Matched Filter Technique Research Articles

Study of Terahertz Superresolution Imaging Scheme With Real-Time Capability Based on Frequency Scanning Antenna

In this paper, a terahertz (THz) imaging scheme with real-time capability is proposed based on frequency- controlled beam scanning. The scheme holds a concise system architecture comprising a frequency scanning reflector antenna (FSRA) as the transmitting antenna, an omnidirectional antenna as the receiving antenna, and a vector network analyzer as the transceiver. By employing the diffraction enhancement mechanism to improve the diffraction efficiency and to suppress the specular beam, a high-directivity FSRA with periodic planar binary structure is proposed and developed at 0.235–0.33 THz band for imaging applications. A superresolution algorithm is proposed and developed by combining the direction of arrival (DoA) estimation and the matched filter technique, in which the tradeoff between available range and azimuth information can be successfully overcome. To achieve DoA estimation, the MUltiple SIgnal Classification (MUSIC) algorithm which is commonly used in phased-array antennas is extended to the novel imaging scheme based on FSRA, which is referred to as FS-MUSIC algorithm. The model of FSRA manifold vector is constructed for FS-MUSIC with a modified spatial smoothing method specifically developed to decorrelate the coherent back-scattering signals and to resolve the targets located within a same half-power beamwidth (HPBW). The resolution of the FS-MUSIC algorithm is derived based on the Bayesian approach. Superresolution imaging with real-time capability was demonstrated by both the simulation and the proof-of-principle experiments in the 0.3-THz band. An FSRA operating on 0.3-THz frequency band was developed.

Sensitivity Enhancement in Radiation Portal Monitoring using Adaptive Matched Filtering

Most radiation portal monitors (RPMs) use the max count rate (MCR) or the single interval test (SIT) methods for detecting the illicit transport of radioactive material. Point source detection using matched filtering for discriminating naturally occurring radioactive materials (NORM) from radioactive materials of concern was proposed in the literature for border crossing radiation portal monitoring. We show in this work that it is possible to increase the sensitivity of a radiation portal monitor by fusing the data produced by SIT with that produced by an improved version of the matched filtering technique.

Diagnosing Hypertensive Retinopathy through Retinal Images

The diagnoses of Hypertensive Retinopathy (HR) through retinal images become most important issue today, because HR is rapidly increasing disease that is found in eyes. HR occurs due to the highness of the blood pressure. The most important measurement that is used to diagnose HR through retinal images is arteriovenous ratio (AVR). This paper describe a method to determine AVR by first segment the vessels using match filtering technique and then detect the optic disk in order to determine the Region of Interest. Once the region of Interest is found, it classifies the blood vessels into arteries and veins using Neural Network to determine the AVR. The proposed work is implemented using MATLAB R2014a. This paper is divided into four sections. Section 1 will describe the Introduction. Section 2 will describe the method/ techniques to determine AVR. Section 3 will describe the comparison of results with some previous results. Section 4 will describe the conclusion.

Spectrum Sensing for Cognitive Radio Using Hybrid Matched Filter Single Cycle Cyclostationary Feature Detector

Spectrum sensing is an important task in cognitive radio (CR). Matched filter technique one of the techniques employed for spectrum sensing in cognitive radio which faces the challenge of low frequency offset tolerance in very low SNR environments. Hybrid matched filter architecture is used to improve this frequency offset tolerance. But, overall even such kind of architecture results in coarse detection. In very low SNR environments, where primary user is highly mobile, the multipath profile results in unknown phase of signal. Such kind of signal cannot even be detected by Hybrid Matched Filter. In this paper we propose combination of Hybrid Matched Filter and Single Cycle Cyclostationary Feature Detector to enhance the detection of such architecture. This results in both high frequency offset tolerance as well as fine detection of signal with unknown phase in very low SNR environments. Simulation results show significant improvement in the probability of detection and false alarm of the proposed scheme over Hybrid Matched Filter.

