Matched Filter Technique Research Articles

Diagnostic ultrasound tooth imaging using fractional fourier transform

An ultrasound contact imaging method is proposed to measure the enamel thickness in the human tooth. A delay-line transducer with a working frequency of 15 MHz is chosen to achieve a minimum resolvable distance of 400 μm in human enamel. To confirm the contact between the tooth and the transducer, a verification technique based on the phase shift upon reflection is used. Because of the high attenuation in human teeth, linear frequency-modulated chirp excitation and pulse compression are exploited to increase the penetration depth and improve the SNR. Preliminary measurements show that the enamel-dentin boundary creates numerous internal reflections, which cause the applied chirp signals to interfere arbitrarily. In this work, the fractional Fourier transform (FrFT) is employed for the first time in dental imaging to separate chirp signals overlapping in both time and frequency domains. The overlapped chirps are compressed using the FrFT and matched filter techniques. Micro-computed tomography is used for validation of the ultrasound measurements for both techniques. For a human molar, the thickness of the enamel layer is measured with an average error of 5.5% after compressing with the FrFT and 13.4% after compressing with the matched filter based on the average speed of sound in human teeth.

선형적 위상배열 코일구조의 시뮬레이션을 통한 민감도지도의 공간 해상도 및 필터링 변화에 따른 MR-SENSE 영상재구성 평가

Parallel imaging technique can provide several advantages for a multitude of MRI applications. Especially, in SENSE technique, sensitivity maps were always required in order to determine the reconstruction matrix, therefore, a number of difference approaches using sensitivity information from coils have been demonstrated to improve of image quality. Moreover, many filtering methods were proposed such as adaptive matched filter and nonlinear diffusion technique to optimize the suppression of background noise and to improve of image quality. In this study, we performed SENSE reconstruction using computer simulations to confirm the most suitable method for the feasibility of filtering effect and according to changing order of polynomial fit that were applied on variation of spatial resolution of sensitivity map. The image was obtained at 0.32T(Magfinder II, Genpia, Korea) MRI system using spin-echo pulse sequence(TR/TE = 500/20 ms, FOV = 300 mm, matrix = <TEX>$128{\times}128$</TEX>, thickness = 8 mm). For the simulation, obtained image was multiplied with four linear-array coil sensitivities which were formed of 2D-gaussian distribution and the image was complex white gaussian noise was added. Image processing was separated to apply two methods which were polynomial fitting and filtering according to spatial resolution of sensitivity map and each coil image was subsampled corresponding to reduction factor(r-factor) of 2 and 4. The results were compared to mean value of geomety factor(g-factor) and artifact power(AP) according to r-factor 2 and 4. Our results were represented while changing of spatial resolution of sensitivity map and r-factor, polynomial fit methods were represented the better results compared with general filtering methods. Although our result had limitation of computer simulation study instead of applying to experiment and coil geometric array such as linear, our method may be useful for determination of optimal sensitivity map in a linear coil array.

Narrow-band, transient signals in Central Apennines, Italy: hints for underground fluid migration?

SUMMARY In this paper we investigate nature and properties of narrow-band, transient seismic signals observed by a temporary array deployed in the Val Tiberina area (central Apennines, Italy). These signals are characterized by spindle-shaped, harmonic waveforms with no clear S-wave arrivals. The first portion of the seismograms exhibits a main frequency peak centred at 4.5 Hz, while the spectrum of the slowly decaying coda is peaked at about 2 Hz. Events discrimination is performed using a matched-filtering technique, resulting in a set of 2466 detections spanning the 2010 January–March time interval. From a plane-wave-fitting procedure, we estimate the kinematic properties of signals pertaining to a cluster of similar events. The repetition of measurements over a large number of precisely aligned seismograms allows for obtaining a robust statistics of horizontal slownesses and propagation azimuths associated with the early portion of the waveforms. The P-wave arrival exhibits horizontal slownesses around 0.1 s km−1, thus suggesting waves impinging at the array almost vertically. Separately, we use traveltimes measured at a sparse network to derive independent constraints on epicentral location. Ray parameters and azimuths are calibrated using slowness measurements from a local, well-located earthquake. After this correction, the joint solution from traveltime inversion and array analysis indicates a source region spanning the 1–3 km depth interval. Considerations related to the source depth and energy, and the occurrence rate which is not related to the daily and weekly working cycles, play against a surface, artificial source. Instead, the close resemblance of these signals to those commonly observed in volcanic environments suggest a source mechanism related to the resonance of a fluid–filled fracture, likely associated with instabilities in the flux of pressurized CO2.

