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Showing papers on "Signal-to-noise ratio published in 1975"


Journal ArticleDOI
24 Mar 1975
TL;DR: It is shown that in treating periodic interference the adaptive noise canceller acts as a notch filter with narrow bandwidth, infinite null, and the capability of tracking the exact frequency of the interference; in this case the canceller behaves as a linear, time-invariant system, with the adaptive filter converging on a dynamic rather than a static solution.
Abstract: This paper describes the concept of adaptive noise cancelling, an alternative method of estimating signals corrupted by additive noise or interference. The method uses a "primary" input containing the corrupted signal and a "reference" input containing noise correlated in some unknown way with the primary noise. The reference input is adaptively filtered and subtracted from the primary input to obtain the signal estimate. Adaptive filtering before subtraction allows the treatment of inputs that are deterministic or stochastic, stationary or time variable. Wiener solutions are developed to describe asymptotic adaptive performance and output signal-to-noise ratio for stationary stochastic inputs, including single and multiple reference inputs. These solutions show that when the reference input is free of signal and certain other conditions are met noise in the primary input can be essentiany eliminated without signal distortion. It is further shown that in treating periodic interference the adaptive noise canceller acts as a notch filter with narrow bandwidth, infinite null, and the capability of tracking the exact frequency of the interference; in this case the canceller behaves as a linear, time-invariant system, with the adaptive filter converging on a dynamic rather than a static solution. Experimental results are presented that illustrate the usefulness of the adaptive noise cancelling technique in a variety of practical applications. These applications include the cancelling of various forms of periodic interference in electrocardiography, the cancelling of periodic interference in speech signals, and the cancelling of broad-band interference in the side-lobes of an antenna array. In further experiments it is shown that a sine wave and Gaussian noise can be separated by using a reference input that is a delayed version of the primary input. Suggested applications include the elimination of tape hum or turntable rumble during the playback of recorded broad-band signals and the automatic detection of very-low-level periodic signals masked by broad-band noise.

4,165 citations


Journal ArticleDOI
31 Jul 1975-Nature
TL;DR: The signal-to-noise ratio of electron micrographs can be determined by two-dimensional digital cross correlation even though neither signal nor noise can be analysed separately.
Abstract: The signal-to-noise ratio of electron micrographs can be determined by two-dimensional digital cross correlation even though neither signal nor noise can be analysed separately. Such measurements suggest how best to make use of the electron microscope.

185 citations


Journal ArticleDOI
TL;DR: The theory of heterodyne radiation receivers for the infrared and far-infrared is reviewed in this paper, where only systems based on photoemissive and photoconductive radiation mixers are considered.
Abstract: The theory of heterodyne radiation receivers for the infrared and far-infrared is reviewed. For simplicity, only systems based on photoemissive and photoconductive radiation mixers are considered. The signal-to-noise ratio is derived, and expressions for this quantity under various conditions are given. A brief comparison is made between heterodyne systems and high-resolution spectrometers using direct radiation detectors. It is concluded that for high spectral resolving powers and for relatively small astronomical sources, heterodyne systems are likely to offer a distinct advantage in signal-to-noise ratio, especially at long far-infrared wavelengths.

60 citations


Patent
22 Dec 1975
TL;DR: In this article, a method and apparatus for the determination of the Raylographic information of a body part which is ensonified by acoustical energy pulses by a particularly precisely focused acoustic focusing system to produce acoustic energy echo pulses which are detected in coherent manner Fourier transformation of the pulses from the time to the frequency domain enables frequency domain deconvolution to provide the impulse response with minimization of mathematical instabilities and distortion of the frequency-domain impulse response.
Abstract: Method and apparatus are provided for the determination of the Raylographic information of a body part which is ensonified by acoustical energy pulses by a particularly precisely focused acoustical focusing system to produce acoustical energy echo pulses which are detected in coherent manner Fourier transformation of the pulses from the time to the frequency domain enables frequency domain deconvolution to provide the impulse response with minimization of mathematical instabilities and distortion of the frequency domain impulse response Noise extraction and spatial deconvolution filtering are included to respectively maximize signal to noise ratio and minimize distortive effects of body part surface non-orthogonality and combine with the above to provide for particular stability in the overall results and attendant increase in the axial resolution of Raylographic display and in the overall resolution of body part image displays

58 citations


Patent
23 Jun 1975
TL;DR: In this paper, the authors proposed a circuit for preventing laser receiver overload caused by sunlight wherein feedback network provides a feedback network to cancel the d.c. level of the diode current, and a receiver design alternative to conventional designs wherein higher sensitivity is provided by maximizing the signal to noise ratio and processing by dual equalization to reshape the frequency response to achieve a flat response over the frequency range of interest.
Abstract: A circuit for preventing laser receiver overload caused by sunlight wherein feedback network provides a d.c. current to cancel the d.c. level of the diode current; and, a receiver design alternative to conventional designs wherein higher sensitivity is provided by maximizing the signal to noise ratio and processing by dual equalization to reshape the frequency response to achieve a flat response over the frequency range of interest.

