Signal Enhancement Techniques Research Articles

Doppler Imaging of Stars with Surface Inhomogeneities

AbstractI review recent progress in the field of stellar surface imaging, with particular reference to advanced methods for mapping surface-brightness distributions on magnetically active late-type stars. New signal enhancement techniques, utilising profile information from hundreds or thousands of photospheric lines simultaneously, allow images to be derived for stars several magnitudes fainter than was previously possible. For brighter stars, the same techniques make it possible to map features as small as two or three degrees in extent on the stellar surface. While this opens up whole new areas of research, such as the ability to use starspot tracking to study surface differential rotation patterns on single and binary stars, caution must be exercised in the treatment of “nuisance” parameters such as the stellar rotation rate, surface abundances and radial velocity. At the very high S:N levels we now use, the effects of systematic errors in these parameters are easier to identify, isolate and eliminate. This leads to the possibility of making precise radial velocity variations (at the few hundred m s−2 level or better) in late-type stars even with equatorial rotation speeds as high as 100 km s−1. This is particularly topical given the recent discovery that one of our prime imaging targets, the young southern K0 dwarf AB Doradus, has an astrometric companion in a highly eccentric orbit with an inferred mass close to the H-burning limit.

Blind beamforming on a randomly distributed sensor array system

We consider a digital signal processing sensor array system, based on randomly distributed sensor nodes, for surveillance and source localization applications. In most array processing the sensor array geometry is fixed and known and the steering array vector/manifold information is used in beamformation. In this system, array calibration may be impractical due to unknown placement and orientation of the sensors with unknown frequency/spatial responses. This paper proposes a blind beamforming technique, using only the measured sensor data, to form either a sample data or a sample correlation matrix. The maximum power collection criterion is used to obtain array weights from the dominant eigenvector associated with the largest eigenvalue of a matrix eigenvalue problem. Theoretical justification of this approach uses a generalization of Szego's (1958) theory of the asymptotic distribution of eigenvalues of the Toeplitz form. An efficient blind beamforming time delay estimate of the dominant source is proposed. Source localization based on a least squares (LS) method for time delay estimation is also given. Results based on analysis, simulation, and measured acoustical sensor data show the effectiveness of this beamforming technique for signal enhancement and space-time filtering.

Improved signal enhancement procedures applied to exponential data modeling

Various signal enhancement techniques have been proposed to improve spectral estimation of closely spaced sinusoids in the presence of noise. This correspondence exploits the filtering interpretation of some well-known SVD-based iterative algorithms for signal enhancement to further improve their performance. It is shown that the initial conditions that are used throughout the filtering process may considerably affect the spectral characteristics of the signal. A strategy is proposed to minimize these undesirable effects. The new method improves the performance of fully automated magnetic resonance spectroscopy (MRS) quantitation.

Signal enhancement techniques for chromatography detection systems

The Environmental Protection Act has created a growing need for the measurement and assessment of trace emissions to the environment. This encompasses three main areas of ground, water and the atmosphere. The need to achieve lower emissions has placed a large burden on analytical techniques, particularly in the areas of trace analysis to ppb and ppt levels. Chromatographic techniques are widely used for assessment and measurement of emissions in all three areas. Enhanced detectors using mass spectrometry principles are available to lower detection limits, but these are expensive. Standard chromatography detectors can be used for trace analysis, but this often leads to extensive sample preparation stages to achieve low detection limits. This paper describes the techniques developed by Thomas Swan & Company to introduce a cost effective way of lowering detection limits. The approach taken meets both BATNEEC and BPEO constraints.

Moho signature from wide-angle reflections: preliminary results of the 1993 Trans-Hudson Orogen refraction experiment

In 1993 a combined crustal seismic refraction and wide-angle reflection experiment was conducted over the northern Saskatchewan and Manitoba portion of the Trans-Hudson Orogen by LITHOPROBE. The program included three seismic lines extending over 1900 km in length. The exceptionally high-quality data collected during the field experiment included seismic reflections and refraction events from the Moho and upper lithospheric mantle. The relatively high seismic fold and signal-to-noise ratio of the field observations made it possible to process the wide-angle portion of the data set with standard reflection signal enhancement techniques. The Moho is revealed as a complex interface with significant structural relief (40–52 km) that correlates in first-order fashion with crustal geology and structure. The Moho topography is interpreted as a result of variable ductile reworking and eclogitization of the lower crust.

