Matched Filter Algorithm Research Articles

Robust Matched-Filter Acquisition for Direct-Sequence Ultrawideband Systems

In this paper, we propose and analyze a rapid acquisition loop for a direct-sequence ultrawideband (DS-UWB) system called robust matched-filter acquisition, which is mainly aimed at eliminating the cases of false alarm in signal acquisition. Moreover, we present a study on the acquisition performances of the serial search, conventional matched filter, and robust matched filter in UWB dense multipath environments. The mean acquisition time, the acquisition probability, and the mean number of false alarms are evaluated for CM1-CM4 channel models. We find that the robust matched-filter acquisition provides a significant improvement in performances over the conventional matched-filter algorithm for the specific UWB channel model.

Hardware accelerated optical alignment of lasers using beam-specific matched filters

Accurate automated alignment of laser beams in the National Ignition Facility (NIF) is essential for achieving extreme temperature and pressure required for inertial confinement fusion. The alignment achieved by the integrated control systems relies on algorithms processing video images to determine the position of the laser beam images in real time. Alignment images that exhibit wide variations in beam quality require a matched-filter algorithm for position detection. One challenge in designing a matched-filter-based algorithm is to construct a filter template that is resilient to variations in imaging conditions while guaranteeing accurate position determination. A second challenge is to process images for thousands of templates in under a second, as may be required in future high-energy laser systems. This paper describes the development of a new analytical template that captures key recurring features present in the beam image to accurately estimate the beam position under good image quality conditions. Depending on the features present in a particular beam, the analytical template allows us to create a highly tailored template containing only those selected features. The second objective is achieved by exploiting the parallelism inherent in the algorithm to accelerate processing using parallel hardware that provides significant performance improvement over conventional processors. In particular, a Xilinx Virtex II Pro field programmable gate array (FPGA) hardware implementation processing 32 templates provided a speed increase of about 253 times over an optimized software implementation running on a 2.2 GHz AMD Opteron core.

Testing gravitational-wave searches with numerical relativity waveforms: results from the first Numerical INJection Analysis (NINJA) project

The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitational-wave data analysis communities. The purpose of NINJA is to study the sensitivity of existing gravitational-wave search algorithms using numerically generated waveforms and to foster closer collaboration between the numerical relativity and data analysis communities. We describe the results of the first NINJA analysis which focused on gravitational waveforms from binary black hole coalescence. Ten numerical relativity groups contributed numerical data which were used to generate a set of gravitational-wave signals. These signals were injected into a simulated data set, designed to mimic the response of the initial LIGO and Virgo gravitational-wave detectors. Nine groups analysed this data using search and parameter-estimation pipelines. Matched filter algorithms, un-modelled-burst searches and Bayesian parameter estimation and model-selection algorithms were applied to the data. We report the efficiency of these search methods in detecting the numerical waveforms and measuring their parameters. We describe preliminary comparisons between the different search methods and suggest improvements for future NINJA analyses.

Automated Hyperspectral Cueing for Civilian Search and Rescue

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Hyperspectral remote sensing provides information related to surface material characteristics that can be exploited to perform automated detection of targets of interest and has been applied to a variety of remote sensing applications. This paper explores the application to civilian search and rescue, using the Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance (ARCHER) system developed for the Civil Air Patrol as a key example of how evolving hyperspectral technology can be employed to support these operations. ARCHER combines a visible/near-infrared hyperspectral imaging system, a high-resolution visible panchromatic imaging sensor, and an integrated geopositioning and inertial navigation unit with onboard real-time processing for data acquisition and correction, precision image georegistration, and target detection and cueing. Processing for detecting downed aircraft wreckage and other related objects employs real-time adaptive anomaly detection and matched filtering algorithms, and a non-real-time change detection mode to provide further false alarm reduction in some instances. This paper describes the system technology, with an emphasis on the current and evolving automated target detection methods, and summarizes the operational experience in the airborne employment against civilian search and rescue missions. </para>

Improved covariance matrices for point target detection in hyperspectral data

Our goals in hyperspectral point target detection have been to develop a methodology for algorithm comparison and to advance point target detection algorithms through the fundamental understanding of spatial and spectral statistics. In this paper, we review our methodology as well as present new metrics. We demonstrate improved performance by making better estimates of the covariance matrix. We have found that the use of covariance matrices of statistical stationary segments in the matched-filter algorithm improves the receiver operating characteristic curves; proper segment selection for each pixel should be based on its neighboring pixels. We develop a new type of local covariance matrix, which can be implemented in principal-component space and which also shows improved performance based on our metrics. Finally, methods of fusing the segmentation approach with the local covariance matrix dramatically improve performance at low false-alarm rates while maintaining performance at higher false-alarm rates.

