presently unavoidable. This instability can be dealt with only by a precise spectral monitoring and by replacing the filters accordingly. For this reason attempts would be useful to develop real ozone filters which can replace glass filters. In any case chamber experiments require a careful selection of the filter material used and must be accompanied by a continuous UV-B monitoring.

UV filters for lighting of plants

NASA Technical Reports Server (NTRS)

Doehring, T.; Koefferlein, M.; Thiel, S.; Seidlitz, H. K.; Payer, H. D.

1994-01-01

The wavelength dependent interaction of biological systems with radiation is commonly described by appropriate action spectra. Particularly effective plant responses are obtained for ultraviolet (UV) radiation. Excess shortwave UV-B radiation will induce genetic defects and plant damage. Besides the ecological discussion of the deleterious effects of the excess UV radiation there is increasing interest in horticultural applications of this spectral region. Several metabolic pathways leading to valuable secondary plant products like colors, odors, taste, or resulting in mechanical strength and vitality are triggered by UV radiation. Thus, in ecologically as well as in economically oriented experiments the exact generation and knowledge of the spectral irradiance, particularly near the UV absorption edge, is essential. The ideal filter 'material' to control the UV absorption edge would be ozone itself. However, due to problems in controlling the toxic and chemically aggressive, instable gas, only rather 'small ozone filters' have been realized so far. In artificial plant lighting conventional solid filter materials such as glass sheets and plastic foils (celluloseacetate or cellulosetriacetate) which can be easily handled have been used to absorb the UV-C and the excess shortwave UV-B radiation of the lamp emissions. Different filter glasses are available which provide absorption properties suitable for gradual changes of the spectral UV-B illumination of artificial lighting. Using a distinct set of lamps and filter glasses an acceptable simulation of the UV-B part of natural global radiation can be achieved. The aging of these and other filter materials under the extreme UV radiation in the lamphouse of a solar simulator is presently unavoidable. This instability can be dealt with only by a precise spectral monitoring and by replacing the filters accordingly. For this reason attempts would be useful to develop real ozone filters which can replace glass filters. In any case chamber experiments require a careful selection of the filter material used and must be accompanied by a continuous UV-B monitoring.

Characterization of flotation color by machine vision

NASA Astrophysics Data System (ADS)

Siren, Ari

1999-09-01

Flotation is the most common industrial method by which valuable minerals are separated from waste rock after crushing and grinding the ore. For process control, flotation plants and devices are equipped with conventional and specialized sensors. However, certain variables are left to the visual observation of the operator, such as the color of the froth and the size of the bubbles in the froth. The ChaCo-Project (EU-Project 24931) was launched in November 1997. In this project a measuring station was built at the Pyhasalmi flotation plant. The system includes an RGB camera and a spectral color measuring instrument for the color inspection of the flotation. The RGB camera or visible spectral range is also measured to compare the operators' comments on the color of the froth relating to the sphalerite concentration and the process balance. Different dried mineral (sphalerite) ratios were studied with iron pyrite to find out about the minerals' typical spectral features. The correlation between sphalerite spectral reflectance and sphalerite concentration over various wavelengths are used to select the proper camera system with filters or to compare the results with the color information from the RGB camera. Various machine vision candidate techniques are discussed for this application and the preprocessed information of the dried mineral colors is used and adapted to the online measuring station. Moving froth bubbles produce total reflections, disturbing the color information. Polarization filters are used and the results are reported. Also the reflectance outside the visible light is studied and reported.

The multi-spectral line-polarization MSE system on Alcator C-Mod

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mumgaard, R. T., E-mail: mumgaard@psfc.mit.edu; Khoury, M.; Scott, S. D.

A multi-spectral line-polarization motional Stark effect (MSE-MSLP) diagnostic has been developed for the Alcator C-Mod tokamak wherein the Stokes vector is measured in multiple wavelength bands simultaneously on the same sightline to enable better polarized background subtraction. A ten-sightline, four wavelength MSE-MSLP detector system was designed, constructed, and qualified. This system consists of a high-throughput polychromator for each sightline designed to provide large étendue and precise spectral filtering in a cost-effective manner. Each polychromator utilizes four narrow bandpass interference filters and four custom large diameter avalanche photodiode detectors. Two filters collect light to the red and blue of the MSEmore » emission spectrum while the remaining two filters collect the beam pi and sigma emission generated at the same viewing volume. The filter wavelengths are temperature tuned using custom ovens in an automated manner. All system functions are remote controllable and the system can be easily retrofitted to existing single-wavelength line-polarization MSE systems.« less

The multi-spectral line-polarization MSE system on Alcator C-Mod

DOE PAGES

Mumgaard, R. T.; Scott, S. D.; Khoury, M.

2016-08-17

A multi-spectral line-polarization motional Stark effect (MSE-MSLP) diagnostic has been developed for the Alcator C-Mod tokamak wherein the Stokes vector is measured in multiple wavelength bands simultaneously on the same sightline to enable better polarized background subtraction. A ten-sightline, four wavelength MSE-MSLP detector system was designed, constructed, and qualified. This system consists of a high-throughput polychromator for each sightline designed to provide large étendue and precise spectral filtering in a cost-effective manner. Each polychromator utilizes four narrow bandpass interference filters and four custom large diameter avalanche photodiode detectors. Two filters collect light to the red and blue of the MSEmore » emission spectrum while the remaining two filters collect the beam pi and sigma emission generated at the same viewing volume. The filter wavelengths are temperature tuned using custom ovens in an automated manner. Furthermore, all system functions are remote controllable and the system can be easily retrofitted to existing single-wavelength line-polarization MSE systems.« less

Designed microstructure based on color filter and metallic nanoslit for multiband spectral compatible control

NASA Astrophysics Data System (ADS)

Zhan, Zhigang; Han, Yuge

2018-01-01

Controlling the spectral characteristics by regulating the geometry of microstructure has become an effective method to meet the requirements of various applications. To mediate the spectral characteristics, metallic subwavelength slits with different structures and color filters consisting of diverse materials were discussed, and then a designed microstructure composed of color filter and metallic slits, which were surrounded by grooves, was put forward for a compatible effect of controlling the spectral characteristics. Afterward, the spectral characteristics of the proposed structure were simulated by finite-difference time-domain method in the wavelength range of 300 to 10,000 nm. Additionally, the effects of geometric parameters on the spectral characteristics were studied. The results show that the presented microstructure can reflect a monochromatic color at the wavelength of 600 nm and its reflectance is ˜40%. The average absorptance near the wavelength of 1060 nm is more than 95%, and the average reflectance in the infrared band exceeds 80%. In conclusion, the compatible spectrum control in three bands (i.e., visible, near-infrared, and mid-infrared) was realized.

Integrated programmable photonic filter on the silicon-on-insulator platform.

PubMed

Liao, Shasha; Ding, Yunhong; Peucheret, Christophe; Yang, Ting; Dong, Jianji; Zhang, Xinliang

2014-12-29

We propose and demonstrate a silicon-on-insulator (SOI) on-chip programmable filter based on a four-tap finite impulse response structure. The photonic filter is programmable thanks to amplitude and phase modulation of each tap controlled by thermal heaters. We further demonstrate the tunability of the filter central wavelength, bandwidth and variable passband shape. The tuning range of the central wavelength is at least 42% of the free spectral range. The bandwidth tuning range is at least half of the free spectral range. Our scheme has distinct advantages of compactness, capability for integrating with electronics.

A numerical spectral approach to solve the dislocation density transport equation

NASA Astrophysics Data System (ADS)

Djaka, K. S.; Taupin, V.; Berbenni, S.; Fressengeas, C.

2015-09-01

A numerical spectral approach is developed to solve in a fast, stable and accurate fashion, the quasi-linear hyperbolic transport equation governing the spatio-temporal evolution of the dislocation density tensor in the mechanics of dislocation fields. The approach relies on using the Fast Fourier Transform algorithm. Low-pass spectral filters are employed to control both the high frequency Gibbs oscillations inherent to the Fourier method and the fast-growing numerical instabilities resulting from the hyperbolic nature of the transport equation. The numerical scheme is validated by comparison with an exact solution in the 1D case corresponding to dislocation dipole annihilation. The expansion and annihilation of dislocation loops in 2D and 3D settings are also produced and compared with finite element approximations. The spectral solutions are shown to be stable, more accurate for low Courant numbers and much less computation time-consuming than the finite element technique based on an explicit Galerkin-least squares scheme.

Real-time color measurement using active illuminant

NASA Astrophysics Data System (ADS)

Tominaga, Shoji; Horiuchi, Takahiko; Yoshimura, Akihiko

2010-01-01

This paper proposes a method for real-time color measurement using active illuminant. A synchronous measurement system is constructed by combining a high-speed active spectral light source and a high-speed monochrome camera. The light source is a programmable spectral source which is capable of emitting arbitrary spectrum in high speed. This system is the essential advantage of capturing spectral images without using filters in high frame rates. The new method of real-time colorimetry is different from the traditional method based on the colorimeter or the spectrometers. We project the color-matching functions onto an object surface as spectral illuminants. Then we can obtain the CIE-XYZ tristimulus values directly from the camera outputs at every point on the surface. We describe the principle of our colorimetric technique based on projection of the color-matching functions and the procedure for realizing a real-time measurement system of a moving object. In an experiment, we examine the performance of real-time color measurement for a static object and a moving object.

Linear variable narrow bandpass optical filters in the far infrared (Conference Presentation)

NASA Astrophysics Data System (ADS)

Rahmlow, Thomas D.

2017-06-01

We are currently developing linear variable filters (LVF) with very high wavelength gradients. In the visible, these filters have a wavelength gradient of 50 to 100 nm/mm. In the infrared, the wavelength gradient covers the range of 500 to 900 microns/mm. Filter designs include band pass, long pass and ulta-high performance anti-reflection coatings. The active area of the filters is on the order of 5 to 30 mm along the wavelength gradient and up to 30 mm in the orthogonal, constant wavelength direction. Variation in performance along the constant direction is less than 1%. Repeatable performance from filter to filter, absolute placement of the filter relative to a substrate fiducial and, high in-band transmission across the full spectral band is demonstrated. Applications include order sorting filters, direct replacement of the spectrometer and hyper-spectral imaging. Off-band rejection with an optical density of greater than 3 allows use of the filter as an order sorting filter. The linear variable order sorting filters replaces other filter types such as block filters. The disadvantage of block filters is the loss of pixels due to the transition between filter blocks. The LVF is a continuous gradient without a discrete transition between filter wavelength regions. If the LVF is designed as a narrow band pass filter, it can be used in place of a spectrometer thus reducing overall sensor weight and cost while improving the robustness of the sensor. By controlling the orthogonal performance (smile) the LVF can be sized to the dimensions of the detector. When imaging on to a 2 dimensional array and operating the sensor in a push broom configuration, the LVF spectrometer performs as a hyper-spectral imager. This paper presents performance of LVF fabricated in the far infrared on substrates sized to available detectors. The impact of spot size, F-number and filter characterization are presented. Results are also compared to extended visible LVF filters.

A Synthesis of Star Calibration Techniques for Ground-Based Narrowband Electron-Multiplying Charge-Coupled Device Imagers Used in Auroral Photometry

NASA Technical Reports Server (NTRS)

Grubbs, Guy II; Michell, Robert; Samara, Marilia; Hampton, Don; Jahn, Jorg-Micha

2016-01-01

A technique is presented for the periodic and systematic calibration of ground-based optical imagers. It is important to have a common system of units (Rayleighs or photon flux) for cross comparison as well as self-comparison over time. With the advancement in technology, the sensitivity of these imagers has improved so that stars can be used for more precise calibration. Background subtraction, flat fielding, star mapping, and other common techniques are combined in deriving a calibration technique appropriate for a variety of ground-based imager installations. Spectral (4278, 5577, and 8446 A ) ground-based imager data with multiple fields of view (19, 47, and 180 deg) are processed and calibrated using the techniques developed. The calibration techniques applied result in intensity measurements in agreement between different imagers using identical spectral filtering, and the intensity at each wavelength observed is within the expected range of auroral measurements. The application of these star calibration techniques, which convert raw imager counts into units of photon flux, makes it possible to do quantitative photometry. The computed photon fluxes, in units of Rayleighs, can be used for the absolute photometry between instruments or as input parameters for auroral electron transport models.

Gas filter correlation radiometry: Report of panel

NASA Technical Reports Server (NTRS)

Reichle, Henry G., Jr.; Barringer, A. A.; Nichols, Ralph; Russell, James M., III

1987-01-01

To measure the concentration of a gas in the troposphere, the gas filter radiometer correlates the pattern of the spectral lines of a sample of gas contained within the instrument with the pattern of the spectral lines in the upwelling radiation. A schematic diagram of a generalized gas filter radiometer is shown. Three instruments (the Gas Filter Radiometer, GFR; the Halogen Occultation Experiment, HALOE; and the Gas Filter Correlation Spectrometer, GASCOFIL) that have application to remotely measuring tropospheric constituents are described. A set of preliminary calculations to determine the feasibility of performing a multiple-layer, tropospheric carbon monoxide measurement experiment was performed. It can be seen that a three-layer measurement in the troposphere is possible.

Gas filter correlation radiometry: Report of panel

NASA Astrophysics Data System (ADS)

Reichle, Henry G., Jr.; Barringer, A. A.; Nichols, Ralph; Russell, James M., III

1987-02-01

To measure the concentration of a gas in the troposphere, the gas filter radiometer correlates the pattern of the spectral lines of a sample of gas contained within the instrument with the pattern of the spectral lines in the upwelling radiation. A schematic diagram of a generalized gas filter radiometer is shown. Three instruments (the Gas Filter Radiometer, GFR; the Halogen Occultation Experiment, HALOE; and the Gas Filter Correlation Spectrometer, GASCOFIL) that have application to remotely measuring tropospheric constituents are described. A set of preliminary calculations to determine the feasibility of performing a multiple-layer, tropospheric carbon monoxide measurement experiment was performed. It can be seen that a three-layer measurement in the troposphere is possible.

Radical protection by differently composed creams in the UV/VIS and IR spectral ranges.

PubMed

Meinke, Martina C; Syring, Felicia; Schanzer, Sabine; Haag, Stefan F; Graf, Rüdiger; Loch, Manuela; Gersonde, Ingo; Groth, Norbert; Pflücker, Frank; Lademann, Jürgen

2013-01-01

Modern sunscreens are well suited to provide sufficient protection in the UV range because the filter substances absorb or scatter UV radiation. Although up to 50% of radicals are formed in the visible and infrared spectral range during solar radiation protection strategies are not provided in this range. Previous investigations of commercially available products have shown that in addition to physical filters, antioxidants (AO) are necessary to provide protective effects in the infrared range by neutralizing already formed radicals. In this study, the efficacy of filter substances and AO to reduce radical formation in both spectral ranges was investigated after UV/VIS or IR irradiation. Optical properties and radical protection were determined for the investigated creams. It was found that organic UV filters lower radical formation in the UV/VIS range to 35% compared to untreated skin, independent of the presence of AO. Further reduction to 14% was reached by addition of 2% physical filters, whereas physical filters alone were ineffective in the UV/VIS range due to the low concentration. In contrast, this filter type reduced radical formation in the IR range significantly to 65%; similar effects were aroused after application of AO. Sunscreens which contain organic UV filters, physical filters and AO ensure protection in the complete solar spectrum. © 2013 The American Society of Photobiology.

Improvement of contact grating device for efficient terahertz wave generation using bi-angular filter

NASA Astrophysics Data System (ADS)

Nagashima, Keisuke; Tsubouchi, Masaaki; Ochi, Yoshihiro; Maruyama, Momoko

2018-03-01

We have proposed an improved contact grating device for generating terahertz waves efficiently and have succeeded in developing the device with a very high diffraction efficiency and a wide spectral width. This device has a bi-angular filter and a Fabry-Perot-type structure, which are composed of dielectric multilayers. The bi-angular filter is designed to reflect the 0th-order wave and transmit the-1st-order diffraction wave. Numerical calculations indicate that the new device has a maximum diffraction efficiency over 99% and a spectral width of approximately 20 nm. We measured a high efficiency of 90% over a broad spectral range using a fabricated device.

Physically motivated correlation formalism in hyperspectral imaging

NASA Astrophysics Data System (ADS)

Roy, Ankita; Rafert, J. Bruce

2004-05-01

Most remote sensing data-sets contain a limiting number of independent spatial and spectral measurements, beyond which no effective increase in information is achieved. This paper presents a Physically Motivated Correlation Formalism (PMCF) ,which places both Spatial and Spectral data on an equivalent mathematical footing in the context of a specific Kernel, such that, optimal combinations of independent data can be selected from the entire Hypercube via the method of "Correlation Moments". We present an experimental and computational analysis of Hyperspectral data sets using the Michigan Tech VFTHSI [Visible Fourier Transform Hyperspectral Imager] based on a Sagnac Interferometer, adjusted to obtain high SNR levels. The captured Signal Interferograms of different targets - aerial snaps of Houghton and lab-based data (white light , He-Ne laser , discharge tube sources) with the provision of customized scan of targets with the same exposures are processed using inverse imaging transformations and filtering techniques to obtain the Spectral profiles and generate Hypercubes to compute Spectral/Spatial/Cross Moments. PMCF answers the question of how optimally the entire hypercube should be sampled and finds how many spatial-spectral pixels are required for a particular target recognition.

An evaluation of random analysis methods for the determination of panel damping

NASA Technical Reports Server (NTRS)

Bhat, W. V.; Wilby, J. F.

1972-01-01

An analysis is made of steady-state and non-steady-state methods for the measurement of panel damping. Particular emphasis is placed on the use of random process techniques in conjunction with digital data reduction methods. The steady-state methods considered use the response power spectral density, response autocorrelation, excitation-response crosspower spectral density, or single-sided Fourier transform (SSFT) of the response autocorrelation function. Non-steady-state methods are associated mainly with the use of rapid frequency sweep excitation. Problems associated with the practical application of each method are evaluated with specific reference to the case of a panel exposed to a turbulent airflow, and two methods, the power spectral density and the single-sided Fourier transform methods, are selected as being the most suitable. These two methods are demonstrated experimentally, and it is shown that the power spectral density method is satisfactory under most conditions, provided that appropriate corrections are applied to account for filter bandwidth and background noise errors. Thus, the response power spectral density method is recommended for the measurement of the damping of panels exposed to a moving airflow.

Spectral imaging and passive sampling to investigate particle sources in urban desert regions.

PubMed

Wagner, Jeff; Casuccio, Gary

2014-07-01

Two types of electron microscopy analyses were employed along with geographic information system (GIS) mapping to investigate potential sources of PM2.5 and PM10 (airborne particulate matter smaller than 2.5 and 10 μm, respectively) in two urbanized desert areas known to exhibit PM excursions. Integrated spectral imaging maps were obtained from scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) analyses of 13 filters collected in Imperial Valley, California. Seven were from 24 h PM10 Federal Reference Method (FRM) samplers and six were from PM2.5 FRM samplers. This technique enabled extraction of information from particles collected on complex filter matrices, and indicated that all samples exhibited substantial proportions of crustal particles. Six Imperial PM2.5 and PM10 filters selected from unusually high-PM days exhibited more large particles (2.5-15 and 10-30 μm, respectively) than did filters from low-PM days, and were more consistent with soils analyzed from the region. High winds were present on three of the six high-PM days. One of the high-PM2.5 filters also exhibited substantial fine carbonaceous soot PM, suggesting significant contributions from a combustion source. Computer-controlled SEM/EDS (CCSEM/EDS) was conducted on PM collected with UNC Passive samplers from Phoenix, Arizona. The passive samplers showed good agreement with co-located FRM PM10 and PM2.5 measurements (μg m(-3)), and also enabled detailed individual particle analysis. The CCSEM/EDS data revealed mostly crustal particles in both the Phoenix fine and coarse PM10 fractions. GIS maps of multiple dust-related parameters confirm that both Imperial Valley and Phoenix possess favorable conditions for airborne crustal PM from natural and anthropogenic sources.

Time Reversal Acoustic Communication Using Filtered Multitone Modulation

PubMed Central

Sun, Lin; Chen, Baowei; Li, Haisen; Zhou, Tian; Li, Ruo

2015-01-01

The multipath spread in underwater acoustic channels is severe and, therefore, when the symbol rate of the time reversal (TR) acoustic communication using single-carrier (SC) modulation is high, the large intersymbol interference (ISI) span caused by multipath reduces the performance of the TR process and needs to be removed using the long adaptive equalizer as the post-processor. In this paper, a TR acoustic communication method using filtered multitone (FMT) modulation is proposed in order to reduce the residual ISI in the processed signal using TR. In the proposed method, FMT modulation is exploited to modulate information symbols onto separate subcarriers with high spectral containment and TR technique, as well as adaptive equalization is adopted at the receiver to suppress ISI and noise. The performance of the proposed method is assessed through simulation and real data from a trial in an experimental pool. The proposed method was compared with the TR acoustic communication using SC modulation with the same spectral efficiency. Results demonstrate that the proposed method can improve the performance of the TR process and reduce the computational complexity of adaptive equalization for post-process. PMID:26393586

Time Reversal Acoustic Communication Using Filtered Multitone Modulation.

PubMed

Sun, Lin; Chen, Baowei; Li, Haisen; Zhou, Tian; Li, Ruo

2015-09-17

The multipath spread in underwater acoustic channels is severe and, therefore, when the symbol rate of the time reversal (TR) acoustic communication using single-carrier (SC) modulation is high, the large intersymbol interference (ISI) span caused by multipath reduces the performance of the TR process and needs to be removed using the long adaptive equalizer as the post-processor. In this paper, a TR acoustic communication method using filtered multitone (FMT) modulation is proposed in order to reduce the residual ISI in the processed signal using TR. In the proposed method, FMT modulation is exploited to modulate information symbols onto separate subcarriers with high spectral containment and TR technique, as well as adaptive equalization is adopted at the receiver to suppress ISI and noise. The performance of the proposed method is assessed through simulation and real data from a trial in an experimental pool. The proposed method was compared with the TR acoustic communication using SC modulation with the same spectral efficiency. Results demonstrate that the proposed method can improve the performance of the TR process and reduce the computational complexity of adaptive equalization for post-process.

Optical Imagers | CTIO

Science.gov Websites

DECam SAM 0.9-m CCD Goodman SOI Optical Spectrographs CHIRON COSMOS Goodman Filters Telescopes Blanco 4 magnitudes, astrometric, and spectral properties Filters Filter Overview Filter list (all filters up to and including 4x4-inch, sorted by wavelength) Filters - 3 & 4 inch (for SOAR, Schmidt, 0.9-m imaging

Using water raman intensity to determine the effective excitation and emission path lengths of fluorophotometers for correcting fluorescence inner filter effect

USDA-ARS?s Scientific Manuscript database

Fluorescence and Raman inner filter effects (IFE) cause spectral distortion and nonlinearity between spectral signal intensity with increasing analyte concentration. Convenient and effective correction of fluorescence IFE has been an active research goal for decades. Presented herein is the finding ...

Assessing the Temperature Dependence of Narrow-Band Raman Water Vapor Lidar Measurements: A Practical Approach

NASA Technical Reports Server (NTRS)

Whiteman, David N.; Venable, Demetrius D.; Walker, Monique; Cardirola, Martin; Sakai, Tetsu; Veselovskii, Igor

2013-01-01

Narrow-band detection of the Raman water vapor spectrum using the lidar technique introduces a concern over the temperature dependence of the Raman spectrum. Various groups have addressed this issue either by trying to minimize the temperature dependence to the point where it can be ignored or by correcting for whatever degree of temperature dependence exists. The traditional technique for performing either of these entails accurately measuring both the laser output wavelength and the water vapor spectral passband with combined uncertainty of approximately 0.01 nm. However, uncertainty in interference filter center wavelengths and laser output wavelengths can be this large or larger. These combined uncertainties translate into uncertainties in the magnitude of the temperature dependence of the Raman lidar water vapor measurement of 3% or more. We present here an alternate approach for accurately determining the temperature dependence of the Raman lidar water vapor measurement. This alternate approach entails acquiring sequential atmospheric profiles using the lidar while scanning the channel passband across portions of the Raman water vapor Q-branch. This scanning is accomplished either by tilt-tuning an interference filter or by scanning the output of a spectrometer. Through this process a peak in the transmitted intensity can be discerned in a manner that defines the spectral location of the channel passband with respect to the laser output wavelength to much higher accuracy than that achieved with standard laboratory techniques. Given the peak of the water vapor signal intensity curve, determined using the techniques described here, and an approximate knowledge of atmospheric temperature, the temperature dependence of a given Raman lidar profile can be determined with accuracy of 0.5% or better. A Mathematica notebook that demonstrates the calculations used here is available from the lead author.

Images and Spectral Performance of WFC3 Interference Filters

NASA Technical Reports Server (NTRS)

Quijada, Manuel A.; Boucarut, R.; Telfer, R.; Baggett, S.; Quijano, J. Kim; Allen, George; Arsenovic, Peter

2006-01-01

The Wide Field Camera 3 (WFC3) is a panchromatic imager that will be deployed in the Hubble Space Telescope (HST). The mission of the WFC3 is to enhance HST1s imaging capability in the ultraviolet, visible and near-infrared spectral regions. Together with a wavelength coverage spanning 2000A to 1.7 micron, the WFC3 high sensitivity, high spatial resolution, and large field-of-view provide the astronomer with an unprecedented set of tools for exploring all types of exciting astrophysical terrain and for addressing many key questions in astronomy today. The filter compliment, which includes broad, medium, and narrow band filters, naturally reflects the diversity of astronomical programs to be targeted with WFC3. The WFC3 holds 61 UVIS filters elements, 14 IR filters, and 3 dispersive elements. During ground testing, the majority of the UVIS filters were found to exhibit excellent performance consistent with or exceeding expectations; however, a subset of filters showed considerable ghost images; some with relative intensity as high as 10-15%. Replacement filters with band-defining coatings that substantially reduce these ghost images were designed and procured. A state-of-the-art characterization setup was developed to measured the intensity of ghost images, focal shift, wedge direction , transmitted uniformity and surface feature of filters that could effect uniform flat field images. We will report on this new filter characterization methods, as well as the spectral performance measurements of the in-band transmittance and blocking.

Bessel smoothing filter for spectral-element mesh

NASA Astrophysics Data System (ADS)

Trinh, P. T.; Brossier, R.; Métivier, L.; Virieux, J.; Wellington, P.