The properties of brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 6 adaptive matched filter cluster catalogue

We study the properties of Brightest Cluster Galaxies (BCGs) drawn from a catalogue of more than 69000 clusters in the SDSS DR6 based on the adaptive matched filter technique (AMF, Szabo et al., 2010). Our sample consists of more than 14300 galaxies in the redshift range 0.1-0.3. We test the catalog by showing that it includes well-known BCGs which lie in the SDSS footprint. We characterize the BCGs in terms of r-band luminosities and optical colours as well as their trends with redshift. In particular, we define and study the fraction of blue BCGs, namely those that are likely to be missed by either colour-based cluster surveys and catalogues. Richer clusters tend to have brighter BCGs, however less dominant than in poorer systems. 4-9% of our BCGs are at least 0.3 mag bluer in the g-r colour than the red-sequence at their given redshift. Such a fraction decreases to 1-6% for clusters above a richness of 50, where 3% of the BCGs are 0.5 mag below the red-sequence. A preliminary morphological study suggests that the increase in the blue fraction at lower richnesses may have a non-negligible contribution from spiral galaxies. We show that a colour selection based on the g-r red-sequence or on a cut at colour u-r >2.2 can lead to missing the majority of such blue BCGs. We also extend the colour analysis to the UV range by cross-matching our catalogue with publicly available data from Galex GR4 and GR5. We show a clear correlation between offset from the optical red-sequence and the amount of UV-excess. Finally, we cross-matched our catalogue with the ACCEPT cluster sample (Cavagnolo et al., 2009), and find that blue BCGs tend to be in clusters with low entropy and short cooling times. That is, the blue light is presumably due to recent star formation associated to gas feeding by cooling flows. (abridged)

The tidal tails of NGC 2298

We present an implementation of the matched-filter technique to detect tidal tails of globular clusters. The method was tested using SDSS data for the globular cluster Palomar 5 revealing its well known tidal tails. We also ran a simulation of a globular cluster with a tidal tail where we successfully recover the tails for a cluster at the same position and with the same characteristics of NGC 2298. Based on the simulation we estimate that the matched-filter increases the contrast of the tail relative to the background of stars by a factor of 2.5 for the case of NGC 2298. We also present the photometry of the globular cluster NGC 2298 using the MOSAIC2 camera installed on the CTIO 4m telescope. The photometry covers ~ 3deg2 reaching V ~ 23. A fit of a King profile to the radial density profile of NGC 2298 shows that this cluster has a tidal radius of 15.91' \pm 1.07' which is twice as in the literature. The application of the matched-filter to NGC 2298 reveals several extra-tidal structures, including a leading and trailing tail. We also find that NGC 2298 has extra-tidal structures stretching towards and against the Galactic disk, suggesting strong tidal interaction. Finally, we assess how the matched-filter performs when applied to a globular cluster with and without mass segregation taken into account. We find that disregarding the effects of mass segregation may significantly reduce the detection limit of the matched-filter.