Localization of impulsive disturbances in audio signals using template matching

In this paper, a new solution to the problem of elimination of impulsive disturbances from audio signals, based on the matched filtering technique, is proposed. The new approach stems from the observation that a large proportion of noise pulses corrupting audio recordings have highly repetitive shapes that match several typical “patterns”. In many cases a representative set of exemplary pulse waveforms can be extracted from the episodes of silence preceding and succeeding the recorded audio material. Based on such a set, a relatively small number of typical noise patterns, called click templates, can be established. To localize noise pulses, the appropriately modified click templates can be correlated with the sequence of one-step-ahead prediction errors yielded by the model-based signal predictor. It is shown that template matching is an efficient and computationally affordable disturbance localization technique – when combined with the classical detection method based on autoregressive modeling, it can improve restoration results. Since click templates can be created for a particular set of recordings, obtained using a particular audio equipment, an important feature of the proposed approach is its source adaptivity. Even though the paper is focused on restoration of archive recordings, the proposed approach is useful in a much wider context, e.g., it can be applied to elimination of impulsive disturbances corrupting telecommunication channels.

Accurate single-trial detection of movement intention made possible using adaptive wavelet transform.

The outlook of brain-computer interfacing (BCI) is very bright. The real-time, accurate detection of a motor movement task is critical in BCI systems. The poor signal-to-noise-ratio (SNR) of EEG signals and the ambiguity of noise generator sources in brain renders this task quite challenging. In this paper, we demonstrate a novel algorithm for precise detection of the onset of a motor movement through identification of event-related-desynchronization (ERD) patterns. Using an adaptive matched filter technique implemented based on an optimized continues Wavelet transform by selecting an appropriate basis, we can detect single-trial ERDs. Moreover, we use a maximum-likelihood (ML), electrooculography (EOG) artifact removal method to remove eye-related artifacts to significantly improve the detection performance. We have applied this technique to our locally recorded Emotiv(®) data set of 6 healthy subjects, where an average detection selectivity of 85 ± 6% and sensitivity of 88 ± 7.7% is achieved with a temporal precision in the range of -1250 to 367 ms in onset detections of single-trials.

Increasing background seismicity and dynamic triggering behaviors with nearby mining activities around Fangshan Pluton in Beijing, China

AbstractDynamic triggering in western Fangshan Pluton, Beijing, China, has been repeatedly identified, but previous studies are limited by sparse seismic station coverage. Here we systematically analyze continuous waveforms recorded by both permanent stations and a temporary seismic network 40 days before and after the 11 March 2011 Mw 9.1 Tohoku‐Oki and the 14 April 2012 Mw 8.6 Indian Ocean earthquakes. We first build a template database using a short‐term average to long‐term average method. Next, we apply the matched filter technique that cross correlates the template waveforms with continuous data to detect additional seismic events. Overall, we detect 1956 and 950 seismic events around the Tohoku‐Oki and Indian Ocean main shocks, respectively. Most detected events are shallow (<5 km) and clustered at Beiling Syncline in western Fangshan Pluton, which is adjacent to a running coalmine. Seven and 10 events are detected during the large‐amplitude surface waves of the two main shocks, respectively, but no similar burst is detected following their major foreshock and aftershocks. Multiple statistical tests indicate that the short‐term bursts after the two main shocks are dynamically triggered. We suggest that mining‐related activities may perturb the subsurface stress conditions and hence make the region more susceptible for dynamic triggering than other places.

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan

We analyzed seismicity linked to the 2014 phreatic eruption of Mount Ontake, Japan, on 27 September 2014. We first relocated shallow volcano tectonic (VT) earthquakes and long-period (LP) events from August to September 2014. By applying a matched-filter technique to continuous waveforms using these relocated earthquakes, we detected numerous additional micro-earthquakes beneath the craters. The relocated VT earthquakes aligned on a near-vertical plane oriented NNW–SSE, suggesting they occurred around a conduit related to the intrusion of magmatic–hydrothermal fluids into the craters. The frequency of VT earthquakes gradually increased from 6 September 2014 and reached a peak on 11 September 2014. After the peak, seismicity levels remained elevated until the eruption. b-values gradually increased from 1.2 to 1.7 from 11 to 16 September 2014 then declined gradually and dropped to 0.8 just before the eruption. During the 10-min period immediately preceding the phreatic eruption, VT earthquakes migrated in the up-dip direction as well as laterally along the NNW–SSE feature. The migrating seismicity coincided with an accelerated increase of pre-eruptive tremor amplitude and with an anomalous tiltmeter signal that indicated summit upheaval. Therefore, the migrating seismicity suggests that the vertical conduit was filled with pressurized fluids, which rapidly propagated to the surface during the final 10 min before the eruption.