2017-06-01

Smoothing filters are extremely important tools in seismic imaging and inversion, such as for traveltime tomography, migration and waveform inversion. For efficiency, and as they can be used a number of times during inversion, it is important that these filters can easily incorporate prior information on the geological structure of the investigated medium, through variable coherent lengths and orientation. In this study, we promote the use of the Bessel filter to achieve these purposes. Instead of considering the direct application of the filter, we demonstrate that we can rely on the equation associated with its inverse filter, which amounts to the solution of an elliptic partial differential equation. This enhances the efficiency of the filter application, and also its flexibility. We apply this strategy within a spectral-element-based elastic full waveform inversion framework. Taking advantage of this formulation, we apply the Bessel filter by solving the associated partial differential equation directly on the spectral-element mesh through the standard weak formulation. This avoids cumbersome projection operators between the spectral-element mesh and a regular Cartesian grid, or expensive explicit windowed convolution on the finite-element mesh, which is often used for applying smoothing operators. The associated linear system is solved efficiently through a parallel conjugate gradient algorithm, in which the matrix vector product is factorized and highly optimized with vectorized computation. Significant scaling behaviour is obtained when comparing this strategy with the explicit convolution method. The theoretical numerical complexity of this approach increases linearly with the coherent length, whereas a sublinear relationship is observed practically. Numerical illustrations are provided here for schematic examples, and for a more realistic elastic full waveform inversion gradient smoothing on the SEAM II benchmark model. These examples illustrate well the efficiency and flexibility of the approach proposed.

Australian Oceanographic Data Centre Bulletin 16.

DTIC Science & Technology

1983-05-01

iable that with the quantities of data involved sonic bad data will be archived. In order to exclude this various filtering techniques will be employed. 4...analysed for statistical properties (e.g. burst nican. variance, exceedance and spectral properties) and certain values are correlated with relevant forcing...seconds) < DAY N 0 : 281 z. -15 ,E: o E < INSTRUMENT: MMI 585 .- X AXIS BEARING: 280 0 DATA POINT Z MEAN RESOLVED CURRENT - 15 MAGNITUDE: 7. 1 Cm/s

Performance comparisons on spatial lattice algorithm and direct matrix inverse method with application to adaptive arrays processing

NASA Technical Reports Server (NTRS)

An, S. H.; Yao, K.

1986-01-01

Lattice algorithm has been employed in numerous adaptive filtering applications such as speech analysis/synthesis, noise canceling, spectral analysis, and channel equalization. In this paper the application to adaptive-array processing is discussed. The advantages are fast convergence rate as well as computational accuracy independent of the noise and interference conditions. The results produced by this technique are compared to those obtained by the direct matrix inverse method.

Experimental applications of multispectral data to natural resource inventory and survey

NASA Technical Reports Server (NTRS)

Mallon, H. J.

1970-01-01

The feasibility of using multispectral, color, color infrared, thermal infrared imagery and related ground data to recognize, identify, determine and monitor the status of mineral ore and metals stockpiles is studied. An attempt was made to identify valid, unique spectral signatures of such materials for possible use under a wide variety of environmental circumstances. Research emphasis was upon the analysis of the multiband imagery from the various film-filter combinations, using density analysis techniques.

Controlling pulse delay by light and low magnetic fields: slow light in emerald induced by transient spectral hole-burning.

PubMed

Rajan, Rajitha Papukutty; Riesen, Hans; Rebane, Aleksander

2013-11-15

Slow light based on transient spectral hole-burning is reported for emerald, Be(3)Al(2)Si(6)O(18):Cr(3+). Experiments were conducted in π polarization on the R(1)(± 3/2) line (E2 ← A(2)4) at 2.2 K in zero field and low magnetic fields B||c. The hole width was strongly dependent on B||c, and this allowed us to smoothly tune the pulse delay from 40 to 154 ns between zero field and B||c = 15.2 mT. The latter corresponds to a group velocity of 16 km/s. Slow light in conjunction with a linear filter theory can be used as a powerful and accurate technique in time-resolved spectroscopy, e.g., to determine spectral hole-widths as a function of time.

Galileo's Earth-Moon portrait

NASA Astrophysics Data System (ADS)

Simarski, Lynn Teo

Research reported at an AGU session on Galileo's Earth/Moon flyby refined the spacecraft's distinctive portrait of the Earth-Moon system. The Galileo team presented dramatic new views of the Earth and Moon taken last December. Andrew P. Ingersoll showed a color movie of the rotating Earth, made through spectral filters with which Galileo viewed the Earth almost continuously for 25 hours.Galileo also made finely tuned observations of vegetation and clouds, using three very closely spaced spectral wavelengths in the near-infrared, explained W. Reid Thompson. In the resulting images, Argentinian grassland and Brazilian rain forest are clearly distinguished, demonstrating the applicability of this technique for routine monitoring of deforestation, shifts in vegetation due to climate, and other phenomena. Thompson suggested that this capability could be used on the Earth Observing System. One of the spectral bands may also have potential for monitoring cloud condensation, as it appears to differentiate actively condensing, vapor-heavy clouds from higher and drier clouds.

High-resolution NMR characterization of low abundance oligomers of amyloid-β without purification

NASA Astrophysics Data System (ADS)

Kotler, Samuel A.; Brender, Jeffrey R.; Vivekanandan, Subramanian; Suzuki, Yuta; Yamamoto, Kazutoshi; Monette, Martine; Krishnamoorthy, Janarthanan; Walsh, Patrick; Cauble, Meagan; Holl, Mark M. Banaszak; Marsh, E. Neil. G.; Ramamoorthy, Ayyalusamy

2015-07-01

Alzheimer’s disease is characterized by the misfolding and self-assembly of the amyloidogenic protein amyloid-β (Aβ). The aggregation of Aβ leads to diverse oligomeric states, each of which may be potential targets for intervention. Obtaining insight into Aβ oligomers at the atomic level has been a major challenge to most techniques. Here, we use magic angle spinning recoupling 1H-1H NMR experiments to overcome many of these limitations. Using 1H-1H dipolar couplings as a NMR spectral filter to remove both high and low molecular weight species, we provide atomic-level characterization of a non-fibrillar aggregation product of the Aβ1-40 peptide using non-frozen samples without isotopic labeling. Importantly, this spectral filter allows the detection of the specific oligomer signal without a separate purification procedure. In comparison to other solid-state NMR techniques, the experiment is extraordinarily selective and sensitive. A resolved 2D spectra could be acquired of a small population of oligomers (6 micrograms, 7% of the total) amongst a much larger population of monomers and fibers (93% of the total). By coupling real-time 1H-1H NMR experiments with other biophysical measurements, we show that a stable, primarily disordered Aβ1-40 oligomer 5-15 nm in diameter can form and coexist in parallel with the well-known cross-β-sheet fibrils.

High-resolution NMR characterization of low abundance oligomers of amyloid-β without purification

PubMed Central

Kotler, Samuel A.; Brender, Jeffrey R.; Vivekanandan, Subramanian; Suzuki, Yuta; Yamamoto, Kazutoshi; Monette, Martine; Krishnamoorthy, Janarthanan; Walsh, Patrick; Cauble, Meagan; Holl, Mark M. Banaszak; Marsh, E. Neil. G.; Ramamoorthy, Ayyalusamy

2015-01-01

Alzheimer’s disease is characterized by the misfolding and self-assembly of the amyloidogenic protein amyloid-β (Aβ). The aggregation of Aβ leads to diverse oligomeric states, each of which may be potential targets for intervention. Obtaining insight into Aβ oligomers at the atomic level has been a major challenge to most techniques. Here, we use magic angle spinning recoupling 1H-1H NMR experiments to overcome many of these limitations. Using 1H-1H dipolar couplings as a NMR spectral filter to remove both high and low molecular weight species, we provide atomic-level characterization of a non-fibrillar aggregation product of the Aβ1-40 peptide using non-frozen samples without isotopic labeling. Importantly, this spectral filter allows the detection of the specific oligomer signal without a separate purification procedure. In comparison to other solid-state NMR techniques, the experiment is extraordinarily selective and sensitive. A resolved 2D spectra could be acquired of a small population of oligomers (6 micrograms, 7% of the total) amongst a much larger population of monomers and fibers (93% of the total). By coupling real-time 1H-1H NMR experiments with other biophysical measurements, we show that a stable, primarily disordered Aβ1-40 oligomer 5–15 nm in diameter can form and coexist in parallel with the well-known cross-β-sheet fibrils. PMID:26138908

High-resolution NMR characterization of low abundance oligomers of amyloid-β without purification.

PubMed

Kotler, Samuel A; Brender, Jeffrey R; Vivekanandan, Subramanian; Suzuki, Yuta; Yamamoto, Kazutoshi; Monette, Martine; Krishnamoorthy, Janarthanan; Walsh, Patrick; Cauble, Meagan; Holl, Mark M Banaszak; Marsh, E Neil G; Ramamoorthy, Ayyalusamy

2015-07-03

Alzheimer's disease is characterized by the misfolding and self-assembly of the amyloidogenic protein amyloid-β (Aβ). The aggregation of Aβ leads to diverse oligomeric states, each of which may be potential targets for intervention. Obtaining insight into Aβ oligomers at the atomic level has been a major challenge to most techniques. Here, we use magic angle spinning recoupling (1)H-(1)H NMR experiments to overcome many of these limitations. Using (1)H-(1)H dipolar couplings as a NMR spectral filter to remove both high and low molecular weight species, we provide atomic-level characterization of a non-fibrillar aggregation product of the Aβ1-40 peptide using non-frozen samples without isotopic labeling. Importantly, this spectral filter allows the detection of the specific oligomer signal without a separate purification procedure. In comparison to other solid-state NMR techniques, the experiment is extraordinarily selective and sensitive. A resolved 2D spectra could be acquired of a small population of oligomers (6 micrograms, 7% of the total) amongst a much larger population of monomers and fibers (93% of the total). By coupling real-time (1)H-(1)H NMR experiments with other biophysical measurements, we show that a stable, primarily disordered Aβ1-40 oligomer 5-15 nm in diameter can form and coexist in parallel with the well-known cross-β-sheet fibrils.

Performance Assessment of Different Pulse Reconstruction Algorithms for the ATHENA X-Ray Integral Field Unit

NASA Technical Reports Server (NTRS)

Peille, Phillip; Ceballos, Maria Teresa; Cobo, Beatriz; Wilms, Joern; Bandler, Simon; Smith, Stephen J.; Dauser, Thomas; Brand, Thorsten; Den Haretog, Roland; de Plaa, Jelle;

Model-independent Exoplanet Transit Spectroscopy

NASA Astrophysics Data System (ADS)

Aronson, Erik; Piskunov, Nikolai

2018-05-01

We propose a new data analysis method for obtaining transmission spectra of exoplanet atmospheres and brightness variation across the stellar disk from transit observations. The new method is capable of recovering exoplanet atmosphere absorption spectra and stellar specific intensities without relying on theoretical models of stars and planets. We simultaneously fit both stellar specific intensity and planetary radius directly to transit light curves. This allows stellar models to be removed from the data analysis. Furthermore, we use a data quality weighted filtering technique to achieve an optimal trade-off between spectral resolution and reconstruction fidelity homogenizing the signal-to-noise ratio across the wavelength range. Such an approach is more efficient than conventional data binning onto a low-resolution wavelength grid. We demonstrate that our analysis is capable of reproducing results achieved by using an explicit quadratic limb-darkening equation and that the filtering technique helps eliminate spurious spectral features in regions with strong telluric absorption. The method is applied to the VLT FORS2 observations of the exoplanets GJ 1214 b and WASP-49 b, and our results are in agreement with previous studies. Comparisons between obtained stellar specific intensity and numerical models indicates that the method is capable of accurately reconstructing the specific intensity. The proposed method enables more robust characterization of exoplanetary atmospheres by separating derivation of planetary transmission and stellar specific intensity spectra (that is model-independent) from chemical and physical interpretation.

Cooled optical filters for Q-band infrared astronomy (15-40 μm)

NASA Astrophysics Data System (ADS)

Hawkins, Gary J.; Sherwood, Richard E.; Djotni, Karim; Threadgold, Timothy M.

2016-07-01

With a growing interest in mid- and far-infrared astronomy using cooled imaging and spectrometer instruments in highaltitude observatories and spaceflight telescopes, it is becoming increasingly important to characterise and assess the spectral performance of cooled multilayer filters across the Q-band atmospheric window. This region contains spectral features emitted by many astrophysical phenomena and objects fundamental to circumstellar and planetary formation theories. However extending interference filtering to isolate radiation at progressively longer wavelengths and improve photometric accuracy is an area of ongoing and challenging thin-film research. We have successfully fabricated cooled bandpass and edge filters with high durability for operation across the 15-30 μm Q-band region. In this paper we describe the rationale for selection of optical materials and properties of fabricated thin-film coatings for this region, together with FTIR spectral measurements and assessment of environmental durability.

Uncertainty analysis technique for OMEGA Dante measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

May, M. J.; Widmann, K.; Sorce, C.

2010-10-15

The Dante is an 18 channel x-ray filtered diode array which records the spectrally and temporally resolved radiation flux from various targets (e.g., hohlraums, etc.) at x-ray energies between 50 eV and 10 keV. It is a main diagnostic installed on the OMEGA laser facility at the Laboratory for Laser Energetics, University of Rochester. The absolute flux is determined from the photometric calibration of the x-ray diodes, filters and mirrors, and an unfold algorithm. Understanding the errors on this absolute measurement is critical for understanding hohlraum energetic physics. We present a new method for quantifying the uncertainties on the determinedmore » flux using a Monte Carlo parameter variation technique. This technique combines the uncertainties in both the unfold algorithm and the error from the absolute calibration of each channel into a one sigma Gaussian error function. One thousand test voltage sets are created using these error functions and processed by the unfold algorithm to produce individual spectra and fluxes. Statistical methods are applied to the resultant set of fluxes to estimate error bars on the measurements.« less

Uncertainty Analysis Technique for OMEGA Dante Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

May, M J; Widmann, K; Sorce, C

2010-05-07

The Dante is an 18 channel X-ray filtered diode array which records the spectrally and temporally resolved radiation flux from various targets (e.g. hohlraums, etc.) at X-ray energies between 50 eV to 10 keV. It is a main diagnostics installed on the OMEGA laser facility at the Laboratory for Laser Energetics, University of Rochester. The absolute flux is determined from the photometric calibration of the X-ray diodes, filters and mirrors and an unfold algorithm. Understanding the errors on this absolute measurement is critical for understanding hohlraum energetic physics. We present a new method for quantifying the uncertainties on the determinedmore » flux using a Monte-Carlo parameter variation technique. This technique combines the uncertainties in both the unfold algorithm and the error from the absolute calibration of each channel into a one sigma Gaussian error function. One thousand test voltage sets are created using these error functions and processed by the unfold algorithm to produce individual spectra and fluxes. Statistical methods are applied to the resultant set of fluxes to estimate error bars on the measurements.« less

Lamp mapping technique for independent determination of the water vapor mixing ratio calibration factor for a Raman lidar system

NASA Astrophysics Data System (ADS)

Venable, Demetrius D.; Whiteman, David N.; Calhoun, Monique N.; Dirisu, Afusat O.; Connell, Rasheen M.; Landulfo, Eduardo

2011-08-01

We have investigated a technique that allows for the independent determination of the water vapor mixing ratio calibration factor for a Raman lidar system. This technique utilizes a procedure whereby a light source of known spectral characteristics is scanned across the aperture of the lidar system's telescope and the overall optical efficiency of the system is determined. Direct analysis of the temperature-dependent differential scattering cross sections for vibration and vibration-rotation transitions (convolved with narrowband filters) along with the measured efficiency of the system, leads to a theoretical determination of the water vapor mixing ratio calibration factor. A calibration factor was also obtained experimentally from lidar measurements and radiosonde data. A comparison of the theoretical and experimentally determined values agrees within 5%. We report on the sensitivity of the water vapor mixing ratio calibration factor to uncertainties in parameters that characterize the narrowband transmission filters, the temperature-dependent differential scattering cross section, and the variability of the system efficiency ratios as the lamp is scanned across the aperture of the telescope used in the Howard University Raman Lidar system.

Spectral radiance source based on supercontinuum laser and wavelength tunable bandpass filter: the spectrally tunable absolute irradiance and radiance source.

PubMed

Levick, Andrew P; Greenwell, Claire L; Ireland, Jane; Woolliams, Emma R; Goodman, Teresa M; Bialek, Agnieszka; Fox, Nigel P

2014-06-01

A new spectrally tunable source for calibration of radiometric detectors in radiance, irradiance, or power mode has been developed and characterized. It is termed the spectrally tunable absolute irradiance and radiance source (STAIRS). It consists of a supercontinuum laser, wavelength tunable bandpass filter, power stabilization feedback control scheme, and output coupling optics. It has the advantages of relative portability and a collimated beam (low étendue), and is an alternative to conventional sources such as tungsten lamps, blackbodies, or tunable lasers. The supercontinuum laser is a commercial Fianium SC400-6-02, which has a wavelength range between 400 and 2500 nm and a total power of 6 W. The wavelength tunable bandpass filter, a PhotonEtc laser line tunable filter (LLTF), is tunable between 400 and 1000 nm and has a bandwidth of 1 or 2 nm depending on the wavelength selected. The collimated laser beam from the LLTF filter is converted to an appropriate spatial and angular distribution for the application considered (i.e., for radiance, irradiance, or power mode calibration of a radiometric sensor) with the output coupling optics, for example, an integrating sphere, and the spectral radiance/irradiance/power of the source is measured using a calibration optical sensor. A power stabilization feedback control scheme has been incorporated that stabilizes the source to better than 0.01% for averaging times longer than 100 s. The out-of-band transmission of the LLTF filter is estimated to be < -65 dB (0.00003%), and is sufficiently low for many end-user applications, for example the spectral radiance calibration of earth observation imaging radiometers and the stray light characterization of array spectrometers (the end-user optical sensor). We have made initial measurements of two end-user instruments with the STAIRS source, an array spectrometer and ocean color radiometer.

Analysis of hyperspectral fluorescence images for poultry skin tumor inspection

NASA Astrophysics Data System (ADS)

Kong, Seong G.; Chen, Yud-Ren; Kim, Intaek; Kim, Moon S.

2004-02-01

We present a hyperspectral fluorescence imaging system with a fuzzy inference scheme for detecting skin tumors on poultry carcasses. Hyperspectral images reveal spatial and spectral information useful for finding pathological lesions or contaminants on agricultural products. Skin tumors are not obvious because the visual signature appears as a shape distortion rather than a discoloration. Fluorescence imaging allows the visualization of poultry skin tumors more easily than reflectance. The hyperspectral image samples obtained for this poultry tumor inspection contain 65 spectral bands of fluorescence in the visible region of the spectrum at wavelengths ranging from 425 to 711 nm. The large amount of hyperspectral image data is compressed by use of a discrete wavelet transform in the spatial domain. Principal-component analysis provides an effective compressed representation of the spectral signal of each pixel in the spectral domain. A small number of significant features are extracted from two major spectral peaks of relative fluorescence intensity that have been identified as meaningful spectral bands for detecting tumors. A fuzzy inference scheme that uses a small number of fuzzy rules and Gaussian membership functions successfully detects skin tumors on poultry carcasses. Spatial-filtering techniques are used to significantly reduce false positives.

Aperiodic nanoplasmonic devices for directional colour filtering and sensing.

PubMed

Davis, Matthew S; Zhu, Wenqi; Xu, Ting; Lee, Jay K; Lezec, Henri J; Agrawal, Amit

2017-11-07

Exploiting the wave-nature of light in its simplest form, periodic architectures have enabled a panoply of tunable optical devices with the ability to perform useful functions such as filtering, spectroscopy, and multiplexing. Here, we remove the constraint of structural periodicity to enhance, simultaneously, the performance and functionality of passive plasmonic devices operating at optical frequencies. By using a physically intuitive, first-order interference model of plasmon-light interactions, we demonstrate a simple and efficient route towards designing devices with flexible, multi-spectral optical response, fundamentally not achievable using periodic architectures. Leveraging this approach, we experimentally implement ultra-compact directional light-filters and colour-sorters exhibiting angle- or spectrally-tunable optical responses with high contrast, and low spectral or spatial crosstalk. Expanding the potential of aperiodic systems to implement tailored spectral and angular responses, these results hint at promising applications in solar-energy harvesting, optical signal multiplexing, and integrated sensing.

Polarization-independent tunable spectral slicing filter in Ti:LiNbO3.

PubMed

Rabelo, Renato C; Eknoyan, Ohannes; Taylor, Henry F

2011-02-01

A two-port polarization-independent tunable spectral slicing filter at the 1530 nm wavelength regime is presented. The design utilizes an asymmetric interferometer with a sparse index grating along its arms. The sparse grating makes it possible to select equally spaced frequency channels from an incident WDM signal and to place nulls between them to coincide with the signal comb frequency. The number of selected channels and nulls between them depends on the number of coupling regions used in the sparse grating. The free spectral range depends on the spacing between the coupling regions. The Z-transform method is used to synthesize the filter and determine the spectral response. The operation of a device with six coupling regions is demonstrated, and good agreement with theoretical predictions is obtained. A 3 dB bandwidth of ∼1 nm and thermal tuning over a range of ∼13 nm are measured.

An Improved Framework for Confound Regression and Filtering for Control of Motion Artifact in the Preprocessing of Resting-State Functional Connectivity Data

PubMed Central

Satterthwaite, Theodore D.; Elliott, Mark A.; Gerraty, Raphael T.; Ruparel, Kosha; Loughead, James; Calkins, Monica E.; Eickhoff, Simon B.; Hakonarson, Hakon; Gur, Ruben C.; Gur, Raquel E.; Wolf, Daniel H.

2013-01-01

Several recent reports in large, independent samples have demonstrated the influence of motion artifact on resting-state functional connectivity MRI (rsfc-MRI). Standard rsfc-MRI preprocessing typically includes regression of confounding signals and band-pass filtering. However, substantial heterogeneity exists in how these techniques are implemented across studies, and no prior study has examined the effect of differing approaches for the control of motion-induced artifacts. To better understand how in-scanner head motion affects rsfc-MRI data, we describe the spatial, temporal, and spectral characteristics of motion artifacts in a sample of 348 adolescents. Analyses utilize a novel approach for describing head motion on a voxelwise basis. Next, we systematically evaluate the efficacy of a range of confound regression and filtering techniques for the control of motion-induced artifacts. Results reveal that the effectiveness of preprocessing procedures on the control of motion is heterogeneous, and that improved preprocessing provides a substantial benefit beyond typical procedures. These results demonstrate that the effect of motion on rsfc-MRI can be substantially attenuated through improved preprocessing procedures, but not completely removed. PMID:22926292

Color Restoration of RGBN Multispectral Filter Array Sensor Images Based on Spectral Decomposition.

PubMed

Park, Chulhee; Kang, Moon Gi

2016-05-18

A multispectral filter array (MSFA) image sensor with red, green, blue and near-infrared (NIR) filters is useful for various imaging applications with the advantages that it obtains color information and NIR information simultaneously. Because the MSFA image sensor needs to acquire invisible band information, it is necessary to remove the IR cut-offfilter (IRCF). However, without the IRCF, the color of the image is desaturated by the interference of the additional NIR component of each RGB color channel. To overcome color degradation, a signal processing approach is required to restore natural color by removing the unwanted NIR contribution to the RGB color channels while the additional NIR information remains in the N channel. Thus, in this paper, we propose a color restoration method for an imaging system based on the MSFA image sensor with RGBN filters. To remove the unnecessary NIR component in each RGB color channel, spectral estimation and spectral decomposition are performed based on the spectral characteristics of the MSFA sensor. The proposed color restoration method estimates the spectral intensity in NIR band and recovers hue and color saturation by decomposing the visible band component and the NIR band component in each RGB color channel. The experimental results show that the proposed method effectively restores natural color and minimizes angular errors.

Color Restoration of RGBN Multispectral Filter Array Sensor Images Based on Spectral Decomposition

PubMed Central

Park, Chulhee; Kang, Moon Gi

2016-01-01

A multispectral filter array (MSFA) image sensor with red, green, blue and near-infrared (NIR) filters is useful for various imaging applications with the advantages that it obtains color information and NIR information simultaneously. Because the MSFA image sensor needs to acquire invisible band information, it is necessary to remove the IR cut-offfilter (IRCF). However, without the IRCF, the color of the image is desaturated by the interference of the additional NIR component of each RGB color channel. To overcome color degradation, a signal processing approach is required to restore natural color by removing the unwanted NIR contribution to the RGB color channels while the additional NIR information remains in the N channel. Thus, in this paper, we propose a color restoration method for an imaging system based on the MSFA image sensor with RGBN filters. To remove the unnecessary NIR component in each RGB color channel, spectral estimation and spectral decomposition are performed based on the spectral characteristics of the MSFA sensor. The proposed color restoration method estimates the spectral intensity in NIR band and recovers hue and color saturation by decomposing the visible band component and the NIR band component in each RGB color channel. The experimental results show that the proposed method effectively restores natural color and minimizes angular errors. PMID:27213381

A mean-based filter to remove power line harmonic noise from seismic reflection data

NASA Astrophysics Data System (ADS)

Karslı, Hakan; Dondurur, Derman

2018-06-01

Power line harmonic noise generated by power lines during the seismic data acquisition in land and marine seismic surveys generally appears as a single frequency with 50/60 Hz (or multiples of these frequencies) and contaminates seismic data leading to complicate the identification of fine details in the data. Commonly applied method during seismic data processing to remove the harmonic noise is classical notch filter (or very narrow band-stop filter), however, it also attenuates all recorded data around the notch frequencies and results in a complete loss of available information which corresponds to fine details in the seismic data. In this study, we introduce an application of the algorithm of iterative trimmed and truncated mean filter method (ITTM) to remove the harmonic noise from seismic data, and here, we name the method as local ITTM (LITTM) since we applied it to the seismic data locally in spectral domain. In this method, an optimal value is iteratively searched depending on a threshold value by trimming and truncating process for the spectral amplitude samples within the specified spectral window. Therefore, the LITTM filter converges to the median, but, there is no need to sort the data as in the case of conventional median filters. On the other hand, the LITTM filtering process doesn't require any reference signal or a precise estimate of the fundamental frequency of the harmonic noise, and only approximate frequency band of the noise within the amplitude spectra is considered. The only required parameter of the method is the width of this frequency band in the spectral domain. The LITTM filter is first applied to synthetic data and then we analyze a real marine dataset to compare the quality of the output after removing the power line noise by classical notch, median and proposed LITTM filters. We observe that the power line harmonic noise is completely filtered out by LITTM filter, and unlike the conventional notch filter, without any damage on the available frequencies around the notch frequency band. It also provides a more balanced amplitude spectrum since it does not produce amplitude notches in the spectrum.

[Study on Application of NIR Spectral Information Screening in Identification of Maca Origin].

