Showing papers on "Signal-to-noise ratio published in 1976"

The generalized correlation method for estimation of time delay

Abstract: A maximum likelihood (ML) estimator is developed for determining time delay between signals received at two spatially separated sensors in the presence of uncorrelated noise. This ML estimator can be realized as a pair of receiver prefilters followed by a cross correlator. The time argument at which the correlator achieves a maximum is the delay estimate. The ML estimator is compared with several other proposed processors of similar form. Under certain conditions the ML estimator is shown to be identical to one proposed by Hannan and Thomson [10] and MacDonald and Schultheiss [21]. Qualitatively, the role of the prefilters is to accentuate the signal passed to the correlator at frequencies for which the signal-to-noise (S/N) ratio is highest and, simultaneously, to suppress the noise power. The same type of prefiltering is provided by the generalized Eckart filter, which maximizes the S/N ratio of the correlator output. For low S/N ratio, the ML estimator is shown to be equivalent to Eckart prefiltering.

Angle Estimation with Adaptive Arrays in External Noise Fields

Abstract: A method of estimating the angle of arrival of a signal at an array of sensors in an external noise environment is outlined. The development is based on a maximum likelihood estimator and leads naturally to adaptive sum and difference beams which null the external noise sources. An algorithm for estimating angle of arrival, based on the outputs of adaptively distorted sum and differnce beams, is shown to perform well in the presence of sidelobe and/or main beam interference.

Static Performance Model for Thermal Imaging Systems

Abstract: Performance models can be used to design systems to meet specific applications, evaluate competitive designs, or direct research into areas of potentially large payoffs in system performance. This paper presents a validated performance model for thermal imaging devices, where performance is defined as static (non-time varying) detection, recognition and identification as a function of target range. The target, atmosphere, device, and subjective observer behavior are described by mathematical equations which result in predictions of system noise equivalent temperature, minimum resolvable temperature and minimum detectable temperature. Detection, recognition, and identification are then based on these quantities through experimentally determined algorithms using required signal-to-noise ratio and subjective resolution.

Time delay estimation

Abstract: A maximum likelihood (ML) estimator is derived for determining time delay between two signals observed in the presence of uncorrelated noise, under the assumptions of known signal and noise spectral characteristics. This ML estimator can be realized as a pair of receiver prefilters followed by a cross correlator. The time argument at which the correlator achieves a maximum is the delay estimate. Qualitatively, the role of the prefilters is to weight the signal passed to the correlator according to the strength of the coherence function. Other realizations of the ML processor are also discussed. The variance of a generalized correlation time delay estimator is derived when the estimate is in the neighborhood of the true delay. An example using these results is given with emphasis on the effect of erroneously specifying the frequency weighting to be employed. Limitations of the derived results are also discussed.

A Feedback Receive Amplifier for Optical Transmission Systems

Abstract: We consider the design and implementation of a lownoise feedback receive amplifier for use in optical communication systems. The feedback amplifier configuration is advantageous in that it offers a wide bandwidth with good signal to noise ratio.

Data-gathering device for scanning data having a variable amplitude modulation and signal to noise ratio

Abstract: A light pen is scanned across a bar coded label to produce a reflected light signal having a modulated intensity. The average peak-to-peak value of the plus and minus peaks of the return signal is continuously generated to provide a reference for detecting each subsequent positive and negative transistion. The instantaneous average peak-to-peak reference permits the positive transistions to be distinguished from the negative transistions in spite of large deviations in the amplitude modulation and large shifts in the signal to ambient light level ratio of the return signal. Initially the light pen is operated in a low power pulsed mode. The initial transistions in the return signal cause the pen to temporarily illuminate the bar coded label with a continuous light, and activate plus and minus peak detectors.

The design and operation of practical charge-transfer transversal filters

Abstract: Some of the design considerations for charge-transfer split-electrode transversal filters are discussed. Clock frequency, filter length, and chip area are important design parameters. The relationship of these parameters to filter performance and accuracy is described. Both random and tap weight quantization errors are considered, and the optimum filter length is related to tap weight error. A parallel charge-transfer channel, which balances both capacitance and background charge, and a coupling diffusion between split electrodes greatly improves accuracy. A one-phase clock is used to simplify the readout circuitry. Two off-chip readout circuits are described, and the performance of two low-pass filters using these readout circuits is given. Signal to noise ratios of 90 dB/kHz and an overall linearity of 60 dB have been achieved with this readout circuitry.