Using a matched-filter technique at the Mikhnevo small-aperture seismic array

The Mikhnevo small-aperture array (SAA) was designed as an instrument for various regional seismic studies, including the compilation of a detailed catalogue of industrial blasts in the East European craton. This array includes 12 observation points arranged in three circles and equipped with SM3-KV shortperiod seismometers. The Institute of Geospheres Dynamics launched the array in 2004, and since that time it has been detecting up to 1000 industrial blasts per year. The Mikhnevo SAA uses beam formation for array processing. The stacking of individual waveforms reduced to a reference point allows the suppression of microseismic noise and improving the signal-to-noise ratio (SNR) relative to a three-component station. An improved SNR for a given signal is equivalent to a reduced detection threshold: much weaker signals can be detected with the use of a beam-formation technique. In turn, much more signals from small industrial explosions are detected. Weak signals are difficult to identify because of the higher uncertainty in the estimates of such characteristics as azimuth, slowness, and amplitude. Having a ten-year catalog of industrial blasts and the archive of raw digital records for this period, we apply a waveform cross-correlation (matched filter) technique, which has an extremely high relative location accuracy and thus identification capability. We have created a set of master events with relevant waveform templates for automatic data processing and creation of an accurate catalogue of industrial blasts.

Comparison of active-set method deconvolution and matched-filtering for derivation of an ultrasound transit time spectrum

The quality of ultrasound computed tomography imaging is primarily determined by the accuracy of ultrasound transit time measurement. A major problem in analysis is the overlap of signals making it difficult to detect the correct transit time. The current standard is to apply a matched-filtering approach to the input and output signals. This study compares the matched-filtering technique with active set deconvolution to derive a transit time spectrum from a coded excitation chirp signal and the measured output signal. The ultrasound wave travels in a direct and a reflected path to the receiver, resulting in an overlap in the recorded output signal. The matched-filtering and deconvolution techniques were applied to determine the transit times associated with the two signal paths. Both techniques were able to detect the two different transit times; while matched-filtering has a better accuracy (0.13 μs versus 0.18 μs standard deviations), deconvolution has a 3.5 times improved side-lobe to main-lobe ratio. A higher side-lobe suppression is important to further improve image fidelity. These results suggest that a future combination of both techniques would provide improved signal detection and hence improved image fidelity.

Evidence of tidal distortions and mass-loss from the old open cluster NGC 6791

We present the first evidence of clear signatures of tidal distortions in the density distribution of the fascinating open cluster NGC 6791. We used deep and wide-field data obtained with the Canada-France-Hawaii-Telescope covering a 2x2 square degrees area around the cluster. The two-dimensional density map obtained with the optimal matched filter technique shows a clear elongation and an irregular distribution starting from ~300" from the cluster center. At larger distances, two tails extending in opposite directions beyond the tidal radius are also visible. These features are aligned to both the absolute proper motion and to the Galactic center directions. Moreover, other overdensities appear to be stretched in a direction perpendicular to the Galactic plane. Accordingly to the behaviour observed in the density map, we find that both the surface brightness and the star count density profiles reveal a departure from a King model starting from ~600" from the center. These observational evidence suggest that NGC 6791 is currently experiencing mass loss likely due to gravitational shocking and interactions with the tidal field. We use this evidence to argue that NGC 6791 should have lost a significant fraction of its original mass. A larger initial mass would in fact explain why the cluster survived so long. Using available recipes based on analytic studies and N-body simulations, we derived the expected mass loss due to stellar evolution and tidal interactions and estimated the initial cluster mass to be M_ini=(1.5-4) x 10^5 M_sun.