PubMed

Wang, Yuan-zhong; Zhao, Yan-li; Zhang, Ji; Jin, Hang

2016-02-01

Medicinal and edible plant Maca is rich in various nutrients and owns great medicinal value. Based on near infrared diffuse reflectance spectra, 139 Maca samples collected from Peru and Yunnan were used to identify their geographical origins. Multiplication signal correction (MSC) coupled with second derivative (SD) and Norris derivative filter (ND) was employed in spectral pretreatment. Spectrum range (7,500-4,061 cm⁻¹) was chosen by spectrum standard deviation. Combined with principal component analysis-mahalanobis distance (PCA-MD), the appropriate number of principal components was selected as 5. Based on the spectrum range and the number of principal components selected, two abnormal samples were eliminated by modular group iterative singular sample diagnosis method. Then, four methods were used to filter spectral variable information, competitive adaptive reweighted sampling (CARS), monte carlo-uninformative variable elimination (MC-UVE), genetic algorithm (GA) and subwindow permutation analysis (SPA). The spectral variable information filtered was evaluated by model population analysis (MPA). The results showed that RMSECV(SPA) > RMSECV(CARS) > RMSECV(MC-UVE) > RMSECV(GA), were 2. 14, 2. 05, 2. 02, and 1. 98, and the spectral variables were 250, 240, 250 and 70, respectively. According to the spectral variable filtered, partial least squares discriminant analysis (PLS-DA) was used to build the model, with random selection of 97 samples as training set, and the other 40 samples as validation set. The results showed that, R²: GA > MC-UVE > CARS > SPA, RMSEC and RMSEP: GA < MC-UVE < CARS

Coherent Structures and Spectral Energy Transfer in Turbulent Plasma: A Space-Filter Approach.

PubMed

Camporeale, E; Sorriso-Valvo, L; Califano, F; Retinò, A

2018-03-23

Plasma turbulence at scales of the order of the ion inertial length is mediated by several mechanisms, including linear wave damping, magnetic reconnection, the formation and dissipation of thin current sheets, and stochastic heating. It is now understood that the presence of localized coherent structures enhances the dissipation channels and the kinetic features of the plasma. However, no formal way of quantifying the relationship between scale-to-scale energy transfer and the presence of spatial structures has been presented so far. In the Letter we quantify such a relationship analyzing the results of a two-dimensional high-resolution Hall magnetohydrodynamic simulation. In particular, we employ the technique of space filtering to derive a spectral energy flux term which defines, in any point of the computational domain, the signed flux of spectral energy across a given wave number. The characterization of coherent structures is performed by means of a traditional two-dimensional wavelet transformation. By studying the correlation between the spectral energy flux and the wavelet amplitude, we demonstrate the strong relationship between scale-to-scale transfer and coherent structures. Furthermore, by conditioning one quantity with respect to the other, we are able for the first time to quantify the inhomogeneity of the turbulence cascade induced by topological structures in the magnetic field. Taking into account the low space-filling factor of coherent structures (i.e., they cover a small portion of space), it emerges that 80% of the spectral energy transfer (both in the direct and inverse cascade directions) is localized in about 50% of space, and 50% of the energy transfer is localized in only 25% of space.

Coherent Structures and Spectral Energy Transfer in Turbulent Plasma: A Space-Filter Approach

NASA Astrophysics Data System (ADS)

Camporeale, E.; Sorriso-Valvo, L.; Califano, F.; Retinò, A.

2018-03-01

Plasma turbulence at scales of the order of the ion inertial length is mediated by several mechanisms, including linear wave damping, magnetic reconnection, the formation and dissipation of thin current sheets, and stochastic heating. It is now understood that the presence of localized coherent structures enhances the dissipation channels and the kinetic features of the plasma. However, no formal way of quantifying the relationship between scale-to-scale energy transfer and the presence of spatial structures has been presented so far. In the Letter we quantify such a relationship analyzing the results of a two-dimensional high-resolution Hall magnetohydrodynamic simulation. In particular, we employ the technique of space filtering to derive a spectral energy flux term which defines, in any point of the computational domain, the signed flux of spectral energy across a given wave number. The characterization of coherent structures is performed by means of a traditional two-dimensional wavelet transformation. By studying the correlation between the spectral energy flux and the wavelet amplitude, we demonstrate the strong relationship between scale-to-scale transfer and coherent structures. Furthermore, by conditioning one quantity with respect to the other, we are able for the first time to quantify the inhomogeneity of the turbulence cascade induced by topological structures in the magnetic field. Taking into account the low space-filling factor of coherent structures (i.e., they cover a small portion of space), it emerges that 80% of the spectral energy transfer (both in the direct and inverse cascade directions) is localized in about 50% of space, and 50% of the energy transfer is localized in only 25% of space.

Design of tunable thermo-optic C-band filter based on coated silicon slab

NASA Astrophysics Data System (ADS)

Pinhas, Hadar; Malka, Dror; Danan, Yossef; Sinvani, Moshe; Zalevsky, Zeev

2018-03-01

Optical filters are required to have narrow band-pass filtering in the spectral C-band for applications such as signal tracking, sub-band filtering or noise suppression. These requirements lead to a variety of filters such as Mach-Zehnder interferometer inter-leaver in silica, which offer thermo-optic effect for optical switching, however, without proper thermal and optical efficiency. In this paper we propose tunable thermo-optic filtering device based on coated silicon slab resonator with increased Q-factor for the C-band optical switching. The device can be designed either for long range wavelength tuning of for short range with increased wavelength resolution. Theoretical examination of the thermal parameters affecting the filtering process is shown together with experimental results. Proper channel isolation with an extinction ratio of 20dBs is achieved with spectral bandpass width of 0.07nm.

Advanced photonic filters based on cascaded Sagnac loop reflector resonators in silicon-on-insulator nanowires

NASA Astrophysics Data System (ADS)

Wu, Jiayang; Moein, Tania; Xu, Xingyuan; Moss, David J.

2018-04-01

We demonstrate advanced integrated photonic filters in silicon-on-insulator (SOI) nanowires implemented by cascaded Sagnac loop reflector (CSLR) resonators. We investigate mode splitting in these standing-wave (SW) resonators and demonstrate its use for engineering the spectral profile of on-chip photonic filters. By changing the reflectivity of the Sagnac loop reflectors (SLRs) and the phase shifts along the connecting waveguides, we tailor mode splitting in the CSLR resonators to achieve a wide range of filter shapes for diverse applications including enhanced light trapping, flat-top filtering, Q factor enhancement, and signal reshaping. We present the theoretical designs and compare the CSLR resonators with three, four, and eight SLRs fabricated in SOI. We achieve versatile filter shapes in the measured transmission spectra via diverse mode splitting that agree well with theory. This work confirms the effectiveness of using CSLR resonators as integrated multi-functional SW filters for flexible spectral engineering.

Development of an optimal filter substrate for the identification of small microplastic particles in food by micro-Raman spectroscopy.

PubMed

Oßmann, Barbara E; Sarau, George; Schmitt, Sebastian W; Holtmannspötter, Heinrich; Christiansen, Silke H; Dicke, Wilhelm

2017-06-01

When analysing microplastics in food, due to toxicological reasons it is important to achieve clear identification of particles down to a size of at least 1 μm. One reliable, optical analytical technique allowing this is micro-Raman spectroscopy. After isolation of particles via filtration, analysis is typically performed directly on the filter surface. In order to obtain high qualitative Raman spectra, the material of the membrane filters should not show any interference in terms of background and Raman signals during spectrum acquisition. To facilitate the usage of automatic particle detection, membrane filters should also show specific optical properties. In this work, beside eight different, commercially available membrane filters, three newly designed metal-coated polycarbonate membrane filters were tested to fulfil these requirements. We found that aluminium-coated polycarbonate membrane filters had ideal characteristics as a substrate for micro-Raman spectroscopy. Its spectrum shows no or minimal interference with particle spectra, depending on the laser wavelength. Furthermore, automatic particle detection can be applied when analysing the filter surface under dark-field illumination. With this new membrane filter, analytics free of interference of microplastics down to a size of 1 μm becomes possible. Thus, an important size class of these contaminants can now be visualized and spectrally identified. Graphical abstract A newly developed aluminium coated polycarbonate membrane filter enables automatic particle detection and generation of high qualitative Raman spectra allowing identification of small microplastics.

3D Display Using Conjugated Multiband Bandpass Filters

NASA Technical Reports Server (NTRS)

Bae, Youngsam; White, Victor E.; Shcheglov, Kirill

2012-01-01

Stereoscopic display techniques are based on the principle of displaying two views, with a slightly different perspective, in such a way that the left eye views only by the left eye, and the right eye views only by the right eye. However, one of the major challenges in optical devices is crosstalk between the two channels. Crosstalk is due to the optical devices not completely blocking the wrong-side image, so the left eye sees a little bit of the right image and the right eye sees a little bit of the left image. This results in eyestrain and headaches. A pair of interference filters worn as an optical device can solve the problem. The device consists of a pair of multiband bandpass filters that are conjugated. The term "conjugated" describes the passband regions of one filter not overlapping with those of the other, but the regions are interdigitated. Along with the glasses, a 3D display produces colors composed of primary colors (basis for producing colors) having the spectral bands the same as the passbands of the filters. More specifically, the primary colors producing one viewpoint will be made up of the passbands of one filter, and those of the other viewpoint will be made up of the passbands of the conjugated filter. Thus, the primary colors of one filter would be seen by the eye that has the matching multiband filter. The inherent characteristic of the interference filter will allow little or no transmission of the wrong side of the stereoscopic images.

[Analysis of color gamut of LCD system based on LED backlight with area-controlling technique].

PubMed

Li, Fu-Wen; Jin, Wei-Qi; Shao, Xi-Bin; Zhang, Li-Lei; Wan, Li-Fang

2010-05-01

Color gamut as a significant performance index for display system describes the color reproduction ability IN real scenes. Liquid crystal display (LCD) is the most popular technology in flat panel display. However, conventional cold cathode fluorescent lamp (CCFL) backlight of LCD can not behave high color gamut compared with cathode ray tube (CRT). The common used method of color gamut measuring for LCD system is introduced at the beginning. According to the inner structure and display principle of LCD system, there are three major factors deciding LCD's color gamut: spectral properties of backlight, transmittance properties of color filters and performance of liquid crystal panel. Instead of conventional backlight CCFL, RGB-LED backlight is used for improving color reproduction of LCD display system. Due to the imperfect match between RGB-LED' s spectra and color filter's transmittance, the color filter would reduce the color gamut of LCD system more or less. Therefore, LCD system based on LED backlight with area-control technique is introduced which modifies backlight control signal according to the input signal After analyzing and calculating the spectra of LED backlight which passes through the color filters using method of colorimetry, the area sizes of color gamut triangles of RGB-LED backlight with area-control and RGB-LED backlight without area-control LCD systems are compared and the relationship between color gamut and varying contrast of liquid crystal panel is analyzed. It is indicated that LED backlight with area-control technique can avoid color saturation dropping and have little effects on the contrast variation of liquid crystal panel. In other words, LED backlight with area-control technique relaxes the requirements of both color filter performance and liquid crystal panel. Thus, it is of importance to improve the color gamut of the current LCD system with area-control LED backlight.

High brightness diode lasers controlled by volume Bragg gratings

NASA Astrophysics Data System (ADS)

Glebov, Leonid

2017-02-01

Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass are holographic optical elements that are effective spectral and angular filters withstanding high power laser radiation. Reflecting VBGs are narrow-band spectral filters while transmitting VBGs are narrow-band angular filters. The use of these optical elements in external resonators of semiconductor lasers enables extremely resonant feedback that provides dramatic spectral and angular narrowing of laser diodes radiation without significant power and efficiency penalty. Spectral narrowing of laser diodes by reflecting VBGs demonstrated in wide spectral region from near UV to 3 μm. Commercially available VBGs have spectral width ranged from few nanometers to few tens of picometers. Efficient spectral locking was demonstrated for edge emitters (single diodes, bars, modules, and stacks), vertical cavity surface emitting lasers (VCSELs), grating coupled surface emitting lasers (GCSELs), and interband cascade lasers (ICLs). The use of multiplexed VBGs provides multiwavelength emission from a single emitter. Spectrally locked semiconductor lasers demonstrated CW power from milliwatts to a kilowatt. Angular narrowing by transmitting VBGs enables single transverse mode emission from wide aperture diode lasers having resonators with great Fresnel numbers. This feature provides close to diffraction limit divergence along a slow axis of wide stripe edge emitters. Radiation exchange between lasers by means of spatially profiled or multiplexed VBGs enables coherent combining of diode lasers. Sequence of VBGs or multiplexed VBGs enable spectral combining of spectrally narrowed diode lasers or laser modules. Thus the use of VBGs for diode lasers beam control provides dramatic increase of brightness.

Digital filtering implementations for the detection of broad spectral features by direct analysis of passive Fourier transform infrared interferograms.

PubMed

Tarumi, Toshiyasu; Small, Gary W; Combs, Roger J; Kroutil, Robert T

2004-04-01

Finite impulse response (FIR) filters and finite impulse response matrix (FIRM) filters are evaluated for use in the detection of volatile organic compounds with wide spectral bands by direct analysis of interferogram data obtained from passive Fourier transform infrared (FT-IR) measurements. Short segments of filtered interferogram points are classified by support vector machines (SVMs) to implement the automated detection of heated plumes of the target analyte, ethanol. The interferograms employed in this study were acquired with a downward-looking passive FT-IR spectrometer mounted on a fixed-wing aircraft. Classifiers are trained with data collected on the ground and subsequently used for the airborne detection. The success of the automated detection depends on the effective removal of background contributions from the interferogram segments. Removing the background signature is complicated when the analyte spectral bands are broad because there is significant overlap between the interferogram representations of the analyte and background. Methods to implement the FIR and FIRM filters while excluding background contributions are explored in this work. When properly optimized, both filtering procedures provide satisfactory classification results for the airborne data. Missed detection rates of 8% or smaller for ethanol and false positive rates of at most 0.8% are realized. The optimization of filter design parameters, the starting interferogram point for filtering, and the length of the interferogram segments used in the pattern recognition is discussed.

Sub-GHz-resolution C-band Nyquist-filtering interleaver on a high-index-contrast photonic integrated circuit.

PubMed

Zhuang, Leimeng; Zhu, Chen; Corcoran, Bill; Burla, Maurizio; Roeloffzen, Chris G H; Leinse, Arne; Schröder, Jochen; Lowery, Arthur J

2016-03-21

Modern optical communications rely on high-resolution, high-bandwidth filtering to maximize the data-carrying capacity of fiber-optic networks. Such filtering typically requires high-speed, power-hungry digital processes in the electrical domain. Passive optical filters currently provide high bandwidths with low power consumption, but at the expense of resolution. Here, we present a passive filter chip that functions as an optical Nyquist-filtering interleaver featuring sub-GHz resolution and a near-rectangular passband with 8% roll-off. This performance is highly promising for high-spectral-efficiency Nyquist wavelength division multiplexed (N-WDM) optical super-channels. The chip provides a simple two-ring-resonator-assisted Mach-Zehnder interferometer, which has a sub-cm² footprint owing to the high-index-contrast Si₃N₄/SiO₂ waveguide, while manifests low wavelength-dependency enabling C-band (> 4 THz) coverage with more than 160 effective free spectral ranges of 25 GHz. This device is anticipated to be a critical building block for spectrally-efficient, chip-scale transceivers and ROADMs for N-WDM super-channels in next-generation optical communication networks.

Monte-Carlo modelling to determine optimum filter choices for sub-microsecond optical pyrometry.

PubMed

Ota, Thomas A; Chapman, David J; Eakins, Daniel E

2017-04-01

When designing a spectral-band pyrometer for use at high time resolutions (sub-μs), there is ambiguity regarding the optimum characteristics for a spectral filter(s). In particular, while prior work has discussed uncertainties in spectral-band pyrometry, there has been little discussion of the effects of noise which is an important consideration in time-resolved, high speed experiments. Using a Monte-Carlo process to simulate the effects of noise, a model of collection from a black body has been developed to give insights into the optimum choices for centre wavelength and passband width. The model was validated and then used to explore the effects of centre wavelength and passband width on measurement uncertainty. This reveals a transition centre wavelength below which uncertainties in calculated temperature are high. To further investigate system performance, simultaneous variation of the centre wavelength and bandpass width of a filter is investigated. Using data reduction, the effects of temperature and noise levels are illustrated and an empirical approximation is determined. The results presented show that filter choice can significantly affect instrument performance and, while best practice requires detailed modelling to achieve optimal performance, the expression presented can be used to aid filter selection.

High-extinction virtually imaged phased array-based Brillouin spectroscopy of turbid biological media

NASA Astrophysics Data System (ADS)

Fiore, Antonio; Zhang, Jitao; Shao, Peng; Yun, Seok Hyun; Scarcelli, Giuliano

2016-05-01

Brillouin microscopy has recently emerged as a powerful technique to characterize the mechanical properties of biological tissue, cell, and biomaterials. However, the potential of Brillouin microscopy is currently limited to transparent samples, because Brillouin spectrometers do not have sufficient spectral extinction to reject the predominant non-Brillouin scattered light of turbid media. To overcome this issue, we combined a multi-pass Fabry-Perot interferometer with a two-stage virtually imaged phased array spectrometer. The Fabry-Perot etalon acts as an ultra-narrow band-pass filter for Brillouin light with high spectral extinction and low loss. We report background-free Brillouin spectra from Intralipid solutions and up to 100 μm deep within chicken muscle tissue.

Ultrasonic imaging of seismic physical models using a fringe visibility enhanced fiber-optic Fabry-Perot interferometric sensor.

PubMed

Zhang, Wenlu; Chen, Fengyi; Ma, Wenwen; Rong, Qiangzhou; Qiao, Xueguang; Wang, Ruohui

2018-04-16

A fringe visibility enhanced fiber-optic Fabry-Perot interferometer based ultrasonic sensor is proposed and experimentally demonstrated for seismic physical model imaging. The sensor consists of a graded index multimode fiber collimator and a PTFE (polytetrafluoroethylene) diaphragm to form a Fabry-Perot interferometer. Owing to the increase of the sensor's spectral sideband slope and the smaller Young's modulus of the PTFE diaphragm, a high response to both continuous and pulsed ultrasound with a high SNR of 42.92 dB in 300 kHz is achieved when the spectral sideband filter technique is used to interrogate the sensor. The ultrasonic reconstructed images can clearly differentiate the shape of models with a high resolution.

Vector magnetic fields in sunspots. I - Stokes profile analysis using the Marshall Space Flight Center magnetograph

NASA Technical Reports Server (NTRS)

Balasubramaniam, K. S.; West, E. A.

1991-01-01

The Marshall Space Flight Center (MSFC) vector magnetograph is a tunable filter magnetograph with a bandpass of 125 mA. Results are presented of the inversion of Stokes polarization profiles observed with the MSFC vector magnetograph centered on a sunspot to recover the vector magnetic field parameters and thermodynamic parameters of the spectral line forming region using the Fe I 5250.2 A spectral line using a nonlinear least-squares fitting technique. As a preliminary investigation, it is also shown that the recovered thermodynamic parameters could be better understood if the fitted parameters like Doppler width, opacity ratio, and damping constant were broken down into more basic quantities like temperature, microturbulent velocity, or density parameter.

Imaging spectrometry - Technology and applications

NASA Technical Reports Server (NTRS)

Solomon, Jerry E.

1989-01-01

The development history and current status of NASA imaging-spectrometer (IS) technology are discussed in a review covering the period 1982-1988. Consideration is given to the Airborne IS first flown in 1982, the second-generation Airborne Visible and IR IS (AVIRIS), the High-Resolution IS being developed for the EOS polar platform, improved two-dimensional focal-plane arrays for the short-wave IR spectral region, and noncollinear acoustooptic tunable filters for use as spectral dispersing elements. Also examined are approaches to solving the data-processing problems posed by the high data volumes of state-of-the-art ISs (e.g., 160 MB per 600 x 600-pixel AVIRIS scene), including intelligent data editing, lossless and lossy data compression techniques, and direct extraction of scientifically meaningful geophysical and biophysical parameters.

Two-tint pump-probe measurements using a femtosecond laser oscillator and sharp-edged optical filters.

PubMed

Kang, Kwangu; Koh, Yee Kan; Chiritescu, Catalin; Zheng, Xuan; Cahill, David G

2008-11-01

We describe a simple approach for rejecting unwanted scattered light in two types of time-resolved pump-probe measurements, time-domain thermoreflectance (TDTR) and time-resolved incoherent anti-Stokes Raman scattering (TRIARS). Sharp edged optical filters are used to create spectrally distinct pump and probe beams from the broad spectral output of a femtosecond Ti:sapphire laser oscillator. For TDTR, the diffusely scattered pump light is then blocked by a third optical filter. For TRIARS, depolarized scattering created by the pump is shifted in frequency by approximately 250 cm(-1) relative to the polarized scattering created by the probe; therefore, spectral features created by the pump and probe scattering can be easily distinguished.

Multi-Dimensional High Order Essentially Non-Oscillatory Finite Difference Methods in Generalized Coordinates

NASA Technical Reports Server (NTRS)

Shu, Chi-Wang

1998-01-01

This project is about the development of high order, non-oscillatory type schemes for computational fluid dynamics. Algorithm analysis, implementation, and applications are performed. Collaborations with NASA scientists have been carried out to ensure that the research is relevant to NASA objectives. The combination of ENO finite difference method with spectral method in two space dimension is considered, jointly with Cai [3]. The resulting scheme behaves nicely for the two dimensional test problems with or without shocks. Jointly with Cai and Gottlieb, we have also considered one-sided filters for spectral approximations to discontinuous functions [2]. We proved theoretically the existence of filters to recover spectral accuracy up to the discontinuity. We also constructed such filters for practical calculations.

Solid optical ring interferometer for high-throughput feedback-free spectral analysis and filtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrak, B.; Peiris, M.; Muller, A., E-mail: mullera@usf.edu

2015-02-15

We describe a simple and inexpensive optical ring interferometer for use in high-resolution spectral analysis and filtering. It consists of a solid cuboid, reflection-coated on two opposite sides, in which constructive interference occurs for waves in a rhombic trajectory. Due to its monolithic design, the interferometer’s resonance frequencies are insensitive to environmental disturbances over time. Additional advantages are its simplicity of alignment, high-throughput, and feedback-free operation. If desired, it can be stabilized with a secondary laser without disturbance of the primary signal. We illustrate the use of the interferometer for the measurement of the spectral Mollow triplet from a quantummore » dot and characterize its long-term stability for filtering applications.« less

Separable spectro-temporal Gabor filter bank features: Reducing the complexity of robust features for automatic speech recognition.

PubMed

Schädler, Marc René; Kollmeier, Birger

2015-04-01

To test if simultaneous spectral and temporal processing is required to extract robust features for automatic speech recognition (ASR), the robust spectro-temporal two-dimensional-Gabor filter bank (GBFB) front-end from Schädler, Meyer, and Kollmeier [J. Acoust. Soc. Am. 131, 4134-4151 (2012)] was de-composed into a spectral one-dimensional-Gabor filter bank and a temporal one-dimensional-Gabor filter bank. A feature set that is extracted with these separate spectral and temporal modulation filter banks was introduced, the separate Gabor filter bank (SGBFB) features, and evaluated on the CHiME (Computational Hearing in Multisource Environments) keywords-in-noise recognition task. From the perspective of robust ASR, the results showed that spectral and temporal processing can be performed independently and are not required to interact with each other. Using SGBFB features permitted the signal-to-noise ratio (SNR) to be lowered by 1.2 dB while still performing as well as the GBFB-based reference system, which corresponds to a relative improvement of the word error rate by 12.8%. Additionally, the real time factor of the spectro-temporal processing could be reduced by more than an order of magnitude. Compared to human listeners, the SNR needed to be 13 dB higher when using Mel-frequency cepstral coefficient features, 11 dB higher when using GBFB features, and 9 dB higher when using SGBFB features to achieve the same recognition performance.

Facilities and Techniques for X-Ray Diagnostic Calibration in the 100-eV to 100-keV Energy Range

NASA Astrophysics Data System (ADS)

Gaines, J. L.; Wittmayer, F. J.

1986-08-01

The Lawrence Livermore National Laboratory (LLNL) has been a pioneer in the field of x-ray diagnostic calibration for more than 20 years. We have built steady state x-ray sources capable of supplying fluorescent lines of high spectral purity in the 100-eV to 100-keV energy range, and these sources have been used in the calibration of x-ray detectors, mirrors, crystals, filters, and film. This paper discusses our calibration philosophy and techniques, and describes some of our x-ray sources. Examples of actual calibration data are presented as well.

Rapid calibrated high-resolution hyperspectral imaging using tunable laser source

NASA Astrophysics Data System (ADS)

Nguyen, Lam K.; Margalith, Eli

2009-05-01

We present a novel hyperspectral imaging technique based on tunable laser technology. By replacing the broadband source and tunable filters of a typical NIR imaging instrument, several advantages are realized, including: high spectral resolution, highly variable field-of-views, fast scan-rates, high signal-to-noise ratio, and the ability to use optical fiber for efficient and flexible sample illumination. With this technique, high-resolution, calibrated hyperspectral images over the NIR range can be acquired in seconds. The performance of system features will be demonstrated on two example applications: detecting melamine contamination in wheat gluten and separating bovine protein from wheat protein in cattle feed.

Filter Selection for Optimizing the Spectral Sensitivity of Broadband Multispectral Cameras Based on Maximum Linear Independence.

PubMed

Li, Sui-Xian

2018-05-07

Previous research has shown that the effectiveness of selecting filter sets from among a large set of commercial broadband filters by a vector analysis method based on maximum linear independence (MLI). However, the traditional MLI approach is suboptimal due to the need to predefine the first filter of the selected filter set to be the maximum ℓ₂ norm among all available filters. An exhaustive imaging simulation with every single filter serving as the first filter is conducted to investigate the features of the most competent filter set. From the simulation, the characteristics of the most competent filter set are discovered. Besides minimization of the condition number, the geometric features of the best-performed filter set comprise a distinct transmittance peak along the wavelength axis of the first filter, a generally uniform distribution for the peaks of the filters and substantial overlaps of the transmittance curves of the adjacent filters. Therefore, the best-performed filter sets can be recognized intuitively by simple vector analysis and just a few experimental verifications. A practical two-step framework for selecting optimal filter set is recommended, which guarantees a significant enhancement of the performance of the systems. This work should be useful for optimizing the spectral sensitivity of broadband multispectral imaging sensors.

Auditory color constancy: calibration to reliable spectral properties across nonspeech context and targets.

