Showing papers on "Signal-to-noise ratio published in 1980"

Frequency domain data transmission using reduced computational complexity algorithms

Abstract: In this paper we describe a frequency domain data transmission method to be used for digital data transmission over analog telephone lines which exploits recently derived reduced computational complexity algorithms, such as the Winograd Fourier Transform, to achieve a significantly lower computational rate than comparable time domain QAM modems implemented digitally using signal processing techniques. In addition to the lower computational rate, the proposed method also allows for better channel bandwidth utilization by allowing optimal signal power allocation based on the channel's signal to noise versus frequency characteristics. Experimental results on this method are presented, indicating that it may be possible to send over 10,000 BPS over an unconditioned telephone line while maintaining a 10-5BER.

A Computer Model For Underwater Camera Systems

Abstract: A computer model is presented which allows the image components of an underwater camera system to be computed. Input parameters to the model are system geometry, source properties, and water optical properties. Output products are the irradiances due to non scattered object light, scattered object light and backscattered light. From these basic quantities other useful parameters such as contrast transmittances and signal to noise ratio can be calculated over the entire field of view of the camera. Sample calculations are presented.

Data-adaptive principal component signal processing

Abstract: Principal component (eigenvalue-eigenvector) analysis is applied to processing of narrow band signals in noise. The amount of data available is assumed to be limited. Principal eigenvalues and eigenvectors of a sample correlation matrix are used to improve the signal to noise ratio (SNR) in the data and to increase the resolution capability of nonlinear least squares at low SNR and linear prediction based frequency estimation methods. Relation to Pronylike methods is explored. Performance of different methods is compared experimentally among themselves and to the Cramer-Rao (CR) bound.

Transcutaneous Blood Flow Measurements Using Pseudorandom Noise Doppler System

Abstract: In order to obviate the limitations of the conventional coherent ultrasonic Doppler flowmeters we have developed a new device. In this apparatus the continuous wave is replaced by a pseudorandom signal. We show, both theoretically (Waag et al. [12]) and experimentally, that the pseudorandom system offers advantages. The most important result concerns the improvement of the signal-to-noise ratio which can be as large as 20 dB. Furthermore, it is possible to decrease the frequency and the distance ambiguity by a factor of two. Compared to the "random noise flowmeter" (Newhouse et al. [7], Jethwa et al. [5]) our system measures flow near the wall of vessels or in ultrasonic field in which there are important fixed echoes. To illustrate the feasibility of this new device, we show some results obtained by the transcutaneous method.

Integrated Optic Spectrum Analyzer

Abstract: This paper describes the integrated-optic implementation of a Bragg spectrum analyzer that employs the interaction between a coherent optical guided wave and a surface acoustic wave to determine the power spectral density of the input. The integrated-optic spectrum analyzer consists of an injection laser diode, a thin-film optical waveguide, waveguide lenses, a surface-acoustic-wave transducer, and a linear detector array with CCD readout. Design principles are given for selecting component parameters such as optical beam width, detector cell size, lens aperture and focal length, and acoustic transducer design so as to obtain specific rf resolution, spurious level, and signal-to-noise ratio. Design parameters are presented for a 750- to 1250-MHz spectrum analyzer with a resolution of 4 MHz and a 40-dB dynamic range. Also described in the paper is the development of state-of-the-art component technology for the spectrum analyzer.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Infrared detector system

Abstract: An improved infrared detector system includes a pair of thin film thermopile sensing elements that receives reflected energy from aspheric reflectors that are designed to provide optimum energy resolution. An absorbing coating can be placed above the sensors and extending beyond the periphery to improve the signal to noise ratio. A high gain low noise D.C. amplifier is coupled to the output of the infrared sensing elements while a high pass amplifier and low pass amplifier are designed to pass an amplified signal in the frequency range from approximately 0.2 Hz to 15 Hz. Finally, a combined peak detector and time dependent integrator summing amplifier circuit provides an enabling predetermined threshhold detection gate that requires either a predetermined large signal level or a multiple of small electrical signals within a preselected interval to produce an alarm enabling signal.

Estimation of the signal‐to‐noise ratio of seismic data with an application to stacking*

Abstract: The amplitude of the signal and the energy of the noise on each of at least three traces can be estimated provided that the signal has the same form (but not necessarily the same amplitude) on these traces and that the noise on any trace is correlated with neither the signal nor the noise on any other trace. This estimation of signal amplitude and noise energy can be achieved by a rather simple algorithm. The accuracy of the estimate depends, of course, on the degree to which the assumption that signal and noise on the different traces are mutually uncorrelated is actually met. The accuracy tends to improve with increasing number of traces.

