Matched Filter Technique Research Articles

LONG-TERM MERIS LAND PRODUCT ACCURACY ASSESSMENT BASED ON VICARIOUS CALIBRATION AND REGIONAL VALIDATION

Since the launch of MERIS on board of ENVISAT long term activities using vicarious calibration approaches have been set in place to monitor potential drifts in the calibration of the radiance products of MERIS. In this paper, a stable and well monitored reference calibration site named Railroad Valley Playa (Nevada, USA) is used to derive the calibration uncertainties of the MERIS FR TOA radiance over time. Subsequently, a linear interpolation of these uncertainties is performed for a set of images covering the whole of the Netherlands (which is used as a validation site). After this, the images over the Netherlands were corrected on the basis of the previously interpolated uncertainties and classified in 9 land use classes using linear spectral unmixing and matched filtering techniques. The classification endmembers were derived from an image-based land use map of the Netherlands (LGN4) after determining the most homogeneous areas for each land use type by means of a standard purity index and a moving window filter to minimize possible adjacency effects. Finally, the impact of the calibration accuracy over the land use classification is assessed by comparing classification results both for corrected and uncorrected images. We conclude that the classification performance may significantly be increased, when taking into account long-term vicarious calibration results.

Gravitational waves from hyper-accretion on to nascent black holes

We examine the possibility that hyper-accretion on to newly born black holes occurs in highly intermittent, non-asymmetric fashion favourable to gravitational-wave emission in a neutrino-cooled disc. This picture of near-hole accretion is motivated by magnetorotationally induced, ultrarelativistic disc dynamics in the region of the flow bounded from below by the marginally bound geodesic radius r mb . For high spin values, a largely coherent magnetic field in this region has the dynamical implication of compact mass segregation at the displacement nodes of the non-axisymmetric, magnetorotational instability modes. When neutrino stress competes favourably for the disc dynamical structure, the matter clumps may be rather dense and sufficiently long-lived to excite the quasi-normal ringing (QNR) modes of the Kerr geometry upon infall. We find that this accretion flow may drive bar-like, quadrupole (1, m = 2, 2) modes in nearly resonant fashion for spin parameters a ≥ 0.9. The ensuing build-up in strain amplitude of the undamped oscillations warrants a brisk rate of energy deposition into gravitational waves. A detectability assessment for the LIGO interferometers through the match filtering technique is given by integrating the energy flux over a one-second epoch of resonant hyper-accretion at 1 M ○. s -1 . Thus, a 15-M ○. Kerr black hole spinning at a ≃ 0.98 (f QNR ≃ 1677 Hz), and located at 27 Mpc (e.g. GRB 980425), will deliver a characteristic strain amplitude, h char ≃ 2.2 -21 , large enough to be detectable by LIGO II. If resonant hyper-accretion were sustainable for a longer period (or at higher rates) possibly associated with a second broad hump in a gamma-ray burst light curve, these objects could be detected by LIGO I at very low redshifts.

Dynamic matched filters for gravitational wave detection

The algorithms for the detection of gravitational waves are usually very complex due to the low signal-to-noise ratio. In particular, the search for signals coming from coalescing binary systems can be very demanding in terms of computing power, as in the case of the well-known standard matched filter technique. To overcome this problem, we tested a dynamic matched filter technique, based on matched filters, whose main advantage is the requirement of a lower computing power. In this work this technique is described, together with its possible application, as a pre-data analysis algorithm. The results on simulated data are also reported.

A Low-Complexity Blind Multiuser Receiver for Long-Code CDMA

Receivers for long-code systems are for computational reasons usually based on simple matched-filter techniques, and hence suffer from multiaccess interference. Decorrelating RAKE and MMSE receivers do not have this problem but have not been widely studied due to the apparent complexity of the inversion of a large code matrix. Tong, van der Veen Dewilde, and Sung (IEEE Tr. Signal Proc., 2003) derived a blind decorrelating RAKE receiver (DRR) and channel estimation algorithm for long-code CDMA systems, and showed how it can be efficiently implemented. In this paper, we continue on that work. We propose both single-user and multiuser blind source-channel estimation algorithms by making use of an iterative estimation scheme initialized by the DRR. Simulation results show significant improvement, even in heavily loaded systems. Moreover, with an implementation based on time-varying system theory, the proposed algorithm can be implemented efficiently at a cost similar to the RAKE.