Trigger and Analysis Tools for Dark Matter Search in CUORE-0

The CUORE and CUORE-0 experiments have the possibility to search for Dark Matter interactions. To reach this goal is necessary to use a dedicated trigger, the Optimum Trigger, based on the matched filter technique, that pushes the energy threshold down to the keV region, where the signal is expected to lie. In addition, new low energy analysis tools are described.

Search for polycyclic aromatic hydrocarbons in the Perseus molecular cloud with the Green Bank Telescope

Polycyclic Aromatic Hydrocarbons (PAHs) are believed to be the small-size tail of the interstellar carbonaceous dust grain population. Their vibrational emission is the most widely accepted source of the aromatic near-infrared features, and their rotational radiation is a likely explanation for the dust-correlated anomalous microwave emission (AME). Yet, no individual interstellar PAH molecule has been identified to date. It was recently recognized that quasi-symmetric planar PAHs ought to have a well identifiable comb-like rotational spectrum, and suggested to search for them in spectroscopic data with matched-filtering techniques. We report the results of the first such search, carried out with the Green Bank Telescope, and targeting the star-forming region IC348 in the Perseus molecular cloud, a known source of AME. Our observations amounted to 16.75 hours and spanned a 3 GHz-wide band extending from 23.3 to 26.3 GHz. Using frequency switching, we achieved a sensitivity of 0.4 mJy per 0.4 MHz channel (1-sigma). The non-detection of comb-like spectra allowed us to set upper bounds on the abundance of specific quasi-symmetric PAH molecules (specified uniquely by their moments of inertia) of approximately 0.1% of the total PAH abundance. This bound generically applies to PAHs with approximately 15 to 100 carbon atoms.

The preparatory phase of the 2009 Mw 6.3 L'Aquila earthquake by improving the detection capability of low‐magnitude foreshocks

AbstractWe explored the detection capability of low‐magnitude earthquakes before the 6 April 2009 Mw 6.3 L'Aquila event by using a matched filter technique and 512 foreshocks as templates. We analyzed continuous waveforms from 10 broadband seismic stations in a 60 km radius from the epicenter and for ~3 months before the main shock. More than 3000 new events, mostly located on the main shock fault, were detected to define the spatial‐temporal evolution of micro‐seismicity. The foreshock sequence was active northwest of the Mw 6.3 hypocenter in January, then migrated toward it at a speed of ~0.5 km/day in middle of February. At that time, in a ~4 km2 patch close to the main shock nucleation point, the cumulative number of earthquakes gradually increased until the Mw 6.3 event. This patch, characterized by a low b‐value, played a key role in controlling the preparation stage to the 2009 L'Aquila main rupture.

Multiple slow‐slip events during a foreshock sequence of the 2014 Iquique, Chile Mw 8.1 earthquake

AbstractTo obtain a precise record of the foreshock sequence before the 2014 Iquique, Chile Mw 8.1 earthquake, we applied a matched filter technique to continuous seismograms recorded near the source region. We newly detected about 10 times the number of seismic events listed in the routinely constructed earthquake catalog and identified multiple sequences of earthquake migrations at speeds of 2–10 km/d, both along strike and downdip on the fault plane, updip of the main shock area. In addition, we found out repeating earthquakes from the newly detected events, likely indicating aseismic slip along the plate boundary fault during the foreshock sequence. These observations suggest the occurrence of multiple slow‐slip events updip of the main shock area. The final slow‐slip event migrated toward the main shock nucleation point. We interpret that several parts of the plate boundary fault perhaps experienced slow slip, causing stress loading on the prospective largest slip patch of the main shock rupture.

Pattern recognition based on the correlated intensity fluctuations of thermal light.

Here we present a pattern recognition scheme based on the intensity correlation of thermal light. We prove theoretically that under spatially incoherent illumination the matched filtering technique can be realized in the ghost imaging field. Using the matched filtering technique, it is possible to distinguish an object from a preestablished set of objects through their ghost images, which are extracted by means of intensity correlation measurement. According to the pattern recognition scheme, we present a numerical simulation in which we can easily identify the character inserted into the object arm from a set of two characters through the position of the autocorrelation peak. This pattern recognition scheme opens up the possibility of performing coherent optical processing under spatially incoherent illumination.