Film Grain Noise In Partially Coherent Imaging

Abstract: Optical image formation (and processing) is strongly affected by film grain noise. The noise effects depend on the spatial coherence of the illumination. In this paper we shall analyze these phenomena in the case of Kohler illumination. The effective transmittance of any photographic image is instrument dependent due to diffusion by the grain (Callier effect). Thus the question arises: what is the meaningful physical quantity in image formation? The Callier effect directly influences the contrast of weak modulations, which happens to be maximum in symmetric partially coherent illumination. Ultimately, the detection of weak modulations is not limited by the contrast but by the signal-to-noise ratio. Using reasonable statistical assumptions for the noise behavior, the optimal conditions for weak modula-tion detection will be discussed. This study is primarily devoted to imaging problems, but its results may be partly extended to double-slit microdensitometry. In that case, however, the illumination setup makes the complete study more difficult than in the Kohler illumination case.

Perceptual Coding In The Cosine Transform Domain

Abstract: Source encoding for digital image transmission is revisited with an energy distribution approach in the perceptual domain. Past investigations have utilized power spectral density in conjunction with the Frei eye model and full image Fourier transform coding. In this investigation, the cosine transform is utilized on a partitioned image. A cosine energy function is defined and weighted by the eye model. This results in a circular symmetric form of a bit map which simplifies source coding. This approach outperforms a standard bit allocation procedure allowing graceful degradation at 1, .75, and .5 bits/pixel. Analysis includes the perceptual mean square error and peak signal-to-noise ratio as metrics of performance. This procedure suggests a more rapid hardware implementation.

Phase-slipped time delay and integration scanning system

Abstract: A scanning system wherein a linear array of N detector elements having a form spacing of X cm between their centers is oriented parallel to the line scan dimension of a raster so that each element of the array optically scans the entire field of view at a rate of V cm. per second. The detector elements are sampled every t s seconds where ##EQU1## k being an integer, and each produces, when sampled, an output signal proportional to the integrated energy exposure thereof between samplings. The output signals of the various detector elements are delayed as a function of each element's position within the array and the line scan rate. The delayed imaging signals add to provide an improved signal to noise ratio. The variability of the waveform of the composite output signal for smallsized distant targets is minimized by introducing a progressively increasing phase shift in the relative timing of the sampling signals and initial contact of the image at successive detector elements. The composite output signal of the array then corresponds to an average over all possible relative timings of sampling signals and initial contact of the image at a detector element.

The cause of line splitting in Burg maximum-entropy spectral analysis

Abstract: Burg's algorithm for maximum-entropy autoregressive spectral estimation is analyzed for the case of one and two complex sinusoidal signals in additive white noise. In the latter case, two biases are found which can account for the line splitting and line shifting that occur in simulation studies when the SNR is very high. These biases vanish completely if the two complex sinusoids are in phase quadrature at the middle of the data record. If the data record contains an integral number of half-cycles of the difference frequency, the magnitude of the power spectral estimate will be biased, although the effects believed to cause splitting and shifting will be eliminated. For infinite SNR, the effect of these biases is to prevent perfect cancellation of the coherent signal by the correct-order Burg prediction-error filter (PEF). Then higher order PEF's can be based on the uncancelled signal. It is conjectured that the severity of splitting and shifting is closely related to the relative magnitude of the uncancelled signal. Results of simulation studies to verify this conjecture are presented. The analysis also shows that lengthening the observation interval by including more data recorded at the original sampling rate should reduce the magnitude of the biases, but that increasing the number of data by increasing the sampling rate, while maintaining the observation interval unchanged, is of little use.

Delay and optimum amplitude equalizers for a readback circuit

Abstract: A pulse improvement circuit for a magnetic readback system produces a data representative signal having symmetrical, equal-amplitude pulses of limited time widths. The circuit includes an equalizer made in accordance to a final transfer function produced as a result of a mathematical convolution of first and second transfer functions. The first transfer function is based on the theory of a matched filter for receiving a signal having data representative and non-white noise pulses contained therein to produce a filter signal having maximum signal to noise ratio. The second transfer function is based on the theory of a Papoulis window function for slimming the pulses contained in the filter signal. A specific circuit implementation of the final transfer function is an eight-pole, inductor-capacitor, ladder network for amplitude equalization coupled to an inductor-capacitor, lattice network including first and second order sections for phase equalization.