PubMed

Stilp, Christian E; Alexander, Joshua M; Kiefte, Michael; Kluender, Keith R

2010-02-01

Brief experience with reliable spectral characteristics of a listening context can markedly alter perception of subsequent speech sounds, and parallels have been drawn between auditory compensation for listening context and visual color constancy. In order to better evaluate such an analogy, the generality of acoustic context effects for sounds with spectral-temporal compositions distinct from speech was investigated. Listeners identified nonspeech sounds-extensively edited samples produced by a French horn and a tenor saxophone-following either resynthesized speech or a short passage of music. Preceding contexts were "colored" by spectral envelope difference filters, which were created to emphasize differences between French horn and saxophone spectra. Listeners were more likely to report hearing a saxophone when the stimulus followed a context filtered to emphasize spectral characteristics of the French horn, and vice versa. Despite clear changes in apparent acoustic source, the auditory system calibrated to relatively predictable spectral characteristics of filtered context, differentially affecting perception of subsequent target nonspeech sounds. This calibration to listening context and relative indifference to acoustic sources operates much like visual color constancy, for which reliable properties of the spectrum of illumination are factored out of perception of color.

Spectrum splitting metrics and effect of filter characteristics on photovoltaic system performance.

PubMed

Russo, Juan M; Zhang, Deming; Gordon, Michael; Vorndran, Shelby; Wu, Yuechen; Kostuk, Raymond K

2014-03-10

During the past few years there has been a significant interest in spectrum splitting systems to increase the overall efficiency of photovoltaic solar energy systems. However, methods for comparing the performance of spectrum splitting systems and the effects of optical spectral filter design on system performance are not well developed. This paper addresses these two areas. The system conversion efficiency is examined in detail and the role of optical spectral filters with respect to the efficiency is developed. A new metric termed the Improvement over Best Bandgap is defined which expresses the efficiency gain of the spectrum splitting system with respect to a similar system that contains the highest constituent single bandgap photovoltaic cell. This parameter indicates the benefit of using the more complex spectrum splitting system with respect to a single bandgap photovoltaic system. Metrics are also provided to assess the performance of experimental spectral filters in different spectrum splitting configurations. The paper concludes by using the methodology to evaluate spectrum splitting systems with different filter configurations and indicates the overall efficiency improvement that is possible with ideal and experimental designs.

Optical monitor for observing turbulent flow

DOEpatents

Albrecht, Georg F.; Moore, Thomas R.

1992-01-01

The present invention provides an apparatus and method for non-invasively monitoring turbulent fluid flows including anisotropic flows. The present invention uses an optical technique to filter out the rays travelling in a straight line, while transmitting rays with turbulence induced fluctuations in time. The output is two dimensional, and can provide data regarding the spectral intensity distribution, or a view of the turbulence in real time. The optical monitor of the present invention comprises a laser that produces a coherent output beam that is directed through a fluid flow, which phase-modulates the beam. The beam is applied to a temporal filter that filters out the rays in the beam that are straight, while substantially transmitting the fluctuating, turbulence-induced rays. The temporal filter includes a lens and a photorefractive crystal such as BaTiO.sub.3 that is positioned in the converging section of the beam near the focal plane. An imaging system is used to observe the filtered beam. The imaging system may take a photograph, or it may include a real time camera that is connected to a computer. The present invention may be used for many purposes including research and design in aeronautics, hydrodynamics, and combustion.

a New Broadband Cavity Enhanced Frequency Comb Spectroscopy Technique Using GHz Vernier Filtering.

NASA Astrophysics Data System (ADS)

Morville, Jérôme; Rutkowski, Lucile; Dobrev, Georgi; Crozet, Patrick

2015-06-01

We present a new approach to Cavity Enhanced - Direct Frequency Comb Spectroscopy where the full emission bandwidth of a Titanium:Sapphire laser is exploited at GHz resolution. The technique is based on a low-resolution Vernier filtering obtained with an appreciable -actively stabilized- mismatch between the cavity Free Spectral Range and the laser repetition rate, using a diffraction grating and a split-photodiode. This particular approach provides an immunity to frequency-amplitude noise conversion, reaching an absorption baseline noise in the 10-9 cm-1 range with a cavity finesse of only 3000. Spectra covering 1800 cm-1 (˜ 55 THz) are acquired in recording times of about 1 second, providing an absorption figure of merit of a few 10-11 cm-1/√{Hz}. Initially tested with ambient air, we report progress in using the Vernier frequency comb method with a discharge source of small radicals. Rutkowski et al, Opt. Lett., 39(23)2014

Analysis of polarization characteristics of plant canopies using land-based remote sensing measurements for development of ground truth methods

NASA Astrophysics Data System (ADS)

Sidko, Aleksandr; Pisman, Tamara; Botvich, Irina; Shevyrnogov, Anatoly

In order to develop satellite technology for monitoring of terrestrial plant canopies and land-based optical remote sensing techniques, one should employ new approaches to identifying farmlands and determining the plant species composition. The results present a study on polarized characteristics of spectral reflection factor of plant canopies (forests and farm crop canopies) under field conditions, using optical remote sensing techniques. The polarized components of the reflectance factor and the degree of polarization were calculated. Measurements were performed using a spectrophotometer with a polarized light filter attachment. Measurements were done within the spectral range from 400 to 840 nm. The viewing angle was no greater than 200 with respect to the nadir. Measurements of the polarization characteristics of the vegetation on the test ranges were conducted during June-July month when the height of the sun was at its zenith. Different wavelength dependences of the spectral reflection factor polarized component (Rq) and degree of polarization (P) were found both for the coniferous and broadleaf forests (pine and birch) and for farm crops (wheat and corn) and grass canopies. These differences can be used to determine species composition of plant canopies.

Spectrally resolved, broadband frequency response characterization of photodetectors using continuous-wave supercontinuum sources

NASA Astrophysics Data System (ADS)

Choudhury, Vishal; Prakash, Roopa; Nagarjun, K. P.; Supradeepa, V. R.

2018-02-01

A simple and powerful method using continuous wave supercontinuum lasers is demonstrated to perform spectrally resolved, broadband frequency response characterization of photodetectors in the NIR Band. In contrast to existing techniques, this method allows for a simple system to achieve the goal, requiring just a standard continuous wave(CW) high-power fiber laser source and an RF spectrum analyzer. From our recent work, we summarize methods to easily convert any high-power fiber laser into a CW supercontinuum. These sources in the time domain exhibit interesting properties all the way down to the femtosecond time scale. This enables measurement of broadband frequency response of photodetectors while the wide optical spectrum of the supercontinuum can be spectrally filtered to obtain this information in a spectrally resolved fashion. The method involves looking at the RF spectrum of the output of a photodetector under test when incident with the supercontinuum. By using prior knowledge of the RF spectrum of the source, the frequency response can be calculated. We utilize two techniques for calibration of the source spectrum, one using a prior measurement and the other relying on a fitted model. Here, we characterize multiple photodetectors from 150MHz bandwidth to >20GHz bandwidth at multiple bands in the NIR region. We utilize a supercontinuum source spanning over 700nm bandwidth from 1300nm to 2000nm. For spectrally resolved measurement, we utilize multiple wavelength bands such as around 1400nm and 1600nm. Interesting behavior was observed in the frequency response of the photodetectors when comparing broadband spectral excitation versus narrower band excitation.

Maximally reliable spatial filtering of steady state visual evoked potentials.

PubMed

Dmochowski, Jacek P; Greaves, Alex S; Norcia, Anthony M

2015-04-01

Due to their high signal-to-noise ratio (SNR) and robustness to artifacts, steady state visual evoked potentials (SSVEPs) are a popular technique for studying neural processing in the human visual system. SSVEPs are conventionally analyzed at individual electrodes or linear combinations of electrodes which maximize some variant of the SNR. Here we exploit the fundamental assumption of evoked responses--reproducibility across trials--to develop a technique that extracts a small number of high SNR, maximally reliable SSVEP components. This novel spatial filtering method operates on an array of Fourier coefficients and projects the data into a low-dimensional space in which the trial-to-trial spectral covariance is maximized. When applied to two sample data sets, the resulting technique recovers physiologically plausible components (i.e., the recovered topographies match the lead fields of the underlying sources) while drastically reducing the dimensionality of the data (i.e., more than 90% of the trial-to-trial reliability is captured in the first four components). Moreover, the proposed technique achieves a higher SNR than that of the single-best electrode or the Principal Components. We provide a freely-available MATLAB implementation of the proposed technique, herein termed "Reliable Components Analysis". Copyright © 2015 Elsevier Inc. All rights reserved.

Fabrication of optical filters using multilayered porous silicon

NASA Astrophysics Data System (ADS)

Gaber, Noha; Khalil, Diaa; Shaarawi, Amr

2011-02-01

In this work we describe a method for fabricating optical filters using multilayered porous silicon 1D photonic structure. An electrochemical cell is constructed to control the porosity of variable layers in p-type Si wafers. Porous silicon multilayered structures are formed of λ/4 (or multiples) thin films that construct optical interference filters. By changing the anodizing current density of the cell during fabrication, different porosities can be obtained as the optical refractive index is a direct function of the layer porosity. To determine the morphology, the wavelength dependent refractive index n and absorption coefficient α, first, porous silicon free standing mono-layers have been fabricated at different conditions and characterized in the near infrared region (from 1000 to 2500nm). Large difference in refractive index (between 1.6 and 2.6) is obtained. Subsequently, multilayer structures have been fabricated and tested. Their spectral response has been measured and it shows good agreement with numerical simulations. A technique based on inserting etching breaks is adopted to ensure the depth homogeneity. The effect of differing etching/break times on the reproducibility of the filters is studied.

A Multi-domain Spectral Method for Supersonic Reactive Flows

NASA Technical Reports Server (NTRS)

Don, Wai-Sun; Gottlieb, David; Jung, Jae-Hun; Bushnell, Dennis M. (Technical Monitor)

2002-01-01

This paper has a dual purpose: it presents a multidomain Chebyshev method for the solution of the two-dimensional reactive compressible Navier-Stokes equations, and it reports the results of the application of this code to the numerical simulations of high Mach number reactive flows in recessed cavity. The computational method utilizes newly derived interface boundary conditions as well as an adaptive filtering technique to stabilize the computations. The results of the simulations are relevant to recessed cavity flameholders.

Sensitivity studies and laboratory measurements for the laser heterodyne spectrometer experiment

NASA Technical Reports Server (NTRS)

Allario, F.; Katzberg, S. J.; Larsen, J. C.

1980-01-01

Several experiments involving spectral scanning interferometers and gas filter correlation radiometers (ref. 2) using limb scanning solar occultation techniques under development for measurements of stratospheric trace gases from Spacelab and satellite platforms are described. An experiment to measure stratospheric trace constituents by Laser Heterodyne Spectroscopy, a summary of sensitivity analyses, and supporting laboratory measurements are presented for O3, ClO, and H2O2 in which the instrument transfer function is modeled using a detailed optical receiver design.

Information Retrieval from SAGE II and MFRSR Multi-Spectral Extinction Measurements

NASA Technical Reports Server (NTRS)

Lacis, Andrew A.; Hansen, James E. (Technical Monitor)

2001-01-01

Direct beam spectral extinction measurements of solar radiation contain important information on atmospheric composition in a form that is essentially free from multiple scattering contributions that otherwise tend to complicate the data analysis and information retrieval. Such direct beam extinction measurements are available from the solar occultation satellite-based measurements made by the Stratospheric and Aerosol Gas Experiment (SAGE II) instrument and by ground-based Multi-Filter Shadowband Radiometers (MFRSRs). The SAGE II data provide cross-sectional slices of the atmosphere twice per orbit at seven wavelengths between 385 and 1020 nm with approximately 1 km vertical resolution, while the MFRSR data provide atmospheric column measurements at six wavelengths between 415 and 940 nm but at one minute time intervals. We apply the same retrieval technique of simultaneous least-squares fit to the observed spectral extinctions to retrieve aerosol optical depth, effective radius and variance, and ozone, nitrogen dioxide, and water vapor amounts from the SAGE II and MFRSR measurements. The retrieval technique utilizes a physical model approach based on laboratory measurements of ozone and nitrogen dioxide extinction, line-by-line and numerical k-distribution calculations for water vapor absorption, and Mie scattering constraints on aerosol spectral extinction properties. The SAGE II measurements have the advantage of being self-calibrating in that deep space provides an effective zero point for the relative spectral extinctions. The MFRSR measurements require periodic clear-day Langley regression calibration events to maintain accurate knowledge of instrument calibration.

Imaginary refractive index and other microphysical properties of volcanic ash, Sarahan dust, and other mineral aerosols

NASA Astrophysics Data System (ADS)

Rocha Lima, A.; Martins, J.; Krotkov, N. A.; Artaxo, P.; Todd, M.; Ben Ami, Y.; Dolgos, G.; Espinosa, R.

2013-12-01

Aerosol properties are essential to support remote sensing measurements, atmospheric circulation and climate models. This research aims to improve the understanding of the optical and microphysical properties of different types of aerosols particles. Samples of volcanic ash, Saharan dust and other mineral aerosols particles were analyzed by different techniques. Ground samples were sieved down to 45um, de-agglomerated and resuspended in the laboratory using a Fluidized Bed Aerosol Generator (FBAG). Particles were collected on Nuclepore filters into PM10, PM2.5, or PM1.0. and analyzed by different techniques, such as Scanning Electron Microscopy (SEM) for determination of size distribution and shape, spectral reflectance for determination of the optical absorption properties as a function of the wavelength, material density, and X-Ray fluorescence for the elemental composition. The spectral imaginary part of refractive index from the UV to the short wave infrared (SWIR) wavelength was derived empirically from the measurements of the spectral mass absorption coefficient, size distribution and density of the material. Some selected samples were also analyzed with the Polarized Imaging Nephelometer (PI-Neph) instrument for the characterization of the aerosol polarized phase function. This work compares results of the spectral refractive index of different materials obtained by our methodology with those available in the literature. In some cases there are significant differences both in magnitude and spectral dependence of the imaginary refractive index. These differences are evaluated and discussed in this work.

Performance characterization of a pressure-tuned wide-angle Michelson interferometric spectral filter for high spectral resolution lidar

NASA Astrophysics Data System (ADS)

Seaman, Shane T.; Cook, Anthony L.; Scola, Salvatore J.; Hostetler, Chris A.; Miller, Ian; Welch, Wayne

2015-09-01

High Spectral Resolution Lidar (HSRL) is typically realized using an absorption filter to separate molecular returns from particulate returns. NASA Langley Research Center (LaRC) has designed and built a Pressure-Tuned Wide-Angle Michelson Interferometer (PTWAMI) as an alternate means to separate the two types of atmospheric returns. While absorption filters only work at certain wavelengths and suffer from low photon efficiency due to light absorption, an interferometric spectral filter can be designed for any wavelength and transmits nearly all incident photons. The interferometers developed at LaRC employ an air spacer in one arm, and a solid glass spacer in the other. Field widening is achieved by specific design and selection of the lengths and refractive indices of these two arms. The principal challenge in using such an interferometer as a spectral filter for HSRL aboard aircraft is that variations in glass temperature and air pressure cause changes in the interferometer's optical path difference. Therefore, a tuning mechanism is needed to actively accommodate for these changes. The pressure-tuning mechanism employed here relies on changing the pressure in an enclosed, air-filled arm of the interferometer to change the arm's optical path length. However, tuning using pressure will not adjust for tilt, mirror warpage, or thermally induced wavefront error, so the structural, thermal, and optical behavior of the device must be well understood and optimized in the design and manufacturing process. The PTWAMI has been characterized for particulate transmission ratio, wavefront error, and tilt, and shows acceptable performance for use in an HSRL instrument.

A compact bio-inspired visible/NIR imager for image-guided surgery (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gao, Shengkui; Garcia, Missael; Edmiston, Chris; York, Timothy; Marinov, Radoslav; Mondal, Suman B.; Zhu, Nan; Sudlow, Gail P.; Akers, Walter J.; Margenthaler, Julie A.; Liang, Rongguang; Pepino, Marta; Achilefu, Samuel; Gruev, Viktor

2016-03-01

Inspired by the visual system of the morpho butterfly, we have designed, fabricated, tested and clinically translated an ultra-sensitive, light weight and compact imaging sensor capable of simultaneously capturing near infrared (NIR) and visible spectrum information. The visual system of the morpho butterfly combines photosensitive cells with spectral filters at the receptor level. The spectral filters are realized by alternating layers of high and low dielectric constant, such as air and cytoplasm. We have successfully mimicked this concept by integrating pixelated spectral filters, realized by alternating silicon dioxide and silicon nitrate layers, with an array of CCD detectors. There are four different types of pixelated spectral filters in the imaging plane: red, green, blue and NIR. The high optical density (OD) of all spectral filters (OD>4) allow for efficient rejections of photons from unwanted bands. The single imaging chip weighs 20 grams with form factor of 5mm by 5mm. The imaging camera is integrated with a goggle display system. A tumor targeted agent, LS301, is used to identify all spontaneous tumors in a transgenic PyMT murine model of breast cancer. The imaging system achieved sensitivity of 98% and selectivity of 95%. We also used our imaging sensor to locate sentinel lymph nodes (SLNs) in patients with breast cancer using indocyanine green tracer. The surgeon was able to identify 100% of SLNs when using our bio-inspired imaging system, compared to 93% when using information from the lymphotropic dye and 96% when using information from the radioactive tracer.

Identification of microplastics by FTIR and Raman microscopy: a novel silicon filter substrate opens the important spectral range below 1300 cm(-1) for FTIR transmission measurements.

PubMed

Käppler, Andrea; Windrich, Frank; Löder, Martin G J; Malanin, Mikhail; Fischer, Dieter; Labrenz, Matthias; Eichhorn, Klaus-Jochen; Voit, Brigitte

2015-09-01

The presence of microplastics in aquatic ecosystems is a topical problem and leads to the need of appropriate and reliable analytical methods to distinctly identify and to quantify these particles in environmental samples. As an example transmission, Fourier transform infrared (FTIR) imaging can be used to analyze samples directly on filters without any visual presorting, when the environmental sample was afore extracted, purified, and filtered. However, this analytical approach is strongly restricted by the limited IR transparency of conventional filter materials. Within this study, we describe a novel silicon (Si) filter substrate produced by photolithographic microstructuring, which guarantees sufficient transparency for the broad mid-infrared region of 4000-600 cm(-1). This filter type features holes with a diameter of 10 μm and exhibits adequate mechanical stability. Furthermore, it will be shown that our Si filter substrate allows a distinct identification of the most common microplastics, polyethylene (PE), and polypropylene (PP), in the characteristic fingerprint region (1400-600 cm(-1)). Moreover, using the Si filter substrate, a differentiation of microparticles of polyesters having quite similar chemical structure, like polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), is now possible, which facilitates a visualization of their distribution within a microplastic sample by FTIR imaging. Finally, this Si filter can also be used as substrate for Raman microscopy-a second complementary spectroscopic technique-to identify microplastic samples.

Fixed Pattern Noise pixel-wise linear correction for crime scene imaging CMOS sensor

NASA Astrophysics Data System (ADS)

Yang, Jie; Messinger, David W.; Dube, Roger R.; Ientilucci, Emmett J.

2017-05-01

Filtered multispectral imaging technique might be a potential method for crime scene documentation and evidence detection due to its abundant spectral information as well as non-contact and non-destructive nature. Low-cost and portable multispectral crime scene imaging device would be highly useful and efficient. The second generation crime scene imaging system uses CMOS imaging sensor to capture spatial scene and bandpass Interference Filters (IFs) to capture spectral information. Unfortunately CMOS sensors suffer from severe spatial non-uniformity compared to CCD sensors and the major cause is Fixed Pattern Noise (FPN). IFs suffer from "blue shift" effect and introduce spatial-spectral correlated errors. Therefore, Fixed Pattern Noise (FPN) correction is critical to enhance crime scene image quality and is also helpful for spatial-spectral noise de-correlation. In this paper, a pixel-wise linear radiance to Digital Count (DC) conversion model is constructed for crime scene imaging CMOS sensor. Pixel-wise conversion gain Gi,j and Dark Signal Non-Uniformity (DSNU) Zi,j are calculated. Also, conversion gain is divided into four components: FPN row component, FPN column component, defects component and effective photo response signal component. Conversion gain is then corrected to average FPN column and row components and defects component so that the sensor conversion gain is uniform. Based on corrected conversion gain and estimated image incident radiance from the reverse of pixel-wise linear radiance to DC model, corrected image spatial uniformity can be enhanced to 7 times as raw image, and the bigger the image DC value within its dynamic range, the better the enhancement.

Techniques for identifying dust devils in mars pathfinder images

USGS Publications Warehouse

Metzger, S.M.; Carr, J.R.; Johnson, J. R.; Parker, T.J.; Lemmon, M.T.

2000-01-01

Image processing methods used to identify and enhance dust devil features imaged by IMP (Imager for Mars Pathfinder) are reviewed. Spectral differences, visible red minus visible blue, were used for initial dust devil searches, driven by the observation that Martian dust has high red and low blue reflectance. The Martian sky proved to be more heavily dust-laden than pre-Pathfinder predictions, based on analysis of images from the Hubble Space Telescope. As a result, these initial spectral difference methods failed to contrast dust devils with background dust haze. Imager artifacts (dust motes on the camera lens, flat-field effects caused by imperfections in the CCD, and projection onto a flat sensor plane by a convex lens) further impeded the ability to resolve subtle dust devil features. Consequently, reference images containing sky with a minimal horizon were first subtracted from each spectral filter image to remove camera artifacts and reduce the background dust haze signal. Once the sky-flat preprocessing step was completed, the red-minus-blue spectral difference scheme was attempted again. Dust devils then were successfully identified as bright plumes. False-color ratios using calibrated IMP images were found useful for visualizing dust plumes, verifying initial discoveries as vortex-like features. Enhancement of monochromatic (especially blue filter) images revealed dust devils as silhouettes against brighter background sky. Experiments with principal components transformation identified dust devils in raw, uncalibrated IMP images and further showed relative movement of dust devils across the Martian surface. A variety of methods therefore served qualitative and quantitative goals for dust plume identification and analysis in an environment where such features are obscure.

A Dual-Line Detection Rayleigh Scattering Diagnostic Technique for the Combustion of Hydrocarbon Fuels and Filtered UV Rayleigh Scattering for Gas Velocity Measurements

NASA Technical Reports Server (NTRS)

Otugen, M. Volkan

1997-01-01

Non-intrusive techniques for the dynamic measurement of gas flow properties such as density, temperature and velocity, are needed in the research leading to the development of new generation high-speed aircraft. Accurate velocity, temperature and density data obtained in ground testing and in-flight measurements can help understand the flow physics leading to transition and turbulence in supersonic, high-altitude flight. Such non-intrusive measurement techniques can also be used to study combustion processes of hydrocarbon fuels in aircraft engines. Reliable, time and space resolved temperature measurements in various combustor configurations can lead to a better understanding of high temperature chemical reaction dynamics thus leading to improved modeling and better prediction of such flows. In view of this, a research program was initiated at Polytechnic University's Aerodynamics Laboratory with support from NASA Lewis Research Center through grants NAG3-1301 and NAG3-1690. The overall objective of this program has been to develop laser-based, non-contact, space- and time-resolved temperature and velocity measurement techniques. In the initial phase of the program a ND:YAG laser-based dual-line Rayleigh scattering technique was developed and tested for the accurate measurement of gas temperature in the presence of background laser glare. Effort was next directed towards the development of a filtered, spectrally-resolved Rayleigh/Mie scattering technique with the objective of developing an interferometric method for time-frozen velocity measurements in high-speed flows utilizing the uv line of an ND:YAG laser and an appropriate molecular absorption filter. This effort included both a search for an appropriate filter material for the 266 nm laser line and the development and testing of several image processing techniques for the fast processing of Fabry-Perot images for velocity and temperature information. Finally, work was also carried out for the development of a new laser-based strain-rate and vorticity technique for the time-resolved measurement of vorticity and strain-rates in turbulent flows.

Spectral analysis using CCDs

NASA Technical Reports Server (NTRS)

Hewes, C. R.; Brodersen, R. W.; De Wit, M.; Buss, D. D.

1976-01-01

Charge-coupled devices (CCDs) are ideally suited for performing sampled-data transversal filtering operations in the analog domain. Two algorithms have been identified for performing spectral analysis in which the bulk of the computation can be performed in a CCD transversal filter; the chirp z-transform and the prime transform. CCD implementation of both these transform algorithms is presented together with performance data and applications.

The Time-Domain Matched Filter and the Spectral-Domain Matched Filter in 1-Dimensional NMR Spectroscopy.

PubMed

Spencer, Richard G

2010-09-01

A type of "matched filter" (MF), used extensively in the processing of one-dimensional spectra, is defined by multiplication of a free-induction decay (FID) by a decaying exponential with the same time constant as that of the FID. This maximizes, in a sense to be defined, the signal-to-noise ratio (SNR) in the spectrum obtained after Fourier transformation. However, a different entity known also as the matched filter was introduced by van Vleck in the context of pulse detection in the 1940's and has become widely integrated into signal processing practice. These two types of matched filters appear to be quite distinct. In the NMR case, the "filter", that is, the exponential multiplication, is defined by the characteristics of, and applied to, a time domain signal in order to achieve improved SNR in the spectral domain. In signal processing, the filter is defined by the characteristics of a signal in the spectral domain, and applied in order to improve the SNR in the temporal (pulse) domain. We reconcile these two distinct implementations of the matched filter, demonstrating that the NMR "matched filter" is a special case of the matched filter more rigorously defined in the signal processing literature. In addition, two limitations in the use of the MF are highlighted. First, application of the MF distorts resonance ratios as defined by amplitudes, although not as defined by areas. Second, the MF maximizes SNR with respect to resonance amplitude, while intensities are often more appropriately defined by areas. Maximizing the SNR with respect to area requires a somewhat different approach to matched filtering.

Multiband tissue classification for ultrasonic transmission tomography using spectral profile detection

NASA Astrophysics Data System (ADS)

Jeong, Jeong-Won; Kim, Tae-Seong; Shin, Dae-Chul; Do, Synho; Marmarelis, Vasilis Z.

2004-04-01

Recently it was shown that soft tissue can be differentiated with spectral unmixing and detection methods that utilize multi-band information obtained from a High-Resolution Ultrasonic Transmission Tomography (HUTT) system. In this study, we focus on tissue differentiation using the spectral target detection method based on Constrained Energy Minimization (CEM). We have developed a new tissue differentiation method called "CEM filter bank". Statistical inference on the output of each CEM filter of a filter bank is used to make a decision based on the maximum statistical significance rather than the magnitude of each CEM filter output. We validate this method through 3-D inter/intra-phantom soft tissue classification where target profiles obtained from an arbitrary single slice are used for differentiation in multiple tomographic slices. Also spectral coherence between target and object profiles of an identical tissue at different slices and phantoms is evaluated by conventional cross-correlation analysis. The performance of the proposed classifier is assessed using Receiver Operating Characteristic (ROC) analysis. Finally we apply our method to classify tiny structures inside a beef kidney such as Styrofoam balls (~1mm), chicken tissue (~5mm), and vessel-duct structures.