An algorithm for the detection of transits of planets around eclipsing binaries in CoRoT

AbstractWe present a matched filter algorithm to detect transits of planets that orbit both components of close eclipsing binaries in CoRoT targets. The formation of binary systems surrounded by disks is one of the most common outcomes of stellar formation; their detection would therefore constitute an important discovery. In an eclipsing binary system, the binary-planet alignment gives raised transit probabilities and the special transit shapes from circumbinary planets provide a unique identifier for their planetary nature; the problems of false alarms are largely avoided. CoRoT data have unprecedented time coverage and photometric precision that make them especially suitable for the search of transits of planets across eclipsing binaries. No reliable detections of circumbinary planets have been reported yet, and their discovery would constitute a new class of planets.

Golay Pulse Encoding for Microbubble Contrast Imaging in Ultrasound

We present a technique that uses Golay phase encoding, pulse inversion, and amplitude modulation (GPIAM) for microbubble contrast agent imaging with ultrasound. This technique improves the contrast-to-tissue ratio (CTR) by increasing the time-bandwidth product of the insonating waveforms. A nonlinear pulse compression algorithm is used to compress the signal energy upon receive. A 6.5-dB improvement in CTR was observed using an 8-chip GPIAM sequence compared to a conventional pulse-inversion amplitude-modulation sequence. The CTR improvement comes at the cost of a reduction in frame rate: GPIAM coding uses four input pulses whereas most contrast imaging sequences require two or three pulses. Our results showed that the microbubble response can be phase encoded and subsequently compressed using a nonlinear matched-filtering algorithm, in order to enhance the signal from the contrast agent, while maintaining resolution and suppressing the tissue signal.

Optical Cluster Finding with an Adaptive Matched‐Filter Technique: Algorithm and Comparison with Simulations

We present a modified adaptive matched filter algorithm designed to identify clusters of galaxies in wide-field imaging surveys such as the Sloan Digital Sky Survey. The cluster-finding technique is fully adaptive to imaging surveys with spectroscopic coverage, multicolor photometric redshifts, no redshift information at all, and any combination of these within one survey. It works with high efficiency in multi-band imaging surveys where photometric redshifts can be estimated with well-understood error distributions. Tests of the algorithm on realistic mock SDSS catalogs suggest that the detected sample is {approx} 85% complete and over 90% pure for clusters with masses above 1.0 x 10{sup 14}h{sup -1} M and redshifts up to z = 0.45. The errors of estimated cluster redshifts from maximum likelihood method are shown to be small (typically less that 0.01) over the whole redshift range with photometric redshift errors typical of those found in the Sloan survey. Inside the spherical radius corresponding to a galaxy overdensity of {Delta} = 200, we find the derived cluster richness {Lambda}{sub 200} a roughly linear indicator of its virial mass M{sub 200}, which well recovers the relation between total luminosity and cluster mass of the input simulation.

Sequencing points of the spatial image of a group point object based on amplitude-phase representation

Amplitude-phase representation of spatial group point objects given as quaternion signals is considered. The problem of estimating the rotation parameters and sequencing the point marks incorporated in a group object is solved. The obtained results allow using the matched filtering algorithm to solve the problem of recognizing spatial group point objects with unknown parameters of rotation and numbering of points in the object.