Signal-to-noise ratio and smallest detectable vibration amplitude in frequency-translated holography: an analysis

Abstract: The theoretical and experimental analysis of SNR in frequency-translated holography that is applied to the detection of small vibration amplitude is presented in this paper. The feature of the experiments lies on the usage of acoustic surface waves as the vibrating test object, since the acoustic surface waves give the reliable vibration amplitude and the easiness of the measurement of SNR. Furthermore the detectable smallest amplitude is estimated as 2.7 × 10−4 λ, which is several tenths smaller than the previously presented estimations, and the dependences of the detectable smallest vibration amplitude on the experimental arrangements are also made clear.

Likelihood ratios for signals in additive white noise

Abstract: We present a formula for likelihood functionals for signals in which the corrupting noise is modelled as white noise rather than the usual Wiener process. The main difference is the appearance of an additional term corresponding to the conditional mean square error. By way of one application we consider the ‘order-disorder’ problem of Shiryayev.

Semiconductor optical image sensing device

Abstract: A semiconductor optical image sensing device having a signal line connected to the drain electrodes of MOS field effect transistors each corresponding to a picture element, wherein the source electrodes of the MOS field effect transistors are connected to photo-diodes, capacitors of MOS structures are connected between the gate electrodes of the MOS field effect transistors and a noise line, and the signal line and the noise line are connected to input terminals of a differential amplifier. The capacitors of MOS structures are formed in the same way as the gates and drains of the MOS field effect transistors. By applying a scanning pulse to the gate electrodes of the MOS field effect transistors to scan the MOS field effect transistors for switching the same, a signal output and a noise output are produced from the signal line while another noise output is produced from the noise line. The signal to noise ratio can be enhanced by producing only the signal output from the differential amplifier.

Electronic optical transfer function analyzer

Abstract: An electronic optical analyzer for use in systems such as optical transfer function analyzers eliminates mechanical scanning systems and comprises entirely electronic image dissection means for dissecting an image transmitted by an optical system under test and producing an electric output signal representative of the beam intensity at a selected element of the image. The image dissection means is preferably (in the case of visible light) an image dissector tube whose positioning coils serve as an image element addressing means. The system is useable with any optical system including visible light, other electromagnetic radiation or charged particles (ions or electrons) so long as the image dissection means is responsive to the beam in question. The optical system under test must produce a real image at the image dissection surface of the image dissection means in order for readily evaluatable data to be obtained. The entire system is preferably computer controlled in order to obtain the necessary data quickly and accurately and to calculate the optical transfer function of the optical system under test on line. With this system both the modulation transfer function and the phase transfer function may be calculated. The digital computer can control the analyzer in any of several modes such as single scan, multiple scan with averaging of values to improve the signal to noise ratio and pass/fail production testing. output from the computer can be in any of several forms, such as displays on display devices, printouts or process control commands such as accept/reject commands in production testing.

On noise in digital recording

Abstract: A set of rules, equations and relations are given for the effects of coherent and statistical noise on digital recorders. Simple formulas, intended for laboratory use, are given for the change in signal to noise ratio (SNR) caused by the channel. Bit error probability is related to SNR and channel parameters for the zero-crossing detector channels typical of digital computer disk and tape recorders, and many digital instrumentation recorders. Valid and invalid ways to calculate error rate statistics are discussed for situations where bit errors are correlated, i.e. not statistically independent.

System for inspecting can lids for through the lid flaws

Abstract: A method for detecting light passing flaws in discrete elements, which are normally opaque to visible light, characterized by a sampling technique to enhance the signal to noise ratio of the ultimate signal. The ultimate signal is a composite signal generated by the addition of a number of discrete sample signals, each signal representing both a repeating reaction of a photosensitive means to light passing through flaws in the normally opaque element, and random ambient signal noise.

Processing of two noise contaminated, substantially identical signals to improve signal-to-noise ratio

Abstract: When two substantially identical signals contaminated by uncorrelated noise are received over two channels, combining of the contaminated signals in a linear manner results in a maximum signal-to-noise ratio improvement of 3 dB. The present disclosure relates to combining such contaminated signals through a process whose parameters vary as short time functions of the signal and noise powers in each channel. This processing produces a signal-to-noise ratio improvement which is greater than that achievable through linear processing.