Signal enhancement using pattern recognition techniques with application to near vertical crustal seismic reflection experiments

Most near‐vertical crustal seismic reflection experiments are conducted over regions where in the past the crust has undergone some form of tectonic deformation. The deep structures differ from the near surface sedimentary structures in that they are generally not layered. Seismic energy after travelling through long ray paths in such media arrives at slightly different times at the receivers and hence tends to be poorly aligned along its respective theoretical travel time curves. Conventional seismic processing routines which attempt to increase the signal to noise ratio (S/N) by some stacking technique can in many cases actually destroy the poorly aligned signals such that the resultant subsurface images are not very satisfactory. Our study focuses on a signal enhancement technique based on a pattern recognition approach which is applied in the prestack processing stream in an effort to increase the S/N ratio. The discrimination between signal and noise is based on attributes such as the frequency, amplitude, waveshape, and lateral continuity of the signal. The method was first tested on synthetic data, and then applied to real data acquired over the Canadian shield. Signal enhancement using a pattern recognition approach as outlined in this paper dramatically improved the subsurface images over those obtained by more conventional stacking methods.

Microwave cavity spectrometer for process monitoring of ethylene oxide sterilization

This article reports a novel and simple cavity spectrometer for process monitoring of ethylene oxide sterilization, in which the source frequency, cavity resonant frequency, and gas absorption center frequency are asynchronous with respect to each other, thus, enabling sophisticated signal enhancement techniques to be employed without the need to engage the Stark effect. The operation of the device is such that the source frequency sweeps across a given range (F1 to F2) which contains one of the absorption peaks of the analyte gas (gases) of interest while the cavity resonant frequency Fr is oscillated within the profile of the absorption peak. Signal enhancement is achieved by adding a relatively small magnitude/high-frequency ‘‘dither’’ signal to the source frequency sweep pattern. The salient information of the gas absorption due to the oscillation of the resonant frequency of the cavity is carried by the ‘‘dither’’ signal and amplified and extracted by a series of tuned amplifiers and demodulators. Although the device is still at the initial design stage, a working prototype has been constructed in order to test the feasibility of the novel asynchronous modulation technique. This was achieved by successfully demonstrating that the device operates in an expected manner to within a standard error of 8.3%. It is believed that this error largely results from mechanical components. The significance of this error is greatly reduced when the spectrometer is operated in a large signal scanning mode as is the case when we apply the ‘‘power saturation’’ technique to measure the concentration of ethylene oxide in the resonant cavity. This measurement showed that there is a good linear correlation between the output signal and the concentration of ethylene oxide gas (to within a standard error of 4%).

Detection of Delaminations in Art Objects Using Air-Coupled Ultrasound°

ABSTRACTThe possibility of using air-coupled ultrasound to find delaminations between layers in paintings was investigated. Simulations of modern paintings were constructed with hardboard as the support layer, and a layer of gesso, an animal hide glue and chalk, as the upper layer. Delaminations were introduced between the two layers. Scanning the samples using air-coupled ultrasound clearly showed these flaws. A transmitting transducer, which was 25 mm in diameter and had a focal length of 51 mm, was placed 11 mm from the back surface of the sample and an identical receiving transducer was placed 51 mm from the front surface. The transducers were operated in a tone burst mode at a center frequency of 475 kHz. Signal enhancement techniques were used to improve the contrast of the data.

DEEP STRUCTURAL IMAGING FROM ONSHORE RECORDING OF A MARINE AIR-GUN SOURCE IN THE GIPPSLAND AND BASS BASINS

In 1988 and 1989, the Bureau of Mineral Resources (BMR) completed two regional seismic reflection surveys in the Gippsland and Bass Basins. Seismic arrivals from the routine air-gun shots fired during these surveys were recorded on land by BMR and the Department of Earth Sciences, Monash University. Individual analogue and digital recording stations were deployed in Victoria, Tasmania and Deal Island on the Bassian Rise. Long-offset wide-angle reflection and refraction data were obtained at these stations from traverses across both basins.The data quality was variable, depending on local site conditions, but useful arrivals were observed over 200 km away from the source on some lines. The close shot spacing, either 37.5 or 50 m, and the large number of shots, up to 5000 per traverse, provides the opportunity for stacking and other signal enhancement techniques in areas of poor data quality.The arrival times of the refracted events show significant delays corresponding to changes in basin sediment thickness. Preliminary results suggest no major asymmetry in the rifting process, which would require modification in the current models for rifting of the basins. Sediment and basement apparent velocities obtained from near-station records range from 4.8 to 5.1 km/s; below the deepest part of the basin, the basement apparent velocity is around 5.6 km/s. Deep crustal/upper mantle velocities of 7.2 km/s, and around 8 km/s, are also observed.These velocities, combined with the coincident reflection data provide critical constraints on models of basement geometry. The refraction and wide-angle reflection data can be used to derive the crustal structure associated with the basins and surrounding margins. These sections will complement deep reflection profiling to test and refine tectonic models to guide further exploration.