Classification of visible and infrared hyperspectral images based on image segmentation and edge-preserving filtering

NASA Astrophysics Data System (ADS)

Cui, Binge; Ma, Xiudan; Xie, Xiaoyun; Ren, Guangbo; Ma, Yi

2017-03-01

The classification of hyperspectral images with a few labeled samples is a major challenge which is difficult to meet unless some spatial characteristics can be exploited. In this study, we proposed a novel spectral-spatial hyperspectral image classification method that exploited spatial autocorrelation of hyperspectral images. First, image segmentation is performed on the hyperspectral image to assign each pixel to a homogeneous region. Second, the visible and infrared bands of hyperspectral image are partitioned into multiple subsets of adjacent bands, and each subset is merged into one band. Recursive edge-preserving filtering is performed on each merged band which utilizes the spectral information of neighborhood pixels. Third, the resulting spectral and spatial feature band set is classified using the SVM classifier. Finally, bilateral filtering is performed to remove "salt-and-pepper" noise in the classification result. To preserve the spatial structure of hyperspectral image, edge-preserving filtering is applied independently before and after the classification process. Experimental results on different hyperspectral images prove that the proposed spectral-spatial classification approach is robust and offers more classification accuracy than state-of-the-art methods when the number of labeled samples is small.

Filtered gradient reconstruction algorithm for compressive spectral imaging

NASA Astrophysics Data System (ADS)

Mejia, Yuri; Arguello, Henry

2017-04-01

Compressive sensing matrices are traditionally based on random Gaussian and Bernoulli entries. Nevertheless, they are subject to physical constraints, and their structure unusually follows a dense matrix distribution, such as the case of the matrix related to compressive spectral imaging (CSI). The CSI matrix represents the integration of coded and shifted versions of the spectral bands. A spectral image can be recovered from CSI measurements by using iterative algorithms for linear inverse problems that minimize an objective function including a quadratic error term combined with a sparsity regularization term. However, current algorithms are slow because they do not exploit the structure and sparse characteristics of the CSI matrices. A gradient-based CSI reconstruction algorithm, which introduces a filtering step in each iteration of a conventional CSI reconstruction algorithm that yields improved image quality, is proposed. Motivated by the structure of the CSI matrix, Φ, this algorithm modifies the iterative solution such that it is forced to converge to a filtered version of the residual ΦTy, where y is the compressive measurement vector. We show that the filtered-based algorithm converges to better quality performance results than the unfiltered version. Simulation results highlight the relative performance gain over the existing iterative algorithms.

Flat-topped broadband rugate filters.

PubMed

Imenes, Anne G; McKenzie, David R

2006-10-20

A method of creating rugate interference filters that have flat-topped reflectance across an extended spectral region is presented. The method applies known relations from the classical coupled wave theory to develop a set of equations that gives the spatial frequency distribution of rugate cycles to achieve constant reflectance across a given spectral region. Two examples of the application of this method are discussed: a highly reflective coating for eye protection against harmful laser radiation incident from normal to 45 degrees , and a spectral beam splitter for efficient solar power conversion.

Recent developments at JPL in the application of digital image processing techniques to astronomical images

NASA Technical Reports Server (NTRS)

Lorre, J. J.; Lynn, D. J.; Benton, W. D.

1976-01-01

Several techniques of a digital image-processing nature are illustrated which have proved useful in visual analysis of astronomical pictorial data. Processed digital scans of photographic plates of Stephans Quintet and NGC 4151 are used as examples to show how faint nebulosity is enhanced by high-pass filtering, how foreground stars are suppressed by linear interpolation, and how relative color differences between two images recorded on plates with different spectral sensitivities can be revealed by generating ratio images. Analyses are outlined which are intended to compensate partially for the blurring effects of the atmosphere on images of Stephans Quintet and to obtain more detailed information about Saturn's ring structure from low- and high-resolution scans of the planet and its ring system. The employment of a correlation picture to determine the tilt angle of an average spectral line in a low-quality spectrum is demonstrated for a section of the spectrum of Uranus.

Extreme temperature robust optical sensor designs and fault-tolerant signal processing

DOEpatents

Riza, Nabeel Agha [Oviedo, FL; Perez, Frank [Tujunga, CA

2012-01-17

Silicon Carbide (SiC) probe designs for extreme temperature and pressure sensing uses a single crystal SiC optical chip encased in a sintered SiC material probe. The SiC chip may be protected for high temperature only use or exposed for both temperature and pressure sensing. Hybrid signal processing techniques allow fault-tolerant extreme temperature sensing. Wavelength peak-to-peak (or null-to-null) collective spectrum spread measurement to detect wavelength peak/null shift measurement forms a coarse-fine temperature measurement using broadband spectrum monitoring. The SiC probe frontend acts as a stable emissivity Black-body radiator and monitoring the shift in radiation spectrum enables a pyrometer. This application combines all-SiC pyrometry with thick SiC etalon laser interferometry within a free-spectral range to form a coarse-fine temperature measurement sensor. RF notch filtering techniques improve the sensitivity of the temperature measurement where fine spectral shift or spectrum measurements are needed to deduce temperature.

Energy Conservation in Optical Fibers With Distributed Brick-Walls Filters

NASA Astrophysics Data System (ADS)

Garcia, Javier; Ghozlan, Hassan; Kramer, Gerhard

2018-05-01

A band-pass filtering scheme is proposed to mitigate spectral broadening and channel coupling in the Nonlinear Schr\\"odinger (NLS) fiber optic channel. The scheme is modeled by modifying the NLS Equation to include an attenuation profile with multiple brick-wall filters centered at different frequencies. It is shown that this brick-walls profile conserves the total in-band energy of the launch signal. Furthermore, energy fluctuations between the filtered channels are characterized, and conditions on the channel spacings are derived that ensure energy conservation in each channel. The maximum spectral efficiency of such a system is derived, and a constructive rule for achieving it using Sidon sequences is provided.

A median-Gaussian filtering framework for Moiré pattern noise removal from X-ray microscopy image.

PubMed

Wei, Zhouping; Wang, Jian; Nichol, Helen; Wiebe, Sheldon; Chapman, Dean

2012-02-01

Moiré pattern noise in Scanning Transmission X-ray Microscopy (STXM) imaging introduces significant errors in qualitative and quantitative image analysis. Due to the complex origin of the noise, it is difficult to avoid Moiré pattern noise during the image data acquisition stage. In this paper, we introduce a post-processing method for filtering Moiré pattern noise from STXM images. This method includes a semi-automatic detection of the spectral peaks in the Fourier amplitude spectrum by using a local median filter, and elimination of the spectral noise peaks using a Gaussian notch filter. The proposed median-Gaussian filtering framework shows good results for STXM images with the size of power of two, if such parameters as threshold, sizes of the median and Gaussian filters, and size of the low frequency window, have been properly selected. Copyright © 2011 Elsevier Ltd. All rights reserved.

VO2 and VCO2 variabilities through indirect calorimetry instrumentation.

PubMed

Cadena-Méndez, Miguel; Escalante-Ramírez, Boris; Azpiroz-Leehan, Joaquín; Infante-Vázquez, Oscar

2013-01-01

The aim of this paper is to understand how to measure the VO2 and VCO2 variabilities in indirect calorimetry (IC) since we believe they can explain the high variation in the resting energy expenditure (REE) estimation. We propose that variabilities should be separately measured from the VO2 and VCO2 averages to understand technological differences among metabolic monitors when they estimate the REE. To prove this hypothesis the mixing chamber (MC) and the breath-by-breath (BbB) techniques measured the VO2 and VCO2 averages and their variabilities. Variances and power spectrum energies in the 0-0.5 Hertz band were measured to establish technique differences in steady and non-steady state. A hybrid calorimeter with both IC techniques studied a population of 15 volunteers that underwent the clino-orthostatic maneuver in order to produce the two physiological stages. The results showed that inter-individual VO2 and VCO2 variabilities measured as variances were negligible using the MC while variabilities measured as spectral energies using the BbB underwent 71 and 56% (p < 0.05), increase respectively. Additionally, the energy analysis showed an unexpected cyclic rhythm at 0.025 Hertz only during the orthostatic stage, which is new physiological information, not reported previusly. The VO2 and VCO2 inter-individual averages increased to 63 and 39% by the MC (p < 0.05) and 32 and 40% using the BbB (p < 0.1), respectively, without noticeable statistical differences among techniques. The conclusions are: (a) metabolic monitors should simultaneously include the MC and the BbB techniques to correctly interpret the steady or non-steady state variabilities effect in the REE estimation, (b) the MC is the appropriate technique to compute averages since it behaves as a low-pass filter that minimizes variances, (c) the BbB is the ideal technique to measure the variabilities since it can work as a high-pass filter to generate discrete time series able to accomplish spectral analysis, and (d) the new physiological information in the VO2 and VCO2 variabilities can help to understand why metabolic monitors with dissimilar IC techniques give different results in the REE estimation.

Imaging trace gases in volcanic plumes with Fabry Perot Interferometers

NASA Astrophysics Data System (ADS)

Kuhn, Jonas; Platt, Ulrich; Bobrowski, Nicole; Lübcke, Peter; Wagner, Thomas

2017-04-01

Within the last decades, progress in remote sensing of atmospheric trace gases revealed many important insights into physical and chemical processes in volcanic plumes. In particular, their evolution could be studied in more detail than by traditional in-situ techniques. A major limitation of standard techniques for volcanic trace gas remote sensing (e.g. Differential Optical Absorption Spectroscopy, DOAS) is the constraint of the measurement to a single viewing direction since they use dispersive spectroscopy with a high spectral resolution. Imaging DOAS-type approaches can overcome this limitation, but become very time consuming (of the order of minutes to record a single image) and often cannot match the timescales of the processes of interest for volcanic gas measurements (occurring at the order of seconds). Spatially resolved imaging observations with high time resolution for volcanic sulfur dioxide (SO2) emissions became possible with the introduction of the SO2-Camera. Reducing the spectral resolution to two spectral channels (using interference filters) that are matched to the SO2 absorption spectrum, the SO2-Camera is able to record full frame SO2 slant column density distributions at a temporal resolution on the order of < 1s. This for instance allows for studying variations in SO2 fluxes on very short time scales and applying them in magma dynamics models. However, the currently employed SO2-Camera technique is limited to SO2 detection and, due to its coarse spectral resolution, has a limited spectral selectivity. This limits its application to very specific, infrequently found measurement conditions. Here we present a new approach, based on matching the transmission profile of Fabry Perot Interferometers (FPIs) to periodic spectral absorption features of trace gases. The FPI's transmission spectrum is chosen to achieve a high correlation with the spectral absorption of the trace gas, allowing a high selectivity and sensitivity with still using only a few spectral channels. This would not only improve SO2 imaging, but also allow for the application of the technique to further gases of interest in volcanology (and other areas of atmospheric research). Imaging halogen species would be particularly interesting for volcanic trace gas studies. Bromine monoxide (BrO) and chlorine dioxide (OClO) both yield absorption features that allow their detection with the FPI correlation technique. From BrO and OClO data, ClO levels in the plume could be calculated. We present an outline of applications of the FPI technique to imaging a series of trace gases in volcanic plumes. Sample calculations on the sensitivity and selectivity of the technique, first proof of concept studies and proposals for technical implementations are presented.

Active integrated filters for RF-photonic channelizers.

PubMed

El Nagdi, Amr; Liu, Ke; LaFave, Tim P; Hunt, Louis R; Ramakrishna, Viswanath; Dabkowski, Mieczyslaw; MacFarlane, Duncan L; Christensen, Marc P

2011-01-01

A theoretical study of RF-photonic channelizers using four architectures formed by active integrated filters with tunable gains is presented. The integrated filters are enabled by two- and four-port nano-photonic couplers (NPCs). Lossless and three individual manufacturing cases with high transmission, high reflection, and symmetric couplers are assumed in the work. NPCs behavior is dependent upon the phenomenon of frustrated total internal reflection. Experimentally, photonic channelizers are fabricated in one single semiconductor chip on multi-quantum well epitaxial InP wafers using conventional microelectronics processing techniques. A state space modeling approach is used to derive the transfer functions and analyze the stability of these filters. The ability of adapting using the gains is demonstrated. Our simulation results indicate that the characteristic bandpass and notch filter responses of each structure are the basis of channelizer architectures, and optical gain may be used to adjust filter parameters to obtain a desired frequency magnitude response, especially in the range of 1-5 GHz for the chip with a coupler separation of ∼9 mm. Preliminarily, the measurement of spectral response shows enhancement of quality factor by using higher optical gains. The present compact active filters on an InP-based integrated photonic circuit hold the potential for a variety of channelizer applications. Compared to a pure RF channelizer, photonic channelizers may perform both channelization and down-conversion in an optical domain.

Optical filter having coupled whispering-gallery-mode resonators

NASA Technical Reports Server (NTRS)

Savchenkov, Anatoliy (Inventor); Ilchenko, Vladimir (Inventor); Maleki, Lutfollah (Inventor); Handley, Timothy A. (Inventor)

2006-01-01

Optical filters having at least two coupled whispering-gallery-mode (WGM) optical resonators to produce a second order or higher order filter function with a desired spectral profile. At least one of the coupled WGM optical resonators may be tunable by a control signal to adjust the filtering function.

Multispectral Imager With Improved Filter Wheel and Optics

NASA Technical Reports Server (NTRS)

Bremer, James C.

2007-01-01

Figure 1 schematically depicts an improved multispectral imaging system of the type that utilizes a filter wheel that contains multiple discrete narrow-band-pass filters and that is rotated at a constant high speed to acquire images in rapid succession in the corresponding spectral bands. The improvement, relative to prior systems of this type, consists of the measures taken to prevent the exposure of a focal-plane array (FPA) of photodetectors to light in more than one spectral band at any given time and to prevent exposure of the array to any light during readout. In prior systems, these measures have included, variously the use of mechanical shutters or the incorporation of wide opaque sectors (equivalent to mechanical shutters) into filter wheels. These measures introduce substantial dead times into each operating cycle intervals during which image information cannot be collected and thus incoming light is wasted. In contrast, the present improved design does not involve shutters or wide opaque sectors, and it reduces dead times substantially. The improved multispectral imaging system is preceded by an afocal telescope and includes a filter wheel positioned so that its rotation brings each filter, in its turn, into the exit pupil of the telescope. The filter wheel contains an even number of narrow-band-pass filters separated by narrow, spoke-like opaque sectors. The geometric width of each filter exceeds the cross-sectional width of the light beam coming out of the telescope. The light transmitted by the sequence of narrow-band filters is incident on a dichroic beam splitter that reflects in a broad shorter-wavelength spectral band that contains half of the narrow bands and transmits in a broad longer-wavelength spectral band that contains the other half of the narrow spectral bands. The filters are arranged on the wheel so that if the pass band of a given filter is in the reflection band of the dichroic beam splitter, then the pass band of the adjacent filter is in the longer-wavelength transmission band of the dichroic beam splitter (see Figure 2). Each of the two optical paths downstream of the dichroic beam splitter contains an additional broad-band-pass filter: The filter in the path of the light transmitted by the dichroic beam splitter transmits and attenuates in the same bands that are transmitted and reflected, respectively, by the beam splitter; the filter in the path of the light reflected by the dichroic beam splitter transmits and attenuates in the same bands that are reflected and transmitted, respectively, by the dichroic beam splitter. In each of these paths, the filtered light is focused onto an FPA. As the filter wheel rotates at a constant angular speed, its shaft angle is monitored, and the shaft-angle signal is used to synchronize the exposure times of the two FPAs. When a single narrowband-pass filter on the wheel occupies the entire cross section of the beam of light coming out of the telescope, the spectrum of light that reaches the dichroic beam splitter lies entirely within the pass band of that filter. Therefore, the beam in its entirety is either transmitted by the dichroic beam splitter and imaged on the longer-wavelength FPA or reflected by the beam splitter and imaged onto the shorter-wavelength FPA.

Pixelated filters for spatial imaging

NASA Astrophysics Data System (ADS)

Mathieu, Karine; Lequime, Michel; Lumeau, Julien; Abel-Tiberini, Laetitia; Savin De Larclause, Isabelle; Berthon, Jacques

2015-10-01

Small satellites are often used by spatial agencies to meet scientific spatial mission requirements. Their payloads are composed of various instruments collecting an increasing amount of data, as well as respecting the growing constraints relative to volume and mass; So small-sized integrated camera have taken a favored place among these instruments. To ensure scene specific color information sensing, pixelated filters seem to be more attractive than filter wheels. The work presented here, in collaboration with Institut Fresnel, deals with the manufacturing of this kind of component, based on thin film technologies and photolithography processes. CCD detectors with a pixel pitch about 30 μm were considered. In the configuration where the matrix filters are positioned the closest to the detector, the matrix filters are composed of 2x2 macro pixels (e.g. 4 filters). These 4 filters have a bandwidth about 40 nm and are respectively centered at 550, 700, 770 and 840 nm with a specific rejection rate defined on the visible spectral range [500 - 900 nm]. After an intense design step, 4 thin-film structures have been elaborated with a maximum thickness of 5 μm. A run of tests has allowed us to choose the optimal micro-structuration parameters. The 100x100 matrix filters prototypes have been successfully manufactured with lift-off and ion assisted deposition processes. High spatial and spectral characterization, with a dedicated metrology bench, showed that initial specifications and simulations were globally met. These excellent performances knock down the technological barriers for high-end integrated specific multi spectral imaging.

Properties of multilayer filters

NASA Technical Reports Server (NTRS)

Baumeister, P. W.

1973-01-01

New methods were investigated of using optical interference coatings to produce bandpass filters for the spectral region 110 nm to 200 nm. The types of filter are: triple cavity metal dielectric filters; all dielectric reflection filters; and all dielectric Fabry Perot type filters. The latter two types use thorium fluoride and either cryolite films or magnesium fluoride films in the stacks. The optical properties of the thorium fluoride were also measured.

Design and Characterization of a Photometer-Colorimeter Standard

NASA Astrophysics Data System (ADS)

Eppeldauer, George P.; Rácz, Miklós

2004-05-01

A photometer and tristimulus colorimeter has been developed at the National Institute of Standards and Technology (NIST) to realize a color scale. A novel construction was developed to implement the spectral-responsivity-based scale with small uncertainty. The new device can be used as a reference illuminance and luminance meter as well. Temperature-controlled filter combinations, with 5-8 layers in one package, are used to match the responsivity of a silicon tunnel-trap detector to the CIE color-matching functions with small spectral mismatch values (f1'). Design considerations to extend the tunnel-trap detector with replaceable single and double apertures and changeable filter combinations are described. The design and fabrication of the filter packages and the dependence of the f1' values on the thickness of the filter layers are discussed. The colorimeter was characterized for angular, spatial, and spectral responsivity. An improved preamplifier can convert current to voltage in an 11-decade dynamic range with 0.01% uncertainty.

Design and characterization of a photometer-colorimeter standard.

PubMed

Eppeldauer, George P; Rácz, Miklós

2004-05-01

A photometer and tristimulus colorimeter has been developed at the National Institute of Standards and Technology (NIST) to realize a color scale. A novel construction was developed to implement the spectral-responsivity-based scale with small uncertainty. The new device can be used as a reference illuminance and luminance meter as well. Temperature-controlled filter combinations, with 5-8 layers in one package, are used to match the responsivity of a silicon tunnel-trap detector to the CIE color-matching functions with small spectral mismatch values (f1'). Design considerations to extend the tunnel-trap detector with replaceable single and double apertures and changeable filter combinations are described. The design and fabrication of the filter packages and the dependence of the f1' values on the thickness of the filter layers are discussed. The colorimeter was characterized for angular, spatial, and spectral responsivity. An improved preamplifier can convert current to voltage in an 11-decade dynamic range with 0.01% uncertainty.

Smoothed spectra for enhanced dispersion-free pulse duration reduction of passively Q-switched microchip lasers.

PubMed

Lehneis, R; Jauregui, C; Steinmetz, A; Limpert, J; Tünnermann, A

2014-02-01

We present an enhanced technique for dispersion-free pulse shortening, which exploits the interplay of different third-order nonlinear effects in a waveguide structure. When exceeding a certain value of the pulse energy coupled into the waveguide, the typical oscillations of self-phase modulation (SPM)-broadened spectra vanish during pulse propagation. Such smoothed spectra ensure a high pulse quality of the spectrally filtered and, therefore, temporally shortened pulses independently of the filtering position. A reduction of the pulse duration from 138 to 24 ps has been achieved while preserving a high temporal quality. To the best of our knowledge, the nonlinear smoothing of SPM-broadened spectra is used in the context of dispersion-free pulse duration reduction for the first time.

Narrow bandpass steep edge optical filter for the JAST/T80 telescope instrumentation

NASA Astrophysics Data System (ADS)

Reichel, S.; Brauneck, U.; Bourquin, S.; Marín-Franch, A.

2013-09-01

The Observatorio Astrofisico de Javalambre in Spain observes with its JAST/T80 telescope galaxies in the Local Universe in a systematic study. This is accomplished with a multi-band photometric all sky survey called Javalambre Photometric Local Universe Survey (J-PLUS). A wide field camera receives the signals from universe via optical filters. In this presentation the development and design of a narrow bandpass steep edge filter with wide suppression will be shown. The filter has a full width half maximum in the range of 13-15 nm (with <1 nm tolerance) with central wavelengths in the range 350-860nm and an average transmission larger than 90% in the passband. Signals beyond the passband (blocking range) have to be suppressed down to 250nm and up to 1050nm (spectral regime), where a blocking of OD 5 (transmission < 10-5) is required. The edges have to be steep for a small transition width from 5% to 80%. The spectral requirements result in a large number of layers which are deposited with magnetron sputtering. The transmitted wavefront error of the optical filter must be less than lambda/2 over the 100mm aperture and the central wavelength uniformity must be better than +/- 0.4% over the clear aperture. The filter consists of optical filter glass and a coated substrate in order to reach the spectral requirements. The substrate is coated with more than 120 layers. The total filter thickness was specified to be 8.0mm. Results of steep edge narrow bandpass filters will be demonstrated fulfilling all these demanding requirements.

Spectral methods to detect cometary minerals with OSIRIS on board Rosetta

NASA Astrophysics Data System (ADS)

Oklay, N.; Vincent, J.-B.; Sierks, H.

2013-09-01

Comet 67P/Churyumov-Gerasimenko is going to be observed by the OSIRIS scientific imager (Keller et al. 2007) on board ESA's spacecraft Rosetta in the wavelength range of 250-1000 nm with a combination of 12 filters for the narrow angle camera (NAC) and 14 combination of 12 filters for the narrow angle camera (NAC) and 14 filters in the wavelength range of 240-720 nm for the wide angle camera (WAC). NAC filters are suitable to surface composition studies, while WAC filters are designed for gas and radical emission studies. In order to investigate the composition of the comet surface from the observed images, we need to understand how to detect different minerals and which compositional information can be derived from the NAC filters. Therefore, the most common cometary silicates e.g. enstatite, forsterite are investigated with two hydrated silicates (serpentine and smectite) for the determina- tion of the spectral methods. Laboratory data of those selected minerals are collected from RELAB database (http://www.planetary.brown.edu/relabdocs/relab.htm) and absolute spectra of the minerals observed by OSIRIS NAC filters are calculated. Due to the limited spectral range of the laboratory data, Far-UV and Neutral density filters of NAC are excluded from this analysis. Considered NAC filters in this study are represented in Table 1 and the number of collected laboratory data are presented in Table 2. Detection and separation of the minerals will not only allow us to study the surface composition but also to study observed composition changes due to the cometary activity during the mission.

Multispectral scanner flight model (F-1) radiometric calibration and alignment handbook

NASA Technical Reports Server (NTRS)

1981-01-01

This handbook on the calibration of the MSS-D flight model (F-1) provides both the relevant data and a summary description of how the data were obtained for the system radiometric calibration, system relative spectral response, and the filter response characteristics for all 24 channels of the four band MSS-D F-1 scanner. The calibration test procedure and resulting test data required to establish the reference light levels of the MSS-D internal calibration system are discussed. The final set of data ("nominal" calibration wedges for all 24 channels) for the internal calibration system is given. The system relative spectral response measurements for all 24 channels of MSS-D F-1 are included. These data are the spectral response of the complete scanner, which are the composite of the spectral responses of the scan mirror primary and secondary telescope mirrors, fiber optics, optical filters, and detectors. Unit level test data on the measurements of the individual channel optical transmission filters are provided. Measured performance is compared to specification values.

DigiLens color sequential filtering for microdisplay-based projection applications

NASA Astrophysics Data System (ADS)

Sagan, Stephen F.; Smith, Ronald T.; Popovich, Milan M.

2000-10-01

Application Specific Integrated Filters (ASIFs), based on a unique holographic polymer dispersed liquid crystal (H-PDLC) material system offering high efficiency, fast switching and low power, are being developed for microdisplay based projection applications. A new photonics technology based H-PDLC materials combined with the ability to be electrically switched on and off offers a new approach to color sequential filtering of a white light source for microdisplay-based front and rear projection display applications. Switchable Bragg gratings created in the PDLC are fundamental building blocks. Combined with the well- defined spectral and angular characteristics of Bragg gratings, these selectable filters can provide a large color gamut and a dynamically adjustable white balance. These switchable Bragg gratings can be reflective or transmissive and in each case can be designed to operate in either additive or subtractive mode. The spectral characteristics of filters made from a stack of these Bragg gratings can be configured for a specific lamp spectrum to give high diffractive efficiency over the broad bandwidths required for an illumination system. When it is necessary to reduce the spectral bandwidth, it is possible to use the properties of reflection Bragg holograms to construct very narrow band high efficiency filters. The basic properties and key benefits of ASIFs in projection displays are reviewed.

Interactive Spectral Analysis and Computation (ISAAC)

NASA Technical Reports Server (NTRS)

Lytle, D. M.

1992-01-01

Isaac is a task in the NSO external package for IRAF. A descendant of a FORTRAN program written to analyze data from a Fourier transform spectrometer, the current implementation has been generalized sufficiently to make it useful for general spectral analysis and other one dimensional data analysis tasks. The user interface for Isaac is implemented as an interpreted mini-language containing a powerful, programmable vector calculator. Built-in commands provide much of the functionality needed to produce accurate line lists from input spectra. These built-in functions include automated spectral line finding, least squares fitting of Voigt profiles to spectral lines including equality constraints, various filters including an optimal filter construction tool, continuum fitting, and various I/O functions.

A fast, automated, polynomial-based cosmic ray spike-removal method for the high-throughput processing of Raman spectra.