Properties of Low Precision Analog-to-Digital Converters

Abstract: The problem of quantization and saturation noise introduced by the process of analog-to-digital conversion is addressed. Analog-to-digital converters (ADC) with even versus odd numbers of output states are compared. Expressions are derived and evaluated which yield the signal-to-noise ratio and the gain versus signal level input when the input signal has an assumed Gaussian probability density. The results presented should have application in all fields in which digital signal processing is performed.

Comparison of NVL model and four contractor models for Minimum Resolvable Temperature (MRT)

Abstract: : A comparison among MRT models for thermal systems is made Four IR contractor models are compared to the NVL model Basic assumptions and subjective parameter choices are examined and the differences are shown Validation of the NVL model is documented against eight parallel and serial- scanned systems

Computer program for fast Karhunen Loeve transform algorithm

Abstract: The fast KL transform algorithm was applied for data compression of a set of four ERTS multispectral images and its performance was compared with other techniques previously studied on the same image data. The performance criteria used here are mean square error and signal to noise ratio. The results obtained show a superior performance of the fast KL transform coding algorithm on the data set used with respect to the above stated perfomance criteria. A summary of the results is given in Chapter I and details of comparisons and discussion on conclusions are given in Chapter IV.

In-band signal-to-noise ratio monitor for an FSK relaying system

Abstract: An improved in-band signal-to-noise ratio monitor is used in conjunction with the receiver of an FSK relaying system. The improved monitor measures the signal-to-noise ratio both prior to and after the receiver input signal is filtered by a narrow bandpass filter. The magnitudes of the measured ratios are compared and, if all signal-to-noise ratio permissives are not satisfied, the tripping function of the relaying system at the receiver or local station is blocked or inhibited.

Multiple image storage using a crossed grating

Abstract: We describe a method of storing a number of real amplitude images on a photographic plate by modulating each image on a different spatial carrier. The signal to be stored is placed in contact with a grid (2 crossed gratings) and this ensemble is imaged on a photographic plate. By choosing a different pair of diffracted orders of the grid, each signal is coded on a different fringe system. The grid remains stationary throughout the operation of storage. Upto eight images have been stored. The signal to noise ratio is calculated and the results are given.

Combined use of a lock-in detector and a multichannel analyser for 1/f noise application to tunneling spectroscopy

Abstract: Obtaining a good signal-to-noise ratio (S/N) is of great importance in tunneling spectroscopy, as it has often led to the discovery of new phenomena. The quantities of interest are the derivatives of the tunnel junction I-V curve ; the usual approach to obtain these characteristics is to apply a modulation voltage around a D. C. bias and to detect the proper harmonic with a lock-in detector. In order to improve the S/N ratio, one would think of increasing the detector time-constant (and total sweep time), but experimentalists know that, above a few seconds, such an increase is illusive and even misleading. This is because there are low frequency instabilities in the equipment, but also because there is noise present in the junction characteristic itself. The combined use of a lock-in detector and a multichannel analyser is proposed, in order to average a large number (n) of short sweeps instead of using one single long sweep. The S/N ratio is calculated for such an experiment, and it is found that it depends strongly upon the noise spectral density. For a 1/f spectrum a large improvement (n) is obtained with respect to the usual method, for the same total experimental duration. A system for adapting a commercial multichannel to the plotting of junction characteristics is described, and experiments are performed that demonstrate the advantages of this method. In conclusion, it is emphasized that the limit of the possible improvement of the S/N ratio in tunneling spectroscopy is removed and that the system can be applied to many other types of spectroscopy.

A CCD integrated circuit for transient recorders

Abstract: A 50 MHz CCD integrated circuit is described that has been developed for use in transient analog signal recorders to sample and time expand transient signals. The integrated circuit achieves an effective 200 MHz sample rate by using four 32 stage peristaltic CCDs to sample the transient signal four times each clock period. Dual frequency, 4phi clocking is used to sample and time expand the sampled data. The output signals of the four CCDs are multiplexed on-chip into a single low frequency output data line. When operated with 50 MHz/165 KHz 4phi clocks, this circuit has a 200 MHz sample rate, a record length of 640 nanoseconds, a time expansion factor of 303, and overall signal to noise ratio of 40:1. The signal to noise ratio is limited by fixed pattern noise of the four CCDs.