Step-like migration of early aftershocks following the 2007 Mw 6.7 Noto-Hanto earthquake, Japan

Seismic data reveal that the aftershock zone expands with time after a main shock event. Here we examine the aftershock sequence recorded during the first 32 days following the 2007 Noto-Hanto earthquake, Japan. By applying a matched-filter technique to the data, we detected about 10 times more events than those listed in the routinely constructed earthquake catalog. The aftershock area expanded along the fault strike as a logarithmic function of time, beginning immediately after the main shock. Aftershock expansion toward the SW was especially extensive and developed more rapidly than toward the NE. Interestingly, the aftershock area expanded in a step-like manner by the activation of a series of spatially clustered seismic bursts. Spatial correlation between the aftershock extension and the afterslip distribution suggests that the expansion of the aftershock area could be mainly driven by aseismic afterslip. The aftershock area continues to expand, even though 7 years have now passed since the main shock.

ROC-based estimates of neural-behavioral covariations using matched filters.

Correlations between responses in visual cortex and perceptual performance help draw a functional link between neural activity and visually guided behavior. These correlations are commonly derived with ROC-based neural-behavioral covariances (referred to as choice or detect probability) using boxcar analysis windows. Although boxcar windows capture the covariation between neural activity and behavior during steady-state stimulus presentations, they are not optimized to capture these correlations during short time-varying visual inputs. In this study, we implemented a matched-filter technique, combined with cross-validation, to improve the estimation of ROC-based neural-behavioral covariance under short and dynamic stimulus conditions. We show that this approach maximizes the area under the ROC curve and converges to the true neural-behavioral covariance using a Poisson spiking model. We also demonstrate that the matched filter, combined with cross-validation, reveals the dynamics of the neural-behavioral covariations of individual MT neurons during the detection of a brief motion stimulus.

PERFORMANCE EVALUATION OF ADAPTIVE RECEIVERS FOR UWB COMMUNICATION

UWB (Ultra Wide Band) is a radio technology used at very low energy levels for short-range, high-bandwidth communications using a large portion of the radio spectrum. But MAI (Multiple Access Interference) degrades the performance of UWB systems. To suppress this, an α-stable model along with Fama/Roll-McCulloch parameter estimation technique is used. This model adapts to the noise and interference in the environment and hence it forms a robust technique for adaptive receiver designs. But this technique shows BER performance clearly only in high SNR region. Hence matched filter techniques are proposed here. From simulation results, it is verified that the proposed method provides better BER than the linear and myriad filter detectors.

Miniature ambulatory skin conductance monitor and algorithm for investigating hot flash events

A skin conductance monitoring system was developed and shown to reliably acquire and record hot flash events in both supervised laboratory and unsupervised ambulatory conditions. The 7.2 × 3.8 × 1.2 cm3 monitor consists of a disposable adhesive patch supporting two hydrogel electrodes and a reusable, miniaturized, enclosed electronic circuit board that snaps onto the electrodes. The monitor measures and records the skin conductance for seven days without external wires or telemetry and has an event marker that the subject can press whenever a hot flash is experienced. The accuracy of the system was demonstrated by comparing the number of hot flashes detected by algorithms developed during this research with the number identified by experts in hot flash studies. Three methods of detecting hot flash events were evaluated, but only two were fully developed. The two that were developed were an artificial neural network and a matched filter technique with multiple kernels implemented as a sliding form of the Pearson product-moment correlation coefficient. Both algorithms were trained on a ‘development’ cohort of 17 women and then validated using a second similar ‘validation’ cohort of 20. All subjects were between the ages of 40 and 60 and self-reported ten or more hot flashes per day over a three day period. The matched filter was the most accurate with a mean sensitivity of 0.92 and a mean specificity of 0.90 using the data from the development cohort and a mean sensitivity of 0.92 and a mean specificity of 0.87 using the data from the validation cohort. The matched filter was the method implemented in our processing software.