A new ML detection algorithm for Orthogonal Multicode system in Nakagami fading channel

Based on the Maximum-Likelihood (ML) criterion, this paper proposes a novel noncoherent detection algorithm for Orthogonal Multicode (OM) system in Nakagami fading channel. Some theoretical analysis and simulation results are presented. It is shown that the proposed ML algorithm is at least 0.7 dB better than the conventional Matched-Filter (MF) algorithm for uncoded systems, in both non-fading and fading channels. For the consideration of practical application, it is further simplified in complexity. Compared with the original ML algorithm, the simplified ML algorithm can provide significant reduction in complexity with small degradation in performance.

The Phoenix Deep Survey: The Clustering and Environment of Extremely Red Objects

In this paper we explore the clustering properties and environment of the extremely red objects (EROs; I - K > 4 mag) detected in a ≈180 arcmin2 deep (Ks ≈ 20 mag) Ks-band survey of a region within the Phoenix Deep Survey, an ongoing multiwavelength program aiming to investigate the nature and evolution of faint radio sources. Using our complete sample of 289 EROs brighter than Ks = 20 mag, we estimate a statistically significant (≈3.7 σ) angular correlation function signal with amplitude Aw = 8.7 × 10-3 (assuming w(θ) = Awθ-0.8, with θ in degrees), consistent with earlier work based on smaller samples. This amplitude suggests a clustering length in the range ro = 12-17 h-1 Mpc, implying that EROs trace regions of enhanced density. Using a novel method, we further explore the association of EROs with galaxy overdensities by smoothing the K-band galaxy distribution using the matched filter algorithm of Postman et al. (1996) and then cross-correlating the resulting density maps with the ERO positions. Our analysis provides direct evidence that EROs are associated with overdensities at redshifts z 1. We also exploit the available deep radio 1.4 GHz data (limiting flux 60 μJy) to explore the association of EROs and faint radio sources and whether the two populations trace similar large-scale structures. Cross-correlation of the two samples (after excluding 17 EROs with radio counterparts) gives a 2 σ signal only for the subsample of high-z radio sources (z > 0.6). Although the statistics are poor, this suggests that it is the high-z radio subsample that traces similar structures with EROs.

TheXMM-Newton/2dF survey - III. Comparison between optical and X-ray cluster detection methods

We directly compare X-ray and optical techniques of cluster detection by combining Sloan Digital Sky Survey photometric data with a wide-field (∼1.6 deg 2 ) XMM-Newton survey near the North Galactic Pole region. The optical cluster detection procedure is based on merging two independent selection methods: a smoothing + percolation technique and a matched filter algorithm. The X-ray cluster detection is based on a wavelet-based algorithm, incorporated in the Science Analysis System (SAS) v.5.3 package. The final optical sample counts nine candidate clusters with estimated Automatic Plate Measuring like richness of more than 20 .galaxies, while the X-ray based cluster candidates total four. Three out of these four X-ray cluster candidates are also optically detected. We argue that the cause is that the majority of the optically detected clusters are relatively poor X-ray emitters, with X-ray fluxes fainter than the flux limit (for extended sources) of our survey, f x (0.3-2 keV) ≃ 2 x 10 -14 erg cm -2 s -1 .

Comparison of two optical cluster finding algorithms for the new generation of deep galaxy surveys

We present a comparison between two optical cluster finding methods: a matched filter algorithm using galaxy angular coordinates and magnitudes, and a percolation algorithm using also redshift information. We test the algorithms on two mock catalogues. The first mock catalogue is built by adding clusters to a Poissonian background, while the other is derived from N-body simulations. Choosing the physically most sensible parameters for each method, we carry out a detailed comparison and investigate advantages and limits of each algorithm, showing the possible biases on final results. We show that, combining the two methods, we are able to detect a large part of the structures, thus pointing out the need to search for clusters in different ways in order to build complete and unbiased samples of clusters, to be used for statistical and cosmological studies. In addition, our results show the importance of testing cluster finding algorithms on different kinds of mock catalogues to have a complete assessment of their behaviour.

Searching for planetary transits in the field of open cluster NGC 6819 -- I

We present results from our survey for planetary transits in the field of the intermediate age (~2.5 Gyr), metal-rich ([Fe/H]~+0.07) open cluster NGC 6819. We have obtained high-precision time-series photometry for over 38,000 stars in this field and have developed an effective matched-filter algorithm to search for photometric transits. This algorithm identified 8 candidate stars showing multiple transit-like events, plus 3 stars with single eclipses. On closer inspection, while most are shown to be low mass stellar binaries, some of these events could be due to brown dwarf companions. The data for one of the single-transit candidates indicates a minimum radius for the companion similar to that of HD 209458b.