24 citations


Journal ArticleDOI
TL;DR: Signal averaging has been used to improve the clarity of flaw indications in an electron beam weld as mentioned in this paper, and the delay of an electronic gate has been synchronized to the transducer motion to improve detectability of a tight interface crack in a tensile specimen.
Abstract: Signal averaging has been used to improve the clarity of flaw indications in an electron beam weld. The delay of an electronic gate has been synchronized to the transducer motion to improve the detectability of a tight interface crack in a tensile specimen. Cross-correlation techniques and multiple transducer arrays have been used to improve the signal-to-noise ratio of artificial flaws in welded panels. Signal averaging has been used to reduce random noise in the through-transmission ultrasonic inspection of a honeycomb composite. Megacycle range ultrasonic flaw information has been recorded on a low frequency FM tape recorder by rapidly sweeping an electronic gate through the time interval of interest. A lock-in amplifier has been used to produce quantitative data in both single-coil and double-coil eddy current systems. Cross-correlation techniques and a multiple-coil eddy current probe have been used to reduce surface roughness noise in an eddy current crack detection system.

16 citations


Journal ArticleDOI
TL;DR: Common mode rejection is viewed as a general technique that can be used in certain biological recording situations to increase the signal to noise ratio, in which the noise component is of biological rather than electrical origin.
Abstract: Common mode rejection is viewed as a general technique that can be used in certain biological recording situations to increase the signal to noise ratio, in which the noise component is of biological rather than electrical origin. The recording of conjugate eye movements during sleep is cited as an example.

13 citations


Patent
28 Nov 1975
TL;DR: In this article, an apparatus for automatic measurement of the video signalto-noise ratio in a television channel comprises a video signal pre-processing unit, the inputs thereof being connected to the outputs of a unit measuring the peak-to-peak amplitude of the signal, a sync separator and a control unit respectively.
Abstract: An apparatus for automatic measurement of the video signal-to-noise ratio in a television channel comprises a video signal pre-processing unit, the inputs thereof being connected to the outputs of a unit measuring the peak-to-peak amplitude of the video signal, a sync separator and a control unit respectively. Another output of the sync separator is connected to a series combination of the following units controlled by the control unit; a short pulse shaper, a pulse-amplitude modulator, a switch, a pulse stretcher, a means for converting the pulse amplitude to a number of pulses, a means for producing the differences between samples, an analyzer of the differences between samples, a digital function generator and a digital display. The output of the means for producing the differences between samples is connected to one of the inputs of the unit measuring the peak-to-peak amplitude of the video signal, another input of which is coupled by way of the video signal pre-processing unit to the input of the pulse-amplitude modulator, another output of the unit measuring the peak-to-peak amplitude of the video signal being connected to one in the inputs of the switch.

13 citations


Journal ArticleDOI
TL;DR: In this paper, the theory of the process is discussed and the parameters affecting the quantum efficiencies of the detective quantum process are discussed, as well as its application in the nuclear track emulsion process.
Abstract: Methods of recording photoelectron images in nuclear track emulsions ('eleclronographi) arc descrtbeo. anO the theory of the process is discussed. Parameters affecting the detective quantum efficie...

10 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the character and magnitude of spontaneous electrical field noise recorded in Spain and Holland (1973) and the correlation between simultaneous recorded data at different locations form the subject of this paper.
Abstract: Variations of the spontaneous electrical field appear to be a fundamental noise in geoelectrical resistivity surveying, irrespective of the origin of these variations. The signal-to-noise ratio can decrease to such an extent that investigations to large depths are impossible in some regions. Description of the character and magnitude of the noise recorded in Spain and Holland (1973) and the correlation between simultaneous recorded data at different locations form the subject of this paper.