Dynamic matched filter technique for gravitational wave detection from coalescing binary systems

The detection of gravitational waves from coalescing binary systems requires high-performance data analysis techniques for signal extraction from the detector noise. The optimal solution is the well-known standard matched filter technique, but its effective application may require large amounts of computing power, not always available. To overcome this problem, we developed a dynamic matched filter technique, still based on matched filters, whose main advantage is the requirement of a much lower computing power. In this paper we describe this technique, its possible application as a pre-data analysis algorithm and the tests we performed on simulated data.

Computationally efficient blind MMSE receivers for long code WCMDA using time-varying systems theory

UMTS systems will employ long-code wideband CDMA modulation schemes. Receivers for this system are for computational reasons usually based on simple matched-filter techniques, and hence suffer from multiaccess interference. Decorrelating RAKE and MMSE receivers do not have this problem but, until now, were considered as too complex, due to the inversion of a large code matrix. As is shown in this paper, the code matrix can be interpreted as a time-varying system. Efficient implementations are then possible by carrying out the inversion using time-varying state space theory, yielding a complexity comparable to that of the conventional RAKE receiver.

Elliptical tiling method to generate a 2-dimensional set of templates for gravitational wave search

Searching for a signal depending on unknown parameters in a noisy background with matched filtering techniques always requires an analysis of the data with several templates in parallel in order to ensure a proper match between the filter and the real waveform. The key feature of such an implementation is the design of the filter bank which must be small to limit the computational cost while keeping the detection efficiency as high as possible. This paper presents a geometrical method that allows one to cover the corresponding physical parameter space by a set of ellipses, each of them being associated with a given template. After the description of the main characteristics of the algorithm, the method is applied in the field of gravitational wave (GW) data analysis, for the search of damped sine signals. Such waveforms are expected to be produced during the deexcitation phase of black holes---the so-called ``ringdown'' signals---and are also encountered in some numerically computed supernova signals. First, the number of templates $\mathfrak{N}$ computed by the method is similar to its analytical estimation, despite the overlaps between neighbor templates and the border effects. Moreover, $\mathfrak{N}$ is small enough to test for the first time the performances of the set of templates for different choices of the minimal match $MM,$ the parameter used to define the maximal allowed loss of signal-to-noise ratio (SNR) due to the mismatch between real signals and templates. The main result of this analysis is that the fraction of SNR recovered is on average much higher than $MM,$ which dramatically decreases the mean percentage of false dismissals. Indeed, it goes well below its estimated value of $1\ensuremath{-}{\mathrm{MM}}^{3}$ used as input of the algorithm. Thus, as this feature should be common to any tiling algorithm, it seems possible to reduce the constraint on the value of $\mathrm{MM}$---and indeed the number of templates and the computing power---without losing as many events as expected on average. This should be of great interest for the inspiraling binaries case where the number of templates can reach some hundreds of thousands for the whole parameter space.

Are post-Newtonian templates faithful and effectual in detecting gravitational signals from neutron star binaries?

We compute the overlap function between Post-Newtonian (PN) templates and gravitational signals emitted by binary systems composed of one neutron star and one point mass, obtained by a perturbative approach. The calculations are performed for different stellar models and for different detectors, to estimate how effectual and faithful the PN templates are, and to establish whether effects related to the internal structure of neutron stars may possibly be extracted by the matched filtering technique.

Lack of Precursory Slip to the 1999 Hector Mine, California, Earthquake as Constrained by InSAR

We looked for evidence of interseismic strain occurring between the 1992 Landers earthquake and the 1999 Hector Mine earthquake near the Lavic Lake and Bullion faults by using interferometric synthetic aperture radar (InSAR). Interferograms covering the Hector Mine epicentral region were studied for possible slip along the Bullion and Lavic Lake faults by both visual inspection and a matched filter technique intended to emphasize slip located at the nucleation point. Some indications of possible deformation associated with the 5 July 1992 M L 5.4 Pisgah event was observed, but high decorrelation prevented a conclusive determination. We have seen no evidence for precursory slip in the epicentral region up to 30 days before the Hector Mine event. We estimated that the slip equivalent to a M w 4.5 event would have been observable in the months before the Hector Mine event, and this places an upper bound on the long-term precursory slip, had it occurred. We have noted that InSAR is well suited for detecting precursory slip in general due to the high spatial resolution and the lack of ground instrumentation required but that the detection level depends on the depth and orientation of the slip. [ Back ]