Clusters of Galaxies in the Local Universe

We use a matched filter algorithm to find and study clusters in both N-body simulations artificially populated with galaxies and the Two Micron All Sky Survey (2MASS). In addition to numerous checks of the matched filter algorithm, we present results on the halo multiplicity function and the cluster number function. For a subset of our identified clusters we have information on X-ray temperatures and luminosities that we cross-correlate with optical richness and galaxy velocity dispersions. With all quantities normalized by the spherical radius corresponding to a mass overdensity of ΔM = 200 or the equivalent galaxy number overdensity of ΔN = 200Ω 666, we find that the number of L > L* galaxies in a cluster of mass M200 is log N*666 = (1.44 ± 0.17) + (1.10 ± 0.09) log(M200h/1015 M☉), where the uncertainties are dominated by the scatter created by three choices for relating the observed quantities to the cluster mass. The region inside the virial radius has a K-band cluster mass-to-light ratio of (M/L)K = (116 ± 46)h, which is essentially independent of cluster mass. Integrating over all clusters more massive than M200 = 1014 h-1 M☉, the virialized regions of clusters contain 7% of the local stellar luminosity, quite comparable to the mass fraction in such objects in currently popular ΛCDM models.

A Matched-Filter Analysis of the Tidal Tails of the Globular Cluster Palomar 5

The tidal tails of the globular cluster Palomar 5 are analyzed over a 41 deg2 area of the Sloan Digital Sky Survey photometric catalogs. The matched filter algorithm provides the maximum possible signal-to-noise detection of the cluster stars over the measured background, and the expected and actual effectiveness of the technique in the context of this data set is discussed. The stellar background is examined in some detail for systematic variation as a function of Galactic position in order to assess its effect on the detection efficiency. Of the total number of Pal 5 stars detected, 45% are out in the tails. The tails are found as the only additional 3 σ overdensity of cluster stars over the entire 41 deg2 area studied. The annular-averaged density of stars along the tails is fitted to a power law in radius with best-fit index -1.58 ± 0.07, significantly steeper than that predicted from a constant orbit-averaged mass-loss rate.

Use of hyperspectral images in the identification and mapping of expansive clay soils and the role of spatial resolution

Hyperspectral images were acquired along the Front Range Urban Corridor in Colorado to determine the feasibility of identification and mapping of expansive clay soils with two, high-SNR imaging spectrometers. Swelling soils are a major geologic hazard, and cause extensive damage world-wide every year. The cost of postconstruction mitigation and standard engineering soil tests for creation of regional maps are immense. Smectite is the clay mineral group that has the greatest swelling potential and is responsible for most of the severe swelling soil damage observed in Colorado. Data sets were acquired from 1997 to 1999 with the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and the Hyperspectral Mapper (HyMap). Using a matched filtering algorithm, maps of exposed clay material were produced, despite a strong vegetation cover. Among those exposures, spectral discrimination and identification of variable clay mineralogy such as smectite, smectite/illite, and kaolinite, in decreasing order of swelling potential hazard, was possible. The comparison of the results from the two sensors showed that higher spatial resolution provided purer image endmembers in more heterogeneous sites, but did not exhibit more endmembers and did not identify new natural outcrops that a lower spatial resolution data set would miss in a homogeneous terrain. However, an increase in the signal-to-noise ratio (SNR) of the instrument by pixel summation made possible the identification of low reflectance exposures. This work demonstrates that, using recent instruments and well-established methodologies, imaging spectrometry can be of practical help for the detection and mapping of expansive clays.