10 citations



Journal ArticleDOI
01 Jan 1975
TL;DR: In this paper, an estimation-detection scheme for the estimation of signals with unknown parameters is proposed, where two sets of bounds are used to determine two regions of signal uncertainty and different linear estimators are used for each region.
Abstract: An estimation-detection scheme is proposed for the estimation of signals with unknown parameters. The scheme is illustrated by considering the case of a signal with unknown but bounded variance. Two sets of bounds are used to determine two regions of signal uncertainty, and different linear estimators are used for each region. A detector is then used to select the appropriate estimator. Since no a priori information is assumed on the unknown parameters a weighted minimax criterion is used to optimize the detector and the estimators.

Patent
15 Dec 1975
TL;DR: In this paper, a radio receiver squelch circuit responds to an IF carrier modulated by any of AM voice, AM pulse, CW, interrupted CW, or angle modulated signals.
Abstract: A radio receiver squelch circuit responds to an IF carrier modulated by any of AM voice, AM pulse, CW, interrupted CW, or angle modulated signals. After the IF carrier is amplitude normalized it is supplied to a network for deriving a D.C. voltage having an amplitude indicative of the signal to noise level of the normalized IF. The signal to noise level indicating circuit includes a detector for deriving a waveform that is a replica of the envelope of the normalized IF. In response to the envelope amplitude being above a predetermined threshold level, indicative of the presence of a signal, a capacitor is discharged by a constant current source. In response to the envelope being below the predetermined level for an initial predetermined time, the capacitor is charged by a constant current source. In response to the envelope amplitude being below the predetermined level for in excess of the initial predetermined time, the capacitor is charged by a much smaller current. Thereby, the capacitor voltage level is indicative of the signal to noise ratio of the IF signal. The voltage across the capacitor is monitored with an amplitude comparison including amplitude hysteresis to derive a squelch control signal.

01 Feb 1975
TL;DR: In this article, the authors derived the properties of an N-weight adaptive line enhancer for a single stable input spectral line in both an arbitrary and a white noise background, and discussed the fundamental properties of the adaptive line-enhancer.
Abstract: : The adaptive line enhancer is a new device with unique capabilities. The device has significant applications in the enhancement of narrowband spectral lines in a broadband noise field when there is a poor signal-to-noise ratio at the input and there is insufficient a priori information on which to design appropriate filters. The device automatically filters out the components of the signal which are uncorrelated in time and passes the correlated portions. Since the properties of the device are determined solely by the input signal statistics, the properties of the filter automatically adjust to variations in the input signal statistics to obtain the LMS approximation to a Weiner-Hopf filter. The device will thus track slowly varying spectral lines in broadband noise. This paper derives the properties of an N-weight adaptive line enhancer for a single stable input spectral line in both an arbitrary and a white noise background. The fundamental properties of the adaptive line enhancer are discussed in terms of these solutions. (Author)

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the use of calculation and analysing methods to enable the detection of signal and background noise, as well as the determination of the sources of emission.
Abstract: Die Anwendung der Schallemissionsanalyse zur zerstorungsfreien Prufung von Bauteilen leidet im Betrieb stark unter ungunstigen Signal-Rauschverhaltnissen, so das eine Auffindung der Signale und eine Ermittlung des Schallquellenortes nur mit hohen Ungenauigkeiten moglich ist. Fur diesen Fall werden die Einsatzmoglichkeiten von Rechen- und Analysenverfahren untersucht, die eine Trennung von Nutzsignal und Storgerauschen zum Ziel haben. Acoustic Emission Signal Analysis. Application of acoustic emission analysis in practice is often limited by a high signal to noise ratio. The detection of the signals and the location of the AE-sources can be done only with low accuracy under these conditions. For this reason the use of calculation and analysing methods is being investigated enable differentiation of signal and background noise, as well as the determination of the sources of emission.

ReportDOI
24 Jul 1975
TL;DR: Derivations and programs are presented for evaluation of the required input signal-to-noise ratio for specified output performance of a Greatest-Of- device followed by an integrator, as a function of N, the number of channels in the Greatest- of; M, thenumber of independent samples in the integrator; P sub F, the false alarm probability; and P sub D, the detection probability.
Abstract: : Derivations and programs are presented for evaluation of the required input signal-to-noise ratio for specified output performance of a Greatest-Of- device followed by an integrator, as a function of: N, the number of channels in the Greatest-Of; M, the number of independent samples in the integrator; P sub F, the false alarm probability; and P sub D, the detection probability. Several numerical examples are presented, for the special case of P sub D = 0.5.