PubMed

Schulze, H Georg; Turner, Robin F B

2013-04-01

Raman spectra often contain undesirable, randomly positioned, intense, narrow-bandwidth, positive, unidirectional spectral features generated when cosmic rays strike charge-coupled device cameras. These must be removed prior to analysis, but doing so manually is not feasible for large data sets. We developed a quick, simple, effective, semi-automated procedure to remove cosmic ray spikes from spectral data sets that contain large numbers of relatively homogenous spectra. Although some inhomogeneous spectral data sets can be accommodated--it requires replacing excessively modified spectra with the originals and removing their spikes with a median filter instead--caution is advised when processing such data sets. In addition, the technique is suitable for interpolating missing spectra or replacing aberrant spectra with good spectral estimates. The method is applied to baseline-flattened spectra and relies on fitting a third-order (or higher) polynomial through all the spectra at every wavenumber. Pixel intensities in excess of a threshold of 3× the noise standard deviation above the fit are reduced to the threshold level. Because only two parameters (with readily specified default values) might require further adjustment, the method is easily implemented for semi-automated processing of large spectral sets.

Optical microwave filter based on spectral slicing by use of arrayed waveguide gratings.

PubMed

Pastor, Daniel; Ortega, Beatriz; Capmany, José; Sales, Salvador; Martinez, Alfonso; Muñoz, Pascual

2003-10-01

We have experimentally demonstrated a new optical signal processor based on the use of arrayed waveguide gratings. The structure exploits the concept of spectral slicing combined with the use of an optical dispersive medium. The approach presents increased flexibility from previous slicing-based structures in terms of tunability, reconfiguration, and apodization of the samples or coefficients of the transversal optical filter.

Using AVIRIS for in-flight calibration of the spectral shifts of SPOT-HRV and of AVHRR?

NASA Technical Reports Server (NTRS)

Willart-Soufflet, Veronique; Santer, Richard

1993-01-01

The response of a satellite sensor varies during its lifetime; internal calibration devices can be used to follow the sensor degradation or in-flight calibrations are conducted from estimates of the radiance at satellite level for well predictable situations. Changes in gain are evaluated assuming that the spectral response of the sensor is stable with time; i.e., that the filter response as well as the optics or the electronics are not modified since the prelaunch determinations. Nevertheless, there is some evidence that the SPOT interferometer filters are affected by outgassing effects during the launch. Tests in vacuum chambers indicated a narrowing of the filters with a shift of the upper side towards the blue of about 10 nm which is more over consistant with the loss of gain observed during the launch. Also, during the lifetime of SPOT, the relationship between the loss of sensitivity and the filter bandwidth may correspond to this effect. On the other hand, the inconsistancy of the NOAA7 calibration between two methods (desert and ocean) having a different spectral sensitivity may indicate a spectral problem with a shift of the central wavelength of -20 nm. The basic idea here is to take advantage of the good spectral definition of AVIRIS to monitor these potential spectral degradations with an experimental opportunity provided by a field campaign held in La Crau (S.E. of France) in June 1991 which associated ground-based measurements and AVIRIS, SPOT2, NOAA-11 overpasses over both the calibration site of La Crau and an agricultural area.

Signal-to-noise ratio of arbitrarily filtered spontaneous emission

NASA Astrophysics Data System (ADS)

Šprem, Marko; Bosiljevac, Marko; Babić, Dubravko

2018-02-01

The signal-to-noise ratio (SNR) of filtered incoherent light can be approximated from the product of the coherence time of the light and the equivalent (electrical) noise bandwidth of the detector. This approximation holds only for the light with very short coherence time, that is in the case where the optical bandwidth of the light is much larger than the electrical bandwidth. We present here an expression for accurate evaluation of the SNR of the filtered incoherent light, which computes SNR from arbitrary shapes of optical and electrical filter power spectral densities (PSD). The PSDs of the filters can be measured using optical and electrical spectrum analyzers. Using our expression, we show that the SNR reaches unity when the electrical filter bandwidth is becoming larger than the optical filter bandwidth. To prove the theory, we evaluate and directly measure SNR of an incoherent light source filtered with several optical filters with bandwidths larger and commensurate with the bandwidth of the detector. For later we used optical and electrical filters with 3-dB bandwidths of 15 GHz and 10 GHz, respectively. Using our expression to evaluate SNR we obtained results in a good agreement with directly measured SNR. The results also prove that the approximation for evaluating SNR does not provide accurate results. The PSD of the detector with large noise bandwidth is difficult to measure using spectrum analyzer. There- fore, we report here a method for measuring the electrical noise bandwidth of the detector using the heterodyne linewidth measurement technique with tunable laser.

Adaptive spatial filtering using photochromic glass

NASA Astrophysics Data System (ADS)

Potton, R. J.

1999-12-01

Commercially available photochromic glasses exhibit a wide range of spectral sensitivities and darkening response times. Short wavelengths are more effective than long ones for causing darkening but at least one type of glass is effectively darkened by red light (icons/Journals/Common/lambda" ALT="lambda" ALIGN="TOP"/> = 633 nm) with an intensity of about 1 kW m-2. Used as adaptive spatial filters, these glasses attenuate a wavefront by an amount that depends on their recent exposure to light. One type of optical processing that can be performed with such filters is drift nulling in an interferometer excited by light of a wavelength within the sensitivity spectrum of the photochrome. This form of processing has been demonstrated by dithering the speckle pattern in a single-fibre multimode interferometer. The dither allows phase-sensitive detection techniques to be used in the detection of signal-induced phase variations in a frequency band extending from the inverse response time of the photochrome to the dither frequency.

An analog filter approach to frequency domain fluorescence spectroscopy

DOE PAGES

Trainham, Clifford P.; O'Neill, Mary D.; McKenna, Ian J.

2015-10-01

The rate equations found in frequency domain fluorescence spectroscopy are the same as those found in electronics under analog filter theory. Laplace transform methods are a natural way to solve the equations, and the methods can provide solutions for arbitrary excitation functions. The fluorescence terms can be modeled as circuit components and cascaded with drive and detection electronics to produce a global transfer function. Electronics design tools such as Spicea can be used to model fluorescence problems. In applications, such as remote sensing, where detection electronics are operated at high gain and limited bandwidth, a global modeling of the entiremore » system is important, since the filter terms of the drive and detection electronics affect the measured response of the fluorescence signals. Furthermore, the techniques described here can be used to separate signals from fast and slow fluorophores emitting into the same spectral band, and data collection can be greatly accelerated by means of a frequency comb driver waveform and appropriate signal processing of the response.« less

Spectral optimization for measuring electron density by the dual-energy computed tomography coupled with balanced filter method.

PubMed

Saito, Masatoshi

2009-08-01

Dual-energy computed tomography (DECT) has the potential for measuring electron density distribution in a human body to predict the range of particle beams for treatment planning in proton or heavy-ion radiotherapy. However, thus far, a practical dual-energy method that can be used to precisely determine electron density for treatment planning in particle radiotherapy has not been developed. In this article, another DECT technique involving a balanced filter method using a conventional x-ray tube is described. For the spectral optimization of DECT using balanced filters, the author calculates beam-hardening error and air kerma required to achieve a desired noise level in electron density and effective atomic number images of a cylindrical water phantom with 50 cm diameter. The calculation enables the selection of beam parameters such as tube voltage, balanced filter material, and its thickness. The optimized parameters were applied to cases with different phantom diameters ranging from 5 to 50 cm for the calculations. The author predicts that the optimal combination of tube voltages would be 80 and 140 kV with Tb/Hf and Bi/Mo filter pairs for the 50-cm-diameter water phantom. When a single phantom calibration at a diameter of 25 cm was employed to cover all phantom sizes, maximum absolute beam-hardening errors were 0.3% and 0.03% for electron density and effective atomic number, respectively, over a range of diameters of the water phantom. The beam-hardening errors were 1/10 or less as compared to those obtained by conventional DECT, although the dose was twice that of the conventional DECT case. From the viewpoint of beam hardening and the tube-loading efficiency, the present DECT using balanced filters would be significantly more effective in measuring the electron density than the conventional DECT. Nevertheless, further developments of low-exposure imaging technology should be necessary as well as x-ray tubes with higher outputs to apply DECT coupled with the balanced filter method for clinical use.

Fusion of spectral models for dynamic modeling of sEMG and skeletal muscle force.

PubMed

Potluri, Chandrasekhar; Anugolu, Madhavi; Chiu, Steve; Urfer, Alex; Schoen, Marco P; Naidu, D Subbaram

2012-01-01

In this paper, we present a method of combining spectral models using a Kullback Information Criterion (KIC) data fusion algorithm. Surface Electromyographic (sEMG) signals and their corresponding skeletal muscle force signals are acquired from three sensors and pre-processed using a Half-Gaussian filter and a Chebyshev Type- II filter, respectively. Spectral models - Spectral Analysis (SPA), Empirical Transfer Function Estimate (ETFE), Spectral Analysis with Frequency Dependent Resolution (SPFRD) - are extracted from sEMG signals as input and skeletal muscle force as output signal. These signals are then employed in a System Identification (SI) routine to establish the dynamic models relating the input and output. After the individual models are extracted, the models are fused by a probability based KIC fusion algorithm. The results show that the SPFRD spectral models perform better than SPA and ETFE models in modeling the frequency content of the sEMG/skeletal muscle force data.

Solar Confocal Interferometers for Sub-Picometer-Resolution Spectral Filters

NASA Technical Reports Server (NTRS)

Gary, G. Allen; Pietraszewski, Chris; West, Edward A.; Dines, Terence C.

2006-01-01

The confocal Fabry-Perot interferometer allows sub-picometer spectral resolution of Fraunhofer line profiles. Such high spectral resolution is needed to keep pace with the higher spatial resolution of the new set of large-aperture solar telescopes. The line-of-sight spatial resolution derived for line profile inversions would then track the improvements of the transverse spatial scale provided by the larger apertures. The confocal interferometer's unique properties allow a simultaneous increase in both etendue and spectral power. Methods: We have constructed and tested two confocal interferometers. Conclusions: In this paper we compare the confocal interferometer with other spectral imaging filters, provide initial design parameters, show construction details for two designs, and report on the laboratory test results for these interferometers, and propose a multiple etalon system for future testing of these units and to obtain sub-picometer spectral resolution information on the photosphere in both the visible and near-infrared.

Far infrared filters for a rocket-borne radiometer.

PubMed

Romero, H V; Gursky, J; Blair, A G

1972-04-01

Low pass far infrared radiation filters with cutoff frequencies in the spectral region of 10-25 cm(-1) were required for a rocket-borne radiometer experiment. The paper describes the theory, fabrication, and laboratory transmission measurements of prototype grid filters investigated in a study prior to the construction of flight filters. Characteristics of the final flight filters are also presented.

Water vapor absorption coefficients in the 8-13-micron spectral region - A critical review

NASA Technical Reports Server (NTRS)

Grant, William B.

1990-01-01

Measurements of water vapor absorption coefficients in the thermal IR atmospheric window (8-13 microns) during the past 20 years obtained by a variety of techniques are reviewed for consistency and compared with computed values based on the AFGL spectral data tapes. The methods of data collection considered were atmospheric long path absorption with a CO2 laser or a broadband source and filters, a White cell and a CO2 laser or a broadband source and a spectrometer, and a spectrophone with a CO2 laser. Advantages and disadvantages of each measurement approach are given as a guide to further research. Continuum absorption has apparently been measured accurately to about the 5-10 percent level in five of the measurements reported.

Hyperspectral proximal sensing of Salix Alba trees in the Sacco river valley (Latium, Italy).

PubMed

Moroni, Monica; Lupo, Emanuela; Cenedese, Antonio

2013-10-29

Recent developments in hardware and software have increased the possibilities and reduced the costs of hyperspectral proximal sensing. Through the analysis of high resolution spectroscopic measurements at the laboratory or field scales, this monitoring technique is suitable for quantitative estimates of biochemical and biophysical variables related to the physiological state of vegetation. Two systems for hyperspectral imaging have been designed and developed at DICEA-Sapienza University of Rome, one based on the use of spectrometers, the other on tunable interference filters. Both systems provide a high spectral and spatial resolution with low weight, power consumption and cost. This paper describes the set-up of the tunable filter platform and its application to the investigation of the environmental status of the region crossed by the Sacco river (Latium, Italy). This was achieved by analyzing the spectral response given by tree samples, with roots partly or wholly submerged in the river, located upstream and downstream of an industrial area affected by contamination. Data acquired is represented as reflectance indices as well as reflectance values. Broadband and narrowband indices based on pigment content and carotenoids vs. chlorophyll content suggest tree samples located upstream of the contaminated area are 'healthier' than those downstream.

Ultra-High Efficiency, High-Concentration PV System Based On Spectral Division Between GaInP/GaInAs/Ge And BPC Silicon Cells

NASA Astrophysics Data System (ADS)

Benítez, P.; Mohedano, R.; Buljan, M.; Miñano, J. C.; Sun, Y.; Falicoff, W.; Vilaplana, J.; Chaves, J.; Biot, G.; López, J.

2011-12-01

A novel HCPV nonimaging concentrator concept with high concentration (>500×) is presented. It uses the combination of a commercial concentration GaInP/GaInAs/Ge 3J cell and a concentration Back-Point-Contact (BPC) concentration silicon cell for efficient spectral utilization, and external confinement techniques for recovering the 3J cell's reflection. The primary optical element (POE) is a flat Fresnel lens and the secondary optical element (SOE) is a free-form RXI-type concentrator with a band-pass filter embedded it, both POE and SOE performing Köhler integration to produce light homogenization. The band-pass filter sends the IR photons in the 900-1200 nm band to the silicon cell. Computer simulations predict that four-terminal terminal designs could achieve ˜46% added cell efficiencies using commercial 39% 3J and 26% Si cells. A first proof-of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ˜100× and lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using a 3J with peak efficiency of 36.9%.

Chemical Source Inversion using Assimilated Constituent Observations in an Idealized Two-dimensional System

NASA Technical Reports Server (NTRS)

Tangborn, Andrew; Cooper, Robert; Pawson, Steven; Sun, Zhibin

2009-01-01

We present a source inversion technique for chemical constituents that uses assimilated constituent observations rather than directly using the observations. The method is tested with a simple model problem, which is a two-dimensional Fourier-Galerkin transport model combined with a Kalman filter for data assimilation. Inversion is carried out using a Green's function method and observations are simulated from a true state with added Gaussian noise. The forecast state uses the same spectral spectral model, but differs by an unbiased Gaussian model error, and emissions models with constant errors. The numerical experiments employ both simulated in situ and satellite observation networks. Source inversion was carried out by either direct use of synthetically generated observations with added noise, or by first assimilating the observations and using the analyses to extract observations. We have conducted 20 identical twin experiments for each set of source and observation configurations, and find that in the limiting cases of a very few localized observations, or an extremely large observation network there is little advantage to carrying out assimilation first. However, in intermediate observation densities, there decreases in source inversion error standard deviation using the Kalman filter algorithm followed by Green's function inversion by 50% to 95%.

Design framework for a spectral mask for a plenoptic camera

NASA Astrophysics Data System (ADS)

Berkner, Kathrin; Shroff, Sapna A.

2012-01-01

Plenoptic cameras are designed to capture different combinations of light rays from a scene, sampling its lightfield. Such camera designs capturing directional ray information enable applications such as digital refocusing, rotation, or depth estimation. Only few address capturing spectral information of the scene. It has been demonstrated that by modifying a plenoptic camera with a filter array containing different spectral filters inserted in the pupil plane of the main lens, sampling of the spectral dimension of the plenoptic function is performed. As a result, the plenoptic camera is turned into a single-snapshot multispectral imaging system that trades-off spatial with spectral information captured with a single sensor. Little work has been performed so far on analyzing diffraction effects and aberrations of the optical system on the performance of the spectral imager. In this paper we demonstrate simulation of a spectrally-coded plenoptic camera optical system via wave propagation analysis, evaluate quality of the spectral measurements captured at the detector plane, and demonstrate opportunities for optimization of the spectral mask for a few sample applications.

Compressive Detection of Highly Overlapped Spectra Using Walsh-Hadamard-Based Filter Functions.

PubMed

Corcoran, Timothy C

2018-03-01

In the chemometric context in which spectral loadings of the analytes are already known, spectral filter functions may be constructed which allow the scores of mixtures of analytes to be determined in on-the-fly fashion directly, by applying a compressive detection strategy. Rather than collecting the entire spectrum over the relevant region for the mixture, a filter function may be applied within the spectrometer itself so that only the scores are recorded. Consequently, compressive detection shrinks data sets tremendously. The Walsh functions, the binary basis used in Walsh-Hadamard transform spectroscopy, form a complete orthonormal set well suited to compressive detection. A method for constructing filter functions using binary fourfold linear combinations of Walsh functions is detailed using mathematics borrowed from genetic algorithm work, as a means of optimizing said functions for a specific set of analytes. These filter functions can be constructed to automatically strip the baseline from analysis. Monte Carlo simulations were performed with a mixture of four highly overlapped Raman loadings and with ten excitation-emission matrix loadings; both sets showed a very high degree of spectral overlap. Reasonable estimates of the true scores were obtained in both simulations using noisy data sets, proving the linearity of the method.

A digital algorithm for spectral deconvolution with noise filtering and peak picking: NOFIPP-DECON

NASA Technical Reports Server (NTRS)

Edwards, T. R.; Settle, G. L.; Knight, R. D.

1975-01-01

Noise-filtering, peak-picking deconvolution software incorporates multiple convoluted convolute integers and multiparameter optimization pattern search. The two theories are described and three aspects of the software package are discussed in detail. Noise-filtering deconvolution was applied to a number of experimental cases ranging from noisy, nondispersive X-ray analyzer data to very noisy photoelectric polarimeter data. Comparisons were made with published infrared data, and a man-machine interactive language has evolved for assisting in very difficult cases. A modified version of the program is being used for routine preprocessing of mass spectral and gas chromatographic data.

Multispectral Filter Arrays: Recent Advances and Practical Implementation

PubMed Central

Lapray, Pierre-Jean; Wang, Xingbo; Thomas, Jean-Baptiste; Gouton, Pierre

2014-01-01

Thanks to some technical progress in interferencefilter design based on different technologies, we can finally successfully implement the concept of multispectral filter array-based sensors. This article provides the relevant state-of-the-art for multispectral imaging systems and presents the characteristics of the elements of our multispectral sensor as a case study. The spectral characteristics are based on two different spatial arrangements that distribute eight different bandpass filters in the visible and near-infrared area of the spectrum. We demonstrate that the system is viable and evaluate its performance through sensor spectral simulation. PMID:25407904

Fourier Spectral Filter Array for Optimal Multispectral Imaging.

PubMed

Jia, Jie; Barnard, Kenneth J; Hirakawa, Keigo

2016-04-01

Limitations to existing multispectral imaging modalities include speed, cost, range, spatial resolution, and application-specific system designs that lack versatility of the hyperspectral imaging modalities. In this paper, we propose a novel general-purpose single-shot passive multispectral imaging modality. Central to this design is a new type of spectral filter array (SFA) based not on the notion of spatially multiplexing narrowband filters, but instead aimed at enabling single-shot Fourier transform spectroscopy. We refer to this new SFA pattern as Fourier SFA, and we prove that this design solves the problem of optimally sampling the hyperspectral image data.

[Spectral transmission in blue filter intraocular lenses].

PubMed

Schrage, N

2012-02-01

There is uncertainty in ophthalmology concerning the quality and spectral transmission of light of so-called blue filter intraocular lenses (IOL). Clinical users have noticed that such IOL's appear to have different color intensities. The discussion on medical changes by means of such IOL's is dependent on the real light transmission of these IOL's. To add some objective data we compared these IOL's by systematic transmission measurements and observed technical differences of diffraction and geometry as well as transmission differences. The result gives objective indications that differences between blue filter IOL's from different manufacturers are important and are detailed in this paper.

Filtering and polychromatic vision in mantis shrimps: themes in visible and ultraviolet vision.

PubMed

Cronin, Thomas W; Bok, Michael J; Marshall, N Justin; Caldwell, Roy L

2014-01-01

Stomatopod crustaceans have the most complex and diverse assortment of retinal photoreceptors of any animals, with 16 functional classes. The receptor classes are subdivided into sets responsible for ultraviolet vision, spatial vision, colour vision and polarization vision. Many of these receptor classes are spectrally tuned by filtering pigments located in photoreceptors or overlying optical elements. At visible wavelengths, carotenoproteins or similar substances are packed into vesicles used either as serial, intrarhabdomal filters or lateral filters. A single retina may contain a diversity of these filtering pigments paired with specific photoreceptors, and the pigments used vary between and within species both taxonomically and ecologically. Ultraviolet-filtering pigments in the crystalline cones serve to tune ultraviolet vision in these animals as well, and some ultraviolet receptors themselves act as birefringent filters to enable circular polarization vision. Stomatopods have reached an evolutionary extreme in their use of filter mechanisms to tune photoreception to habitat and behaviour, allowing them to extend the spectral range of their vision both deeper into the ultraviolet and further into the red.

Solar Confocal interferometers for Sub-Picometer-Resolution Spectral Filters

NASA Technical Reports Server (NTRS)

Gary, G. Allen; Pietraszewski, Chris; West, Edward A.; Dines. Terence C.

2007-01-01

The confocal Fabry-Perot interferometer allows sub-picometer spectral resolution of Fraunhofer line profiles. Such high spectral resolution is needed to keep pace with the higher spatial resolution of the new set of large-aperture solar telescopes. The line-of-sight spatial resolution derived for line profile inversions would then track the improvements of the transverse spatial scale provided by the larger apertures. In particular, profile inversion allows improved velocity and magnetic field gradients to be determined independent of multiple line analysis using different energy levels and ions. The confocal interferometer's unique properties allow a simultaneous increase in both etendue and spectral power. The higher throughput for the interferometer provides significant decrease in the aperture, which is important in spaceflight considerations. We have constructed and tested two confocal interferometers. A slow-response thermal-controlled interferometer provides a stable system for laboratory investigation, while a piezoelectric interferometer provides a rapid response for solar observations. In this paper we provide design parameters, show construction details, and report on the laboratory test for these interferometers. The field of view versus aperture for confocal interferometers is compared with other types of spectral imaging filters. We propose a multiple etalon system for observing with these units using existing planar interferometers as pre-filters. The radiometry for these tests established that high spectral resolution profiles can be obtained with imaging confocal interferometers. These sub-picometer spectral data of the photosphere in both the visible and near-infrared can provide important height variation information. However, at the diffraction-limited spatial resolution of the telescope, the spectral data is photon starved due to the decreased spectral passband.

Multiwavelength self-pulsating fibre laser based on cascaded SPM spectral broadening and filtering

NASA Astrophysics Data System (ADS)

Rochette, Martin; Sun, Kai; Hernández-Cordero, Juan; Chen, Lawrence R.

2008-06-01

We experimentally demonstrate the operation of a laser based on self-phase modulation followed by offset spectral filtering. This laser has three operation modes: a continuous-wave mode, a self-pulsating mode where the laser self ignites and produces pulses, and a pulse-buffering mode where no new pulse is formed from spontaneous emission noise but only pulses already propagating or pulses injected in the laser cavity can be sustained. In the self-pulsating and pulse-buffering modes, the laser is multi-wavelength and continuously tunable over the entire gain band of the amplifiers. The output pulse width is quasi transform-limited with respect to the spectral-width of the filters used in the cavity. Overall, this device provides a simple alternative to pulsed laser source and also represents a promising approach for signal buffering.

Assessing invasive plant infestation in freshwater wetlands

NASA Astrophysics Data System (ADS)

Torbick, Nathan M.

Recent shifts in wetland ecosystem management goals have directed efforts toward measuring ecological integrity, rather than only using physical and chemical measures of ecosystems as health indicators. Invasive species pose one of the largest threats to wetlands integrity. Resource managers can benefit from improved methods for identifying invasive plant species, assessing infestation, and monitoring control measures. The utilization of advanced remote sensing tools for species-level mapping has been increasing and techniques need to be explored for identifying species of interest and characterizing infestation. The overarching goal of this research was to develop monitoring technologies to map invasive plants and quantify wetland infestation. The first field-level objective was to characterize absorption and reflectance features and assess processing techniques for separating wetland species. The second field-level objective was to evaluate the abilities of a shape filter to identify wetland invasive plant species. The first landscape-level objective was to classify hyperspectral imagery in order to identify invasives of interest. The second landscape-level objective was to quantify infestation within the study area. Field-level hyperspectral data (350-2500nm) were collected for twenty-two wetland plant species in a wetland located in the lower Muskegon River watershed in Michigan, USA. The Jeffries-Matusita distance measure, continuum removal, and a shape-filter were applied to hyperspectral species reflectance data to characterize spectral features. Generally, continuum removal decreased separation distance for the invasive species of interest. Using the shape-filter, Lythrum salicaria, Phragmites australis, and Typha latifolia possessed maximum separation (distinguished from other species) at the near-infrared edge (700nm) and water absorption region (1350nm), the near-infrared down slope (1000 and 1100nm), and the visible/chlorophyll absorption region (500nm) and near-infrared edge (650nm), respectively. Airborne hyperspectral imagery was classified using a two-step approach in order to obtain an optimal map (overall accuracy ˜ 70%). Information in the near-infrared enabled relatively accurate classification for Phragmites australis using the Spectral Angle Mapper algorithm and image-derived training, while Typha latifolia signatures possessed high spectral overlap and required ISODATA clustering techniques. Landscape pattern metrics relate infestation to disturbances and hydrological controls. The highest levels of infestation and infestation patterns coincide with the most substantial levels of hydrological modifications indicating human disturbances are correlated with Typha and Phragmites percentages in the landscape. Overall the approach was successful and increased the level of information ultimately desired by decision makers. The rapidly advancing field of wetland remote sensing science can obtain more meaningful information from hyperspectral imagery; however, the data are challenging to work with and only the most precisely calibrated datasets will provide utility. Combining these data with traditional wetland assessment techniques can substantially advanced goals of preserving and restoring wetland ecosystem integrity.

Estimating Spectra from Photometry

NASA Astrophysics Data System (ADS)

Kalmbach, J. Bryce; Connolly, Andrew J.

2017-12-01

Measuring the physical properties of galaxies such as redshift frequently requires the use of spectral energy distributions (SEDs). SED template sets are, however, often small in number and cover limited portions of photometric color space. Here we present a new method to estimate SEDs as a function of color from a small training set of template SEDs. We first cover the mathematical background behind the technique before demonstrating our ability to reconstruct spectra based upon colors and then compare our results to other common interpolation and extrapolation methods. When the photometric filters and spectra overlap, we show that the error in the estimated spectra is reduced by more than 65% compared to the more commonly used techniques. We also show an expansion of the method to wavelengths beyond the range of the photometric filters. Finally, we demonstrate the usefulness of our technique by generating 50 additional SED templates from an original set of 10 and by applying the new set to photometric redshift estimation. We are able to reduce the photometric redshifts standard deviation by at least 22.0% and the outlier rejected bias by over 86.2% compared to original set for z ≤ 3.

