Gravity meter observation of free modes excited by the August 19, 1977 Indonesia earthquake

1979 ◽  
Vol 69 (5) ◽  
pp. 1445-1454
Author(s):  
John A. Linton ◽  
D. E. Smylie ◽  
O. G. Jensen
Keyword(s):  
Signal To Noise Ratio ◽  
Quartz Fiber ◽  
Large Signal ◽  
Signal To Noise ◽  
Definitive Evidence ◽  
Long Period ◽  
Noise Ratio

abstract Free modes with signal-to-noise ratio in the range of 40 to 55 dB were observed in the record taken by a vertical broadband quartz fiber gravimeter system opeating in Montreal following the event of August 19, 1977 in Indonesia. The large signal-to-noise ratio has permitted very stable Q estimates to be made for a number of the fundamental spheroidal modes. The very long-period band shows no definitive evidence of signal other than the expected tidal lines.

Metastable yield of argon between 23 and 37 eV by electron impact

1979 ◽  
Vol 57 (10) ◽  
pp. 1624-1633 ◽  
Author(s):  
P. Marchand ◽  
J. Cardinal
Keyword(s):  
Electron Impact ◽  
Excited States ◽  
Signal To Noise Ratio ◽  
Negative Ion ◽  
Photon Yield ◽  
Large Signal ◽  
Signal To Noise ◽  
Monoenergetic Electron ◽  
Yield Curves ◽  
Noise Ratio

The metastable yield of argon excited by monoenergetic electron impact has been measured between 23 and 37 eV. Thanks to a large signal-to-noise ratio, many very small structures have been detected superimposed on the metastable continuum and are attributed to Ar− negative-ion states and to highly excited states of Ar. The results are compared with broadband photon yield curves and electroionization curves.

Non-linear filtering of rare events with large signal-to-noise ratio

1987 ◽  
Vol 24 (04) ◽  
pp. 929-948
Author(s):  
A. J. Heunis
Keyword(s):  
Conditional Distribution ◽  
Signal To Noise Ratio ◽  
Sample Path ◽  
Rare Event ◽  
Dirac Measure ◽  
Linear Filtering ◽  
Large Signal ◽  
Signal To Noise ◽  
Non Linear ◽  
Noise Ratio

The theory of robust non-linear filtering in Clark (1978) and Davis (1980), (1982) is used to evaluate the limiting conditional distribution of a diffusion, given an observation of a ‘rare-event' sample-path of the diffusion, as the signal-to-noise ratio and the diffusion noise-intensity converge to infinity and zero respectively. Under mild conditions it is shown that the limiting conditional distribution is a Dirac measure concentrated at a trajectory which solves a variational problem parametrised by the sample-path of the observed signal.

Long-period seafloor seismology and deformation under ocean waves

1999 ◽  
Vol 89 (6) ◽  
pp. 1535-1542 ◽  
Author(s):  
Spahr C. Webb ◽  
Wayne C. Crawford
Keyword(s):  
Shallow Water ◽  
Signal To Noise Ratio ◽  
Wave Spectrum ◽  
Vertical Component ◽  
Ocean Waves ◽  
Vertical Acceleration ◽  
Noise Levels ◽  
Signal To Noise ◽  
Long Period ◽  
Noise Ratio

Abstract The deformation of the seafloor under loading by long-period ocean waves raises vertical component noise levels at the deep seafloor by 20 to 30 dB above noise levels at good continental sites in the band from 0.001 to 0.04 Hz. This noise substantially limits the detection threshold and signal-to-noise ratio for long-period phases of earthquakes observed by seafloor seismometers. Borehole installation significantly improves the signal-to-noise ratio only if the sensor is installed at more than 1 km below the seafloor because the deformation signal decays slowly with depth. However, the vertical-component deformation signal can be predicted and suppressed using seafloor measurements of pressure fluctuations observed by differential pressure gauges. The pressure observations of ocean waves are combined with measurements of the transfer function between vertical acceleration and pressure to predict the vertical component deformation signal. Subtracting the predicted deformation signal from pressure observations can reduce vertical component noise levels near 0.01 Hz by more than 25 dB, significantly improving signal-to-noise ratios for long-period phases. There is also a horizontal-component deformation signal but it is smaller than the vertical-component signal and only significant in shallow water (<1-km deep). The amplitude of the deformation signal depends both on the long-period ocean-wave spectrum and the elastic-wave velocities in the oceanic crust. It is largest at sedimented sites and in shallow water.

ON THE DISTRIBUTION OF THE PRODUCT OF DIODE DETECTOR WAVEFORMS

1956 ◽  
Vol 34 (7) ◽  
pp. 679-691 ◽  
Author(s):  
E. L. R. Webb
Keyword(s):  
Probability Distribution ◽  
Signal To Noise Ratio ◽  
Rayleigh Distribution ◽  
Large Signal ◽  
Signal To Noise ◽  
Radio Receivers ◽  
Impulse Function ◽  
Diode Detector ◽  
Mean And Variance ◽  
Noise Ratio

The probability distribution of the product of two waveforms such as come from the diode second detectors of radio receivers is examined over the whole range of signal to noise ratios. Computed curves of probability density are given for small and moderate values of signal to noise ratio and the limiting form for large signal to noise indicated. The pure noise case is the only one immediately available in terms of tabulated functions. Compared to the Rayleigh distribution it rises much faster, reaches its maximum sooner and lower, and decays much more slowly. The very large signal to noise ratio case approaches an impulse function. Estimates of mean and variance are given.