Journal ArticleDOI
TL;DR: A neural model is proposed in this paper which produces improved signal-to-noise ratio (SNR) at detector interneurons over the SNR in the photoreceptors and is compatible with known anatomy and physiology in the locust visual system.
Abstract: The descending contralateral movement detector (DCMD) neurons in locusts have been used in studies of limiting spatial resolution of moving, striped objects. The results of such studies have been controversial; one group of workers claiming resolution to below a 0.3° stripe period (Burtt and Catton, 1962, 1969; Northrop, 1974; Grossman and Northrop, 1974), while another group (Palka and Pinter, 1974) not finding significant responses below a 1.5° period when an extremely precise pattern was used. The latter group has justified their experimental findings using classical optical theory which treats the receptor and its dioptic apparatus as a simple convex lens with a 33 μm pupil. It is argued in this paper that this is an oversimplification of this system, and that the best model for the dioptrics of a retinula cell is given by its directional sensitivity function (DSF) which is in effect the spatial impulse response of the in vivo system which relates effective absorbed light intensity to the angular position of a point source. A neural model is proposed in this paper which produces improved signal-to-noise ratio (SNR) at detector interneurons over the SNR in the photoreceptors. The model offers noise reduction from averaging at multisynaptic signal transmission points (Laughlin, 1973), and contrast improvement from multiplicative signal processing (MSP). A numerical example is given to illustrate the plausibility of the model, using reasonable values for known and assumed parameters. The model is compatible with known anatomy and physiology in the locust visual system. However, the existance of a presumed exponential synaptic transfer characteristic and operation of the MSP system in vivo remain to be verified experimentally.


Journal ArticleDOI
TL;DR: In this article, the authors used a multiple pass system which allows to gain a factor of approximately 100 in intensity for Rayleigh scattering experiments on the Tokamak plasmas.
Abstract: In order to overcome the low power of c.w. visible lasers, which prevents their utilization for c.w. Thomson scattering, the authors have used a multiple pass system which allows to gain a factor of approximately 100 in intensity. This system has been tested in a Rayleigh scattering experiment. It is concluded that at present a c.w. Thomson scattering experiment on Tokamak plasmas would have a signal to noise ratio of the order of a few units. Although a small signal to noise ratio could be acceptable in order to measure the electron density, a measurement of the electron temperature will presumably have to wait for a considerable increase in available c.w. power.

Journal ArticleDOI
TL;DR: A scheme is presented which has the capability of detecting fast, swept-frequency transient signals in the presence of many varieties of disturbances within the frequency range of the sweep and with a Blight modification incorporated in the circuit realization.
Abstract: Of several techniques currently available for recognition of swept-frequency transient signals, most are limited fundamentally in their ability to detect signals with high normalized sweep rates (e.g. 100 sec-1 and up‡), and immersed in a noisy environment. Furthermore, common techniques incorporating Phase Lock Loops (PLL) and Voltage Tunable Filters (VTF) are not inherently noise immune and are easily unlocked by noise of various types. A scheme is presented which has the capability of detecting fast, swept-frequency transient signals in the presence of many varieties of disturbances within the frequency range of the sweep. The disturbances tolerated being not completely without restriction, can be characterized by the relationship of their power spectra to factors including filter bandwidths and resonant frequencies, signal sweep rate, and signal to noise ratio. With a Blight modification incorporated in the circuit realization, the detection scheme is able to cope with swept signals of continuously va...

Patent
27 Nov 1975
TL;DR: In this paper, the antenna rod is broken into two parts (1, 2) and a matching circuit (A) connected into the gap between parts, and a transistor (T) is connected after the matching circuit.
Abstract: The transistorised receive antenna has its rod broken into two parts (1, 2) and a matching circuit (A) connected into the gap between parts A transistor (T) is connected after the matching circuit The matching circuit transforms the antenna's impedance at the gap such that the impedance at the matching circuit's output is equal to the impedance that gives the best signal to noise ratio at the output of the transistor The antenna is broken at a point that makes the antenna's impedance at this break the closest approximate to the best possible receive power for the transistor

01 Sep 1975
TL;DR: The objective of this study is to determine reasonable S/I ratios for high frequency audio modulation (HF AM) Navy Tactical communications, to compare these ratios with current International Frequency Registration Board (IFRB) specifications, and to determine the effects of modifying the SIR's.
Abstract: : The objectives of this study are to determine reasonable S/I ratios for high frequency audio modulation (HF AM) Navy Tactical communications, to compare these ratios with current International Frequency Registration Board (IFRB) specifications, and to determine the effects of modifying the SIR's. The approach taken was to develop a mathematical model capable of relating signal, noise, interference and probability of achieving required Signal-to-Noise Ratios (SNR's) and Signal-to-interference Ratios (SIR's).