Using spectral mapping techniques on short wave infrared bands of ASTER remote sensing data for alteration mineral mapping in SE Iran

Spectral mapping techniques were applied on shortwave infrared of advanced spaceborne thermal emission and reflection radiometer (ASTER) data for discriminating between hydrothermal alteration zones, and the identification of high potential mineralized lithologic unit associated with hydrothermal porphyry copper mineralization in the Central Iranian Volcanic Belt. In this study, shortwave infrared radiations of ASTER data were processed with spectral angle mapping, linear spectral unmixing, matched filtering, and mixture tuned matched filtering techniques. Two copper mining districts were used as reference to demonstrate the applicability of the spectral mapping techniques for spectral distinction of specific hydrothermal alteration zones such as argillic, phyllic and propylitic. The results of this study showed that spectral information can be used for generating spatial alteration mineral maps for purely virgin regions, and it can provide a cost-effective method to discriminate the new prospects for porphyry copper exploration prior to detailed and costly ground investigations. Key words: ASTER, spectral mapping techniques, hydrothermal alteration minerals, copper exploration.

Lowering the energy threshold of large-mass bolometric detectors

Large-mass bolometers are used in particle physics experiments tosearch for rare processes. The energy threshold of such detectors plays a critical role intheir capability to search for dark matter interactions and rare nuclear decays. We have developed atrigger and a pulse shape algorithm based on the matched filter technique which, when applied to data from test bolometers of the Cuore experiment, lowered theenergy threshold from tens of keV to the few keV region. The detectionefficiency is in excess of 80%, and nearly all nonphysical pulses are rejected.

DISCOVERY OF TIDAL TAILS AROUND THE DISTANT GLOBULAR CLUSTER PALOMAR 14

We report the detection of a pair of degree-long tidal tails associated with the globular cluster Palomar 14, using images obtained at the CFHT. We reveal a power-law departure from a King profile at large distances to the cluster center. The density map constructed with the optimal matched filter technique shows a nearly symmetrical and elongated distribution of stars on both sides of the cluster, forming a S-shape characteristic of mass loss. This evidence may be the telltale signature of tidal stripping in action. This, together with its large Galactocentric distance, imposes strong constraints on its orbit and/or origin: i) it must follow an external orbit confined to the peripheral region of the Galactic halo and/or ii) it formed in a satellite galaxy later accreted by the Milky Way.

SEARCHING FOR NEEDLES IN HAYSTACKS—LOOKING FOR GAMMA-RAY BURST γ-RAYS WITH THEFERMI/LAT DETECTOR

Since the launch of the Fermi Gamma-ray Space Telescope on June 11, 2008, 55 gamma-ray bursts (GRBs) have been observed at coordinates that fall within 66^\circ of the Fermi Large Area Telescope (LAT) boresight with precise localizations provided by the NASA Swift mission or other satellites. Imposing selection cuts to exclude low Galactic latitudes and high zenith angles reduces the sample size to 41. Using matched filter techniques, the Fermi/LAT photon data for these fields have been examined for evidence of bursts that have so far evaded detection at energies above 100 MeV. Following comparisons with similar random background fields, two events, GRB 080905A and GRB 091208B, stand out as excellent candidates for such an identification. After excluding the six bright bursts previously reported by the LAT team, the remaining 35 events exhibit an excess of LAT "diffuse" photons with a statistical significance greater than 2 sigma, independent of the matched filter analysis. After accounting for the total number of photons in the well-localized fields and including estimates of detection efficiency, one concludes that somewhere in the range of 11% to 19% of all GRBs within the LAT field of view illuminate the detector with two or more energetic photons. These are the most stringent estimates of the high energy photon content of GRBs to date. The two new events associated with high energy photon emission have similar ratios of high to low energy fluences as observed previously. This separates them from bursts with similar low energy fluences by a factor of ten, suggesting a distinct class of events rather than a smooth continuum.

SEARCHING FOR NEEDLES IN HAYSTACKS—USING THE FERMI /GBM TO FIND GRB γ-RAYS WITH THE FERMI /LAT DETECTOR

From the launch of the Fermi Gamma-ray Space Telescope to July 9, 2010, the Gamma-ray Burst Monitor (GBM) has detected 497 probable GRB events. Twenty-two of these satisfy the simultaneous requirements of an estimated burst direction within 52^\circ of the Fermi Large Area Telescope (LAT) boresight and a low energy fluence exceeding 5 $\mu$erg/cm^2. Using matched filter techniques, the spatially correlated Fermi/LAT photon data above 100 MeV have been examined for evidence of bursts that have so far evaded detection at these energies. High energy emission is detected with great confidence for one event, GRB 090228A. Since the LAT has significantly better angular resolution than the GBM, real-time application of these methods could open the door to optical identification and richer characterization of a larger fraction of the relatively rare GRBs that include high energy emission.