Spatial interfrequency correlation effects in a surface‐scatter channel

Abstract: The effect of spatial separation on the cross correlation between the system response functions for a two‐receiver surface‐scatter channel is investigated. The system response at the two receivers is determined for all possible pairs of frequencies. The analysis assumes relatively close separation of receivers and uses the Fresnel‐corrected model for surface scatter in the specular direction. The surface is assumed to be Gaussian, with typical size of boundary deformations small compared to typical Fresnel zones.The analysis shows that the correlation is approximately maximum for zero‐frequency separation and drops off at a rate determined by the reverberation time. For small reverberation times and small grazing angles correlation may extend over fairly large values of frequency difference. The effect of spatial separation is generally a reduction in correlation and a more rapid decrease of correlation with frequency, but this can be compensated to some extent by time shift between the two system respons...

Optimization of recursive cascade filters

Abstract: The optimum design of recursive digital filters in the cascade realization with respect to the output noise is healed here by taking into account the ordering, the pole-zero pairing, and the selection of configurations of the individual sections. In the first part of this paper, the output noise variances are derived for arbitrary realized cascaded configuration employing either the fixed-point or the floating-point arithmetics. The second part presents a simple algorithm to compute the output noise variance without direct evalution of complex integral. An example is presented in which the individual sections are allowed to take on different configurations.

A CCD integrated circuit for transient recorders

Abstract: A 50 MHz CCD integrated circuit is described that was developed for use in transient analog signal recorders to sample and time expand transient signals. The integrated circuit achieves an effective 200 MHz sample rate by using four 32 stage peristaltic CCDs to sample the transient signal four times each clock period. Dual frequency, 4 phi clocking is used to sample and time expand the sampled data. The output signals of the four CCDs are multiplexed on chip into a single low frequency output data line. When operated with 50 MHz/165 KHz 4 phi clocks, this circuit has a 200 MHz sample rate, a record length of 640 nanoseconds, a time expansion factor of 303, and overall signal to noise ratio of 40:1. The signal to noise ratio is limited by fixed pattern noise of the four CCDs.

Fourier Infrared Spectroscopy Of Transients

Abstract: With the realization of simultaneous temporal and spectral multiplexing in the infrared using Fourier Transform Spectrometers, it is possible to study entirely new classes of problems which were not generally accessible to infrared techniques before. Now it is possible to simultaneously obtain high spectral resolution and realize spectral signal to noise normally associated with spectrally multiplexed systems on transient samples whose lifetimes are orders of magnitude shorter than the time required to collect one interferogram. Results of time resolved spectral studies are presented with a discussion of the gains in signal to noise one realizes over rapid scan devices.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Postfiltering in Digital Beamformers

Abstract: Assuming a sinusoidal signal superimposed on a narrow-band Gaussian noise as the input to a receiving array, the output power and signal-to-noise ratio of a digital beamformer with postfiltering were formulated so that subsequent calculations could be made without an analysis in the frequency domain. The formulation utilized the quantizer functions previously given by the author and certain spectral power distribution factors originally attributed to Davenport but more rigorously derived and discussed in the present work. A numerical study based on this formulation for a DIMUS array in a correlated noise field reveals that except for certain rare circumstances, postfiltering generally improves the output SNR or array gain. It is demonstrated that the amount of postfiltering gain not only varies with array input SNR but also depends strongly upon the spacing-to-wavelength ratio, and its meaningful interpretation can only be made in conjunction with both the clipping and noise correlation losses. In particular, balancing postfiltering gain against the two losses suggests that receiving arrays with element spacings smaller than one-half of the operating wavelength may be used to the advantage of system design under certain conditions.

Noise reduction in SEM video signals

Abstract: Linear filtering methods of noise reduction in SEM video signals are discussed. It is shown that time-averaging filters distort and corrupt the signal to obtain optimum signal to noise ratio. Ensemble averaging filters are demonstrated as the better, since no signal distortion occurs. Two types of ensemble averaging filters suitable for the SEM are discussed and experimental results in the form of line-scans are presented.

A solid state detector for a modulation excitation spectrophotometer

Abstract: It is shown that a PIN silicon photodiode gives a superior signal to noise ratio when used as the detector in a modulation excitation spectrophotometer as compared with a photomultiplier. Other advantages of the PIN diode are discussed.