Operation KNOTHOLE, Nevada Proving Grounds. Project 8.4-1. Protection Afforded by Operational Smoke Screens against Thermal Radiation

DTIC Science & Technology

1954-03-01

spectral breakdown is obtained by mounting re- ceiving discs in back of Corning Glass Filters No. 3-69, 2-58, 7-56, and 0-52. The filters transmit...used for measuring the thermal flux under the smoke screen and in making the spectral measurements on radiant energy received under the smoke screen... Spectral Distribution Instrumentation a a a a a a a a a a a 30 2.4.1 Passive Receivers. . . . a a a a a . 30 2 .4 .2 Field Calorimeter * a a a a a a • a a

Terahertz bandwidth photonic Hilbert transformers based on synthesized planar Bragg grating fabrication.

PubMed

Sima, Chaotan; Gates, J C; Holmes, C; Mennea, P L; Zervas, M N; Smith, P G R

2013-09-01

Terahertz bandwidth photonic Hilbert transformers are proposed and experimentally demonstrated. The integrated device is fabricated via a direct UV grating writing technique in a silica-on-silicon platform. The photonic Hilbert transformer operates at bandwidths of up to 2 THz (~16 nm) in the telecom band, a 10-fold greater bandwidth than any previously reported experimental approaches. Achieving this performance requires detailed knowledge of the system transfer function of the direct UV grating writing technique; this allows improved linearity and yields terahertz bandwidth Bragg gratings with improved spectral quality. By incorporating a flat-top reflector and Hilbert grating with a waveguide coupler, an ultrawideband all-optical single-sideband filter is demonstrated.

Methods for computing color anaglyphs

NASA Astrophysics Data System (ADS)

McAllister, David F.; Zhou, Ya; Sullivan, Sophia

2010-02-01

A new computation technique is presented for calculating pixel colors in anaglyph images. The method depends upon knowing the RGB spectral distributions of the display device and the transmission functions of the filters in the viewing glasses. It requires the solution of a nonlinear least-squares program for each pixel in a stereo pair and is based on minimizing color distances in the CIEL*a*b* uniform color space. The method is compared with several techniques for computing anaglyphs including approximation in CIE space using the Euclidean and Uniform metrics, the Photoshop method and its variants, and a method proposed by Peter Wimmer. We also discuss the methods of desaturation and gamma correction for reducing retinal rivalry.

Shot noise limited detection of OH using the technique of laser induced fluorescence

NASA Technical Reports Server (NTRS)

Bakalyar, D. M.; Davis, L. I., Jr.; Guo, C.; James, J. V.; Kakos, S.; Morris, P. T.; Wang, C. C.

1984-01-01

Nearly shot-noise limited detection of OH using the technique of laser-induced fluorescence is reported. A LIDAR configuration is used to excite fluorescence in a large volume and a narrow-bandwidth interference filter provides spectral discrimination. This arrangement alleviates the effect of ozone interference and facilitates image processing at relatively close distances. The detection limit is determined mainly by the shot-noise of the solar background. Ground-based measurements in Dearborn indicate a detection limit of better than 1 x 10 to the 6th power OH/cubic cm over a forty-minute acquisition period. Under favorable conditions, a comparable detection limit was also observed for airborne measurements.

Shot noise limited detection of OH using the technique of laser-induced fluorescence

NASA Technical Reports Server (NTRS)

Bakalyar, D. M.; Davis, L. I., Jr.; Guo, C.; James, J. V.; Wang, C. C.; Kakos, S.; Morris, P. T.

1984-01-01

Nearly shot-noise limited detection of OH using the technique of laser-induced fluorescence is reported. A LIDAR configuration is used to excite fluoresence in a large volume and a narrow-bandwidth interference filter provides spectral discrimination. This arrangement alleviates the effect of ozone interference and facilitates image processing at relatively close distances. The detection limit is determined mainly by the short-noise of the solar background. Ground-based measurements in Dearborn indicate a detection limit of better than 1 x 10 to the 6th power OH/cubic cm over a forty-minute acquisition period. Under favorable conditions, a comparable detection limit was also observed for airborne measurements.

Speech enhancement based on modified phase-opponency detectors

NASA Astrophysics Data System (ADS)

Deshmukh, Om D.; Espy-Wilson, Carol Y.

2005-09-01

A speech enhancement algorithm based on a neural model was presented by Deshmukh et al., [149th meeting of the Acoustical Society America, 2005]. The algorithm consists of a bank of Modified Phase Opponency (MPO) filter pairs tuned to different center frequencies. This algorithm is able to enhance salient spectral features in speech signals even at low signal-to-noise ratios. However, the algorithm introduces musical noise and sometimes misses a spectral peak that is close in frequency to a stronger spectral peak. Refinement in the design of the MPO filters was recently made that takes advantage of the falling spectrum of the speech signal in sonorant regions. The modified set of filters leads to better separation of the noise and speech signals, and more accurate enhancement of spectral peaks. The improvements also lead to a significant reduction in musical noise. Continuity algorithms based on the properties of speech signals are used to further reduce the musical noise effect. The efficiency of the proposed method in enhancing the speech signal when the level of the background noise is fluctuating will be demonstrated. The performance of the improved speech enhancement method will be compared with various spectral subtraction-based methods. [Work supported by NSF BCS0236707.

Accounting for the measurement error of spectroscopically inferred soil carbon data for improved precision of spatial predictions.

PubMed

Somarathna, P D S N; Minasny, Budiman; Malone, Brendan P; Stockmann, Uta; McBratney, Alex B

2018-08-01

Spatial modelling of environmental data commonly only considers spatial variability as the single source of uncertainty. In reality however, the measurement errors should also be accounted for. In recent years, infrared spectroscopy has been shown to offer low cost, yet invaluable information needed for digital soil mapping at meaningful spatial scales for land management. However, spectrally inferred soil carbon data are known to be less accurate compared to laboratory analysed measurements. This study establishes a methodology to filter out the measurement error variability by incorporating the measurement error variance in the spatial covariance structure of the model. The study was carried out in the Lower Hunter Valley, New South Wales, Australia where a combination of laboratory measured, and vis-NIR and MIR inferred topsoil and subsoil soil carbon data are available. We investigated the applicability of residual maximum likelihood (REML) and Markov Chain Monte Carlo (MCMC) simulation methods to generate parameters of the Matérn covariance function directly from the data in the presence of measurement error. The results revealed that the measurement error can be effectively filtered-out through the proposed technique. When the measurement error was filtered from the data, the prediction variance almost halved, which ultimately yielded a greater certainty in spatial predictions of soil carbon. Further, the MCMC technique was successfully used to define the posterior distribution of measurement error. This is an important outcome, as the MCMC technique can be used to estimate the measurement error if it is not explicitly quantified. Although this study dealt with soil carbon data, this method is amenable for filtering the measurement error of any kind of continuous spatial environmental data. Copyright © 2018 Elsevier B.V. All rights reserved.

3D Sound Techniques for Sound Source Elevation in a Loudspeaker Listening Environment

NASA Astrophysics Data System (ADS)

Kim, Yong Guk; Jo, Sungdong; Kim, Hong Kook; Jang, Sei-Jin; Lee, Seok-Pil

In this paper, we propose several 3D sound techniques for sound source elevation in stereo loudspeaker listening environments. The proposed method integrates a head-related transfer function (HRTF) for sound positioning and early reflection for adding reverberant circumstance. In addition, spectral notch filtering and directional band boosting techniques are also included for increasing elevation perception capability. In order to evaluate the elevation performance of the proposed method, subjective listening tests are conducted using several kinds of sound sources such as white noise, sound effects, speech, and music samples. It is shown from the tests that the degrees of perceived elevation by the proposed method are around the 17º to 21º when the stereo loudspeakers are located on the horizontal plane.

Wide-Field Optic for Autonomous Acquisition of Laser Link

NASA Technical Reports Server (NTRS)

Page, Norman A.; Charles, Jeffrey R.; Biswas, Abhijit

2011-01-01

An innovation reported in Two-Camera Acquisition and Tracking of a Flying Target, NASA Tech Briefs, Vol. 32, No. 8 (August 2008), p. 20, used a commercial fish-eye lens and an electronic imaging camera for initially locating objects with subsequent handover to an actuated narrow-field camera. But this operated against a dark-sky background. An improved solution involves an optical design based on custom optical components for the wide-field optical system that directly addresses the key limitations in acquiring a laser signal from a moving source such as an aircraft or a spacecraft. The first challenge was to increase the light collection entrance aperture diameter, which was approximately 1 mm in the first prototype. The new design presented here increases this entrance aperture diameter to 4.2 mm, which is equivalent to a more than 16 times larger collection area. One of the trades made in realizing this improvement was to restrict the field-of-view to +80 deg. elevation and 360 azimuth. This trade stems from practical considerations where laser beam propagation over the excessively high air mass, which is in the line of sight (LOS) at low elevation angles, results in vulnerability to severe atmospheric turbulence and attenuation. An additional benefit of the new design is that the large entrance aperture is maintained even at large off-axis angles when the optic is pointed at zenith. The second critical limitation for implementing spectral filtering in the design was tackled by collimating the light prior to focusing it onto the focal plane. This allows the placement of the narrow spectral filter in the collimated portion of the beam. For the narrow band spectral filter to function properly, it is necessary to adequately control the range of incident angles at which received light intercepts the filter. When this angle is restricted via collimation, narrower spectral filtering can be implemented. The collimated beam (and the filter) must be relatively large to reduce the incident angle down to only a few degrees. In the presented embodiment, the filter diameter is more than ten times larger than the entrance aperture. Specifically, the filter has a clear aperture of about 51 mm. The optical design is refractive, and is comprised of nine custom refractive elements and an interference filter. The restricted maximum angle through the narrow-band filter ensures the efficient use of a 2-nm noise equivalent bandwidth spectral width optical filter at low elevation angles (where the range is longest), at the expense of less efficiency for high elevations, which can be tolerated because the range at high elevation angles is shorter. The image circle is 12 mm in diameter, mapped to 80 x 360 of sky, centered on the zenith.

A filter spectrometer concept for facsimile cameras

NASA Technical Reports Server (NTRS)

Jobson, D. J.; Kelly, W. L., IV; Wall, S. D.

1974-01-01

A concept which utilizes interference filters and photodetector arrays to integrate spectrometry with the basic imagery function of a facsimile camera is described and analyzed. The analysis considers spectral resolution, instantaneous field of view, spectral range, and signal-to-noise ratio. Specific performance predictions for the Martian environment, the Viking facsimile camera design parameters, and a signal-to-noise ratio for each spectral band equal to or greater than 256 indicate the feasibility of obtaining a spectral resolution of 0.01 micrometers with an instantaneous field of view of about 0.1 deg in the 0.425 micrometers to 1.025 micrometers range using silicon photodetectors. A spectral resolution of 0.05 micrometers with an instantaneous field of view of about 0.6 deg in the 1.0 to 2.7 micrometers range using lead sulfide photodetectors is also feasible.

Development and Operation of a Material Identification and Discrimination Imaging Spectroradiometer

NASA Technical Reports Server (NTRS)

Dombrowski, Mark; Willson, paul; LaBaw, Clayton

1997-01-01

Many imaging applications require quantitative determination of a scene's spectral radiance. This paper describes a new system capable of real-time spectroradiometric imagery. Operating at a full-spectrum update rate of 30Hz, this imager is capable of collecting a 30 point spectrum from each of three imaging heads: the first operates from 400 nm to 950 nm, with a 2% bandwidth; the second operates from 1.5 micro-m to 5.5 micro-m with a 1.5% bandwidth; the third operates from 5 micro-m to 12 micro-m, also at a 1.5% bandwidth. Standard image format is 256 x 256, with 512 x 512 possible in the VIS/NIR head. Spectra of up to 256 points are available at proportionately lower frame rates. In order to make such a tremendous amount of data more manageable, internal processing electronics perform four important operations on the spectral imagery data in real-time. First, all data in the spatial/spectral cube of data is spectro-radiometrically calibrated as it is collected. Second, to allow the imager to simulate sensors with arbitrary spectral response, any set of three spectral response functions may be loaded into the imager including delta functions to allow single wavelength viewing; the instrument then evaluates the integral of the product of the scene spectral radiances and the response function. Third, more powerful exploitation of the gathered spectral radiances can be effected by application of various spectral-matched filtering algorithms to identify pixels whose relative spectral radiance distribution matches a sought-after spectral radiance distribution, allowing materials-based identification and discrimination. Fourth, the instrument allows determination of spectral reflectance, surface temperature, and spectral emissivity, also in real-time. The spectral imaging technique used in the instrument allows tailoring of the frame rate and/or the spectral bandwidth to suit the scene radiance levels, i.e., frame rate can be reduced, or bandwidth increased to improve SNR when viewing low radiance scenes. The unique challenges of design and calibration are described. Pixel readout rates of 160 MHz, for full frame readout rates of 1000 Hz (512 x 512 image) present the first challenge; processing rates of nearly 600 million integer operations per second for sensor emulation, or over 2 billion per second for matched filtering, present the second. Spatial and spectral calibration of 66,536 pixels (262,144 for the 512 x 512 version) and up to 1,000 spectral positions mandate novel decoupling methods to keep the required calibration memory to a reasonable size. Large radiometric dynamic range also requires care to maintain precision operation with minimum memory size.

Theoretical analysis of the performance of code division multiple access communications over multimode optical fiber channels. Part 1: Transmission and detection

NASA Astrophysics Data System (ADS)

Walker, Ernest L.

1994-05-01

This paper presents results of a theoretical investigation to evaluate the performance of code division multiple access communications over multimode optical fiber channels in an asynchronous, multiuser communication network environment. The system is evaluated using Gold sequences for spectral spreading of the baseband signal from each user employing direct-sequence biphase shift keying and intensity modulation techniques. The transmission channel model employed is a lossless linear system approximation of the field transfer function for the alpha -profile multimode optical fiber. Due to channel model complexity, a correlation receiver model employing a suboptimal receive filter was used in calculating the peak output signal at the ith receiver. In Part 1, the performance measures for the system, i.e., signal-to-noise ratio and bit error probability for the ith receiver, are derived as functions of channel characteristics, spectral spreading, number of active users, and the bit energy to noise (white) spectral density ratio. In Part 2, the overall system performance is evaluated.

Improvements In The Calculation Of White Light Modulation Transfer Function (MTF) In Japan Optical Engineering Research Association (JOERA)

NASA Astrophysics Data System (ADS)

Minami, Setsuo; Ogawa, Ryota

1980-09-01

Consequences of the working project formed in JOERA (JAPAN OPTICAL ENGINEERING RESEARCH ASSOCIATION) from 1976 to 1978 are to be reported. The question, "What is the most reasonable number of mesh divides of entrance pupil to get monochromatic OTF and the most economical sampling method of spectral wavelengths to calculate White Light MTF?" is important in the actual stage of designing to optimize the conflict relationship between numerical accuracy and computing time. We have examined the spectral characteristics of OTF using some typical lenses such as photographic telephoto lens and wide angled retrofocus lens, cleared the structure of the White Light MTF, and found some techniques to get the reasonable numerical results. As a result of trial experiments to get coincidence between measurements and calculat-ions, the standard filter, which should be added to the MTF lens tester and whose spectral transmittance should be installed in the calculation, are proposed.

Estimation of dimensions and orientation of multiple riverine dune generations using spectral moments

NASA Astrophysics Data System (ADS)

Lisimenka, Aliaksandr; Kubicki, Adam

2017-02-01

A new spectral analysis technique is proposed for rhythmic bedform quantification, based on the 2D Fourier transform involving the calculation of a set of low-order spectral moments. The approach provides a tool for efficient quantification of bedform length and height as well as spatial crest-line alignment. Contrary to the conventional method, it not only describes the most energetic component of an undulating seabed surface but also retrieves information on its secondary structure without application of any band-pass filter of which the upper and lower cut-off frequencies are a priori unknown. Validation is based on bathymetric data collected in the main Vistula River mouth area (Przekop Wisły), Poland. This revealed two generations (distinct groups) of dunes which are migrating seawards along distinct paths, probably related to the hydrological regime of the river. The data enable the identification of dune divergence and convergence zones. The approach proved successful in the parameterisation of topographic roughness, an essential aspect in numerical modelling studies.

Mesoscale monitoring of the soil freeze/thaw boundary from orbital microwave radiometry

NASA Technical Reports Server (NTRS)

Dobson, Craig; Ulaby, Fawwaz T.; Zuerndorfer, Brian; England, Anthony W.

1990-01-01

A technique was developed for mapping the spatial extent of frozen soils from the spectral characteristics of the 10.7 to 37 GHz radiobrightness. Through computational models for the spectral radiobrightness of diurnally heated freesing soils, a distinctive radiobrightness signature was identified for frozen soils, and the signature was cast as a discriminant for unsupervised classification. In addition to large area images, local area spatial averages of radiobrightness were calculated for each radiobrightness channel at 7 meteorologic sites within the test region. Local area averages at the meteorologic sites were used to define the preliminary boundaries in the Freeze Indicator discriminate. Freeze Indicator images based upon Nimbus 7, Scanning Multichannel Microwave Radiometer (SMMR) data effectively map temporal variations in the freeze/thaw pattern for the northern Great Plains at the time scale of days. Diurnal thermal gradients have a small but measurable effect upon the SMMR spectral gradient. Scale-space filtering can be used to improve the spatial resolution of a freeze/thaw classified image.

An improved discriminative filter bank selection approach for motor imagery EEG signal classification using mutual information.

PubMed

Kumar, Shiu; Sharma, Alok; Tsunoda, Tatsuhiko

2017-12-28

Common spatial pattern (CSP) has been an effective technique for feature extraction in electroencephalography (EEG) based brain computer interfaces (BCIs). However, motor imagery EEG signal feature extraction using CSP generally depends on the selection of the frequency bands to a great extent. In this study, we propose a mutual information based frequency band selection approach. The idea of the proposed method is to utilize the information from all the available channels for effectively selecting the most discriminative filter banks. CSP features are extracted from multiple overlapping sub-bands. An additional sub-band has been introduced that cover the wide frequency band (7-30 Hz) and two different types of features are extracted using CSP and common spatio-spectral pattern techniques, respectively. Mutual information is then computed from the extracted features of each of these bands and the top filter banks are selected for further processing. Linear discriminant analysis is applied to the features extracted from each of the filter banks. The scores are fused together, and classification is done using support vector machine. The proposed method is evaluated using BCI Competition III dataset IVa, BCI Competition IV dataset I and BCI Competition IV dataset IIb, and it outperformed all other competing methods achieving the lowest misclassification rate and the highest kappa coefficient on all three datasets. Introducing a wide sub-band and using mutual information for selecting the most discriminative sub-bands, the proposed method shows improvement in motor imagery EEG signal classification.

Indium phosphide all air-gap Fabry-Pérot filters for near-infrared spectroscopic applications

NASA Astrophysics Data System (ADS)

Ullah, A.; Butt, M. A.; Fomchenkov, S. A.; Khonina, S. N.

2016-08-01

Food quality can be characterized by noninvasive techniques such as spectroscopy in the Near Infrared wavelength range. For example, 930 -1450 nm wavelength range can be used to detect diseases and differentiate between meat samples. Miniaturization of such NIR spectrometers is useful for quick and mobile characterization of food samples. Spectrometers can be miniaturized, without compromising the spectral resolution, using Fabry-Pérot (FP) filters consisting of two highly reflecting mirrors with a central cavity in between. The most commonly used mirrors in the design of FP filters are Distributed Bragg Reflections (DBRs) consisting of alternating high and low refractive index material pairs, due to their high reflectivity compared to metal mirrors. However, DBRs have high reflectivity for a selected range of wavelengths known as the stopband of the DBR. This range is usually much smaller than the sensitivity range of the spectrometer detector. Therefore, a bandpass filter is usually required to restrict wavelengths outside the stopband of the FP DBRs. Such bandpass filters are difficult to design and implement. Alternatively, high index contrast materials must be can be used to broaden the stopband width of the FP DBRs. In this work, Indium phosphide all air-gap filters are proposed in conjunction with InGaAs based detectors. The designed filter has a wide stopband covering the entire InGaAs detector sensitivity range. The filter can be tuned in the 950-1450 nm with single mode operation. The designed filter can hence be used for noninvasive meat quality control.

Development of low optical cross talk filters for VIIRS (JPSS)

NASA Astrophysics Data System (ADS)

Murgai, Vijay; Hendry, Derek; Downing, Kevin; Carbone, David; Potter, John

2016-09-01

The Visible/Infrared Imaging Radiometer Suite (VIIRS) is a key sensor on Suomi National Polar-orbiting Partnership (S-NPP) satellite launched on October 28, 2011 into a polar orbit of 824 km nominal altitude and the JPSS sensors currently being built and integrated. VIIRS collects radiometric and imagery data of the Earth's atmosphere, oceans, and land surfaces in 22 spectral bands spanning the visible and infrared spectrum from 0.4 to 12.5 μm. Interference filters assembled in `butcher-block' arrays mounted adjacent to focal plane arrays provide spectral definition. Out-of-band signal and out-of-band optical cross-talk was observed for bands in the 0.4 to 1 μm range in testing of VIIRS for S-NPP. Optical cross-talk is in-band or out-of-band light incident on an adjacent filter or adjacent region of the same filter reaching the detector. Out-of-band optical cross-talk results in spectral and spatial `impurities' in the signal and consequent errors in the calculated environmental parameters such as ocean color that rely on combinations of signals from more than one band. This paper presents results of characterization, specification, and coating process improvements that enabled production of filters with significantly reduced out of band light for Joint Polar Satellite System (JPSS) J1 and subsequent sensors. Total transmission and scatter measurements at a wavelength within the pass band can successfully characterize filter performance prior to dicing and assembling filters into butcher block assemblies. Coating and process development demonstrated performance on test samples followed by production of filters for J1 and J2. Results for J1 and J2 filters are presented.

Directly-deposited blocking filters for high-performance silicon x-ray detectors

NASA Astrophysics Data System (ADS)

Bautz, M.; Kissel, S.; Masterson, R.; Ryu, K.; Suntharalingam, V.

2016-07-01

Silicon X-ray detectors often require blocking filters to mitigate noise and out-of-band signal from UV and visible backgrounds. Such filters must be thin to minimize X-ray absorption, so direct deposition of filter material on the detector entrance surface is an attractive approach to fabrication of robust filters. On the other hand, the soft (E < 1 keV) X-ray spectral resolution of the detector is sensitive to the charge collection efficiency in the immediate vicinity of its entrance surface, so it is important that any filter layer is deposited without disturbing the electric field distribution there. We have successfully deposited aluminum blocking filters, ranging in thickness from 70 to 220nm, on back-illuminated CCD X-ray detectors passivated by means of molecular beam epitaxy. Here we report measurements showing that directly deposited filters have little or no effect on soft X-ray spectral resolution. We also find that in applications requiring very large optical density (> OD 6) care must be taken to prevent light from entering the sides and mounting surfaces of the detector. Our methods have been used to deposit filters on the detectors of the REXIS instrument scheduled to fly on OSIRIS-ReX later this year.

Implicit LES using adaptive filtering

NASA Astrophysics Data System (ADS)

Sun, Guangrui; Domaradzki, Julian A.

2018-04-01

In implicit large eddy simulations (ILES) numerical dissipation prevents buildup of small scale energy in a manner similar to the explicit subgrid scale (SGS) models. If spectral methods are used the numerical dissipation is negligible but it can be introduced by applying a low-pass filter in the physical space, resulting in an effective ILES. In the present work we provide a comprehensive analysis of the numerical dissipation produced by different filtering operations in a turbulent channel flow simulated using a non-dissipative, pseudo-spectral Navier-Stokes solver. The amount of numerical dissipation imparted by filtering can be easily adjusted by changing how often a filter is applied. We show that when the additional numerical dissipation is close to the subgrid-scale (SGS) dissipation of an explicit LES the overall accuracy of ILES is also comparable, indicating that periodic filtering can replace explicit SGS models. A new method is proposed, which does not require any prior knowledge of a flow, to determine the filtering period adaptively. Once an optimal filtering period is found, the accuracy of ILES is significantly improved at low implementation complexity and computational cost. The method is general, performing well for different Reynolds numbers, grid resolutions, and filter shapes.

X ray, extreme and far ultraviolet optical thin films for space applications

NASA Technical Reports Server (NTRS)

Zukic, Muamer; Torr, Douglas G.; Kim, Jongmin

1993-01-01

Far and extreme ultraviolet optical thin film filters find many uses in space astronomy, space astrophysics, and space aeronomy. Spacebased spectrographs are used for studying emission and absorption features of the earth, planets, sun, stars, and the interstellar medium. Most of these spectrographs use transmission or reflection filters. This requirement has prompted a search for selective filtering coatings with high throughput in the FUV and EUV spectral region. Important progress toward the development of thin film filters with improved efficiency and stability has been made in recent years. The goal for this field is the minimization of absorption to get high throughput and enhancement of wavelength selection. The Optical Aeronomy Laboratory (OAL) at the University of Alabama in Huntsville has recently developed the technology to determine optical constants of bulk and film materials for wavelengths extending from x-rays (0.1 nm) to the FUV (200 nm), and several materials have been identified that were used for designs of various optical devices which previously have been restricted to space application in the visible and near infrared. A new design concept called the Pi-multilayer was introduced and applied to the design of optical coatings for wavelengths extending from x-rays to the FUV. Section 3 of this report explains the Pi-multilayer approach and demonstrates its application for the design and fabrication of the FUV coatings. Two layer Pi-stacks have been utilized for the design of reflection filters in the EUV wavelength range from 70 - 100 nm. In order to eliminate losses due to the low reflection of the imaging optics and increase throughput and out-of-band rejection of the EUV instrumentation we introduced a self-filtering camera concept. In the FUV region, MgF2 and LiF crystals are known to be birefringent. Transmission polarizers and quarterwave retarders made of MgF2 or LiF crystals are commercially available but the performances are poor. New techniques for the design of the EUV and FUV polarizers and quarterwave retarders are described in Section 5. X- and gamma-ray detectors rely on a measurement of the electron which is effected when a ray interacts with matter. The design of an x- and gamma-ray telescope to operate in a particular region of the spectrum is, therefore, largely dictated by the mechanism through which the rays interact. Energy selection and the focusing of the incident high energy rays can be achieved with spectrally selective high reflective multilayers. The design and spectral performance of narrowband reflective x-ray Pi-multilayers are presented in section 6.

Statistical analysis of 16-year phase velocity distribution of mesospheric and ionospheric waves in airglow images: Comparison between Rikubetsu and Shigaraki, Japan

NASA Astrophysics Data System (ADS)

Tsuchiya, S.; Shiokawa, K.; Fujinami, H.; Otsuka, Y.; Nakamura, T.; Yamamoto, M.