Local symmetric distortion boosted photon up-conversion and thermometric sensitivity in lanthanum oxide nanospheres

Nanoscale ◽  
2018 ◽  
Vol 10 (19) ◽  
pp. 9245-9251 ◽  
Author(s):  
Hao Suo ◽  
Xiaoqi Zhao ◽  
Zhiyu Zhang ◽  
Rui Shi ◽  
Yanfang Wu ◽  
...  
Keyword(s):  
Lanthanum Oxide ◽  
Signal To Noise Ratio ◽  
Site Symmetry ◽  
Large Signal ◽  
Signal To Noise ◽  
Local Site ◽  
Noise Ratio

Realizing sensitive sub-tissue thermometry with a large signal-to-noise ratio via finely tailoring the local site symmetry in La2O3:Er3+/Yb3+ nanospheres.

A DELTA‐MODULATION RECORDING SYSTEM FOR SEISMIC USE

Geophysics ◽  
1965 ◽  
Vol 30 (1) ◽  
pp. 51-53
Author(s):  
Noel J. Thompson
Keyword(s):  
Signal To Noise Ratio ◽  
Digital Systems ◽  
Digital Recording ◽  
Large Signal ◽  
Signal To Noise ◽  
Tape Transport ◽  
Channel Bandwidth ◽  
Magnetic Tape Recording ◽  
Delta Modulation ◽  
Noise Ratio

A system of delta modulation with magnetic‐tape recording is proposed. It should achieve excellent signal‐to‐noise ratio without excessive equipment complexity. The system would be of use in crustal seismology where large signal‐to‐noise ratio is more important than minimum channel bandwidth. The recording of data in binary form as achieved by delta modulation eliminates tape transport wow and flutter and certain other noise components found in analog recording. Compared to FM recording, delta modulation provides similar complexity of recording and nearly identical “quick‐look” playback equipment. Delta modulation has the advantage, in common with other digital systems, that, with more complete playback equipment (either analog or computer), excellent removal of transport speed variations is possible. Delta modulation is less complex than other digital‐recording systems, and combines many of the best features of both the digital and analog techniques.

scholarly journals ACCURACY COMPARISON OF ALGORITHMS FOR DETERMINATION OF IMAGE CENTER COORDINATES IN OPTOELECTRONIC DEVICES

2018 ◽  
Vol 17 (1) ◽  
pp. 79-86 ◽  
Author(s):  
N. A. Starasotnikau ◽  
R. V. Feodortsau
Keyword(s):  
Mathematical Model ◽  
Shot Noise ◽  
Test Object ◽  
Signal To Noise Ratio ◽  
Large Signal ◽  
Signal To Noise ◽  
Gravity Center ◽  
Image Center ◽  
Noise Ratio

Accuracy in determination of coordinates for image having simple shapes is considered as one of important and significant parameters in metrological optoelectronic systems such as autocollimators, stellar sensors, Shack-Hartmann sensors, schemes for geometric calibration of digital cameras for aerial and space imagery, various tracking systems. The paper describes a mathematical model for a measuring stand based on a collimator which projects a test-object onto a photodetector of an optoelectronic device. The mathematical model takes into account characteristic noises for photodetectors: a shot noise of the desired signal (photon) and a shot noise of a dark signal, readout and spatial heterogeneity of CCD (charge-coupled device) matrix elements. In order to reduce noise effect it is proposed to apply the Wiener filter for smoothing an image and its unambiguous identification and also enter a threshold according to brightness level. The paper contains a comparison of two algorithms for determination of coordinates in accordance with energy gravity center and contour. Sobel, Pruitt, Roberts, Laplacian Gaussian, Canni detectors have been used for determination of the test-object contour. The essence of the algorithm for determination of coordinates lies in search for an image contour in the form of a circle with its subsequent approximation and determination of the image center. An error calculation has been made while determining coordinates of a gravity center for test-objects of various diameters: 5, 10, 20, 30, 40, 50 pixels of a photodetector and also signalto-noise ratio values: 200, 100, 70, 20, 10. Signal-to-noise ratio has been calculated as a difference between maximum image intensity of the test-object and the background which is divided by mean-square deviation of the background. The accuracy for determination of coordinates has been improved by 0.5-1 order in case when there was an increase in a signal-to-noise ratio. Accuracy improvement due to increase of a diameter in a test-object is typical for large signal-to-noise ratios: 70 or more. The conducted investigations have made it possible to establish that the algorithm for determination of coordinates of the energy gravity center is more accurate in comparison with contour methods and requires less computing power (for the MatLab software package), which is related to discreteness while determining a contour.

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