Statistical methods for automatic crack detection based on vibrothermography sequence‐of‐images data

AbstractVibrothermography is a relatively new nondestructive evaluation technique for finding cracks through frictional heat generated from crack surface vibrations under external excitations. The vibrothermography inspection method provides a sequence of infrared images as the output. We use a matched filter technique to increase the signal‐to‐noise ratio of the sequence‐of‐images data. An automatic crack detection criterion based on the features extracted from the matched filter output greatly increases the sensitivity of the vibrothermography inspection method. In this paper, we develop a three‐dimensional matched filter for the sequence‐of‐images data, which presents the statistical analysis for the matched filter output, and evaluate the probability of detection. Our results show the crack detection criterion based on the matched filter output provides an improved detection capability. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Detecting low‐frequency earthquakes within non‐volcanic tremor in southern Taiwan triggered by the 2005 Mw8.6 Nias earthquake

We use a matched filter technique to detect 41 low‐frequency earthquakes (LFEs) within 700‐s of triggered tremor signals in the Southern Central Range in Taiwan during the surface waves of the 2005 Mw8.6 Nias earthquake off the coast of northern Sumatra. The depth distributions of LFEs after double‐difference relocations concentrate at the depth range of 12–38 km below the background seismicity and above the Moho depth inferred from receiver function studies. The locations of LFEs are close to the downward extension of the steep‐dipping Chaochou‐Lishan fault with only modestly high Vp/Vs ratios (1.75–1.85). Our observation indicates that at least portions of triggered tremor consists of many LFEs, similar to ambient tremor observed at other major plate boundary faults.

Blind Multidimensional Matched Filtering Techniques for Single Input Multiple Output Communications

In this paper, blind multidimensional matched filtering techniques for Single Input Multiple Output (SIMO) communications are examined. To improve the signal-to-noise ratio prior to the equalization process, three different techniques are proposed to blindly implement the multidimensional matched filtering. Different from the blind channel identification techniques for SIMO channels in the literature, the proposed techniques require neither the implementation inefficient matrix decomposition methods nor the higher-order statistics of the received data. Therefore, they are favorable over existing methods due to their simplicity in application. The matched filter equivalents are established through the use of an adaptive filter as well as the channel equalization being performed blindly. It has been shown that the equalization performance of the proposed methods are close to the matched filter bound, and to support this, a comparison between the matched filter estimation error performances of our proposed techniques is also provided. A short discussion to improve the convergence speed of the proposed approaches is also included in this paper.

Applying imaging spectroscopy techniques to map saline soils with ASTER images

This work presents a multi-temporal study (years 2000, 2004 and 2007) of saline soils based on multispectral Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images. Its main contribution is the evaluation of different remote sensing methodologies for mapping saline soils in areas highly affected by soil degradation. The study area is located in SE Spain (between the cities of Elche and Alicante) and is characterized by a semiarid climate and the presence of numerous saline soils and salt-flats. Imaging spectroscopy techniques such as Matched Filtering (MF) and Mixture Tuned Matched Filtering (MTMF) techniques were used for mapping saline soils. Two different approaches were applied for mapping saline soils: 1) using image based spectra of saline and non-saline training areas, and 2) using the spectrum of the halite mineral as a proxy to the spectra of saline soils, because halite concentrations are significant in the saline soils of the study area. MF and MTMF mapping techniques were applied in both methodological approaches. Accuracy assessment was evaluated with the Receiver Operating Characteristic (ROC) plot technique. A validation procedure was applied with an independent saline and non-saline validation dataset. Training and validation saline and non-saline pixels were limited to areas with low vegetation coverage to avoid spectral interferences. High ROC values were obtained for the image based approach in the training and validation stages. Large differences between ROC training vs. validation values were not found. The halite spectrum based approach retrieved lower ROC training and validation values. Furthermore, the MTMF technique achieved better results than the MF in the halite spectrum based approach. Significant differences in the mapping performance were evaluated with the ANOVA test for the time of acquisition of scenes, the methodological approach, and the mapping technique factors. The image based approach was found to be the best methodology for saline soil mapping and monitoring.