2017-12-01

A new spectral analysis technique has been developed to obtain power spectra in the horizontal phase velocity by using the 3-D Fast Fourier Transform [Matsuda et al., JGR, 2014]. Takeo et al. (JGR, 2017) studied spectral parameters of atmospheric gravity waves (AGWs) in the mesopause region and medium-scale traveling ionospheric disturbances (MSTIDs) in the thermosphere over 16 years by using airglow images at wavelengths of 557.7 nm (emission altitudes: 90-100 km) and 630.0 nm (200-300 km) obtained at Shigaraki (34.8N, 136.1E), Japan. In this study, we have applied the same spectral analysis technique to the 557.7 nm and 630.0-nm airglow images obtained at Rikubetsu (43.5N, 143.8E), Japan, for 16 years from 1999 to 2014. We compared spectral features of AGWs and MSTIDs over 16 years observed at Shigaraki and Rikubetsu, which are separated by 1,174 km. The propagation direction of mesospheric AGWs seen in 557.7-nm airglow images is northeastward in summer and southwestward in winter at both Shigaraki and Rikubetsu, probably due to wind filtering of these waves by the mesospheric jet. In winter, the propagation direction of AGWs gradually shifted from southwestward to northwestward as time progresses from evening to morning at both stations. We suggest that this local-time shift of propagation direction can also be explained by the wind filtering effect. The propagation direction of AGWs changed from southwestward to northeastward at Rikubetsu on the day of the reversal of eastward zonal wind at 60N and 10 hPa (about 35 km in altitude) by the stratospheric sudden warming (SSW), while such a SSW-associated change was not identified at Shigaraki, indicating that the effect of SSW wind reversal reached only to the Rikubetsu latitudes. For MSTIDs, there is a negative correlation between yearly variation of powers spectral density and F10.7 flux and propagation direction is southwestward in all season at both Shigaraki and Rikubetsu. This negative correlation can be explained by considering the linear growth rate of the Perkins instability which is a cause of the nighttime MSTIDs.

A New Method to Cancel RFI---The Adaptive Filter

NASA Astrophysics Data System (ADS)

Bradley, R.; Barnbaum, C.

1996-12-01

An increasing amount of precious radio frequency spectrum in the VHF, UHF, and microwave bands is being utilized each year to support new commercial and military ventures, and all have the potential to interfere with radio astronomy observations. Some radio spectral lines of astronomical interest occur outside the protected radio astronomy bands and are unobservable due to heavy interference. Conventional approaches to deal with RFI include legislation, notch filters, RF shielding, and post-processing techniques. Although these techniques are somewhat successful, each suffers from insufficient interference cancellation. One concept of interference excision that has not been used before in radio astronomy is adaptive interference cancellation. The concept of adaptive interference canceling was first introduced in the mid-1970s as a way to reduce unwanted noise in low frequency (audio) systems. Examples of such systems include the canceling of maternal ECG in fetal electrocardiography and the reduction of engine noise in the passenger compartment of automobiles. Only recently have high-speed digital filter chips made adaptive filtering possible in a bandwidth as large a few megahertz, finally opening the door to astronomical uses. The system consists of two receivers: the main beam of the radio telescope receives the desired signal corrupted by RFI coming in the sidelobes, and the reference antenna receives only the RFI. The reference antenna is processed using a digital adaptive filter and then subtracted from the signal in the main beam, thus producing the system output. The weights of the digital filter are adjusted by way of an algorithm that minimizes, in a least-squares sense, the power output of the system. Through an adaptive-iterative process, the interference canceler will lock onto the RFI and the filter will adjust itself to minimize the effect of the RFI at the system output. We are building a prototype 100 MHz receiver and will measure the cancellation effectiveness of the system on the 140 ft telescope at Green Bank Observatory.

Detection and tracking of gas plumes in LWIR hyperspectral video sequence data

NASA Astrophysics Data System (ADS)

Gerhart, Torin; Sunu, Justin; Lieu, Lauren; Merkurjev, Ekaterina; Chang, Jen-Mei; Gilles, Jérôme; Bertozzi, Andrea L.

2013-05-01

Automated detection of chemical plumes presents a segmentation challenge. The segmentation problem for gas plumes is difficult due to the diffusive nature of the cloud. The advantage of considering hyperspectral images in the gas plume detection problem over the conventional RGB imagery is the presence of non-visual data, allowing for a richer representation of information. In this paper we present an effective method of visualizing hyperspectral video sequences containing chemical plumes and investigate the effectiveness of segmentation techniques on these post-processed videos. Our approach uses a combination of dimension reduction and histogram equalization to prepare the hyperspectral videos for segmentation. First, Principal Components Analysis (PCA) is used to reduce the dimension of the entire video sequence. This is done by projecting each pixel onto the first few Principal Components resulting in a type of spectral filter. Next, a Midway method for histogram equalization is used. These methods redistribute the intensity values in order to reduce icker between frames. This properly prepares these high-dimensional video sequences for more traditional segmentation techniques. We compare the ability of various clustering techniques to properly segment the chemical plume. These include K-means, spectral clustering, and the Ginzburg-Landau functional.

Experimental Demonstration of Adaptive Infrared Multispectral Imaging Using Plasmonic Filter Array (Postprint)

DTIC Science & Technology

2016-10-10

AFRL-RX-WP-JA-2017-0189 EXPERIMENTAL DEMONSTRATION OF ADAPTIVE INFRARED MULTISPECTRAL IMAGING USING PLASMONIC FILTER ARRAY...March 2016 – 23 May 2016 4. TITLE AND SUBTITLE EXPERIMENTAL DEMONSTRATION OF ADAPTIVE INFRARED MULTISPECTRAL IMAGING USING PLASMONIC FILTER ARRAY...experimental demonstration of adaptive multispectral imagery using fabricated plasmonic spectral filter arrays and proposed target detection scenarios

Temperature Tunable Air-Gap Etalon Filter

NASA Technical Reports Server (NTRS)

Krainak, Michael A.; Stephen, Mark A.; Lunt, David L.

1998-01-01

We report on experimental measurements of a temperature tuned air-gap etalon filter. The filter exhibits temperature dependent wavelength tuning of 54 pm/C. It has a nominal center wavelength of 532 nm. The etalon filter has a 27 pm optical bandpass and 600 pm free spectral range (finesse approximately 22). The experimental results are in close agreement with etalon theory.

Spectral characterization of near-infrared acousto-optic tunable filter (AOTF) hyperspectral imaging systems using standard calibration materials.

PubMed

Bürmen, Miran; Pernuš, Franjo; Likar, Boštjan

2011-04-01

In this study, we propose and evaluate a method for spectral characterization of acousto-optic tunable filter (AOTF) hyperspectral imaging systems in the near-infrared (NIR) spectral region from 900 nm to 1700 nm. The proposed spectral characterization method is based on the SRM-2035 standard reference material, exhibiting distinct spectral features, which enables robust non-rigid matching of the acquired and reference spectra. The matching is performed by simultaneously optimizing the parameters of the AOTF tuning curve, spectral resolution, baseline, and multiplicative effects. In this way, the tuning curve (frequency-wavelength characteristics) and the corresponding spectral resolution of the AOTF hyperspectral imaging system can be characterized simultaneously. Also, the method enables simple spectral characterization of the entire imaging plane of hyperspectral imaging systems. The results indicate that the method is accurate and efficient and can easily be integrated with systems operating in diffuse reflection or transmission modes. Therefore, the proposed method is suitable for characterization, calibration, or validation of AOTF hyperspectral imaging systems. © 2011 Society for Applied Spectroscopy

Thin-film X-ray filters on microstructured substrates and their thermophysical properties

NASA Astrophysics Data System (ADS)

Mitrofanov, A. V.

2018-02-01

It is shown that structured substrates having micron- or submicron-sized through holes and coated with an ultrathin organic film can be used for the fabrication of thin-film X-ray filters via direct growth of functional layers on a substrate by sputter deposition, without additional complex processing steps. An optimised process is considered for the fabrication of X-ray filters on support structures in the form of electroplated fine nickel grids and on track-etched polymer membranes with micron- and submicrondiameter through pores. 'Optimisation' is here taken to mean matching the sputter deposition conditions with the properties of substrates so as to avoid overheating. The filters in question are intended for both imaging and single-channel detectors operating in the soft X-ray and vacuum UV spectral regions, at wavelengths from 10 to 60 nm. Thermal calculations are presented for the heating of ultrathin layers of organic films and thin-film support substrates during the sputter deposition of aluminium or other functional materials. The paper discusses approaches for cooling thinfilm composites during the sputter deposition process and the service of the filters in experiments and gives a brief overview of the works that utilised filters produced by the described technique on microstructured substrates, including orbital solar X-ray research in the framework of the CORONAS programme and laboratory laser plasma experiments.

Variability in surface ECG morphology: signal or noise?

NASA Technical Reports Server (NTRS)

Smith, J. M.; Rosenbaum, D. S.; Cohen, R. J.

1988-01-01

Using data collected from canine models of acute myocardial ischemia, we investigated two issues of major relevance to electrocardiographic signal averaging: ECG epoch alignment, and the spectral characteristics of the beat-to-beat variability in ECG morphology. With initial digitization rates of 1 kHz, an iterative a posteriori matched filtering alignment scheme, and linear interpolation, we demonstrated that there is sufficient information in the body surface ECG to merit alignment to a precision of 0.1 msecs. Applying this technique to align QRS complexes and atrial pacing artifacts independently, we demonstrated that the conduction delay from atrial stimulus to ventricular activation may be so variable as to preclude using atrial pacing as an alignment mechanism, and that this variability in conduction time be modulated at the frequency of respiration and at a much lower frequency (0.02-0.03Hz). Using a multidimensional spectral technique, we investigated the beat-to-beat variability in ECG morphology, demonstrating that the frequency spectrum of ECG morphological variation reveals a readily discernable modulation at the frequency of respiration. In addition, this technique detects a subtle beat-to-beat alternation in surface ECG morphology which accompanies transient coronary artery occlusion. We conclude that physiologically important information may be stored in the variability in the surface electrocardiogram, and that this information is lost by conventional averaging techniques.

Filter and Grid Resolution in DG-LES

NASA Astrophysics Data System (ADS)

Miao, Ling; Sammak, Shervin; Madnia, Cyrus K.; Givi, Peyman

2017-11-01

The discontinuous Galerkin (DG) methodology has proven very effective for large eddy simulation (LES) of turbulent flows. Two important parameters in DG-LES are the grid resolution (h) and the filter size (Δ). In most previous work, the filter size is usually set to be proportional to the grid spacing. In this work, the DG method is combined with a subgrid scale (SGS) closure which is equivalent to that of the filtered density function (FDF). The resulting hybrid scheme is particularly attractive because a larger portion of the resolved energy is captured as the order of spectral approximation increases. Different cases for LES of a three-dimensional temporally developing mixing layer are appraised and a systematic parametric study is conducted to investigate the effects of grid resolution, the filter width size, and the order of spectral discretization. Comparative assessments are also made via the use of high resolution direct numerical simulation (DNS) data.

Polymer based resonant waveguide grating photonic filter with on-chip thermal tuning

NASA Astrophysics Data System (ADS)

Chaudhuri, Ritesh Ray; Enemuo, Amarachukwu N.; Song, Youngsik; Seo, Sang-Woo

2018-07-01

In this paper, we present the development of a multilayer polymer resonant waveguide grating (RWG)-based optical filter with an integrated microheater for on-chip thermal spectral tuning. RWG optical filter is fabricated using polymer-based materials. Therefore, its integration can be applied to different material platforms. Typical RWG structure is sensitive to back optical reflection from the structures below. To reduce the effect of back reflection from the metal heater and improve the quality of the integrated RWG filter output, an intermediate absorption layer was implemented utilizing an epoxy based carbon coating. This approach effectively suppresses the background noise in the RWG characteristics. The central wavelength of the reported filter was designed around 1550 nm. Experimentally, wavelength tuning of 21.96 nm was achieved for operating temperature range of 81 °C with approximately 150mW power consumption. Based on the layer-by-layer fabrication approach, the presented thermally tunable RWG filter on a chip has potential for use in low cost hybrid communication systems and spectral sensing applications.

Low-Dose Contrast-Enhanced Breast CT Using Spectral Shaping Filters: An Experimental Study.

PubMed

Makeev, Andrey; Glick, Stephen J

2017-12-01

Iodinated contrast-enhanced X-ray imaging of the breast has been studied with various modalities, including full-field digital mammography (FFDM), digital breast tomosynthesis (DBT), and dedicated breast CT. Contrast imaging with breast CT has a number of advantages over FFDM and DBT, including the lack of breast compression, and generation of fully isotropic 3-D reconstructions. Nonetheless, for breast CT to be considered as a viable tool for routine clinical use, it would be desirable to reduce radiation dose. One approach for dose reduction in breast CT is spectral shaping using X-ray filters. In this paper, two high atomic number filter materials are studied, namely, gadolinium (Gd) and erbium (Er), and compared with Al and Cu filters currently used in breast CT systems. Task-based performance is assessed by imaging a cylindrical poly(methyl methacrylate) phantom with iodine inserts on a benchtop breast CT system that emulates clinical breast CT. To evaluate detectability, a channelized hoteling observer (CHO) is used with sums of Laguerre-Gauss channels. It was observed that spectral shaping using Er and Gd filters substantially increased the dose efficiency (defined as signal-to-noise ratio of the CHO divided by mean glandular dose) as compared with kilovolt peak and filter settings used in commercial and prototype breast CT systems. These experimental phantom study results are encouraging for reducing dose of breast CT, however, further evaluation involving patients is needed.

Visualization of the spatial and spectral signals of orb-weaving spiders, Nephila pilipes, through the eyes of a honeybee.

PubMed

Chiao, Chuan-Chin; Wu, Wen-Yen; Chen, Sheng-Hui; Yang, En-Cheng

2009-07-01

It is well known that the honeybee has good color vision. However, the spectral range in which the bee can see is different from that of the human eye. To study how bees view their world of colors, one has to see through the eyes of the bee, not the eyes of a human. A conventional way to examine the color signals that animals can detect is to measure the surface reflectance spectra and compute the quantum catches of each photoreceptor type based on its known spectral sensitivity. Color signal and color contrast are then determined from the loci of these quantum catches in the color space. While the point-by-point measurements of the reflectance spectra using a standard spectrometer have yielded a significant amount of data for analyzing color signals, the lack of spatial information and low sampling efficiency constrain their applications. Using a special filter coating technique, a set of filters with transmission spectra that were closely matched to the bee's sensitivity spectra of three photoreceptor types (UV, blue, and green) was custom made. By placing these filters in front of a UV/VIS-sensitive CCD camera and acquiring images sequentially, we could collect images of a bee's receptor with only three shots. This allowed a direct visualization of how bees view their world in a pseudo-color RGB display. With this imaging system, spatial and spectral signals of the orb-weaving spider, Nephila pilipes, were recorded, and color contrast images corresponding to the bee's spatial resolution were constructed and analyzed. The result not only confirmed that the color markings of N. pilipes are of high chromatic contrast to the eyes of a bee, but it also indicated that the spatial arrangement of these markings resemble flower patterns which may attract bees to visit them. Thus, it is likely that the orb-weaving spider (N. pilipes) deploys a similar strategy to that of the Australian crab spider (Thomisus spectabilis) to exploit the bee's pre-existing preference for flowers with color patterning.

The interaction of the outflow with the molecular disk in the Active Galactic Nucleus of NGC 6951

NASA Astrophysics Data System (ADS)

May, D.; Steiner, J. E.; Ricci, T. V.; Menezes, R. B.; Andrade, I. S.

2015-02-01

Context: we present a study of the central 200 pc of NGC 6951, in the optical and NIR, taken with the Gemini North Telescope integral field spectrographs, with resolution of ~ 0''.1 Methods: we used a set of image processing techniques, as the filtering of high spatial and spectral frequencies, Richardson-Lucy deconvolution and PCA Tomography (Steiner et al. 2009) to map the distribution and kinematics of the emission lines. Results: we found a thick molecular disk, with the ionization cone highly misaligned.

Automatic cytometric device using multiple wavelength excitations

NASA Astrophysics Data System (ADS)

Rongeat, Nelly; Ledroit, Sylvain; Chauvet, Laurence; Cremien, Didier; Urankar, Alexandra; Couderc, Vincent; Nérin, Philippe

2011-05-01

Precise identification of eosinophils, basophils, and specific subpopulations of blood cells (B lymphocytes) in an unconventional automatic hematology analyzer is demonstrated. Our specific apparatus mixes two excitation radiations by means of an acousto-optics tunable filter to properly control fluorescence emission of phycoerythrin cyanin 5 (PC5) conjugated to antibodies (anti-CD20 or anti-CRTH2) and Thiazole Orange. This way our analyzer combining techniques of hematology analysis and flow cytometry based on multiple fluorescence detection, drastically improves the signal to noise ratio and decreases the spectral overlaps impact coming from multiple fluorescence emissions.

IPL Processing of the Viking Orbiter Images of Mars

NASA Technical Reports Server (NTRS)

Ruiz, R. M.; Elliott, D. A.; Yagi, G. M.; Pomphrey, R. B.; Power, M. A.; Farrell, W., Jr.; Lorre, J. J.; Benton, W. D.; Dewar, R. E.; Cullen, L. E.

1977-01-01

The Viking orbiter cameras returned over 9000 images of Mars during the 6-month nominal mission. Digital image processing was required to produce products suitable for quantitative and qualitative scientific interpretation. Processing included the production of surface elevation data using computer stereophotogrammetric techniques, crater classification based on geomorphological characteristics, and the generation of color products using multiple black-and-white images recorded through spectral filters. The Image Processing Laboratory of the Jet Propulsion Laboratory was responsible for the design, development, and application of the software required to produce these 'second-order' products.

DLP NIRscan Nano: an ultra-mobile DLP-based near-infrared Bluetooth spectrometer

NASA Astrophysics Data System (ADS)

Gelabert, Pedro; Pruett, Eric; Perrella, Gavin; Subramanian, Sreeram; Lakshminarayanan, Aravind

2016-02-01

The DLP NIRscan Nano is an ultra-portable spectrometer evaluation module utilizing DLP technology to meet lower cost, smaller size, and higher performance than traditional architectures. The replacement of a linear array detector with DLP digital micromirror device (DMD) in conjunction with a single point detector adds the functionality of programmable spectral filters and sampling techniques that were not previously available on NIR spectrometers. This paper presents the hardware, software, and optical systems of the DLP NIRscan Nano and its design considerations on the implementation of a DLP-based spectrometer.

A Ratiometric Method for Johnson Noise Thermometry Using a Quantized Voltage Noise Source

NASA Astrophysics Data System (ADS)

Nam, S. W.; Benz, S. P.; Martinis, J. M.; Dresselhaus, P.; Tew, W. L.; White, D. R.

2003-09-01

Johnson Noise Thermometry (JNT) involves the measurement of the statistical variance of a fluctuating voltage across a resistor in thermal equilibrium. Modern digital techniques make it now possible to perform many functions required for JNT in highly efficient and predictable ways. We describe the operational characteristics of a prototype JNT system which uses digital signal processing for filtering, real-time spectral cross-correlation for noise power measurement, and a digitally synthesized Quantized Voltage Noise Source (QVNS) as an AC voltage reference. The QVNS emulates noise with a constant spectral density that is stable, programmable, and calculable in terms of known parameters using digital synthesis techniques. Changes in analog gain are accounted for by alternating the inputs between the Johnson noise sensor and the QVNS. The Johnson noise power at a known temperature is first balanced with a synthesized noise power from the QVNS. The process is then repeated by balancing the noise power from the same resistor at an unknown temperature. When the two noise power ratios are combined, a thermodynamic temperature is derived using the ratio of the two QVNS spectral densities. We present preliminary results where the ratio between the gallium triple point and the water triple point is used to demonstrate the accuracy of the measurement system with a standard uncertainty of 0.04 %.

CRISM Hyperspectral Data Filtering with Application to MSL Landing Site Selection

NASA Astrophysics Data System (ADS)

Seelos, F. P.; Parente, M.; Clark, T.; Morgan, F.; Barnouin-Jha, O. S.; McGovern, A.; Murchie, S. L.; Taylor, H.

2009-12-01

We report on the development and implementation of a custom filtering procedure for Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) IR hyperspectral data that is suitable for incorporation into the CRISM Reduced Data Record (RDR) calibration pipeline. Over the course of the Mars Reconnaissance Orbiter (MRO) Primary Science Phase (PSP) and the ongoing Extended Science Phase (ESP) CRISM has operated with an IR detector temperature between ~107 K and ~127 K. This ~20 K range in operational temperature has resulted in variable data quality, with observations acquired at higher detector temperatures exhibiting a marked increase in both systematic and stochastic noise. The CRISM filtering procedure consists of two main data processing capabilities. The primary systematic noise component in CRISM IR data appears as along track or column oriented striping. This is addressed by the robust derivation and application of an inter-column ratio correction frame. The correction frame is developed through the serial evaluation of band specific column ratio statistics and so does not compromise the spectral fidelity of the image cube. The dominant CRISM IR stochastic noise components appear as isolated data spikes or column oriented segments of variable length with erroneous data values. The non-systematic noise is identified and corrected through the application of an iterative-recursive kernel modeling procedure which employs a formal statistical outlier test as the iteration control and recursion termination criterion. This allows the filtering procedure to make a statistically supported determination between high frequency (spatial/spectral) signal and high frequency noise based on the information content of a given multidimensional data kernel. The governing statistical test also allows the kernel filtering procedure to be self regulating and adaptive to the intrinsic noise level in the data. The CRISM IR filtering procedure is scheduled to be incorporated into the next augmentation of the CRISM IR calibration (version 3). The filtering algorithm will be applied to the I/F data (IF) delivered to the Planetary Data System (PDS), but the radiance on sensor data (RA) will remain unfiltered. The development of CRISM hyperspectral analysis products in support of the Mars Science Laboratory (MSL) landing site selection process has motivated the advance of CRISM-specific data processing techniques. The quantitative results of the CRISM IR filtering procedure as applied to CRISM observations acquired in support of MSL landing site selection will be presented.

Deeply-etched micromirror with vertical slit and metallic coating enabling transmission-type optical MEMS filters

NASA Astrophysics Data System (ADS)

Othman, Muhammad A.; Sabry, Yasser M.; Sadek, Mohamed; Nassar, Ismail M.; Khalil, Diaa A.

2016-03-01

In this work we report a novel optical MEMS deeply-etched mirror with metallic coating and vertical slot, where the later allows reflection and transmission by the micromirror. The micromirror as well as fiber grooves are fabricated using deep reactive ion etching technology, where the optical axis is in-plane and the components are self-aligned. The etching depth is 150 μm chosen to improve the micromirror optical throughput. The vertical optical structure is Al metal coated using the shadow mask technique. A fiber-coupled Fabry-Pérot filter is successfully realized using the fabricated structure. Experimental measurements were obtained based on a dielectric-coated optical fiber inserted into a fiber groove facing the slotted micromirror. A versatile performance in terms of the free spectral range and 3-dB bandwidth is achieved.

Prototype color field sequential television lens assembly

NASA Technical Reports Server (NTRS)

1974-01-01

The design, development, and evaluation of a prototype modular lens assembly with a self-contained field sequential color wheel is presented. The design of a color wheel of maximum efficiency, the selection of spectral filters, and the design of a quiet, efficient wheel drive system are included. Design tradeoffs considered for each aspect of the modular assembly are discussed. Emphasis is placed on achieving a design which can be attached directly to an unmodified camera, thus permitting use of the assembly in evaluating various candidate camera and sensor designs. A technique is described which permits maintaining high optical efficiency with an unmodified camera. A motor synchronization system is developed which requires only the vertical synchronization signal as a reference frequency input. Equations and tradeoff curves are developed to permit optimizing the filter wheel aperture shapes for a variety of different design conditions.

Spectral Sensitivity of the ctenid spider Cupiennius salei Keys

PubMed Central

Zopf, Lydia M.; Schmid, Axel; Fredman, David; Eriksson, Bo Joakim

2014-01-01

Summary The spectral sensitivity of adult male Cupiennius salei Keys, a nocturnal hunting spider, was studied in a behavioural test. As known from earlier behavioural tests, C. salei walks towards a black target presented in front of a white background. In this study a black target (size 42 × 70 cm) was presented in a white arena illuminated by monochromatic light in the range of 365 to 695 nm using 19 monochromatic filters (HW in the range of 6 – 10 nm). In the first trial, the transmission of the optical filters was between 40 % and 80%. In a second trial the transmission was reduced to 5%, using a neutral density filter. At the high intensity the spiders showed a spectral sensivity in the range from 380 to 670 nm. In the second trial the animals only showed directed walks if the illumination was in the range of 449 to 599 nm, indicating a lower sensitivity at the margins of the spectral sensitivity. In previous intracellular recordings, the measured spectral sensitivity was between 320 and 620 nm. Interestingly, these results do not completely match the behaviourally tested spectral sensitivity of the photoreceptors, where the sensitivity range is shifted to longer wavelengths. In order to investigate the molecular background of spectral sensitivity, we searched for opsin genes in C. salei. We found three visual opsins that correspond to UV and middle to long wavelength sensitive opsins as described for jumping spiders. PMID:23948480

Time-resolved multispectral imaging of combustion reactions

NASA Astrophysics Data System (ADS)

Huot, Alexandrine; Gagnon, Marc-André; Jahjah, Karl-Alexandre; Tremblay, Pierre; Savary, Simon; Farley, Vincent; Lagueux, Philippe; Guyot, Éric; Chamberland, Martin; Marcotte, Frédérick

2015-10-01

Thermal infrared imaging is a field of science that evolves rapidly. Scientists have used for years the simplest tool: thermal broadband cameras. These allow to perform target characterization in both the longwave (LWIR) and midwave (MWIR) infrared spectral range. Infrared thermal imaging is used for a wide range of applications, especially in the combustion domain. For example, it can be used to follow combustion reactions, in order to characterize the injection and the ignition in a combustion chamber or even to observe gases produced by a flare or smokestack. Most combustion gases, such as carbon dioxide (CO2), selectively absorb/emit infrared radiation at discrete energies, i.e. over a very narrow spectral range. Therefore, temperatures derived from broadband imaging are not reliable without prior knowledge of spectral emissivity. This information is not directly available from broadband images. However, spectral information is available using spectral filters. In this work, combustion analysis was carried out using a Telops MS-IR MW camera, which allows multispectral imaging at a high frame rate. A motorized filter wheel allowing synchronized acquisitions on eight (8) different channels was used to provide time-resolved multispectral imaging of combustion products of a candle in which black powder has been burnt to create a burst. It was then possible to estimate the temperature by modeling spectral profiles derived from information obtained with the different spectral filters. Comparison with temperatures obtained using conventional broadband imaging illustrates the benefits of time-resolved multispectral imaging for the characterization of combustion processes.