On the nature of the EIS candidate clusters: Confirmation of $z\lesssim$ 0.6 candidates

We use publicly available V -band imaging data from the wide-angle surveys conducted by the ESO Imaging Survey project (EIS) to further investigate the nature of the EIS galaxy cluster candidates. These were originally identified by applying a matched-filter algorithm which used positional and photometric data of the galaxy sample extracted from the I -band survey images. In this paper, we apply the same technique to the galaxy sample extracted from V -band data and compare the new cluster detections with the original ones. We find that ~75% of the low-redshift cluster candidates ($z\lesssim0.6$) are detected in both passbands and their estimated redshifts show good agreement with the scatter in the redshift differences being consistent with the estimated errors of the method. For the robust I -band detections the matching frequency approaches ~85% . We also use the available $(V-I)$ color to search for the of early-type galaxies observed in rich clusters over a broad range of redshifts. This is done by searching for a simultaneous overdensity in the three-dimensional color-projected distance space. We find significant overdensities for ~75% of the robust candidates with $z_I\lesssim0.6$. We find good agreement between the characteristic color associated to the detected red sequence and that predicted by passive evolution galaxy models for ellipticals at the redshift estimated by the matched-filter. The results presented in this paper show the usefulness of color data, even of two-band data, to both tentatively confirm cluster candidates and to select possible cluster members for spectroscopic observations. Based on the present results, we estimate that ~150 EIS clusters with $z_I\lesssim0.6$ are real, making it one of the largest samples of galaxy clusters in this redshift range currently available in the southern hemisphere.

The Stanford Cluster Search: Scope, Method, and Preliminary Results11The Hobby‐Eberly Telescope (HET) is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig‐Maximillians‐Universität München, and Georg‐August‐Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.

ABSTRACTWe describe the scientific motivation behind, and the methodology of, the Stanford Cluster Search (StaCS), a program to compile a catalog of optically selected galaxy clusters at intermediate and high (0.3≲z≲1) redshifts. The clusters are identified using a matched filter algorithm applied to deep CCD images covering ∼60 deg2 of sky. These images are obtained from several data archives, principally that of the Berkeley Supernova Cosmology Project of Perlmutter et al. Potential clusters are confirmed with spectroscopic observations at the 9.2 m Hobby‐Eberly Telescope. Follow‐up observations at optical, submillimeter, and X‐ray wavelengths are planned in order to estimate cluster masses. Our long‐term scientific goal is to measure the cluster number density as a function of mass and redshift, n(M, z), which is sensitive to the cosmological density parameter Ωm and the amplitude of density fluctuations σ8. The combined data set will contain clusters ranging over an order of magnitude in mass and allow constraints on these parameters accurate to ∼10%. We present our first spectroscopically confirmed cluster candidates and describe how to access them electronically.

Distant Cluster Hunting: A Comparison Between the Optical and X-Ray Luminosity Functions from an Optical/X-Ray Joint Survey

We present a comparison of X-ray and optical luminosities and luminosity functions of cluster candidates from a joint optical/X-ray survey, the ROSAT Optical X-Ray Survey. Completely independent X-ray and optical catalogs of 23 ROSAT fields (4.8 deg2) were created by a matched-filter optical algorithm and by a wavelet technique in the X-ray. We directly compare the results of the optical and X-ray selection techniques. The matched-filter technique detected 74% (26 out of 35) of the most reliable cluster candidates in the X-ray-selected sample; the remainder could be either constellations of X-ray point sources or z > 1 clusters. The matched-filter technique identified approximately 3 times the number of candidates (152 candidates) found in the X-ray survey of nearly the same sky (57 candidates). While the estimated optical and X-ray luminosities of clusters of galaxies are correlated, the intrinsic scatter in this relationship is very large. We can reproduce the number and distribution of optical clusters with a model defined by the X-ray luminosity function and by an LX-Λcl relation if H0 = 75 km s-1 Mpc-1 and if the LX-Λcl relation is steeper than the expected LX ∝ Λ. On statistical grounds, a bimodal distribution of X-ray luminous and X-ray faint clusters is unnecessary to explain our observations. Follow-up work is required to confirm whether the clusters without bright X-ray counterparts are simply X-ray faint for their optical luminosity because of their low mass or youth or are a distinct population of clusters that do not, for some reason, have dense intracluster media. We suspect that these optical clusters are low-mass systems, with correspondingly low X-ray temperatures and luminosities, or that they are not yet completely virialized systems.