DEATH OF A CLUSTER: THE DESTRUCTION OF M67 AS SEEN BY THE SLOAN DIGITAL SKY SURVEY

We probe the spatial and dynamical structure of the old open cluster M67 using photometric data from the Sloan Digital Sky Survey's sixth data release. Making use of an optimal contrast, or matched filter, algorithm, we map the distribution of high probability members of M67. We find an extended and elongated halo of likely members to a radius of nearly 60'. Our measured core radius of Rcore = 8.'24+/-0.'60 is somewhat larger than that of previous estimates. We attribute the larger core radius measurement to the SDSS probing lower mass main sequence stars than has been done before for similar studies of M67, and the exclusion of post main sequence M67 members in the SDSS sample. We estimate the number of M67 members in our SDSS sample to be 1385+/-67 stars. A lower limit on the binary fraction in M67 is measured to be 45%. A higher fraction of binary stars is measured in the core as compared to the halo, and the luminosity function of the core is found to be more depleted of low-mass stars. Thus the halo is consistent with mass segregation within the cluster. The galactic orbit of M67 is calculated from recent proper motion and radial velocity determinations. The elongated halo is roughly aligned to the proper motion of the cluster. This appears to be a result of mass segregation due to the galactic tidal field. Our algorithm is run on 2MASS photometry to directly compare to previous studies of M67. Decreasing core radii are found for stars with greater masses. We test the accuracy of our algorithm using 1000 artificial cluster Monte Carlo simulations. It is found that the matched filter technique is suitable for recovering low-density spatial structures, as well as measuring the binary fraction of the cluster.

A genetic algorithm for a global optimization problem arising in the detection of gravitational waves

The detection of gravitational waves is a long-awaited event in modern physics and, to achieve this challenging goal, detectors with high sensitivity are being used or are under development. In order to extract gravitational signals emitted by coalescing binary systems of compact objects (neutron stars and/or black holes), from noisy data obtained by interferometric detectors, the matched filter technique is generally used. Its computational kernel is a box-constrained global optimization problem with many local solutions and a highly nonlinear and expensive objective function, whose derivatives are not available. To tackle this problem, we designed a real-coded genetic algorithm that exploits characteristic features of the problem itself; special attention was devoted to the choice of the initial population and of the recombination operator. Computational experiments showed that our algorithm is able to compute a reasonably accurate solution of the optimization problem, requiring a much smaller number of function evaluations than the grid search, which is generally used to solve this problem. Furthermore, the genetic algorithm largely outperforms other global optimization algorithms on significant instances of the problem.

Markov Chain, Monte Carlo Global Search and Integration for Bayesian, GPS, Parameter Estimation

Bayesian estimation techniques are applied to the problem of time and frequency offset estimation for Global Positioning System receivers. The estimation technique employs Markov Chain Monte Carlo (MCMC) to estimate unknown system parameters, utilizing a novel, multi-dimensional, Bayesian, global optimization strategy for initializing a Metropolis-Hastings proposal distribution. The technique enables the design of a high performance multi-user GPS receiver, capable of overcoming the near-far problem when the relative signal power is on the order of 5 dB (single antenna element) and 20 dB (4 antenna element array) and providing dramatically improved performance over conventional matched filter techniques against interference and jamming when the relative jammer and satellite signal power is on the order of 20 dB (4 antenna element array).