On the structure and microstructure of stratospheric water vapor

Abstract: Some recent results on the measurement of the mixing ratio of stratospheric water vapor are reported. The instrument uses photodissociation of water followed by fluorescence of the hydroxyl fragment (PFF). This instrument has a large signal to noise ratio at integration times of 1 second, so that potential structure and fine structure of the water mixing ratio profile can be resolved.

Space-time analysis of photon-limited stellar speckle interferometry

Abstract: The standard method of stellar speckle interferometry, in which short exposure photographs are individually analyzed, is not the most general method of extracting object information from the time-varying image intensity. We introduce a space-time analysis in which both spatial and temporal fluctuations are taken into account; the aim is to measure the power spectrum of the image with an increased signal to noise ratio. Surprisingly, our more general space-time analysis does not yield an improved signal to noise ratio at very low light levels.

A Practical Ground Potential Rise Prediction Technique For Power Stations

Abstract: The determination of fault-produced Ground Potential Rise (GPR) at a power station has historically posed a number of practical and technical problems. This paper presents a GPR prediction technique which overcomes these problems without requiring a staged fault test. The technique consists of: 1) the diligent application of the fall-of-potential method for measuring the impedance to remote earth of a power station ground grid with all normal external connections to the grid maintained, using an ac test signal of approximately 60 Hz. 2) the use of electronic instruments with improved sensitivity and signal-to-noise ratio, 3) multiplication of the measured grid impedance by the appropriate total single phase fault current.

Method for collecting and generating composite trace signals with improved signal to noise ratios

Abstract: Arrays of seismic wave sources and seismic wave sensors are towed over an area to be refraction surveyed in such a way that source and sensor geodetic positioning is duplicated during successive source firings. A plurality of traces having these same source/reflection point/sensor geometry are gathered from those produced by each series of successive source firings at the same location and stacked to generate a new trace having improved signal to noise ratio. Positioning is accomplished by uniformly spacing each of the sensors and sources in their respective arrays, the sources being spaced at integer multiples of the spacing of the sensors, and towing both arrays behind the same boat. If irregular or rapidly changing seismic statics are not present, all traces from common reflection points may also be gathered, corrected for normal moveout and stacked to generate a composite trace having enhanced primary reflection returns as well as improved signal to noise ratio.

A Universal Weighted Powed Function of Television Noise and Its Application to High-Definition Tv System Design

Abstract: The author proposes a new weighted function of noise power affecting television picture defined in a two-dimensional picture frequency domain, including the vertical frequency domain. This function is of universal use and applicable to television standards with any aspect ratio and differing number of scanning lines.

Method and apparatus for measuring signal to noise ratio in a TDMA communications system

Abstract: A method and apparatus for measuring signal to noise ratio in a time division multiple access (TDMA) communications system which does not require that normal communications be interrupted. The signal to noise ratio measurement is performed on the unmodulated carrier which typically occurs in the preamble of each information burst in the TDMA format. In order to perform the measurements on the carrier of the same burst in each frame, the carrier and noise powers are sampled at a predetermined time with respect to specified information which occurs at the same time in each frame, normally the frame reference burst. After being converted to the receiver intermediate frequency, the unmodulated carrier is fed to both a narrow band pass filter having a pass band at the intermediate frequency and a narrow band stop filter having a stop band at the intermediate frequency. The ratio of the band pass filter output to the band stop filter output is the signal to noise ratio within a very small error.

Adaptive enhancement of signal-to-noise ratio in television imagery

Abstract: A noise reduction filter for a television receiver in which two running averages of video signal amplitude are generated over regions of the video picture where the brightness level is substantially constant. One or the other of the averages is used to control intensity to obtain a reduction of random noise in the video signal. In areas of the picture where rapid changes in intensity occur, the averages are not used in favor of the unmodified video signal.

Low‐noise photodiode amplifier for absorption changes measurements in the microsecond range

Abstract: — A silicon photodiode equipped with a low-noise amplifier is incorporated in an apparatus of flash absorption spectroscopy. This device provides a good signal to noise ratio in the detection of short-lived species (1µs-5 ms) formed in photobiological processes.