The Aquarius Superclusters. I. Identification of Clusters and Superclusters

We study the distribution of galaxies and galaxy clusters in a 10° × 6° field in the Aquarius region. In addition to 63 clusters in the literature, we have found 39 new candidate clusters using a matched-filter technique and a counts-in-cells analysis. From redshift measurements of galaxies in the direction of these cluster candidates, we present new mean redshifts for 31 previously unobserved clusters, while improved mean redshifts are presented for 35 other systems. About 45% of the projected density enhancements are due to the superposition of clusters and/or groups of galaxies along the line of sight, but we could confirm for 72% of the cases that the candidates are real physical associations similar to the ones classified as rich galaxy clusters. On the other hand, the contamination due to galaxies not belonging to any concentration or located only in small groups along the line of sight is ~10%. Using a percolation radius of 10 h-1 Mpc (spatial density contrast of about 10), we detect two superclusters of galaxies in Aquarius, at z ~ 0.086 and 0.112, respectively, with five and 14 clusters. The latter supercluster may represent a space overdensity of about 160 times the average cluster density as measured from the Abell et al. cluster catalog and is possibly connected to a 40 h-1 Mpc filament from z ~ 0.11 to 0.14.

宇宙用小型高機能ＧＰＳ受信機の開発

This paper presents the development of a multi-functional and miniature GPS receiver in NASDA. The investigation for the design and implementation method for the spaceborne GPS receiver has been conducted. And a bread-board model of parallel signal search on matched filtering technique, which is an essential technique of the multi-functional GPS receiver, was manufactured. And time to acquisition (TTA) of GPS signal was measured using GPS simulator. The test results of the trial product show that TTA is 60ms and time to first fix (TTFF) of the navigation calculation in a low-altitude orbit is within 5.3min in worst case.

Comparing behavioral receiver operating characteristic curves to multidimensional matched filters

Human factors experiments can be used to test whether a sensor can improve operator performance for detecting or recognizing a target.1 Although human factors experiments are of tremendous value, these tests are time consuming and resource intensive. To reduce costs associated with collecting behavioral data, a two-dimensional matched filter is proposed. The objective is to compare and contrast behavioral and matched filter receiver operating characteristic (ROC) plots to determine whether the matched filter technique is a good predictor of human performance. Five different background images (three infrared band images, a chromatic-fused image, and monochromatic-fused image) were used with, and without, a target (airplane) present. False alarm and target detection probabilities were computed and results were plotted on an ROC curve. The matched filter ROC curves were then compared to behavioral ROC curves. Results showed that the matched filter ROC curves were similar to behavioral ROC curves with color fusion, longwave infrared showing the highest sensitivity, and mid-wave and shortwave infrared scenes were significantly less sensitive (near chance). These results indicate that the matched filter analysis may be used to model human behavior.

Chaos and gravitational waves

The gravitational waveforms of a chaotic system will exhibit a sensitive dependence on initial conditions. The waveforms of nearby orbits decohere on a time scale fixed by the largest Lyapunov exponent of the orbit. The loss of coherence has important observational consequences for systems where the Lyapunov time scale is short compared to the chirp time scale. Detectors that rely on matched filtering techniques will be unable to detect gravitational waves from these systems.

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.

Eddy Detection Over Southern Indian Ocean Using TOPEX/POSEIDON Altimeter Data

Mesoscale eddies constitute the most energetic component of the variability of ocean currents. An attempt has been made for the detection of oceanic mesoscale eddy signatures over the Southern Indian Oceanic (SIO) regions using the dynamic topography derived from TOPEX/POSEIDON (T/P) altimeter data, by the signal processing technique, called matched filtering. After applying all the ocean and atmospheric corrections, data of a complete cycle of T/P over SIO has been used for detection of eddy signatures. The geoid undulations are removed from the data of corrected sea surface height from T/P and the resulting dynamic topographic data are passed through a matched filter designed to detect a generic eddy signature of Gaussian signal embedded in noise. The filter is optimized to detect eddies with amplitude 20 to 30 cm and diameters roughly 100?250 km. Out of all the analyzed data of T/P orbits over SIO a few examples are presented for brevity. Qualitative verification of eddies is done with some independent T/P sea level anomaly data over the region. The analysis shows that the matched filtering technique is most suitable for monitoring eddy signatures along the subsatellite track instantly over the remote and most hostile regions of the southern global oceans.