Location and characterization of partial discharge sites in shielded power cables

An instrument capable of detecting and locating partial discharge sites and faults in shielded power cables was developed on behalf of a group of US electric utilities. The instrument uses state-of-the-art electronic hardware and advanced digital signal processing techniques. The partial discharge signals are reconstructed using the cable traveling wave characteristics (transfer function), and noise is reduced both through choice of hardware and by modern signal enhancement techniques. An adjunct instrument was also developed to correlate the location of a partial discharge site along the cable to the position along the surface of the cable burial trench. The principle and the implementation of the instrumentation package are described, and results obtained in the laboratory on a 175 m, 15 kV URD cable are discussed. >

A comparison between temporal coherence and spectral filtering techniques for signal enhancement

Temporal coherence differences between a signal of interest and background illumination can be used to enhance the contrast of the signal. A sensor system that uses this information is demonstrated for both laser and non-laser detection. The performance of this system is then compared to the use of spectral filtering alone. By employing coherence modulation, it is shown that the system gain can be improved by several orders of magnitude.

Nondestructive testing (NDT) techniques to detect contained subsurface hazardous waste

A systematic and comprehensive study was conducted to detect buried containers with nondestructive testing (NDT) remote-sensing techniques. Seventeen techniques were considered but only four were ultimately selected. Those four were electromagnetic induction (EMI), metal detection (MD), magnetometer (MAG), and ground penetrating radar (GPR). The containers — both steel and plastic — varying in size from 5 gal to 55 gal were buried in known distributions in a wide variety of soils; also, some were submerged in water. Five diverse field sites were used. As a result of the work at the five field sites, a relatively complete picture has emerged concerning the strengths and weaknesses of the four NDT subsurface container location techniques. GPR is the only reliable method to detect plastic containers, but it has limitations. GPR, EMI, and MD all suffer severe loss of detection ability when the background electrical conductivity exceeds 40 millimhos/meter. In dry sandy soil EMI, GPR, and MAG are all capable of picking up a single 55-gal steel drum to a depth of at least 10 feet. The MAG method works well for steel under all subsurface conditions, and GPR can usually pickup the side walls of the excavations where waste in dumped. Application of signal enhancement techniques (background suppression) can be expected to enhance NDT utility.

Automatic enhancement of single evoked potentials

Using EEG data acquired during a simple (sRT) or choice (cRT) reaction time task we tested a signal enhancement technique. Our findings indicate that the signal enhancement technique under study substantially reduced background activity while retaining physiologically significant information. For each RT trial, a pre-stimulus epoch was modeled using a canonical variate analysis (CVA) system identification technique to produce a filter. This filter was then applied to the post-stimulus epoch to remove ongoing background activity. Signal/noise enhancement was apparent from comparison of the ensemble averages of seven raw responses and the 7 corresponding CVA-enhanced responses. The extracted single evoked potentials (sEPs) were searched by machine algorithm for an expected negative peak with approximately 200 msec latency, the latency of each identified peak estimated, and correlations between RT and peak latency computed. For the choice task significant correlations were found at the right central placement (C4) for left-handed responses and at the left parietal placement (P3) for right-handed responses. For the simple task with right-handed responses, the most significant results were found at left placements (C3 and T5) with additional significant findings bilaterally (T3, T4, P4 and O1).

Use of an unintensified charge-coupled device detector for low-light-level Raman spectroscopy

Spontaneous Raman scattering from adsorbates on surfaces is a powerful vibrational spectroscopy technique that is due to the very large frequency range and high resolution currently possible with visible lasers and spectrometers. Because of the extremely low Raman cross sections of nonresonant molecules, one must use either some sort of signal-enhancement technique or long integrations using multichannel detection in order to have monolayer sensitivity. We have used a backthinned, unintensified, liquid-nitrogen-cooled charge-coupled device (CCD) detector to obtain high-quality multichannel unenhanced Raman scattering spectra from organic monolayers on surfaces. This system has roughly a factor-of-10 greater sensitivity for very low-light-level visible excitation Raman spectra than intensified multichannel detectors currently on the market. A description of our detection system is given along with a comparison with other commercially available multichannel detectors suitable for low-light-level visible Raman spectroscopy. We discuss the advantages and disadvantages of using CCD’s, the special problems that one encounters in their use as Raman detectors, and our methods for overcoming these problems. Prospects for the future use of CCD’s for low-light-level Raman spectroscopy will also be discussed.