Instrumentation for the size determination of submicron particulates systems by sideway light scattering method

Abstract: A new submicron particle counter using a low output He–Ne laser (unpolarized, 8 mW) is proposed for in situ measurement of particulates. The design is based on calculations and experimental checks of factors governing the signal‐to‐noise ratio. Right angle scattering is found to be the most suitalbe optical system for eliminating miscellaneous noise and fundamental noise components derived from the carrier gas. The present version of the instrument with nine channels is constructed so as to minimized the noise level by reducing the sensing volume. This instrument can actually measure correct size distributions from 0.1 to 10 μm without detectable coincidence loss, at environmental particulate concentrations of up to 5×104/cm3.

Focal-Plane Tomography Image Reconstruction

Abstract: Two different tomographic scanning instruments have been interfaced to a digital computer Digital backprojection is used to produce multiple tomographic images of radioactive distributions Backprojection results in blur artifacts due to off-plane contributions which obscures the detail in images The method of Chang, Macdonald, and Perez-Mendez has been applied to phantom data from both instruments, resulting in substantial blur removal and improved signal-to-noise ratios Clinical images derived from digital back-projection of data from the Searle PHO/CON-192 Multiplane Imager are presented and compared with images from the Searle Microdot imager

Scanning and reproduction system for electronic copiers - uses multiple scanning of picture elements for improving signal=to=noise ratio

Abstract: The scanning system, esp. for electronic copiers, is designed to provide fast scanning and exposure times with good signal/noise ratio. The original is placed on a rotating drum and is scanned point-by-point and line-by-line via a lens. The scanner comprises a row of photo-diodes aligned with one picture line. The output signals from the diodes are passed to an electronic distributor comprising analogue multiplexers and demultiplexers. These are connected to integrators. The operation of the scanner and circuits is such that each picture element is scanned several times in succession and the respective signals are summed. The summing operation is synchronized to the relative movement between scanner and document.

A new adaptive antenna for elevation angle estimation in the presence of multipath

Abstract: A new adaptive antenna is described for elevation angle estimation as encountered in low angle tracking radar. The antenna is used to sense the directions of arrival of both the direct and multipath signal in a symmetric manner. A priori knowledge of the reflection coefficient of the reflecting surface is not necessary. Computer simulation results are included to illustrate the effects of (1) signal-to-noise ratio, and (2) the phase difference between the two signals at the centre of the array, on the performance of the system.

System Design For A Staring Mosaic Sensor

Abstract: In this paper analytic and numerical methods are presented for the design of a staring mosaic sensor system. The calculations are simplified by using the properties of two-dimensional Fourier transforms. The methods permit investigation of the dependence of background suppression and signal-to-noise ratio on characteristics such as: non-isotropic background with two-dimensional spatial power spectral density, background drift rate, optical blur, detector footprint, electronic sensor noise, and target phasing and velocity. Representative examples are discussed along with sample numerical results.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Emission Computed Tomography Simulator

Abstract: We have designed and built a system to simulate emission computed tomography (ECT) devices and measure physical parameters of the component parts in such systems. It consists of a heavy duty X, Y, Z, ? scanning table under computer control through CAMAC with modular NIM electronics for signal processing. The modular approach allows ready reconfigurations of detectors and lead shielding to test new design concepts. Direct computer control allows simulation of complex scanning motions and detector geometries by motion of the object rather than the detectors as well as ready capability in data analysis. A study is presented in which the simulator shows a significant increase in signal to noise ratio in a commercial tomograph by small changes in lead shield geometry.

Confidence bounds for signal-to-noise ratios from magnitude-squared coherence estimates

Abstract: Coherence is used frequently to determine the degree to which one observed voltage is related to another observed voltage. Typically, in practice, these observables are degraded by system noise that is often independent, white, and Gaussian. Often, in measuring coherence, the interest is to determine the fraction of the observed power that is due to coherent signals and the fraction that is due to the uncorrelated noise floor. The term "signal" as used here describes a component of voltage of interest to an observer. With accurate coherence estimates, uncorrelated noise power can be separated from coherent signal power. Therefore, the concern in this article is with the accuracy of signal-to-noise ratio (SNR) calculations made from magnitude-squared coherence (MSC) estimates. Use is made of work by Carter and Scannel [1] in which they determine confidence bounds of MSC estimates for stationary Gaussian processes. Their results are used in this article to derive corresponding confidence bounds for SNR calculations without recourse to the complicated details of the underlying SNR statistics.