Pattern Detection in Gray-Scale Images with Polarization Coding

Most of the matched filtering techniques that have been used for pattern recognition have manipulated amplitude and phase information. Light, however, has another principal type of information that has not yet been used for pattern recognition. We propose a matched filtering technique which manipulates the polarization of light and shows the merits of using polarization information. The amplitude transmittance of input images is coded into the two-dimensional orientation distribution of linearly polarized light. A polarization spatial filter, which can change the light polarization two-dimensionally, is designed by considering the polarization distribution of the Fourier transform of an image to be detected which is polarization-coded. The proposed technique shows a better capacity to discriminate gray-scale images than do the conventional matched filtering techniques.

Comparison of the use of WiFS and LISS images to estimate the area burned in a large forest fire

We evaluate the utility of medium spatial resolution images from the Wide Field Sensor (WiFS) for the estimation of the area burned in a large fire. The performance of methodologies using these images is compared with similar methodologies using high spatial resolution image from the Linear Imaging and Self Scanning Sensor (LISS-III) and other ancillary data. Both sensors are located onboard the Indian Remote Sensing Satellite 1C (IRS-1C). The post-fire LISS image was analysed by means of Matched Filtering (MF) techniques. Two WiFS images (pre- and post-fire) were analysed using MF techniques and also by means of changes in the Normalized Difference Vegetation Index (NDVI). Ground data were used to classify the three thematic images obtained in several post-fire classes. The results show a greater proportion of transition areas between burned and unburned places and a slightly larger area burned estimation in the WiFS than in the LISS analysis. Nevertheless, the results obtained, and the comparisons with ground data, indicate that medium spatial resolution images' estimation of the area burned is a useful tool at regional and national scales.

Matched filtering-parameter estimation method and analysis of whistlers recorded at Varanasi

The matched filtering technique is based on the digital-construction of theoretical whistlers and their comparison with observed whistlers. The parameters estimated from the theoretical and experimental whistler curves are matched to have higher accuracy using digital filters. This yields a resolution ten times better in the time domain. We have tested the applicability of this technique for the analysis of whistlers recorded at Varanasi. It is found that the whistlers have propagated along L>2 and have wave normal angles after exiting from the ionosphere such that they propagate towards equator in the earth-ionosphere wave-guide. High-resolution analysis shows the presence of fine structures present in the dynamic spectrum. An effort is made to interpret the results.

Comparison of the Acquisition Performance of the Matched Filter and Integrate-and-Dump Receivers in a Multipath Delay and Fading Environment

The Matched Filter and the Integrate-and-Dump circuit techniques are both attractive acquisition methods for CDMA systems. Acquisition using the matched filter technique has attracted considerable interest in recent years since it shows a better performance in the presence of Gaussian noise. On the other hand acquisition using an integrate-and-dump circuit is attractive because it is less complex to implement. However, the acquisition performance can be affected significantly by the channel characteristics. In this paper, a numerical method and a computer simulation have been developed in order to compare the two acquisition systems in different propagation environments. Results show that the acquisition using a matched filter is much faster than that using the integrate-and-dump circuit for the reception of spread-spectrum signals in the presence of Gaussian noise. However, in a multipath delay and fading environment, the results show that the mean acquisition time using the matched filter is not always faster than that using the integrate-and-dump circuit. The results show that it depends on the fading, the delay, the number of users and the signal-to-noise ratio.

Possible Supercluster at z ∼ 0.25 towards the South Galactic Pole

We have observed a 0.7×1.2deg2 field in the SGP region with the UT / NAOJ Mosaic CCD Camera attached to the 40-inch Swope Telescope at Las Campanas Observatory, and constructed a sample of 1150 galaxies in the region down to R=20.5. Then we applied to the sample a new, objective cluster-finding technique, which is an improved variant of the so-called “matched-filter technique” pioneered by Postman et al. (1996). Using projected positions and apparent magnitudes of galaxies simultaneously, this technique can, not only find cluster candidates, but also estimate their redshifts and richnesses. A number of Monte Carlo simulations demonstrated enough accuracies of the estimations and much lower spurious detection rate than that by conventional cluster-finding methods which use only surface density of galaxies.