Proceedings ArticleDOI
01 Feb 1975
TL;DR: In this article, the ability of the eye to perceived tail in images is a complex function of image contrast, brightness and noise, and it is concluded that increased resolution capability and displays having greater dynamic range are needed to improve the ability to see fine image detail at low con- trast in characteristically noisy x-ray images.
Abstract: Summary The ability of the eye to perceivedetail in images is a complex function of image contrast, brightness and noise. Image amplifiers can remove the brightness limita-tion but noise sets the final limit on per-formance which can be obtained with weak signals. The manner in which weak signalnoise limits the performance of imaging sys- tems is reviewed. Image amplifier gains required to remove the masking effect ofadditive amplifier noise is calculated as function of image contrast. Finally, thelimitations of finite system aperture re- sponse on overall performance is described. It is concluded that increased resolutioncapability and displays having greaterdynamic range are needed to improve theability to see fine image detail at low con- trast in characteristically noisy x -rayimages.Introduction The formation of images from radiationpatterns involves a noisy process. Thequantum nature of all radiation results indiscontinuities in power flow which producesrandom variations in local area intensity orbrightness which can and will produce noisy

Journal Article
TL;DR: This thesis investigates the problem of automatic transcription of the morse signal, and describes and documents several approaches to filtering, processing, and decoding it for transcription.
Abstract: : This thesis investigates the problem of automatic transcription of the morse signal, and describes and documents several approaches to filtering, processing, and decoding it for transcription. The baseband signal is first modeled as a modified random telegraph wave. A discrete Kalman filter and a linear smoother are then used to process the demodulated signal in order to gain a measure of the effectiveness and applicability of this model. It is shown experimentally that this model and processing yield a significant reduction in the transcription error rate. Next, a Viterbi decoder algorithm based on a simple Markov model of the code is programmed and tested. Finally, the baseband signal model is incorporated in a more general model for pre-detection Kalman filtering. It is shown that this filter permits acceptable recovery of morse signals whose average signal-to-noise ratio is as low as -14 dB in a 2 kHz bandwidth.

Journal ArticleDOI
TL;DR: In this article, a system for detection of gravitational radiation is proposed which consists of a widely-separated pair of drag-free satellites, which can be detected by a Doppler-ranging system.

Journal ArticleDOI
TL;DR: A method for designing and predicting the performance of large aperture sensors is described, modeling the sensor as an elementary optical system combined with a focal plane consisting of many discrete detectors and some of the signal processing.
Abstract: A method for designing and predicting the performance of large aperture sensors is described. The sensor is modeled as an elementary optical system combined with a focal plane consisting of many discrete detectors. The output signals of the detectors are filtered and combined to compute signal-to-noise ratio and to estimate centroiding (target location) error. The dependence of these two performance criteria upon major design parameters is described. The quantum efficiency of the detectors is a critical factor. Optical aperture is also a major factor in design, but lack of a cost function for optical subsystems is a drawback. It is possible to design an optimal focal plane layout for given detector and optics models. The electrical filter is optimized separately. Centroiding error in the crossscan direction depends in an interesting way upon the focal plane layout. Two mathe-matical appendices describe the sensor as a linear, time-invariant system and some of the signal processing.

Proceedings ArticleDOI
02 Jun 1975

Book ChapterDOI
01 Jan 1975
TL;DR: It is stating the obvious to say that no single device and/or image processing system can satisfy all of these desires for a better image simultaneously.
Abstract: The astronomical community has been involved in image processing for centuries. We have gone through a series of levels of sophostication in our image processing using the unaided eye, telescopes, photographic plates, image intensifiers, television type sensors and computers. All of these devices have been developed and used in order to obtain a “better” image. For each of us the word “better” has had many meanings. For example; higher spatial resolution, fainter limiting magnitude, higher signal to noise ratio, greater dynamic range, more uniform photometric response, greater spectral response, etc. It is stating the obvious to say that no single device and/or image processing system can satisfy all of these desires for a better image simultaneously.