Development and performance of the gas sensor system

The design, development, laboratory testing and production of the gas sensing instruments for the Heavy Gas Dispersion Trials are discussed in detail. The gas sensing transducer used in these instruments is an electrochemical cell which gives a signal proportional to the partial pressure of oxygen in the atmosphere. Any gas species is thus detectable by the reduction in oxygen partial pressure caused by its presence. The specification of the instruments and the factors influencing the selection of the electrochemical cell are discussed. The principle of operation of the cell is described, together with the main conclusions of a mathematical analysis for diffusion of oxygen molecules through thin membranes. In order to achieve the required frequency response, an electronic signal-enhancement technique was developed. The basis of this technique is explained and experiments are described which confirmed its effectiveness. The instruments were subjected to laboratory performance checks before delivery to the trials' site. Details of these checks and the results obtained are presented. In order to assure the accuracy of the data produced by the gas measuring system, the on-site performance of the instruments was checked at regular intervals by applying known gas mixtures. The performance of the instruments is discussed and certain design refinements are described. The quality of the data produced by the gas sensing system is of key importance and techniques were developed to validate the data before their release to sponsors. The validation methodology adopted is described. The instruments have performed reliably with minimum maintenance. They are low-cost devices and are capable of working over wide temperature and humidity ranges.

反射波を用いた京都盆地東南部の基盤構造の推定

In a southeastern part of Kyoto basin, we observed the reflected waves from the basement some hundred meter deep by using air gun as a source and signal-enhancement technique by stacking. Both the velocity up to and the depth of the basement were greater than those previously given by KITSUNEZAKI et al. (1971). It is useful to use reflected waves for exploring sharp boundary, such as a basement, because it is relatively easy to observe them at far distances where surface waves are not disturbing. Synthetic seismograms also support the prospect to detect reflected phases from a sharp boundary.

Rotor wake characteristics relevant to rotor-stator interaction noise generation

Mean and turbulence wake properties at three axial locations behind the rotor of an aerodynamically loaded 1.2 pressure ratio fan were measured using a stationary cross film anemometer in an anechoic wind tunnel. Wake characteristics at four radial immersions across the duct at four different fan speeds were determined utilizing a signal enhancement technique. The shapes of the waveforms of the mean rotor relative and mean upwash velocities were shown to change significantly across the span of the blades. In addition, an increase in fan rotational speed caused an increase in the maximum wake turbulence intensity levels near the hub and tip. Spectral analysis was used to describe the complex nature of the rotor wake.

Transfer function method of measuring in-duct acoustic properties. I. Theory

The theory of a transfer function method of measuring normal incident in-duct acoustic properties is presented. In this method, a broadband stationary random acoustic wave in a tube is mathematically decomposed into its incident and reflected components using a simple transfer-function relation between the acoustic pressure at two locations on the tube wall. The wave decomposition leads to the determination of the complex reflection coefficient from which the complex acoustic impedance and the sound absorption coefficient of a material and the transmission loss of a silencer element can be determined. Also presented are the theories of two techniques for improving transfer function estimates: a sensor-switching technique for automatic system calibration and a coherence function technique for signal enhancement.

Method for Crosshole Seismic Testing

Many foundation dynamics and soil-structure interaction problems require in-situ values of shear wave velocities and elastic moduli, or both, for foundation materials. The project engineer has at his disposal several methods for determining these properties in situ. Each of the methods has a particular attribute, but the crosshole survey when conducted properly, lends itself best to signal enhancement techniques and appears most versatile. Development of a nondestructive vertically polarized repeatable shear wave source is presented. Techniques of data acquisition using signal enhancement are considered. Comparison with shear wave velocity data obtained by other methods leads to the conclusion that a vertically polarized shear wave train can be generated and positively identified due to almost total absence of P-wave components. The method for crosshole seismic testing presented will largely free the project engineer from misinterpretation of shear wave velocity data.

Airgun array design techniques

Since airguns were introduced to the oil exploration industry in the late 1960's, they have replaced dynamite as the primary acoustic source for marine seismic profiling. Arrays of airguns compare favorably in the seismic bandwidth to dynamite for depth of penetration and resolution. Multi‐element arrays capable of peak‐to‐peak pressures exceeding 50 bars (at 1 meter) are presently being used in the industry. Independent control of chamber pressure and volume, operating depth and distance between airguns allows the design of airgun arrays which can meet particular resolution or depth of penetration objectives. Array design techniques are reviewed and data from a Shell array is presented to illustrate the degree to which success in meeting the design objectives of a high peak pressure, a high primary‐to‐bubble ratio and broad bandwidth is achieved. Far‐field signatures from the array are shown to possess the necessary shot‐to‐shot stability required of modern signal enhancement techniques when proper care is taken in deploying and towing the array. Boundary effects (ghosting) are shown to reduce shot stability. Some mechanical deployment and towing considerations are discussed.