Details of an Imaging System Based on Reflected GPS Signals and Utilizing SAR Techniques

This research endeavor reveals a method for utilizing reflected Global Positioning System (GPS) signals to form an image of targets within a region of interest. The principle is based upon a type of bistatic synthetic aperture radar (SAR) in which a matched filter technique is employed to perform the image reconstruction. A major challenge was the appalling signal to noise ratio associated with the received reflected GPS signals. Moreover, the reconstruction method resulted in an undesirable point spread function (PSF) which degraded the reconstructed image. The entire GPS signal generation and image reconstruction process was simulated as faithfully as possible and it has been demonstrated that a spatial resolution of the order of the GPS L1 frequency (wavelength of 19 cm) is possible. The smeared image obtained due to poor quality PSF was improved by means of a Wiener filter based deconvolution method. An imaging system based on a stationary receiver has been practically demonstrated with the successful identification of a 0.5 m 2 spherical target.

Beam-forming and matched filter techniques for the underwater acoustic detection of UHE neutrino

The search for UHE neutrinos is one of the most promising fields in astroparticle physics. The experimental techniques proposed to identify cosmic neutrino signatures are mainly three: the detection of Cherenkov blue light originated by charged leptons (electrons, positrons, muons and tauons) from neutrino interaction in water or ice; the detection of acoustic waves produced by neutrino energy deposition in water, ice or salt; the detection of radio pulses following neutrino interaction in ice or salt. Due to the expected neutrino fluxes (≈10 −8 E 2 Gev/cm 2 s sr) and due to their extremely low interaction cross-section (≈10 −32 cm 2 at 10 20 eV), huge target volumes (≈km 3) are required to detect them. Acoustic detection of neutrino is a very suitable technique since the sound attenuation length, at the frequency of interest, is of the order of km. Due to the small amplitude of the expected neutrino bipolar signal (≈10 mPa), it is mandatory to develop an effective algorithm that increases the signal to noise ratio (SNR). In the present work a combination of matched filter, applied to each single hydrophone, and a beam-forming technique applied to a small array of hydrophones is proposed. The matched filter is a well-known technique of signal processing that maximizes the SNR in the presence of white noise. Beam forming is a signal-processing technique used in sensor arrays for directional analysis; the signals from different sensors are combined in such a way that pressure waves arriving from a specific direction are coherently summed. Preliminary results on simulated data will be shown.

Searching for gravitational-wave signals emitted by eccentric compact binaries using a non-eccentric template bank: implications for ground-based detectors

Most of the inspiralling compact binaries are expected to be circularized by the time their gravitational-wave signals enter the frequency band of ground-based detectors such as LIGO or VIRGO. However, it is not excluded that some of these binaries might still possess a significant eccentricity at a few tens of hertz. Despite this possibility, current search pipelines—based on matched filtering techniques—consider only non-eccentric templates. The effect of such an approximation on the loss of signal-to-noise ratio (SNR) has been investigated by Martel and Poisson (1999 Phys. Rev. D 60 124008) in the context of initial LIGO detector. They ascertained that non-eccentric templates will be successful at detecting eccentric signals. We revisit their work by incorporating current and future ground-based detectors and precisely quantify the exact loss of SNR. In order to be more faithful to an actual search, we maximized the SNR over a template bank, whose minimal match is set to 95%. For initial LIGO detector, we claim that the initial eccentricity does not need to be taken into account in our searches for any system with total mass M ∊ [2–45]M⊙ if e0 ≲ 0.05 because the loss of SNR (about 5%) is consistent with the discreteness of the template bank. Similarly, this statement is also true for systems with M ∊ [6–35]M⊙ and e0 ≲ 0.10. However, by neglecting the eccentricity in our searches, significant loss of detection (larger than 10%) may arise as soon as e0 ⩾ 0.05 for neutron-star binaries. We also provide exhaustive results for VIRGO, Advanced LIGO and Einstein Telescope detectors. It is worth noting that for Einstein Telescope, neutron star binaries with e0 ⩾ 0.02 lead to a 10% loss of detection.